Trends in blackfly density, parity, and infection rates from riverside to villages of the Bafia health district in Cameroon: implication for onchocerciasis vector control

Abstract

Abstract Background The reduction of the contacts between humans and blackflies can lead to the interruption of the onchocerciasis transmission. Esperanza window trap (EWT) has been shown to be effective in reducing blackfly densities. Several shape-based improvements to this trapping system have been developed to optimize its performance. However, the optimisation of this trapping system has always been based on the shape of the trap, high blackfly density areas or on the addition of attractants, without considering transmission potentials and parity rates. This study aims to investigate the differences in biting rates and transmission potential between three catching points to guide the choice of EWT placement. Methods Monthly blackfly collection was carried out over one year using human landing method at three catching points along a transect from riverside toward the centre of two first-line villages (Biatsota and Bayomen) of the Mbam valley in Cameroon. Female blackflies caught were counted and dissected, and entomological indicators were computed and compared between catching points and villages. Results A total of 80,732 blackflies were caught and 57,517 dissected, of which 2,743 (4.8%) were parous and 44 (1.6%) infective. Regarding the distance to the river, a vector density gradient was observed, the highest annual biting rates (ABRs) being recorded at riverside. Furthermore, the highest annual transmission potentials were also recorded at riversides (165 vs 255 Infective larvae/man/year in Bayomen and Biatsota, respectively). Globally, the highest parity rates (PR) were recorded at the riverside in Biatsota (5.1%) where various human activities are frequent, and at the centre of the village in Bayomen (6.3%). Conclusion This study reveals that entomological parameters were the highest at riversides and indicates that EWTs or other trapping systems should be set up in priority at riverside for optimal performance in onchocerciasis control.