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AFENET extends technical support towards Liberia’s Onchocerciasis elimination efforts

The African Field Epidemiology Network (AFENET) has extended technical support to the Liberia health ministry in the country’s efforts to eliminate Onchocerciasis.

During a July 2022 visit to Liberia, the AFENET team’s support revolved around the integration of community vector control “Slash and Clear” (S&C) to the much used approach of mass distribution of ivermectin by onchocerciasis elimination programs in Africa.

Context

The World Health Organization (WHO) 2030 Neglected Tropical Diseases (NTD) roadmap sets an ambitious target to eliminate onchocerciasis through interruption of transmission. This requires endemic countries to double their effort and devise new approaches in order to accelerate elimination process.

“However, one of the challenges endemic countries face is that it has been proven that ivermectin treatment alone is not sufficient to interrupt transmission in most of the regions of Africa where vector densities are high,” reads an activity brief co-authored by Mr Lakwo Thomson & Ms Leah Nawegulo. “The need for additional control tools is now critical for programs. Vector control by larviciding has been used as a tool to control onchocerciasis for several decades in Africa, but this is expensive, logistically difficult to plan and ecologically detrimental.”

The brief further notes that a recent development of community vector control “Slash and Clear” (S&C) has demonstrated the potential to reduced biting rates by local populations of S. damnosum sensu stricto. Slash and Clear entails the removal of vegetation from S. damnosum s.str. breeding sites to reduce the number of larval substrates, with the hope that this would have the knock-on effect of reducing the vector biting rates.

While the slash and clear interventions were very successful in the savanna S. damnosum s.str. infested streams of Northern Uganda, it is possible that this method may not generally be applicable in all areas of Africa. The slash and clear vector control approach is to be evaluated in savanna forest of Liberia with the support of AFENET.

Outcomes

The AFENET team therefore provided technical support to Liberia Ministry of Health in form of training the Neglected Tropical Disease program field staff on the slash and clear approach; how to conduct field assessments on the suitability of selected sites for the slash and clear approach; and how to conduct field demonstrations on some of the basic slash and clear entomological techniques.

During a field visit, larval collection was done by wading at the edges of the rivers to pick vegetation and inspecting them for the young stages of river blindness vector. Black fly collection was conducted by human landing catches at the bank of the River St. John in Bong County. Other assessments done were observing the size of the rivers and settlement pattern and distance of the river from the settlements.

A total of fourteen NTD staff from the health ministry were trained on slash and clear approach.

Field assessments were made on the suitability of selected sites and it was confirmed that breeding of onchocerciasis vector is on emergent vegetation - predominantly shrubs hanging in water, thus making it feasible to evaluate slash and clear in Liberia. The presence of large rivers like St. John was confirmed to be breeding with presence of black flies. Medium size rivers recommended for slash and clear were also encountered in some of the sites visited. It was then concluded that slash and clear could be evaluated in Liberia, with the field team tasked to identify one medium size and a large river for this evaluation.