Mvolo County, an Onchocerciasis Endemic Area in Western Equatoria State, South Sudan: An Entomological Study to Prepare for a “Slash and Clear” Community-Based Vector Control Intervention

Abstract

Thomson Luroni Lakwo,1 Peter Alinda,1 Stephen Raimon Jada,2 Moses Tionga,2 Constantino Doggale Remijo Marcello,3 Deng Gai Dual War,3 Robert Colebunders4,5 1Ministry of Health, Vector Control Division, Kampala, Uganda; 2Amref Health Africa, Juba, South Sudan; 3Ministry of Health, National Malaria Control Program, Juba, South Sudan; 4Global Health Institute, University of Antwerp, Antwerp, Belgium; 5Department of Tropical Disease Pathology, Liverpool School of Tropical Medicine, Liverpool, UKCorrespondence: Robert Colebunders, Email [email protected]: Mvolo in Western Equatoria of South Sudan has been a hotspot for Onchocerca volvulus transmission since the 1940s. In Mvolo onchocerciasis is a disease of public health importance, associated with onchocerciasis-associated epilepsy including nodding syndrome.Methods: We conducted an entomological study to map the breeding sites of blackflies (Simulium damnosum, sensu lato) on the river Naam, to allow the removal of vegetation from vector breeding sites, the “slash and clear”. Three blackfly catching sites were established along the river. Focus group discussions were also conducted to assess the willingness of the communities to support the “slash and clear” intervention and the semi-annual distribution of ivermectin.Results: A total of 2466 female S. damnosum s.l. were caught in 14× 11h (06.00– 15.00) catches. The highest biting density of 4210.25 flies/month/h and monthly biting rate (MBR) of 11,482.25 bites/man/month were observed in November 2023. Biting density and MBR reduced to zero in the intervention site by April 2024. While the mean parity rate was 31% (CI: 0.2976± 0.9176). Two diurnal biting peaks were observed, one from 9:00– 10:00 (at the bridge site) and a prominent one from 14:00– 15:00 in the two catching sites in Mvolo. Along the river Naam, only one site was found productive for S. damnosum s.l.; and the larvae and adults were morphologically associated with the anthropophilic S. damnosum. The “slash and clear” intervention was implemented at Dogoyabolu along the river Naam. Communities expressed willingness to support a “slash and clear” intervention and the semi-annual distribution of ivermectin.Conclusion: S. damnosum active breeding was identified along the river Naam in a stretch of 3– 5 km close to human settlements. Highest blackfly biting density was 4210.25 flies/month/h, and two fly biting peaks were observed. A community “slash and clear” vector control was implemented, and will be prospectively monitored.Keywords: onchocerciasis, South Sudan, entomology, slash and clear, ivermectin

Keywords

• onchocerciasis
• south sudan
• entomology
• slash and clear
• ivermectin