"Slash and Clear", a Community-Based Vector Control Method to Reduce Onchocerciasis Transmission by Simulium sirbanum in Maridi, South Sudan: A Prospective Study.

Stephen Raimon,Rory J Post,Jane Y Carter,Joseph Nelson Siewe Fodjo,Peter Alinda,Robert Colebunders,Tom L Lakwo,Wilson John Sebit

doi:10.3390/pathogens10101329

Stephen Raimon, Rory J Post + Show 6 more

Open Access

https://doi.org/10.3390/pathogens10101329

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Abstract

Background: High ongoing Onchocerca volvulus transmission was recently documented in Maridi County, South Sudan. To complement community-directed treatment with ivermectin (CDTI) as the main onchocerciasis control strategy, we initiated a community-based vector control method “slash and clear” at the Maridi dam, a Simulium damnosum s.l. breeding site, to reduce O. volvulus transmission. Methods: Simulium damnosum s.l. biting rates were collected before and during the twenty months following the “slash and clear” intervention using the human landing catches. Black flies were dissected to measure parity rates before and twelve months after the intervention. Larvae and pupae of S. damnosum s.l. were collected from the dam for morphological and chromosomal characterization to identify the cytospecies involved. Results: Biting rates of S. damnosum s.l. close to the Maridi dam spillway decreased by >90% post-“slash and clear” for more than six months. Twelve months after the “slash and clear” intervention, the reduction in biting rates was still at <50% (p = 0.0007). Parity rates reduced from 13% pre-“slash and clear” (November 2019) to 5.6% post-“slash and clear” (November 2020). Larvae collected from the dam were identified as Simulium sirbanum. Conclusion: The “slash and clear” method was found to be an effective and cheap community-based method to reduce black fly biting rates caused by S. sirbanum. When repeated at least annually together with a high CDTI coverage, this intervention has the potential to considerably accelerate onchocerciasis elimination.

Highlights

Onchocerciasis is a disease of major public health importance in Maridi County, South Sudan, where it is associated with a high prevalence of epilepsy, including nodding syndrome [1,2]
The small number of specimens examined cannot rule out the possibility of the ‘Sudanese form’ of S. sirbanum, but this is unlikely because the two males extracted from pupae were found to have ‘Type IV’ scutal patterns, which is characteristic of the ‘Type IV form’, whilst the ‘Sudanese form’ usually has type III scutal patterns [20]
Our study shows that black fly biting rates in Maridi, South Sudan, were drastically reduced by >90% in all sites following implementation of the “slash and clear” exercise, and biting rates remained low for several months afterwards

Summary

Introduction

In 2018, in a door-to-door survey, an epilepsy prevalence of 4.4% and Pathogens 2021, 10, x FOR PEER REVIEW annual incidence of 373.9/100,000 person years were documented in villages close to the Maridi. High ongoing Onchocerca volvulus transmission was recently documented in Maridi County, South Sudan. As the main onchocerciasis control strategy, we initiated a community-based vector control method “slash and clear” at the Maridi dam, a Simulium damnosum s.l. breeding site, to reduce O. volvulus transmission. Methods: Simulium damnosum s.l. biting rates were collected before and during the twenty months following the “slash and clear” intervention using the human landing catches. Results: Biting rates of S. damnosum s.l. close to the Maridi dam spillway decreased by >90% post-“slash and clear” for more than six months

Results

Discussion

Conclusion