Epidemiological activities: overview

ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA Expert Advisory Committee Fourteenth session Ouaeadoueou. 7-l I June 1993 Briefing session, 5 June, I993 OCP/EACIA/Briefing paper no 4 ORIGINAL : ENGLISH EPIDEMIOLOGTCAL ACTIVITIES : OVERVIEW l. Epidemiological evaluation Epidemiological evaluations were carried out in 56 villages in the Central Programme area. In all l0 river basins were involved. These were the Banifing IY in Mali, Comoe Bou- Bandama and the Black Volta in Cote d'Ivoire, Black Yolta and White Yolta, the Kulpawn , Mole and Oti in Ghana , the Oti in Togo, the Sota and Koumongou in Benin and the Niger in Niger. The evaluations in the Nzi basin will be undertaken towards the end of the year. The villages on the Comoe, Bou-Bandama, Black Volta and the White Yolta were evaluated to help in deciding whether larviciding could be stopped in these basins. The results from these areas were very good. The prevalence in most of the villages was below 4%. The results for the lower portion of the Bou-Bandama, however, were not satisfactory. Prevalences here were of the order of l0% to 23%. On the Banifing IY in Mali, the Niger basin in Niger and Oti in Togo the villages were evaluated as part of the surveillance activities. The results were excellent with prevalence below2%. Results obtained from a cluster of three villages near Kuntili village on the Oti basin(Ghana) were unsatisfactory with prevalence ranging from 6.9% to l2.lo/o. In the areas, where there is a combination of larviciding and ivermectin distribution, 48 villages were evaluated. The parasitologically negative individuals will form a cohort of individuals for follow-up for incidence of infection. The basins were in the Southern extension, the intermediate zone in cote d'Ivoire and the southern part of Guinea. In Guinea, pre-treatment and one month post-ivermectin treatment evaluations were carried out in three villages as a start of in vivo surveillance on possible parasite resistance to ivermectin use. The results from this initial small sample showed more than 85% reduction in the skin microfilaria load level one month after treatment. There was no evidence of parasite resistance to ivermectin. This type of evaluation will be continued in other randomly selected villages in the ivermectin distribution areas. 2. Ophthetniological evaluations Ophthalmological evaluations were carried out in three villages in the Asubende focus(Ghana) and in nine villages in Guinea. In both situations, these evaluations were being carried out after five years of annual ivermectin treatment in the villages. The results of the ophthalmological evaluations in Asubende were compared to the base line data to determine the medium term evolution of ocular onchocerciasis. In the cohort of follow up individuals the results showed a complete elimination of living microfilaria. The microfilaria load in the anterior chamber of the eye had been reduced from an arithmetic mean value of I l.3l to a very low level of 0.21. It is noteworthy that it takes l0 years of vector control to observe similar results. There was significant reduction in lesions of the t OCP/EAC l4lBrief ing PaPer no 4 Page 2 anterior chamber i.e iridocyclitis and sclerosing keratitis. There was, however, a continuing incidence of 5.5% of optic nerve disease but no significant changes associated with chorio- retinitis. The overall rlsults show a beneficial effect of ivermectin treatment on the ocular disease of the population of Asubende. Data from the evaluations carried out in Guinea is presently being analYzed. 3. Migration Two migration studies were undertaken. These were in the Kulpawn Basin in Ghana in which the main uittage Goreba Somum plus two satellite villages were involved. The second was on the Bou- Banda-a Blanc in Cote d'Ivoire where 14 villages were studied' In the villages on the Kulpawn basin the high level of prevalence observed was due entirely to residents. On ttre Bandama Blanc however there was the presence of parasitologically positive migrants in eight of the eleven villages with onchocercal infection. In these eight uillages, moie than 90 % of the oncho-positive individuals were migrants. 4. Ivermectin distribution During the period from June 1992 to May 1993 ivermectin distribution was carried out in over SZ0O vittages spread out in 42 river basins. About 1.4 million individuals received ivermectin through lr"iious modes of distribution: large-scale distribution, community self treatment, mobile outreach mechanisms and passive distribution. The coverage was on the average, 70%. Compliance was good, and there were no serious adverse reactions. The treatment was carried out by national teams with OCP support and also in collaboration with Non- Governmental Organization. 5. Immunodiagnosis Further testing of antigens for the TDR/OCP initiative to develop immunodiagnostic test for onchocerciasis iniection was carried out. The priority for the test is the detection of recrudescence of infection. Serum collected from Pendie, Niarba (Bukina Faso) and Manambougou (Mali) was used for the testing of a tri-cocktail antigen (Ov7, Ovl I and Ovl6). The resultsitrowed seropositivity of 80% with respect to early patent infections, and more than 60% for prepatent infections. These results were deemed promising enough to justify large-scale operational field trial of the cocktail antigen in the OCP area. Such a trial will be undertaken between May and June 1993. 6. Studies on the percelved benefits from ivermectin treatment A randomized, double blind cross-over studies on patients' perceived benefits from ivermectin treatment were carried out in the northern degraded forest zone of Sierra Leone on the Kaba, Mabole and Kabala river valleys. An almost identical study with a slight modification in the selection of groups was also undertaken in the Sassandra river basin in Cote d'Ivoire. The cross over period is-scheduled for end of April/early May. Results are expected at the beginning of June. Results from a pre-study, Knowledge Attitude and Practice (KAP) interviews in the Kaba area, showed that less than 40 % of the communities interviewed knew about onchocerciasis.