**2. Basic characteristics about** *T. gondii*

*Toxoplasma gondii* is a protozoan parasite of great medical and veterinary importance. Toxoplasmosis is one of the most common parasitic zoonoses in the world afflicting a broad range of both mammals and birds. The aetiological agent is *T. gondii* whose definite hosts are representatives of the family of *Felidae* infected by oocysts from the environment, or by tachyzoites and bradyzoites from intermediary hosts, such as all kinds of vertebrates, including humans. It is a pantropical cosmopolite and facultative heterogenic coccidia*. T. gondii* causes a mild infection in immuno-competent hosts, but in the immuno-compromised hosts, foetus and neonates, toxoplasmosis is severe even leading to death [1].

Toxoplasmosis may affect a number of organs, but it primarily affects lungs, the CNS (central nervous system) and eyes. Canine and feline toxoplasmosis is a multi-systemic disease; however a latent form of the disease usually develops. Dogs may act as a mechanical factor in transmitting toxoplasmosis to humans by rolling in foul-smelling substances and by ingesting fecal material. Just remember that 50% of stray dogs and dogs carry *T. gondii* antibodies, which means that they have been infected and may transmit the parasite. Cats are very important hosts in the epidemiological cycle of *T. gondii*, a zoonotic protozoan parasite that can infect humans and many other animal species worldwide. People and especially immuno-compromised individuals and pregnant women should observe the hygienic principles not only after contact with soil, cats, before eating, but also after contact with dogs. In gravid animals, particularly in sheep and goats, the *T. gondii* infection causes embryonic mortality, foetus death or abortion depending on the stage of gravidity in which the infection occurred. Variation in the clinical presentation and severity of disease has been attributed to several factors, including the heterogeneity of the host and the genotype of the infective parasite. The sources of the contamination by oocysts are mainly moist and shady places with the occurrence of cats where are suitable conditions for surviving of oocysts for a long period in the external environment [2]. Sheep were in fact the first mammals in which congenital toxoplasmosis were proven with abortions, dead-born fetuses and frequent manifestations of infection including infertility. The first case of manifest toxoplasmosis in sheep with symptoms of encephalomyelitis and tachycardia was described by Olafson and Monlux [3]. Sheep are most frequently infected with *T. gondii* from environment, i.e. from feed and pasture.

**Figure 1.** *T.* gondii - life cycle

76 Toxoplasmosis – Recent Advances

infection.

of using in the detection of parasites.

diagnostic approach based our data.

**2. Basic characteristics about** *T. gondii*

don´ t solve the problems of diagnosis in the early stage of infection or in the case of latent infection. For diagnostics of these stages are required more sensitive laboratory methods. In At present molecular methods based on the detection of the nucleic acid are used in the laboratories. A polymerase chain reaction (PCR - standard or quantitative) has wide range

Toxoplasmosis is an acute parasitic infection monitored based on the epidemiological situation in the country. Therefore it is necessary to interconnect an epidemiological monitoring of infection in humans and animals because of a zoonotic character of this

We here review the information available on the seroprevalence of *T. gondii* infection in livestock and pet animals in Slovakia. In addition we discuss the various serological and molecular methods available for the diagnosis of toxoplasmosis (in animals) and suggest a

*Toxoplasma gondii* is a protozoan parasite of great medical and veterinary importance. Toxoplasmosis is one of the most common parasitic zoonoses in the world afflicting a broad range of both mammals and birds. The aetiological agent is *T. gondii* whose definite hosts are representatives of the family of *Felidae* infected by oocysts from the environment, or by tachyzoites and bradyzoites from intermediary hosts, such as all kinds of vertebrates, including humans. It is a pantropical cosmopolite and facultative heterogenic coccidia*. T. gondii* causes a mild infection in immuno-competent hosts, but in the immuno-compromised

Toxoplasmosis may affect a number of organs, but it primarily affects lungs, the CNS (central nervous system) and eyes. Canine and feline toxoplasmosis is a multi-systemic disease; however a latent form of the disease usually develops. Dogs may act as a mechanical factor in transmitting toxoplasmosis to humans by rolling in foul-smelling substances and by ingesting fecal material. Just remember that 50% of stray dogs and dogs carry *T. gondii* antibodies, which means that they have been infected and may transmit the parasite. Cats are very important hosts in the epidemiological cycle of *T. gondii*, a zoonotic protozoan parasite that can infect humans and many other animal species worldwide. People and especially immuno-compromised individuals and pregnant women should observe the hygienic principles not only after contact with soil, cats, before eating, but also after contact with dogs. In gravid animals, particularly in sheep and goats, the *T. gondii* infection causes embryonic mortality, foetus death or abortion depending on the stage of gravidity in which the infection occurred. Variation in the clinical presentation and severity of disease has been attributed to several factors, including the heterogeneity of the host and the genotype of the infective parasite. The sources of the contamination by oocysts are mainly moist and shady places with the occurrence of cats where are suitable conditions for surviving of oocysts for a long period in the external environment [2]. Sheep were in fact the first mammals in which congenital toxoplasmosis were proven with abortions, dead-born

hosts, foetus and neonates, toxoplasmosis is severe even leading to death [1].

#### **3.** *T.* **and the immune system**

*T. gondii* is able to survive and persist in immuno-competent intermediate hosts for the host's life. This is despite the induction of a vigorous humoral and more importantly cellmediated immune response during infection. *T. gondii* has evolved multiple strategies to avoid or to interfere with potentially efficient anti-parasitic immune responses of the host immune evasion includes indirect mechanisms by altering the expression and secretion of immunomodulatory cytokines or by altering the viability of immune cells and direct mechanisms by establishing a lifestyle within a suitable intracellular niche and by interference with intracellular signaling cascades, thereby abolishing a number of antimicrobial effector mechanisms of the host [4].

#### **4. Non-specific immune response**

In immuno-competent hosts this parasite activates asymptomatic chronic infection, what make possible its transmission and survival. The infection of *T. gondii* may be lethal for immuno-compromised patients. At the beginning of immune response parasite changes to bradyzoites, which persist in tissue cyst for life. *T. gondii* is capable of triggering the nonspecific activation of macrophages and natural killer cells (NK-cells) along with other haematopoietic and non-haematopoietic cells. This activation is intended to limit parasite proliferation due to its direct or indirect cytotoxic action and to trigger a specific immune response due to the presentation of *T.* antigens. Non-specific response begins immediately following the first contact between the parasite and the host [5]. NK-cells take part in early phase of immune response. During the early phase of the infection, it is through the combined and synergetic action of the NK-cells and the macrophages, activated by IFN-γ. In activated macrophages vacuoles of lived tachyzoites merge with lysosomes and then follow out the destruction of parasites. Neutrophils and, very probably, eosinophils, and mast cells rapidly interfere to the infection and are involved in setting up a non-specific early immune response *via* the production of IL-12 and various proinflammatory factors [6].

Toxoplasmosis in Livestock and Pet Animals in Slovakia 79

IgM antibodies may appear earlier and decline more rapidly than IgG antibodies. The serum IgM only appears at the end of the first week following infection. These immunoglobulins are the best activators of the complement system. Due to their structure, they enable excellent agglutination and have a high level of cytotoxicity. This phenomenon is used especially in serological diagnosis techniques. Their persistence is subject to a high level of individual variation and can be as much as a year in most cases, thanks to the use of

IgA may be detected in sera of actuely infected adults and congenitally infected infants. In acquired toxoplasmosis, the appearance of IgA is not systematic. In immunodepressed subjects, IgA is thought to be an early marker in 50 % of cases. In congenital toxoplasmosis, the detection of IgA is valuable, since these can be detected in the absence of IgM. IgA (like IgM) do not cross the placenta and are actively involved in the diagnosis of congenital

IgE antibodies are detectable in sera of actually infected adults, congenitally infected infants and children with congenital toxoplasmic chorioretinitis. The appearance on IgE in acute or congenital toxoplasmosis is random. The presence of this isotype is correlated with the beginning of complications, such as adenopathies, chorioretinitis, and *T.* reactivations in

Cell-mediated immune responses are essential for host control of intracellular infections. *T. gondii* is a protozoan parasite that infects multiple vertebrate species and invades multiple cell types. Upon initial encounter with the immune system, the parasite rapidly induces production of the protective cytokine IL-12 most likely from a subpopulation of dendritic cells. NK and T-lymphocytes are then activated and triggered to synthesize IFN-γ, the major mediator of host resistance during the acute and chronic phases of infection. Cytokine (IFNγ and TNF-alpha) rather than cytotoxicity-based effector functions are more critical for protective immunity both during the acute and chronic phases of *T. gondii* infection. [10].

The T-lymphocytes, macrophages, and activity of interleukin IL-12 and IFN-γ is necessary for maintaining quiescence of chronic *T gondii* infection. IFN-γ stimulates anti-*T. gondii* activity, not only of macrophages, but also of nonphagocytic cells. TNF-alpha is another

Congenital toxoplasmosis poses a public health problem, being capable of causing foetal death and ocular and neurological sequelae in congenitally infected children. Congenital infection occurs only when mothers first encounter *T. gondii* during pregnancy. Resistance to *T. gondii* is mainly mediated by protective cytokines, such as IFN-γ and interleukin 2 (IL-2), whereas regulatory cytokines, such as IL-4 and IL-10, are associated with increased susceptibility to infection. Susceptibility of the pregnant host to toxoplasmosis may be due to a regulatory

cytokine essential for control of chronic infection with *T. gondii* [11].

increasingly sensitive detection techniques [6].

toxoplasmosis [2,13].

immunodepressed subjects [1].

**8. Congenital infection** 

**7. Acute and chronic infection** 

#### **5. Specific immune response**

The non-specific immune response has led to differentiation of macrophages and Blymphocytes into antigen presenting cells. The effector cells are stimulated by dendritic cells presenting the antigen to T-lymphocytes. This mechanism requires a close interaction between the antigen presenting cell and the T-lymphocytes [7]. The interaction of parasite with mechanisms of non-specific immune response is important to orientation of progress of specific immunity. The induction of IL-12 and then IFN-γ stimulate the progression of Th1 subpopulations so that polarize the immune response for behoof cellular immunity. After acute infection, the cells presenting antigens (macrophages) are exciting to produce IL-12 and initiate differentiation of immature CD4 T-lymphocytes to Th1. The cellular immunity initiates the production of IFN-γ. This cytokine effects as a major mediator of cellular immunity during toxoplasmosis. The key function in specific immune response plays Tlymphocytes. These effector cells, which are involved in resistance to *T.* infection, then exert their function via a cytotoxic activity and/or the secretion of cytokines involved in the regulation of immune response [8].

CD4+ and CD8+ T-lymphocytes are the main players involved in resistance of the host to *T.*  infection CD4+ T-lymphocytes are required for the development of resistance during the early phase of the infection, and for immunity during vaccination. The CD8+ T-lymphocytes exert a cytotoxic activity against tachyzoites or cells infected with *T. gondii* [9].

#### **6. Humoral immune response**

Antibodies play a minor role but remain the essential means for diagnosing toxoplasmosis. The production of specific IgG antibodies usually begins 4 weeks after the infection and can continue for several months while the dynamics of antibody production does not yield substantial change during the course of disease. IgG are the second immunoglobulins to appear in toxoplasmosis. They play a role in protection of the foetus because they are capable of crossing the placenta. The main target antigens of IgG are the surface antigens of the parasite [6].

IgM antibodies may appear earlier and decline more rapidly than IgG antibodies. The serum IgM only appears at the end of the first week following infection. These immunoglobulins are the best activators of the complement system. Due to their structure, they enable excellent agglutination and have a high level of cytotoxicity. This phenomenon is used especially in serological diagnosis techniques. Their persistence is subject to a high level of individual variation and can be as much as a year in most cases, thanks to the use of increasingly sensitive detection techniques [6].

IgA may be detected in sera of actuely infected adults and congenitally infected infants. In acquired toxoplasmosis, the appearance of IgA is not systematic. In immunodepressed subjects, IgA is thought to be an early marker in 50 % of cases. In congenital toxoplasmosis, the detection of IgA is valuable, since these can be detected in the absence of IgM. IgA (like IgM) do not cross the placenta and are actively involved in the diagnosis of congenital toxoplasmosis [2,13].

IgE antibodies are detectable in sera of actually infected adults, congenitally infected infants and children with congenital toxoplasmic chorioretinitis. The appearance on IgE in acute or congenital toxoplasmosis is random. The presence of this isotype is correlated with the beginning of complications, such as adenopathies, chorioretinitis, and *T.* reactivations in immunodepressed subjects [1].
