An Early Indication of the Rebound of W. Bancrofti Infection in Zanzibar
Abstract Background Lymphatic filariasis (LF) is a debilitating neglected tropical disease which is targeted for elimination through co-administration of a single dose of ivermectin and albendazole in the affected population. Following implementation of such a treatment campaign over a period of years, control programmes are urged to conduct a transmission assessment survey to monitor the impact of the treatment and to ascertain whether the transmission is interrupted to a level that can no longer sustain transmission and hence mass drug administration (MDA) can be halted. Objective:This study was carried out to determine the prevalence of LF infection in Zanzibar communities, 13 years after stopping MDA, so as to inform and guide the control program. MethodologyA Finger prick blood sample was collected from each participant after obtaining informed consent. The sample was assessed for the presence of Wucheria bancrofti circulating antigen using rapid immunochromatographic test. ResultsA total of 2555 subjects were enrolled (1231 in Pemba and 1324 in Unguja) in the study with a mean age of 23.0yrs ± SD 18.9 (95% CI = 22.3-23.8). There were more female (53.9%) than male (46.1%); and their mean age significantly differed (t-test = 7.5, p = 0.00001). Only 2478 individuals gave blood sample . Of these, 88 (3.55%) were found to be infected with W. bancrofti. Overall, the prevalence of infection was higher in Pemba (5.1%) than in Unguja (2.1%). The prevalence of infection was similar between different older age groups , children aged 1-5yrs in Pemba had the highest prevalence indicating that transmission is ongoing. Observation of development of clinical manifestation, lymphoedema and hydrocele was also assessed. Overall, only 1.1% of the individuals had lymphoedema/elephantiasis; with male presented with more of those signs (1.6%) than female (0.7%). There was no male subject found to have hydrocele , although 8.3% of male had filariasis.The assessment of treatment history revealed that majority (64.7%) of the respondents had received at least one treatment round during their lifetime. Historical treatments with ivermectin did not correlate with current individual levels of infection but individuals who reported to have received 2 and 4 rounds of treatment were not found to be infected with filariasis.Conclusion and RecommendationIn view of our findings it clearly shows that the prevalence of LF in Zanzibar is still high to exceed the set threshold for discontinuation of MDA campaign. Children as young as 5yrs were found infected. It is therefore important to consider continuation of MDA so as to prevent potential disease sequel which might develop.