Factors associated with persistence of onchocerciasis transmission after two decades of community-directed treatment with ivermectin in Ulanga District, Tanzania

Abstract

ABSTRACT Background: Community Directed Treatment with Ivermectin (CDTI) was initiated in Tanzania since 1997 in Mahenge focus endemic for onchocerciasis with an operational prediction for interruption of transmission after 14-17 years. Ulanga as one of the hyperendemic districts, have received 20 rounds of annual CDTI. However a transmission assessment survey done on 2017 showed there was persistent transmission. Knowledge, attitudes and perceptions of the community drug distributors (CDDs) and individuals in the community towards onchocerciasis and preventive chemotherapy potentially affects CDTI coverage, consequently leading to persistent transmission. This study sought to investigate the current burden and its associated factors. Objective: The study examined the current O.volvulus prevalence and the associated factors in Ulanga district, two decades after initiation of mass drug administration for control. Methodology: A cross sectional study involving both quantitative and qualitative methods was carried out using primary and secondary data. The primary data entailed structured community interviews among 422 community members on their knowledge regarding onchocerciasis, attitude and perception on the preventive use of Ivermectin. This was complimented with qualitative data using key informants, in-depth interviews and focused group discussions. Secondary data from NTDCP was used for establishing, the current prevalence of O.volvulus. The quantitative data were organized to obtain proportions and their 95% CI. Associations between variables were assessed by the Chi-square test at significance level of 0.05. The qualitative data were organized in themes and content analysis. Results: Out of 587 children < 10 years of age tested for the presence of IgG4 antibodies to antigen Ov16; 17 (2.9% [95% CI: 1.7- 4.4]) were positive showing active transmission of onchocerciasis. There was association between duration of residence and age of the children with being infected; children aged 5 to 9 years were more infected than children less than 5 years of age (p=0.032) which was contributed with duration the children have stayed in Ulanga. The older children were at higher risk of exposure to O. volvulus infection compared to children aged less than 5 years (OR = 6.626; 95% CI: 0.864-50.824). Out of 422 household members interviewed; majority (94.1%) were found to have heard about onchocerciasis. However, they had inadequate knowledge on causative agent, transmission, treatment and prevention. Of the participants interviewed; 49.2% had low level of the knowledge, 35.5% had moderate level of knowledge and few 15.4% had high level of knowledge. Furthermore the community held negative attitudes (46.2%) and perceptions (44%) towards ivermectin treatment. All community drug distributors interviewed could not tell the causative agent of onchocerciasis and how transmission occurs despite distributing ivermectin for several years. However, they had positive attitude and perception that ivermectin is the best drug for treatment and elimination of the disease in Ulanga. Conclusion: Two decades of CDTI have not interrupted transmission of onchocerciasis in Ulanga district as shown by the 2.9% prevalence in children < 10 years. However, there was a borderline level of knowledge on the causative agent, transmission, treatment and prevention as only about a half (50.8%) had moderate to high level of knowledge. The low level of knowledge coupled with negative perceptions and attitudes in a section of the community have the potential of affecting uptake and therefore total coverage of CDTI hence the persistence of transmission. Recommendations: Public health education should be reinforced in the community and community should be given an opportunity to participate in selection of the drug distributors that they think are capable so as to improve the participation in CDTI program.