Studies on the prevalence of human onchocerciasis and experience with serodiagnosis of the disease in Tanzania

Abstract

Prevalence of human onchocerciasis in Tanzania is described. The prevalence is high in Bwakira (63.6%), Mahenge (58.6%) and Ruvuma (31.9%); and low in Amani (22.4%) when compared to that reported in 1970. The increase and decrease on the prevalence indicate that the disease transmission has been increasing or decreasing in the respective foci. It is speculated that bush-clearing and deforestation in general, had positive effects on the transmission of the disease where Simulium damnosum complex is a vector and the negative effects with Simulium neavei complex. In this study, Indirect Haemagglutination Antibody (IHA) test was also established for serodiagnosis of onchocerciasis, using crude heterologous antigen of adult Onchocerca gutturosa. with this antigen, IHA titres (serum •dilutions) of 1/320 and above were used as positive for onchocerciasis because they discriminated 8ross-reaction effects due to other helminths and under these circumstances, the IRA test was considered to be sufficiently valid for the diagnosis of the disease in Tanzania. The established IHA test for diagnosing onchocerciasis was found to be complementary to the skin snip and clinical diagnostic methods. High sensitivity of the IHA test was found in Amani (93.7%), Bwak i r a (89.7%), Kilosa (81.8%) and

(iv) and Ruvuma (75.0%) foci. However, the IHA test was complementary to the parasitological diagnosis in assessing age disribution of

the disease.

There was significant association between IHA

response and parasitological diagnosis, and skin changes due to onchocerciasis in certain foci; indicating a well established balance between the Q.volvulus parasite and the host, and also emphasizing the importance of IHA test in ascertaining the disease in these people with skin changes due to disease. A report on the development of Q,gutturosa to infective stage

in Simulium vorax Pomeroy is presented (Appendix D4).

A more

descriptive report on Q,gutturosa in Tanzania cattle is presented! (Appendix D3). This second report highlights the importance of continuing checking for Q,gutturosa in cattle in all areas where the presence of Q,volvulus has been'established, because there is evidence that S,vorax which transmits Q,gutturosa in cattle is also a potential vector of Q,volyulus, Raising infective stage larvae

of Q. gutturosa in S .yorax for antigen was attempted.

But the

average number (2.3) 6f the microfilariae per fly, taken during the infective blood~mealfrom a cow infected with the parasite, was considered to be quite small for sufficient recovery to provide sufficient amount of the infective stage larvae for antigen. -- - - -----~- ----- - -- -