**3. Laboratory diagnosis in malaria**

#### **3.1 Role of presumptive versus laboratory diagnosis for treatment**

The policy and strategies for Malaria control by the WHO hinges on Malaria prevention, diagnosis and treatment. Diagnosis of malaria has been a challenge in both endemic and non endemic countries alike: the former having overdiagnosis with consequences of wastage of resources for treatment, excessive drug pressure and antimalarial drug resistance and the latter under diagnosis or even missed diagnosis which in some cases lead to malaria mortality. Gwer et al (2007) in an over view of problems associated with overdiagnosis in severe malaria identified the unavailability and unreliable parasitological confirmation of parasitemia as the greatest challenge in endemic countries.

The commonest symptom of malaria is fever and the subject of how many febrile episodes in susceptible populations in endemic areas even in the face of detectable parasitemia is attributable to malaria has been of immense research. Mc Guiness et al (1998) proposed some clinical case definitions for malaria in southern Ghana. Using logistic regression to model fever risk as continuous function of parasite density, fever attributable to malaria was defined by season and age groups. It was concluded that attributable fever was 51% and 22% in wet and dry seasons respectively for infants while in the children older than one year, it was higher in both seasons: 89% and 36% respectively. They also observed a lower estimated parasite density threshold for initiation of a febrile episode in infants than the older child. In another study Rougement et al (1991) working in Niger, West Africa investigated parasitemia based on 3 criteria of febrile episodes: the duration, intensity and possibility of a non malarial cause. The proportion of febrile cases attributable to parasitemia ranged from 0 to 0.92 but there was no association between parasitemia and low intensity fevers, or fever of greater than 3 days duration in the presence of an obvious non malaria cause. They however also found highly significant relationship between parasitemia and fever in the high transmission season. It seems from these studies that making a

was commonly observed in their study. Algorithms on the one hand may lead to wastefulness of treatment supplies and on the other hand endanger lives for other possibly

The school aged child in an area of high endemicity typically has malaria parasite prevalence rates of up to 75%. Despite this high rates of parasitemia, theses children largely remain asymptomatic, having developed sufficient immunity which is both antiparastic and antitoxic to keep them from having clinical infection (Bruce Chwatt et al as cited by Orogade et al, 2002). In their study, Orogade et al (2002) also observed that these asymptomatic children had high levels of gametocytaemia (65%). Possible association between asymptomatic parasitemia and the utilization of vector control measures were analyzed. Vector control measure utilization was strongly related and inversely associated with the rates of ASMP. The estimation of ASMP is therefore recommended for use as an index for

The policy and strategies for Malaria control by the WHO hinges on Malaria prevention, diagnosis and treatment. Diagnosis of malaria has been a challenge in both endemic and non endemic countries alike: the former having overdiagnosis with consequences of wastage of resources for treatment, excessive drug pressure and antimalarial drug resistance and the latter under diagnosis or even missed diagnosis which in some cases lead to malaria mortality. Gwer et al (2007) in an over view of problems associated with overdiagnosis in severe malaria identified the unavailability and unreliable parasitological confirmation of

The commonest symptom of malaria is fever and the subject of how many febrile episodes in susceptible populations in endemic areas even in the face of detectable parasitemia is attributable to malaria has been of immense research. Mc Guiness et al (1998) proposed some clinical case definitions for malaria in southern Ghana. Using logistic regression to model fever risk as continuous function of parasite density, fever attributable to malaria was defined by season and age groups. It was concluded that attributable fever was 51% and 22% in wet and dry seasons respectively for infants while in the children older than one year, it was higher in both seasons: 89% and 36% respectively. They also observed a lower estimated parasite density threshold for initiation of a febrile episode in infants than the older child. In another study Rougement et al (1991) working in Niger, West Africa investigated parasitemia based on 3 criteria of febrile episodes: the duration, intensity and possibility of a non malarial cause. The proportion of febrile cases attributable to parasitemia ranged from 0 to 0.92 but there was no association between parasitemia and low intensity fevers, or fever of greater than 3 days duration in the presence of an obvious non malaria cause. They however also found highly significant relationship between parasitemia and fever in the high transmission season. It seems from these studies that making a

**2.4.1 Asymptomatic malaria parasitemia and its implication for malaria control** 

life threatening conditions.

**2.4 School aged 5-12years** 

evaluation of malaria vector control programmes.

**3.1 Role of presumptive versus laboratory diagnosis for treatment** 

parasitemia as the greatest challenge in endemic countries.

**3. Laboratory diagnosis in malaria**

diagnosis by clinical case definitions based on epidemiological factors may be a useful tool in areas where laboratory facilities are not always available or reliable.

However, Valerie et al (2010) again observed from studies done over 20years that there was a growing decline in malaria transmission in East Africa and a subsequent proportion of fever associated with Plasmodium falciparum. They concluded that the decline provides evidence for policy change from presumptive antimalarial therapy to laboratory diagnosis before treatment (Valerie et al 2009, 2010). Much has gone into training of personnel for laboratory diagnosis and as Ngasala et al (2008) reported on the impact of training in clinical and microscopy diagnosis of childhood malarial on prescription and health outcome: microscopy reduces prescription but there is great variation in accuracy of readings. With this observation, the caution by English et al (2009) might be only apt that rapid universal policy change that abandons presumptive antimalarial treatment for African children might be premature and in fact cause more harm than good.

## **3.2 Comparisons between rapid diagnostic tests and microscopy in malaria**

The gold standard for malaria parasite identification and quantification has been the microscopic examination of thick and fixed thin blood smears using Giemsa stain. In cases of anticipated low malaria parasite densities, care should be taken to maintain the pH of the stain around 7 and a freshly prepared stain achieves better results (Orogade et al, 2008). Other techniques utilised to enhance microscopy include the acridine orange fluorescent technique ( Keiser el al, 2002; Lowe et al, 1996; Nicholas, 1997). This has proved to be quite useful but requires the additional requirements of fluorescent microscopy. Maintenance of a good quality, effective microscopy service involves the provision of high quality supplies, reagents, microscopes as well as technical competence and an adequate work environment to prepare usable blood films (Coleman et al, 2002; Durrheim et al, 1997, Kachur et al, 1998; Kain et al, 1998; Kilan et al, 2000; Omeara et al, 2005 as cited in Bell et al, 2006).

Obstacles to lab diagnosis of malaria as have been reported in Mali (Dolo et al, 2010) are the same experience in most developing countries where malaria is endemic. These includeunderuse of laboratory diagnosis by clinicians, absence of qualified laboratory facilities in some locations, and poor continuous professional education of laboratory technicians.

Introduction of Rapid Diagnostic tests was intended to fill the need for accuracy, speed and reliability which standard microscopy has fallen short of. These are antigen detecting rapid diagnostic tests which detect the histidine rich protein 2(HRP2) and Plasmodium lactate dehydrogenase(pLDH) which are usually produced during the erythrocytic cycle. Several studies have evaluated the effectiveness of these tests compared with microscopy and the results have consistently shown high sensitivity and specificity but inability to differentiate mixed infections (Chinkhumba, 2010; Gatti et al, 2007; Tomas et al, 2001). However the successful implementation of RDT has been bedevilled by poor product performance, inadequate methods to determine the quality of products and a lack of emphasis and capacity to deal with these.(Bell et al 2006) Another group (Christopher et al, 2008) described the limitations of RDTs as having: all or none test results, inability to diagnose non falciparum malaria, variable heat stability and safety risks related to blood sampling (especially HIV and hepatitis B). Also of equal concern is that negative RDT results are often ignored and patients are treated anyway.

Current Issues in Clinical and Laboratory Diagnosis in Malaria 169

• Reliance on rapid diagnostic tests should be put into context. Areas with mixed malaria parasite infection would need some other confirmatory tests while in other areas, uncertain distribution of reagents and trained personnel could limit the effectiveness of

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**5. References**
