**3. Epidemiology and risk factor**

About 20% to 40% of individuals with AIDS develop TE from the reactivation of a latent *T. gondii* infection when the CD4 cell count falls below 100/mm3 (Luft & Remington, 1992; Sukthana, 2000; Ajzenberg, 2009). The incidence of TE is thus directly proportional to the prevalence of antibodies to *Toxoplasma* in any given population. Before the advent of HIV/AIDS epidemic in 1981, toxoplasmosis was occasionally reported in immunocompromised patients, mostly in those with malignancies of the reticuloendothelial system and cardiac transplant recipients with lesions mostly outside the CNS. But, TE has become one of the commonest causes of focal brain lesions in Western Europe and North America due to AIDS pandemic (Luft & Remington, 1988). Since then, more and more TE cases in HIV/AIDS individuals were diagnosed worldwide. Nearly three decades from that point, nowadays to get a clearer picture of its epidemiology and clinical course, herein, three periods could be divided as: 1) TE during the beginning of AIDS pandemic period (1980s), 2) TE during prophylaxis period (1990s) and 3) TE during HAART period (1997-present).

#### **3.1 TE during the beginning of AIDS pandemic period (1980s)**

At the beginning of the 1980s, more and more of the mysterious cases with severe manifestations and fatal outcomes presented in homosexual men, hemophiliacs and Haitian. HIV was subsequently identified as the cause that impaired host immunity causing acquired immunodeficiency syndrome (AIDS) and opportunistic infections. In November 1982, the Centers for Disease Control (CDC) reported 19,744 AIDS cases from the United States, with

Toxoplasmic Encephalitis 285

**Prevalence** 

All developed TE with disseminated toxoplasmosis

Haitian 39% Fever

**Clinical features** 

1wk-18 mo prodromic period Brain involvement with other organs affected such as lung, retina and heart

Headache Alteration of semsorium Hemiparesis Ataxia

17% 62% focal

neurological deficit 58% fever 47%headache 45% altered consciousness 18% seizures

Fever with 92% sen and 56% spec Neurological focal signs with 59% sen and 82% spec Headache with 41% sen and 69% spec

**Diagnostic procedures** 

Serology (IgG and all negative IgM)

Histological diagnosis by Biopsy or Autopsy Immunoperoxidase staining CT showing multiple enhanced ring-shaped lesions

CT findings: focal mass 60% with and 40% without ring

enhancement 59% multiple lesions 58% with brain edema

65% by blood serology with 95% sen and 30% spec 49% by CSF serology with 77% sen and 56% spec By CT with 65% sen and 82% spec 125 patients by Autopsy

Mice inoculation

**Patients Risk factors TE** 

Host immune deficiency by unknown cause in homosexual men, IVDU and Haitians.

**Study period [References]** 

1981-1982 [Luft et al, 1983]

1980-1984 [Berger et al, 1987]

1985-1990 [Ragnaud et al, 1993]

1985-1999 [Wainstein et al, 1993]

**Study Location** 

> 10 patients with acute encephalitis from

Belgium, USA and Canada

132 AIDS patients with symptomatic AIDS (including : 55%Haitian, 27%homosexual men and 11%IVDU )

428 AIDS patients with initial CD4= 72 cell/mm3

516 AIDS patients

M:F= 2.8:1 Mean age 36.2 yrs 43% homosexual men 30% IVDU


presumptive diagnosis and 22% by definite diagnosis

Research Institute, Palo Alto Medical Foundation, USA

Jackson Memorial Hospital, Miami, Florida, USA

Bordeaux Regional Hospital, France

Hospital de Clinicas de Porto Alegre, Brasil

287 deaths and 54 cases have been reported from foreign countries (Gapen, 1982). Neurological involvement was seen in three out of four AIDS patients and TE was one of the most common neurological complications. Luft and colleagues (1983) reported acute encephalitis caused by *Toxoplasma* in 10 patients from Belgium, USA and Canada who had no underlying history associated with toxoplasmosis. All patients had a prodrome which varied from one week to 18 months. Three patients had disseminated toxoplasmosis with several organs affected (Table 1). Half of them had concomitant infections including tuberculosis, pneumocystosis, cytomegalovirus infection (CMV) and candidiasis. Other studies revealed similar pictures which reported neurological complications ranging from 20% to 41% with TE as the most or the second most common neurological disorders in HIV/AIDS patients (Luff, et al, 1983; Levy, et al, 1985; Berger, et al, 1987).

A 10-year observational studies from USA (Luft, & Castro, 1991; Richards et al, 1995) revealed at the end of 1989, there were 5,614 cases of toxoplasmosis reported to the CDC as the AIDS indicator disease and it increased to 14,059 (5.1%) of 274,150 adults and adolescents in the United States. The risk factors were observed as black male, intravenous drug users (IVDU), homosexual men, immigrants, Haitian and different geographic location. Richards and colleagues demonstrated that TE was more common among black males than white (5.2% vs. 4.2%, P < .0001) and was also more common among IVDU than among men with male sex partners (5.9% vs. 4.6%, P < .0001). Immigrants to the USA from Africa, Latin America and Haiti were three to four times more likely to develop TE than American-born (Luft, & Castro, 1991). The rate of TE was higher in the northeastern and southern states of America (5.6% vs. 5.5%) than in the north-central and western states (4.4% vs. 4.1%, P < .0001) this was related to the *Toxoplasma* IgG seroprevalence which was observed twice higher in the northern and northeastern regions than those in the western and southwestern regions (Richards et al, 1995).

In Africa, Europe, and South America, where the prevalences of chronic *T. gondii* infection were as high as 60%-75%, patients with AIDS who developed TE were three to four times greater than that in the United States whereas HIV-infected adults with latent *T. gondii*  infection was less than 40%, only one-third of those patients developed TE (Luft & Remington, 1992). In France, 11% of AIDS-defining illness was due to TE in 1987, and rose to 23% in 1992 (Oksenhendler et al, 1994). Studies from France and Brazil in 1985 to 1990 reported the prevalence of TE in AIDS patients at 17% and 13% by presumptive diagnosis compared with 22% by definite diagnosis, respectively (Ragnaud et al, 1993; Wainstein et al, 1993). In Asia, the seroprevalence of toxoplasmosis was low, from 4% to 42.5% in Japan, Korea, Taiwan and Thailand, but was higher in India, Malaysia and Indonesia as 22.4% to 67.8% (Nissapatorn, 2009). The first documented case of TE reported in an international journal was from Thailand in 1992 (Sukthana, 2000), but a report in a local textbook showed 9.7% of cerebral toxoplasmosis as AIDS-defining illnesses from 1987 to 1994 and increased to 10.5% in 2001 and to 14.8% in 2002 (Chankrachang, 2004).

#### **3.2 TE during prophylaxis regimen period (1990s)**

In the 1990s, numerous TE cases as one of the common opportunistic infections in HIV/AIDS individuals were being diagnosed; medical researchers thus developed a clearer picture of its epidemiology and clinical features. For example, the incidence of TE was found to be 20.5 per 100 patient-years in France (Bossi et al., 1998), 15.9 per 100 patient-years in Swiss HIV Cohort study group (Furrer et al, 1999) and 4.0 per 100 patient-years in nine US cities (Jones et al, 1996). Khetsuriani and colleagues (Khetsuriani et al, 2002) studied the

287 deaths and 54 cases have been reported from foreign countries (Gapen, 1982). Neurological involvement was seen in three out of four AIDS patients and TE was one of the most common neurological complications. Luft and colleagues (1983) reported acute encephalitis caused by *Toxoplasma* in 10 patients from Belgium, USA and Canada who had no underlying history associated with toxoplasmosis. All patients had a prodrome which varied from one week to 18 months. Three patients had disseminated toxoplasmosis with several organs affected (Table 1). Half of them had concomitant infections including tuberculosis, pneumocystosis, cytomegalovirus infection (CMV) and candidiasis. Other studies revealed similar pictures which reported neurological complications ranging from 20% to 41% with TE as the most or the second most common neurological disorders in

A 10-year observational studies from USA (Luft, & Castro, 1991; Richards et al, 1995) revealed at the end of 1989, there were 5,614 cases of toxoplasmosis reported to the CDC as the AIDS indicator disease and it increased to 14,059 (5.1%) of 274,150 adults and adolescents in the United States. The risk factors were observed as black male, intravenous drug users (IVDU), homosexual men, immigrants, Haitian and different geographic location. Richards and colleagues demonstrated that TE was more common among black males than white (5.2% vs. 4.2%, P < .0001) and was also more common among IVDU than among men with male sex partners (5.9% vs. 4.6%, P < .0001). Immigrants to the USA from Africa, Latin America and Haiti were three to four times more likely to develop TE than American-born (Luft, & Castro, 1991). The rate of TE was higher in the northeastern and southern states of America (5.6% vs. 5.5%) than in the north-central and western states (4.4% vs. 4.1%, P < .0001) this was related to the *Toxoplasma* IgG seroprevalence which was observed twice higher in the northern and northeastern regions than those in the western

In Africa, Europe, and South America, where the prevalences of chronic *T. gondii* infection were as high as 60%-75%, patients with AIDS who developed TE were three to four times greater than that in the United States whereas HIV-infected adults with latent *T. gondii*  infection was less than 40%, only one-third of those patients developed TE (Luft & Remington, 1992). In France, 11% of AIDS-defining illness was due to TE in 1987, and rose to 23% in 1992 (Oksenhendler et al, 1994). Studies from France and Brazil in 1985 to 1990 reported the prevalence of TE in AIDS patients at 17% and 13% by presumptive diagnosis compared with 22% by definite diagnosis, respectively (Ragnaud et al, 1993; Wainstein et al, 1993). In Asia, the seroprevalence of toxoplasmosis was low, from 4% to 42.5% in Japan, Korea, Taiwan and Thailand, but was higher in India, Malaysia and Indonesia as 22.4% to 67.8% (Nissapatorn, 2009). The first documented case of TE reported in an international journal was from Thailand in 1992 (Sukthana, 2000), but a report in a local textbook showed 9.7% of cerebral toxoplasmosis as AIDS-defining illnesses from 1987 to 1994 and increased

In the 1990s, numerous TE cases as one of the common opportunistic infections in HIV/AIDS individuals were being diagnosed; medical researchers thus developed a clearer picture of its epidemiology and clinical features. For example, the incidence of TE was found to be 20.5 per 100 patient-years in France (Bossi et al., 1998), 15.9 per 100 patient-years in Swiss HIV Cohort study group (Furrer et al, 1999) and 4.0 per 100 patient-years in nine US cities (Jones et al, 1996). Khetsuriani and colleagues (Khetsuriani et al, 2002) studied the

HIV/AIDS patients (Luff, et al, 1983; Levy, et al, 1985; Berger, et al, 1987).

and southwestern regions (Richards et al, 1995).

to 10.5% in 2001 and to 14.8% in 2002 (Chankrachang, 2004).

**3.2 TE during prophylaxis regimen period (1990s)** 


Toxoplasmic Encephalitis 287

was not recommended as a first-line regimen for primary prophylaxis of TE, some medical researchers considered pyrimethamine for patients who were intolerant to TMP-SMZ,

TMP-SMZ was the drug of choice for prophylaxis for both PCP and toxoplasmosis (Carr et al, 1992; Richards et al, 1995). Therefore, there were various regimens ranging from 1 double-strength1 (DS) tablet twice daily to 1 DS tablet 3 times weekly (14 DS tablets to 3 DS tablets per week) have been used. Ribera and colleagues (1999) found that since 1992, patients received either one of the following 5 regimens of TMP-SMZ for TE prophylaxis i.e.1 DS tablet daily (7DS tab/wk), 2 DS tablets daily 3 times weekly (6 DS tab/wk), 1 DS tablet 5 times weekly (5 DS tab/wk), 1 DS tablet 3 times weekly (3 DS tab/wk), and 1 singlestrength (SS) tablet daily (3.5 DS tab/wk), they noticed the more frequent doctors began prescribing low doses of TMP-SMZ the higher number of patients receiving TMP-SMZ prophylaxis developed TE. Therefore, they studied to assess the efficacy of the various doses of TMP-SMZ as primary prophylaxis for TE and concluded that patients receiving low dose TMP-SMZ (<4 DS tab/wk) had a higher risk of developing TE than those who received high dose TMP-SMZ indicating 89% protective efficacy for high doses. An insufficient concentration of the low dose TMP-SMZ within the CNS may be an additional problem in the prevention of toxoplasmosis. Moreover, they also studied the potential interactions between rifampin and TMP-SMZ and hypothesized that rifampin may reduce the efficacy of

Dapsone combined with pyrimethamine (200/75 mg once weekly) was more effective in the primary prophylaxis of TE than aerosolized pentamidine (300 mg every 4 weeks) and had the advantage of a lower cost and easier administration (Torres et al, 1993; Opravil et al, 1995). Girard and colleagues (1993) revealed dapsone plus pyrimethamine prevented first episodes of TE better, but they were more toxic than aerosolized pentamidine (42 patients discontinued dapsone plus pyrimethamine while only 3 patients stopped aerosolized

In conclusion, primary prophylaxis was the important strategy to prevent TE occurrence in the 1990s period. TMP-SMZ was the drug of first choice which was prescribed when HIV/AIDS seropositive to *T. gondii* antibody had low CD4 <200 cell/mm3. By this practice, the prevalence of TE was reduced from 19% in 1988 to 6% in 1994 (Katlama, 1995). The incidence of TE was 3.9 cases/100 person-years (95% CI, 3.7–4.1 cases/100 person-years),

Since 1997, protease inhibitor, an antiretroviral drug, had been widely available, HIVinfected persons have lived longer and healthier lives. Since then, in the period of 15 years, that development was considered one of the great success stories of modern medicine. The death rate from HIV disease was reduced by 50 to 80% and changed from a fatal and hopeless illness to what is now a manageable chronic disease. The simultaneous combination of three or more different antiretroviral drugs was known as Highly Active Antiretroviral Therapy or HAART (Cooper 1996). It significantly delayed the onset of AIDS in HIV-infected individuals as well as reduced almost all opportunistic infections. The

1 double-strength (DS) tablet contains 160 mg of trimethoprim and 800 mg of sulfamethoxazole, while

single-strength (SS) contains 80 mg of trimethoprim and 400 mg of sulfamethoxazole.

patients who discontinued TMP-SMZ increased the risk of TE (Abgrall et al, 2001).

especially in high risk patients with CD4 <100 cell/mm3 (Leport et al, 1996).

TMP-SMZ.

pyrimethamine, p<0.001)

**3.3 TE during HAART period (1997-present)** 


Table 1. Summary of the data from studies on epidemiology and clinical course of toxoplasmic encephalitis (TE) during the beginning of AIDS pandemic period (1980s). IVDU = Intravenous drug user, mo = month(s), sen = sensitivity, spec = specificity, wk = week(s).

burden of encephalitis in USA from 1988 to 1997 and revealed TE accounted for the majority of 34.1% known causes of hospitalization due to encephalitis (21,504 hospitalizations; SE, ± 2,583). More than 97% of TE had been reactivated from the chronic quiescent *Toxoplasma*  infection, nevertheless, few TE cases developed as acute infection (Richards et al, 1995). Only 30%-50% of HIV-positive patients with chronic *T. gondii* infection developed TE when their immune system became severely compromised. These were because host factors or virulence among different strains of *Toxoplasma* played a role in predisposing those patients to recrudescence of active clinical symptoms and signs (Luft & Remington, 1992). The research questions in that period was focused on when and what caused the reactivation to occur and how patients could be taken care of.

There were various retro- and prospective studies on the prevalence of TE, risk factors and prophylaxis worldwide (Table 2). To combat aggressive opportunistic infections (OIs) in HIV/AIDS patients including PCP, CMV infection and toxoplasmosis, medical researchers have unanimously agreed in giving primary prophylaxis to the population at risk of those OIs in suitable time. Primary prophylaxis should be given to prevent OIs when immune deficiency occurs and secondary prophylaxis would be continuously prescribed after acute opportunistic infections subsided. In general, HIV/AIDS individuals were mostly prescribed penthamedine, cotrimoxazole and dapsone as the prophylaxis of PCP and CMV infection which were more aggressive and occurred earlier than toxoplasmosis, when their CD4 were < 200 cell/mm3. The matters had arisen whether those medications were also preventing TE and were good candidate regimens of appropriate dosage with acceptable adverse effect and adherence or compliance of the patients. In the case of TE, there were two things to be considered for primary prophylaxis which were HIV/AIDS infected person who was also seropositive of *T. gondii* antibody and CD4 was lower than 100 cell/mm3 (Oksenhendler et al, 1994; Richards et al, 1995; Leport et al, 1996).

Table 2 summarized the data from studies which were carried out in the 1990s concerning TE epidemiology, prophylaxis regimens and outcomes. Cotrimoxazole or trimethoprimsulfamethoxazole (TMP-SMZ) was the most popular regimen for TE primary prophylaxis, while Fansidar (pyrimethamine-sulfadiazine) was prescribed at the beginning of 1990 when CD4 was lower than 200 cell/mm3 (Carr et al, 1992; Köppen et al, 1992). However, it was not recommended for the primary prophylaxis of TE because of its side-effects especially rash and allergy. Thus patients discontinued the prophylaxis and had higher TE reactivation. Pyrimethamine had bone marrow toxicity. When patients received without leucovorin supplement the survival rate reduced (Jacobson et al, 1994). Even though pyrimethamine

**Prevalence** 

cases/perso n-year of observation

0.05

**Clinical features** 


**Diagnostic procedures** 

**Patients Risk factors TE** 

IVDU, Homosexual men, Black male, geographic difference

Table 1. Summary of the data from studies on epidemiology and clinical course of

toxoplasmic encephalitis (TE) during the beginning of AIDS pandemic period (1980s). IVDU = Intravenous drug user, mo = month(s), sen = sensitivity, spec = specificity, wk = week(s). burden of encephalitis in USA from 1988 to 1997 and revealed TE accounted for the majority of 34.1% known causes of hospitalization due to encephalitis (21,504 hospitalizations; SE, ± 2,583). More than 97% of TE had been reactivated from the chronic quiescent *Toxoplasma*  infection, nevertheless, few TE cases developed as acute infection (Richards et al, 1995). Only 30%-50% of HIV-positive patients with chronic *T. gondii* infection developed TE when their immune system became severely compromised. These were because host factors or virulence among different strains of *Toxoplasma* played a role in predisposing those patients to recrudescence of active clinical symptoms and signs (Luft & Remington, 1992). The research questions in that period was focused on when and what caused the reactivation to

There were various retro- and prospective studies on the prevalence of TE, risk factors and prophylaxis worldwide (Table 2). To combat aggressive opportunistic infections (OIs) in HIV/AIDS patients including PCP, CMV infection and toxoplasmosis, medical researchers have unanimously agreed in giving primary prophylaxis to the population at risk of those OIs in suitable time. Primary prophylaxis should be given to prevent OIs when immune deficiency occurs and secondary prophylaxis would be continuously prescribed after acute opportunistic infections subsided. In general, HIV/AIDS individuals were mostly prescribed penthamedine, cotrimoxazole and dapsone as the prophylaxis of PCP and CMV infection which were more aggressive and occurred earlier than toxoplasmosis, when their CD4 were < 200 cell/mm3. The matters had arisen whether those medications were also preventing TE and were good candidate regimens of appropriate dosage with acceptable adverse effect and adherence or compliance of the patients. In the case of TE, there were two things to be considered for primary prophylaxis which were HIV/AIDS infected person who was also seropositive of *T. gondii* antibody and CD4 was lower than 100 cell/mm3

Table 2 summarized the data from studies which were carried out in the 1990s concerning TE epidemiology, prophylaxis regimens and outcomes. Cotrimoxazole or trimethoprimsulfamethoxazole (TMP-SMZ) was the most popular regimen for TE primary prophylaxis, while Fansidar (pyrimethamine-sulfadiazine) was prescribed at the beginning of 1990 when CD4 was lower than 200 cell/mm3 (Carr et al, 1992; Köppen et al, 1992). However, it was not recommended for the primary prophylaxis of TE because of its side-effects especially rash and allergy. Thus patients discontinued the prophylaxis and had higher TE reactivation. Pyrimethamine had bone marrow toxicity. When patients received without leucovorin supplement the survival rate reduced (Jacobson et al, 1994). Even though pyrimethamine

**Study period [References]** 

> 1981-1990 [Richards et al,1995]

**Study Location** 

occur and how patients could be taken care of.

(Oksenhendler et al, 1994; Richards et al, 1995; Leport et al, 1996).

Homosexual men, with AIDS

San Francisco, USA

was not recommended as a first-line regimen for primary prophylaxis of TE, some medical researchers considered pyrimethamine for patients who were intolerant to TMP-SMZ, especially in high risk patients with CD4 <100 cell/mm3 (Leport et al, 1996).

TMP-SMZ was the drug of choice for prophylaxis for both PCP and toxoplasmosis (Carr et al, 1992; Richards et al, 1995). Therefore, there were various regimens ranging from 1 double-strength1 (DS) tablet twice daily to 1 DS tablet 3 times weekly (14 DS tablets to 3 DS tablets per week) have been used. Ribera and colleagues (1999) found that since 1992, patients received either one of the following 5 regimens of TMP-SMZ for TE prophylaxis i.e.1 DS tablet daily (7DS tab/wk), 2 DS tablets daily 3 times weekly (6 DS tab/wk), 1 DS tablet 5 times weekly (5 DS tab/wk), 1 DS tablet 3 times weekly (3 DS tab/wk), and 1 singlestrength (SS) tablet daily (3.5 DS tab/wk), they noticed the more frequent doctors began prescribing low doses of TMP-SMZ the higher number of patients receiving TMP-SMZ prophylaxis developed TE. Therefore, they studied to assess the efficacy of the various doses of TMP-SMZ as primary prophylaxis for TE and concluded that patients receiving low dose TMP-SMZ (<4 DS tab/wk) had a higher risk of developing TE than those who received high dose TMP-SMZ indicating 89% protective efficacy for high doses. An insufficient concentration of the low dose TMP-SMZ within the CNS may be an additional problem in the prevention of toxoplasmosis. Moreover, they also studied the potential interactions between rifampin and TMP-SMZ and hypothesized that rifampin may reduce the efficacy of TMP-SMZ.

Dapsone combined with pyrimethamine (200/75 mg once weekly) was more effective in the primary prophylaxis of TE than aerosolized pentamidine (300 mg every 4 weeks) and had the advantage of a lower cost and easier administration (Torres et al, 1993; Opravil et al, 1995). Girard and colleagues (1993) revealed dapsone plus pyrimethamine prevented first episodes of TE better, but they were more toxic than aerosolized pentamidine (42 patients discontinued dapsone plus pyrimethamine while only 3 patients stopped aerosolized pyrimethamine, p<0.001)

In conclusion, primary prophylaxis was the important strategy to prevent TE occurrence in the 1990s period. TMP-SMZ was the drug of first choice which was prescribed when HIV/AIDS seropositive to *T. gondii* antibody had low CD4 <200 cell/mm3. By this practice, the prevalence of TE was reduced from 19% in 1988 to 6% in 1994 (Katlama, 1995). The incidence of TE was 3.9 cases/100 person-years (95% CI, 3.7–4.1 cases/100 person-years), patients who discontinued TMP-SMZ increased the risk of TE (Abgrall et al, 2001).

#### **3.3 TE during HAART period (1997-present)**

Since 1997, protease inhibitor, an antiretroviral drug, had been widely available, HIVinfected persons have lived longer and healthier lives. Since then, in the period of 15 years, that development was considered one of the great success stories of modern medicine. The death rate from HIV disease was reduced by 50 to 80% and changed from a fatal and hopeless illness to what is now a manageable chronic disease. The simultaneous combination of three or more different antiretroviral drugs was known as Highly Active Antiretroviral Therapy or HAART (Cooper 1996). It significantly delayed the onset of AIDS in HIV-infected individuals as well as reduced almost all opportunistic infections. The

 1 double-strength (DS) tablet contains 160 mg of trimethoprim and 800 mg of sulfamethoxazole, while single-strength (SS) contains 80 mg of trimethoprim and 400 mg of sulfamethoxazole.

Toxoplasmic Encephalitis 289

PY: 50 mg three time a week after a 100-mg loading dose on the first day plus folinic acid 15 mg three

Placebo: the similar in appearance and taste to PY plus folinic acid 15

AP: aerosolized Pentamidine 300

TMP-SMZ: trimethoprim 160 mg and sulfamethoxazole 800 mg every

D/PY: dapsone-pyrimethamine 100 mg/ wk and pyrimethamine 25

Low doses TMP-SMZ:< 4 DS (8SS) tab/wk (i.e. 3 DS tablets per week and 7 SS tablets per week) H igh doses TMP-SMZ: 14 DS/wk (7, 6, and 5 DS tablets per week).

mg three time a week

time a week

mg/mo

alternative day

mg every 2wk

**Drug Regimens Outcomes Significance** 

PY was not recommended as a primary prophylaxis of TE, but it should be considered for patients who are intolerant to TMP-SMZ, especially in high-risk patients with < 100 CD4 cells/mm3.

Intermittent TMP-SMZ was more effective preventing TE than low-dose D/PY and

High doses of TMP-SMZ were more effective than low doses for lowering the risk of TE in HIVinfected patients. Patients receiving concomitant rifampin treatment, rifampin may reduce the efficacy of TMP-SMZ.

AP D/PY was associated with a shorter survival.

TE occurrence 12% in PY gr. 13%in placebo (RR 0.9; 95% CI, 0.6-1.4), The survival rate was similar, 85% and 80% (RR, 0.9; 95% CI, 0.7-1.2).

TE occurred

AP gr.

D/PY gr.

89%).

Table 2. (cont.) Data from the studies on toxoplasmic encephalitis during prophylaxis regimen period (1990-1997). AP = aerosol pentamidine, D = dapsone, DS = double-strength, gr. = group, mo. = month(s), P= pentamidine, PY/S = pyrimethamine/sulfadiazine, PCP = *Peumocystis carinii* pneumonia, RR = relative risk, SS = single-strength, Tab = tablet, TMP-SMZ = trimethoprim + sulfamethoxazole, TE= Toxoplasmic Encephalitis, wk. = week(s)

for the development of TE (Yazdanpanah et al, 2001; Antinori et al, 2004).

and untreated HIV-infected persons, especially among severe immunodeficients and in the absence of prophylaxis (Antinori et al, 2004). The significant risk factors for TE occurrence were identified as decreased CD4 count and lack of prophylaxis against infection with *Toxoplasma* species. As demonstrated by Abgrall and colleagues (2001), patients who discontinued TMP-SMZ prophylaxis, received before and after HAART period, had 4.8 and 4.2 times increased risk of TE respectively. During HAART, patients whose CD4 cell counts increased to >200 cells/mm3, the incidence of TE was only 0.1 case/100 person-years (95% CI, 0.0–0.2) and TE was not increased even with the discontinuation of TMP-SMZ. On other hand, in HIV-infected individuals whose CD4 was lower than 50 cell/mm3, TE occurred in 12.6/100 person-years, the most common opportunistic infection followed by PCP at 11.4/100 person-years (Yazdanpanah et al, 2001). Other problems affecting TE occurrence even with the widespread use of HAART were patients unaware of their HIV serostatus and those who lacked exposure to HAART or prophylaxis. Thus they presented more with TE as AIDS defining illness than the pre HAART era. In cases who were accessible to HAART, the issues of patients' adherence, drug resistance, failure and cross-resistance were major risks

The decreased incidence of TE and other OIs in HIV-infected patients from HAART raised the issue of discontinuation of primary prophylaxis preventing those OIs and secondary

25.6/100 person-year in

Patients receiving low dose TMP-SMZ had a higher risk of developing TE than those patients receiving high dose TMP-SMZ (estimated protective efficacy for high doses,

 8.9/100 person-year inTMP-SMZ gr. 9.4/100 person-year in

**Study Design [References]**

**The placebo-controlled study, randomized, double-blind trial. 554 HIV-infected patients who had CD4 < 200 cell/mm3 were recruited in France, USA and Spain. [Leport et al, 1995]** 

**Randomized, open label, prospective trial in 197AIDS patients who had CD4<200 cell/mm3 and no history of previous PCP or TE [Antinori et** 

**Case-control study in 521 HIV-infection cohort study from 1993 – 97 by selecting 32 TE cases compared with 64 non-TE cases who were matched by CD4 and** *Toxoplasma gondii* **serostatus. [Ribera et** 

**al, 1995]** 

**al, 1999]** 

incidence of TE was, with no exception, decreased from 3.9 cases per 100 person-years in the period before the availability of HAART to 1.0 case per 100 person-years in the HAART era (Sacktor et al, 1990; Abgrall et al, 2001). However, TE remained the most prevalent CNS disorder, accounting for one-fourth of all documented cases in both antiretroviral-treated


incidence of TE was, with no exception, decreased from 3.9 cases per 100 person-years in the period before the availability of HAART to 1.0 case per 100 person-years in the HAART era (Sacktor et al, 1990; Abgrall et al, 2001). However, TE remained the most prevalent CNS disorder, accounting for one-fourth of all documented cases in both antiretroviral-treated

> Aerosolized Pentamidine (AP) IAP: Primary prophylaxis IIAP: Secondary prophylaxis

TMP-SMZ: 60 patients received trimethoprim 160 mg + sulfamethoxazole800 mg Lowdose i.e. 2 tab twice a week AP or P: Pentamidine (AP) and 17 patients received intravenous

D/PY: 173 patients received Dapsone 50 mg(D ) plus Pyrimethamine 50

AP: 176 patients received aerosolized Pentamidine 300 mg (AP)

D: patients received Dapsone 100 mg, twice per wk

PY: 264 patients received

Placebo: 132 patients received

per wk

placebo

AP: 176 patients received aerosolized Pentamidine 100 mg every 2 wk

Pyrimethamine 25 mg (PY) trice

Pentamidine (P)

mg (PY)

(pyrimethamine/sulfadiazine PY/S) Ib: Primary prophylaxis IIb: Secondary prophylaxis

Fansidar

**Drug Regimens Outcomes Significance** 

No TE occurred in patient who received TMP-SMZ with 1,153 days follow

TE occurred 10.9% in D/PY gr. (19 out of 173) and 18.2% in AP gr. (32 out

Patients receiving AP had 1.81 times higher risk of TE than those receiving D/PY (95%, CI; 1.12 – 2.94, p= 0.02) Patients infected by *T. gondii*, TE risk was 2.37 times (95% CI, 1.3 -4.4,

33% TE occurred in patients who received AP or P (95% CI, 19% - 51%, P=0.008) and TE occurred even patients have already received prophylaxis for 460 days

of 176)

P =0.006)

(p = 0.01).

p=.006)

groups

Patients received PY had higher death rate (RR, 2.5; 95% CI, 1.3-4.8;

No difference between two groups of TE occurrence, this may be due to concomitant PCP prophylaxis with TMP-SMZ in both

6 TE events occurring among those receiving AP, compared to none among those taking D

Fansidar (PY/S) was recommended for use as prophylaxis when AIDS patients with ≤ 100 cell/mm3 , if CD4 100-200

Low-dose TMP-SMZ was more effective (P<.008) than AP in preventing TE

HIV-infected patients with previous PCP

D/PY prevents first episodes of TE better, but more toxicity than AP (42 patients discontinued D/PY while only 3 patients stopped AP,

D was more effective in the primary prophylaxis of TE and has the advantage of a lower cost

PY had bone marrow toxicity when patients received without leucovorin supplement will reduce the survival rate, thus primary prophylaxis for TE with

p<0.001)

and easier administration.

PY was not recommended.

/mm3 AP was recommended

in

TE occurrence 73% in IAP 30.9% in IIAP 5% in IPY/S 2.3% in IIPY/S

up

**Study Design [References]**

**Retrospective study in 155 AIDS patients who were referred to tertiary referral teaching hospital after PCP for following up of the TE complication within 3 year periods [Carr et al, 1992]** 

**Randomized trial in AIDS patients who had CD4 < 200 cell/mm3 with the 539 days follow up period [Girard et al, 1993]** 

**Prospective study in 278 AIDS patients who had CD4 <250 cell/mm3 and follow up TE occurrence for 42-44** 

**[Torres et al, 1994]** 

**Multicenter, doubleblind randomized clinical trial in 378 AIDS patients who had CD4<200 cell/mm3 with 2.5 yrs follow up period [Jacobson et al,** 

**wks** 

**1994]** 

**Cohort study in 83 AIDS patients comparing primary and secondary prophylaxis to prevent TE with follow up duration of 3-41 mo (median = 8 mo) [Köppen et al, 1992]** 


Table 2. (cont.) Data from the studies on toxoplasmic encephalitis during prophylaxis regimen period (1990-1997). AP = aerosol pentamidine, D = dapsone, DS = double-strength, gr. = group, mo. = month(s), P= pentamidine, PY/S = pyrimethamine/sulfadiazine, PCP = *Peumocystis carinii* pneumonia, RR = relative risk, SS = single-strength, Tab = tablet, TMP-SMZ = trimethoprim + sulfamethoxazole, TE= Toxoplasmic Encephalitis, wk. = week(s)

and untreated HIV-infected persons, especially among severe immunodeficients and in the absence of prophylaxis (Antinori et al, 2004). The significant risk factors for TE occurrence were identified as decreased CD4 count and lack of prophylaxis against infection with *Toxoplasma* species. As demonstrated by Abgrall and colleagues (2001), patients who discontinued TMP-SMZ prophylaxis, received before and after HAART period, had 4.8 and 4.2 times increased risk of TE respectively. During HAART, patients whose CD4 cell counts increased to >200 cells/mm3, the incidence of TE was only 0.1 case/100 person-years (95% CI, 0.0–0.2) and TE was not increased even with the discontinuation of TMP-SMZ. On other hand, in HIV-infected individuals whose CD4 was lower than 50 cell/mm3, TE occurred in 12.6/100 person-years, the most common opportunistic infection followed by PCP at 11.4/100 person-years (Yazdanpanah et al, 2001). Other problems affecting TE occurrence even with the widespread use of HAART were patients unaware of their HIV serostatus and those who lacked exposure to HAART or prophylaxis. Thus they presented more with TE as AIDS defining illness than the pre HAART era. In cases who were accessible to HAART, the issues of patients' adherence, drug resistance, failure and cross-resistance were major risks for the development of TE (Yazdanpanah et al, 2001; Antinori et al, 2004).

The decreased incidence of TE and other OIs in HIV-infected patients from HAART raised the issue of discontinuation of primary prophylaxis preventing those OIs and secondary

Toxoplasmic Encephalitis 291

2001; Ghosn et al, 2003). TE patients, from two large HIV centres in Germany, receiving HAART was studied regarding the restoration of *T. gondii-*specific immune response and IFN- as well as the longitudinal clinical characteristics/outcomes of TE (Hoffmann et al, 2007). Patients were grouped according to the date of TE diagnoses i.e. period 1, 1990-1993; period 2, 1994-1996; period 3, 1997-1999 considered as early HAART period and period 4, 2000-2004 as late HAART period (figure 2). The data from that study indicated several characteristics of TE that have changed since the availability of HAART such as a marked increase in 5-year survival rate as 7% in period 1 compared to 78% in period 3 (p <0.0001). However, accumulative survival in the late HAART era was significantly lower than in the early HAART era (Figure 2). TE was found to be the first AIDS-defining illness more frequently than in earlier periods, therefore, patients who were co-infected with HIV and TE in HAART era did not receive antiretroviral therapy or any prophylaxis. More interestingly, persistent neurological deficits caused by TE such as hemiparesis, seizures, cognitive or other deficits were present in TE patients who survived during HAART higher than in pre

Fig. 2. Comparing cumulative survival of toxoplasmic encephalitis (TE) patients during pre-,

Hoffmann and colleagues found significant decrease in the *T. gondii*-specific immune response and IFN- (IL-12 and IL-15) in patients with acute episodes or relapses of TE more than in those who did not relapse even when maintenance therapy was discontinued. The latter was an adequate restoration group, while the former was a poor one in whom TE developed even on HAART and plasma HIV RNA level was below the detection limit for >6 months and their CD4 count were >200 cell/mm3. There were evidences showing that functional immune restoration during HAART in advanced AIDS patients may be incomplete because quantitative increased CD4 count may not always reflect the quality of antigen-specific responses (Hoffmann et al, 2007; Furco et al, 2008). A multicentre study conducted by Spanish *Toxoplasma gondii* Study Group proposed whether *in vitro* lymphocyte

early- and late-HAART eras (Hoffmann et al, 2007)

HAART era (45% and 37%).

prophylaxis against opportunistic diseases. Furrer et al (1999) demonstrated no case of *P. carinii* pneumonia (PCP) and TE in patients receiving a combined antiretroviral therapy and their primary prophylaxis were discontinued after CD4 increased to >200 cells/mm3 for at least 12 weeks, plus 14% of the total lymphocyte count. They also calculated the upper 99% confidence limits for the incidence of PCP at 1.93/100 patient-years, while it was 4.20/100 patient-years for TE. They thus recommended stopping primary prophylaxis against PCP, but not TE, in HIV-infected patients who received HAART and had a sustained increase (longer than 12 weeks) in their CD4 counts to >200 cells/mm3 and to at least 14% of total lymphocytes. Because the number of TE patients who had been assessed were insufficient to recommend stopping prophylaxis, the same researcher group thus extended their study by accommodating more patients who were seropositive to *T gondii* with longer follow-up (up to 272 person-years) period. They reassured that stopping primary prophylaxis was safe in HIV- and *T gondii-*infected patients who responded to potent antiretroviral treatment with a sustained elevation in immunological markers (14% of peripheral lymphocyte count and the CD4 count remaining higher than 200 cell/mm3 for at least 12 weeks), especially in the regions where the prevalence of *Toxoplasma* infection was high as in central and western Europe (Furrer et al, 2000).

Because of high toxicity, the discontinuation of secondary or maintenance prophylaxis of CMV infection and PCP were evaluated first and revealed safety discontinuing for patients receiving HAART whose their CD4 count was increased to >200 cells/mm3 (Zeller et al, 2002)*.* It was known that the risk of relapse after a TE episode was as high as 50% - 80% among patients who did not receive secondary/maintenance prophylaxis and survived more than 6-12 months (Miro et al, 2006). Studies were later undertaken to evaluate the safety of TE secondary/maintenance prophylaxis discontinuation. Concomitant results supported the recommendations of the US Public Health Service (USPHS) guidelines which suggested that secondary prophylaxis for TE can be discontinued for patients receiving HAART in whom either their CD4 counts remained >200 cells/mm3 for 3–6 months or CD4 counts were >100 cells/mm3 with their plasma HIV RNA loads were <500 copies/mL (Soriano et al, 2000; Zeller et al, 2002). However, those studies were primarily aimed at evaluating PCP prophylaxis discontinuation in the patients' CD4 threshold of <200 cells/mm3. Miro and the GESIDA study group conducted a randomized, multicenter clinical trial by stratified HIV-infected patients according to the high risk of TE reactivation as CD4 count of <100 cell/mm3. They found no episode of TE during a median follow-up of 25 months (409 person-years). Thus, they recommended discontinuation of primary prophylaxis in patients with sustained increase in the CD4 count of >200 cell/mm3 for at least 3 months and advised to resume primary prophylaxis when the CD4 count was decreased to <100 cells/mm3 (Miro et al, 2006). This group also followed 20 patients who developed acute TE and received HAART. It revealed the majority of their T cell responded to *T. gondii* antigen, interferon (IFN)- production and CD4 count of >200 cell/mm3 were restored after at least 1 year of HAART. They concluded that the criteria for safely stopping TE secondary/maintenance prophylaxis should be when patients were on HAART for at least 1 year with an increase in CD4 count to >200 cell/mm3 and with totally (<5,000 copies/mL) or partially (<10,000 copies/mL) suppressed viral replication for at least 3-6 months. Similar to primary prophylaxis, reintroducing secondary/maintenance prophylaxis whenever the CD4 count was decreased to <200 cell/mm3 was a prudent practice.

It has been nearly 15 years since HAART was widely administered in advanced AIDS. Many benefits were well recognised and appreciated. However, there were reports of TE relapse after discontinuation of maintenance prophylaxis despite high CD4 count (Tsambiras et al,

prophylaxis against opportunistic diseases. Furrer et al (1999) demonstrated no case of *P. carinii* pneumonia (PCP) and TE in patients receiving a combined antiretroviral therapy and their primary prophylaxis were discontinued after CD4 increased to >200 cells/mm3 for at least 12 weeks, plus 14% of the total lymphocyte count. They also calculated the upper 99% confidence limits for the incidence of PCP at 1.93/100 patient-years, while it was 4.20/100 patient-years for TE. They thus recommended stopping primary prophylaxis against PCP, but not TE, in HIV-infected patients who received HAART and had a sustained increase (longer than 12 weeks) in their CD4 counts to >200 cells/mm3 and to at least 14% of total lymphocytes. Because the number of TE patients who had been assessed were insufficient to recommend stopping prophylaxis, the same researcher group thus extended their study by accommodating more patients who were seropositive to *T gondii* with longer follow-up (up to 272 person-years) period. They reassured that stopping primary prophylaxis was safe in HIV- and *T gondii-*infected patients who responded to potent antiretroviral treatment with a sustained elevation in immunological markers (14% of peripheral lymphocyte count and the CD4 count remaining higher than 200 cell/mm3 for at least 12 weeks), especially in the regions where the prevalence of *Toxoplasma* infection was high as in central and western

Because of high toxicity, the discontinuation of secondary or maintenance prophylaxis of CMV infection and PCP were evaluated first and revealed safety discontinuing for patients receiving HAART whose their CD4 count was increased to >200 cells/mm3 (Zeller et al, 2002)*.* It was known that the risk of relapse after a TE episode was as high as 50% - 80% among patients who did not receive secondary/maintenance prophylaxis and survived more than 6-12 months (Miro et al, 2006). Studies were later undertaken to evaluate the safety of TE secondary/maintenance prophylaxis discontinuation. Concomitant results supported the recommendations of the US Public Health Service (USPHS) guidelines which suggested that secondary prophylaxis for TE can be discontinued for patients receiving HAART in whom either their CD4 counts remained >200 cells/mm3 for 3–6 months or CD4 counts were >100 cells/mm3 with their plasma HIV RNA loads were <500 copies/mL (Soriano et al, 2000; Zeller et al, 2002). However, those studies were primarily aimed at evaluating PCP prophylaxis discontinuation in the patients' CD4 threshold of <200 cells/mm3. Miro and the GESIDA study group conducted a randomized, multicenter clinical trial by stratified HIV-infected patients according to the high risk of TE reactivation as CD4 count of <100 cell/mm3. They found no episode of TE during a median follow-up of 25 months (409 person-years). Thus, they recommended discontinuation of primary prophylaxis in patients with sustained increase in the CD4 count of >200 cell/mm3 for at least 3 months and advised to resume primary prophylaxis when the CD4 count was decreased to <100 cells/mm3 (Miro et al, 2006). This group also followed 20 patients who developed acute TE and received HAART. It revealed the majority of their T cell responded to *T. gondii* antigen, interferon (IFN)- production and CD4 count of >200 cell/mm3 were restored after at least 1 year of HAART. They concluded that the criteria for safely stopping TE secondary/maintenance prophylaxis should be when patients were on HAART for at least 1 year with an increase in CD4 count to >200 cell/mm3 and with totally (<5,000 copies/mL) or partially (<10,000 copies/mL) suppressed viral replication for at least 3-6 months. Similar to primary prophylaxis, reintroducing secondary/maintenance prophylaxis

whenever the CD4 count was decreased to <200 cell/mm3 was a prudent practice.

It has been nearly 15 years since HAART was widely administered in advanced AIDS. Many benefits were well recognised and appreciated. However, there were reports of TE relapse after discontinuation of maintenance prophylaxis despite high CD4 count (Tsambiras et al,

Europe (Furrer et al, 2000).

2001; Ghosn et al, 2003). TE patients, from two large HIV centres in Germany, receiving HAART was studied regarding the restoration of *T. gondii-*specific immune response and IFN- as well as the longitudinal clinical characteristics/outcomes of TE (Hoffmann et al, 2007). Patients were grouped according to the date of TE diagnoses i.e. period 1, 1990-1993; period 2, 1994-1996; period 3, 1997-1999 considered as early HAART period and period 4, 2000-2004 as late HAART period (figure 2). The data from that study indicated several characteristics of TE that have changed since the availability of HAART such as a marked increase in 5-year survival rate as 7% in period 1 compared to 78% in period 3 (p <0.0001). However, accumulative survival in the late HAART era was significantly lower than in the early HAART era (Figure 2). TE was found to be the first AIDS-defining illness more frequently than in earlier periods, therefore, patients who were co-infected with HIV and TE in HAART era did not receive antiretroviral therapy or any prophylaxis. More interestingly, persistent neurological deficits caused by TE such as hemiparesis, seizures, cognitive or other deficits were present in TE patients who survived during HAART higher than in pre HAART era (45% and 37%).

Fig. 2. Comparing cumulative survival of toxoplasmic encephalitis (TE) patients during pre-, early- and late-HAART eras (Hoffmann et al, 2007)

Hoffmann and colleagues found significant decrease in the *T. gondii*-specific immune response and IFN- (IL-12 and IL-15) in patients with acute episodes or relapses of TE more than in those who did not relapse even when maintenance therapy was discontinued. The latter was an adequate restoration group, while the former was a poor one in whom TE developed even on HAART and plasma HIV RNA level was below the detection limit for >6 months and their CD4 count were >200 cell/mm3. There were evidences showing that functional immune restoration during HAART in advanced AIDS patients may be incomplete because quantitative increased CD4 count may not always reflect the quality of antigen-specific responses (Hoffmann et al, 2007; Furco et al, 2008). A multicentre study conducted by Spanish *Toxoplasma gondii* Study Group proposed whether *in vitro* lymphocyte

Toxoplasmic Encephalitis 293

documents (Martin-Blondel et al, 2010). Their findings with other suggestion (Shelburbe et al, 2006) were proposed as a definition of unmasking TE-IRIS as 1) absence of neurological features related to TE in patients before starting HAART but presented afterwards; 2) at the onset of TE-IRIS, patients' CD4 counts were higher than when starting HAART and their viral load were decreased > 1 log10; 3) histological features showed a profound inflammatory response with predominantly CD8 lymphocytes and 4) symptoms and signs were not due to other newly acquired infections, the expected TE course or drug toxicity. Paradoxical TE-IRIS cases, in which an exacerbation of a past known and usually treated TE occurred, were also reported (Pfeffer et al, 2009; Tremont-Lukats et al, 2009; Cabral et al, 2010). Two HIV-infected known cases, without antiretroviral treatment, developed TE when their CD4 count was low. They thus received specific TE treatment and HAART and their immune status was restored as indicated by lowering of viral load and increased CD4 count. One and 3 months later, they presented with deterioration of clinical signs and symptoms related to TE. Imaging studies showed significant increase in size and stronger enhancement of the lesions as well as appearance of new nodular areas. Pathological study found an intense perivascular inflammatory infiltration, predominated by CD8 lymphocytes. One case (Pfeffer et al, 2009) showed both stages of cysts containing *Toxoplasma* bradyzoites and few tachyzoites, but negative in another (Cabral et al, 2010). Tremont-Lukats and colleagues (2009) reported a case of paradoxical TE, but was argued by another group (Martin-Blondel et al, 2009) because of finding abundant tachyzoites on brain biopsy, which is an active viable form of *T. gondii*, but not bradyzoite*.* Also, there was no evidence of an immune response of the affected tissues, so they suggested that the case might be due to an

unfavourable course of a previously diagnosed toxoplasmosis than a TE-IRIS.

HAART, and ongoing treatment for toxoplasmosis could resolve the problem.

**4. Clinical features** 

Despite toxoplasmosis-associated IRIS being a very rare phenomenon, nevertheless, it occurs. Low metabolism of intracellular *Toxoplasma* bradyzoites with less expression of immunogenic surface proteins hides it from the host's immunity, immune reconstitution during HAART is thus attenuated. The patients at highest risk are those with low CD4 count, HAART-naïve, of young age and starting HAART close to a recent diagnosis of opportunistic infections (Shelburne et al, 2006). If TE-IRIS is suspected, close observation is recommended within 2 weeks. The use of magnetic resonance imaging in association with clinical and laboratory data can reduce the number of unnecessary cerebral biopsies (Cabral et al, 2010). A high steroid dose to control IRIS (Venkataramana et al, 2006), uninterrupted

Toxoplasmic encephalitis (TE) is the most common cause of focal brain lesion (FBL) in HIV/AIDS individuals with profound immune deficiency. Clinical presentations of TE depended on the location, number and size of the lesions. It may present with generalized cerebral dysfunction or focal signs and symptoms of the central nervous system (CNS) or with psychiatric abnormalities (Table 3). The majority of patients present with a combination of generalized and focal CNS abnormalities (Table 1) such as headache, fever, alteration of consciousness, confusion, cognitive impairment, hemiparesis, facial nerve palsy and convulsion (Berger et al, 1987; Ragnaud et al, 1993; Wainstein et al, 1993, Sukthana et al, 2000; Anrinori et al, 2004; Nissapatorn et al, 2004b; Chankrachang, 2004; Miro et al; 2006; Hoffmann et al, 2007; Ho et al, 2008). Headache was a more frequent symptom than fever ranging from 47% to 100%, while fever was found 45.6% to 64.5%. However, Ragnaud and

proliferative response (LPR) and IFN– production in response to *T. gondii* soluble antigen extract (SATg) could be used as a useful biomarker indicating immune restoration in AIDS patients receiving HAART. They found that severe immunosuppressed patients whose CD4 count <200 cells/mm3 with experience in current or previous TE did not develop immune restoration indicated by almost absent of SATg-specific LPR and IFN-γ production. Those biomarkers were found in patients receiving successful HAART and in immnunocompetent asymptomatic patients who did not receive TE prophylaxis, however, they may be absent in HIV-1–uninfected and *T. gondii*-positive healthy subjects. Therefore, they cannot be used as biomarkers to detect the status of immune protection against *T. gondii* reactivation. Nevertheless, the discontinuation of TE prophylaxis, especially secondary prophylaxis, can be safely withdrawn after successful HAART as shown by CD4 count >200 cells/mm3 and a sustained reduction in viral load (Lejeune et al, 2011).

#### **3.3.1 Immune reconstitution inflammatory syndrome (IRIS)**

The administration of HAART in HIV-infected patients restores protective immune responses against a wide variety of pathogens and dramatically decreases mortality. An immune restoration process occurs by the suppression of HIV-1 viral replication followed by an increasing CD4 count. In some patients, however, during the initial institution of HAART, the restoration process may be complicated by immune reconstitution inflammatory syndrome or IRIS leading to worsening of clinical, laboratory and/or radiological features. Its histology showed an intense inflammatory reaction against intact subclinical pathogens or residual antigens of opportunistic infections and non-infectious agents. It occurs either by disclosure of occult subclinical infection or enhanced inflammatory response to a treated infection. The former is named "unmasking IRIS" while the latter is called "paradoxical IRIS". About 10-25% of patients on HAART may develop IRIS, particularly in those patients with profound immune suppression, which may occur days to months after starting HAART, but normally within the first 2 months (Howard & Manji, 2009).

The common neurological IRIS had been reported in cryptococcosis, tuberculosis, and mycobacteriosis (Murdoch et al, 2007). Despite TE being the most common opportunistic neurologic disease in HIV-infected patients, neurological IRIS associated with cerebral toxoplasmosis was rarely reported and has been doubted regarding insufficient clinical details challenging the diagnosis of IRIS. In contrast, Subsai and colleagues showed that TE and other abnormalities such as stroke, progressive multifocal leukoencephalopathy (PML), and cytomegalovirus (CMV) retinitis were among the commonest kinds of neurological IRIS in northern Thai AIDS patients (Subsai et al, 2006). Their findings were TE-IRIS accounting for 0.29 and 0.59 per 100 person-years in the first and second year follow-up, respectively. Moreover, they found the incidence rate of TE-IRIS lower than the previous incidence during pre-HAART era.

Sungkanuparpha and colleagues from 4 medical centres in Thailand reported one fatal case of toxoplasmosis after initial HAART institution in HIV-infected patient with very low median (range) CD4 count as 9 (0–147) cells/mm3. In their study, 20% developed unmasking OIs and tuberculosis was the most common followed by cryptococcal meningitis. They thus proposed that immune reconstitution response to occult pathogens may explain those phenomena (Sungkanuparpha et al, 2002). Researchers from Toulouse University, France reported 9 unmasking TE-IRIS cases; 3 out of 65 TE cases from their institution with a study period of 9 years and the 6 remaining cases from published

proliferative response (LPR) and IFN– production in response to *T. gondii* soluble antigen extract (SATg) could be used as a useful biomarker indicating immune restoration in AIDS patients receiving HAART. They found that severe immunosuppressed patients whose CD4 count <200 cells/mm3 with experience in current or previous TE did not develop immune restoration indicated by almost absent of SATg-specific LPR and IFN-γ production. Those biomarkers were found in patients receiving successful HAART and in immnunocompetent asymptomatic patients who did not receive TE prophylaxis, however, they may be absent in HIV-1–uninfected and *T. gondii*-positive healthy subjects. Therefore, they cannot be used as biomarkers to detect the status of immune protection against *T. gondii* reactivation. Nevertheless, the discontinuation of TE prophylaxis, especially secondary prophylaxis, can be safely withdrawn after successful HAART as shown by CD4 count >200 cells/mm3 and a

The administration of HAART in HIV-infected patients restores protective immune responses against a wide variety of pathogens and dramatically decreases mortality. An immune restoration process occurs by the suppression of HIV-1 viral replication followed by an increasing CD4 count. In some patients, however, during the initial institution of HAART, the restoration process may be complicated by immune reconstitution inflammatory syndrome or IRIS leading to worsening of clinical, laboratory and/or radiological features. Its histology showed an intense inflammatory reaction against intact subclinical pathogens or residual antigens of opportunistic infections and non-infectious agents. It occurs either by disclosure of occult subclinical infection or enhanced inflammatory response to a treated infection. The former is named "unmasking IRIS" while the latter is called "paradoxical IRIS". About 10-25% of patients on HAART may develop IRIS, particularly in those patients with profound immune suppression, which may occur days to months after starting HAART, but normally within the first 2 months (Howard &

The common neurological IRIS had been reported in cryptococcosis, tuberculosis, and mycobacteriosis (Murdoch et al, 2007). Despite TE being the most common opportunistic neurologic disease in HIV-infected patients, neurological IRIS associated with cerebral toxoplasmosis was rarely reported and has been doubted regarding insufficient clinical details challenging the diagnosis of IRIS. In contrast, Subsai and colleagues showed that TE and other abnormalities such as stroke, progressive multifocal leukoencephalopathy (PML), and cytomegalovirus (CMV) retinitis were among the commonest kinds of neurological IRIS in northern Thai AIDS patients (Subsai et al, 2006). Their findings were TE-IRIS accounting for 0.29 and 0.59 per 100 person-years in the first and second year follow-up, respectively. Moreover, they found the incidence rate of TE-IRIS lower than the previous incidence

Sungkanuparpha and colleagues from 4 medical centres in Thailand reported one fatal case of toxoplasmosis after initial HAART institution in HIV-infected patient with very low median (range) CD4 count as 9 (0–147) cells/mm3. In their study, 20% developed unmasking OIs and tuberculosis was the most common followed by cryptococcal meningitis. They thus proposed that immune reconstitution response to occult pathogens may explain those phenomena (Sungkanuparpha et al, 2002). Researchers from Toulouse University, France reported 9 unmasking TE-IRIS cases; 3 out of 65 TE cases from their institution with a study period of 9 years and the 6 remaining cases from published

sustained reduction in viral load (Lejeune et al, 2011).

Manji, 2009).

during pre-HAART era.

**3.3.1 Immune reconstitution inflammatory syndrome (IRIS)** 

documents (Martin-Blondel et al, 2010). Their findings with other suggestion (Shelburbe et al, 2006) were proposed as a definition of unmasking TE-IRIS as 1) absence of neurological features related to TE in patients before starting HAART but presented afterwards; 2) at the onset of TE-IRIS, patients' CD4 counts were higher than when starting HAART and their viral load were decreased > 1 log10; 3) histological features showed a profound inflammatory response with predominantly CD8 lymphocytes and 4) symptoms and signs were not due to other newly acquired infections, the expected TE course or drug toxicity. Paradoxical TE-IRIS cases, in which an exacerbation of a past known and usually treated TE occurred, were also reported (Pfeffer et al, 2009; Tremont-Lukats et al, 2009; Cabral et al, 2010). Two HIV-infected known cases, without antiretroviral treatment, developed TE when their CD4 count was low. They thus received specific TE treatment and HAART and their immune status was restored as indicated by lowering of viral load and increased CD4 count. One and 3 months later, they presented with deterioration of clinical signs and symptoms related to TE. Imaging studies showed significant increase in size and stronger enhancement of the lesions as well as appearance of new nodular areas. Pathological study found an intense perivascular inflammatory infiltration, predominated by CD8 lymphocytes. One case (Pfeffer et al, 2009) showed both stages of cysts containing *Toxoplasma* bradyzoites and few tachyzoites, but negative in another (Cabral et al, 2010). Tremont-Lukats and colleagues (2009) reported a case of paradoxical TE, but was argued by another group (Martin-Blondel et al, 2009) because of finding abundant tachyzoites on brain biopsy, which is an active viable form of *T. gondii*, but not bradyzoite*.* Also, there was no evidence of an immune response of the affected tissues, so they suggested that the case might be due to an unfavourable course of a previously diagnosed toxoplasmosis than a TE-IRIS.

Despite toxoplasmosis-associated IRIS being a very rare phenomenon, nevertheless, it occurs. Low metabolism of intracellular *Toxoplasma* bradyzoites with less expression of immunogenic surface proteins hides it from the host's immunity, immune reconstitution during HAART is thus attenuated. The patients at highest risk are those with low CD4 count, HAART-naïve, of young age and starting HAART close to a recent diagnosis of opportunistic infections (Shelburne et al, 2006). If TE-IRIS is suspected, close observation is recommended within 2 weeks. The use of magnetic resonance imaging in association with clinical and laboratory data can reduce the number of unnecessary cerebral biopsies (Cabral et al, 2010). A high steroid dose to control IRIS (Venkataramana et al, 2006), uninterrupted HAART, and ongoing treatment for toxoplasmosis could resolve the problem.
