Applicability of direct agglutination test (DAT) at a rural health setting in Bangladesh and feasibility of local antigen production.

As part of a large-scale sero-epidemiological survey on visceral leishmaniasis (VL) carried out in Mymensingh district of Bangladesh, applicability of DAT was assessed at the level of a rural health setting in Trishal (upazila) subdistrict. Despite the relatively less optimal conditions encountered, 5854 inhabitants from 7 villages appendant to Trishal were assessed for VL. The demographic distribution for sero-positivity obtained at the rural setting was comparable to that found by DAT as executed at the central laboratory (IEDC&R, Dhaka) on 9619 inhabitants from the same upazila. The overall sero-prevalence rate was 4.4% compared to 3.7% obtained in the population assessed at the central laboratory. In either study, similar VL prevalence rates of 2.1% were obtained in the male populations. Irrespective of sex, younger population (< 20 years) in both studies appeared to have higher VL incidence rate (2.3% and 2.6%) than others of 21- > or = 90 years (1.4% and 1.8%). Local production of DAT antigen employing an authochtonus L. donovani isolate was attempted at the central laboratory (IEDC&R) in Dhaka. By comparison with the reference antigen, titres obtained in all 33 VL sera tested were equally higher (1:6400- > or =: 51200) than in 35 out of 38 negative controls (< or = 1:400-1:1600). A comparable level of reactivity was also obtained in 53 VL and 52 negative control sera using a well characterized L. donovani strain (MHOM/IN/80/D88) from India. However, unlike the reference strain, titres obtained in 7 endemic controls were significantly higher with the authochtonous and homologous antigen (1:3200 - 1:6400) than with the reference (1:100 - 1:1600). The results signify the advantage of employing indigenous L. donovani isolates to further improve DAT sensitivity for detection of early and sub-clinical VL.

Prevalence of agglutinating anti-Leishmania antibodies in two multi-thousand Bengoli communities.

Control of endemic visceral leishmaniasis (VL) in large communities requires a feasible epidemiological indicator capable of monitoring on-going transmission rather than mere exposure to the parasite. Following confirmation of the desired level of reliability for laboratory diagnosis of VL, the direct agglutination test (DAT) was employed to estimate VL sero-prevalence in the endemic upazilas (subdistricts) of Trishal and Shahjadpur within Mymensingh and Sirajganj districts of Bangladesh. DAT antigen production was duly increased to allow coverage of a study population of 17826 inhabitants, 9619 of whom resided in Trishal, 7328 in Shahjadpur and 879 in Teknaf (Cox's Bazar), a known Leishmania-free district in Bangladesh. Despite large-scale production in batches of 1120-4000 ml (each sufficient for 1176-6400 screening doses), all DAT antigen batches performed as required in quality control tests for sensitivity, specificity and stability. It was convenient for both collection and testing to take the required samples of whole blood by finger prick. A cross-sectional survey revealed VL point prevalences of 4.40% in Trishal and 6.75% in Shahjadpur, compared with an extremely low rate of 0.34% in non-endemic Teknaf. In both endemic upazilas (Trishal and Shahjadpur) VL was more prevalent (2.56-4.5%) in persons up to 20 years of age than in those 21 years of age and older (1.84-2.25%). Of 918 subjects recorded as seropositives, 539 were VL-asymptomatic and 379 were VL-symptomatic with various degrees of suspicion. Diagnosis of VL was established in 125 symptomatic seropositives subjects, either by demonstrating the presence of Leishmania amastigotes (29), or by positive DAT results combined with presentation of typical VL signs (96).(ABSTRACT TRUNCATED AT 250 WORDS)