Spatio-Temporal Distribution of Two Cytospecies of Adult Host-Seeking Black Fly ( Simulium damnosum ) in Delta State, Nigeria

Abstract

The black fly (Simulium damnosum) is the vector of onchocerciasis which is currently regarded as one of the neglected tropical diseases in Nigeria. Current global climate changes are being said to influence the distribution and the rate of spread of this disease vector. This research was conducted to identify the current habitat distribution of two cytospecies of the adult Simulium fly in Delta State, Nigeria. Adult black flies were caught using human attractants each day at the peak biting periods of morning and dusk once weekly; over a period of one year from three local government areas in Delta state. The trapped species were described and classified in situ using standard morphological keys and the collected data were analyzed statistically to reflect the annual population dynamics and seasonal species distributions. A marked disparity in the spatio-temporal distribution of the caught Simulium was noticed in the different locations. Two species: the forest dwelling species (FDS) and savannah dwelling species (SDS) were identified. The FDS were more abundant than the SDS in the three studied locations: Aganiki Camp, Oshimili North LGA (Mean 59.8: 12.3; ±47.5), Ugbodu, Aniocha North LGA (Mean 45.1: 10.7; ±34.4) and Umute, Aniocha South LGA (Mean 27: 7.9; ±19.1). Aganiki Camp has the highest number of the flies (total=867; monthly Mean=72) followed by Ugbodu (total=669; with monthly Mean=55.8) and the least Umute (total=424; with a monthly Mean of 35). The species distribution was significant F=4.844, (P<0.05). The average monthly population was 163; the distribution peaked in August (242) and ebbed in March (110). Overall, the FDS (Mean=132.3) were more abundant than the SDS (Mean=30.9); with a range value of ±101.4. It is critical that two cytospecies of the Simulium fly: FDS and SDS exist in the study area with significant presence all the year round. This will predictably make the transmission occurrence and intensity of the disease an annual event and therefore has the implications for a strengthened all the year round preventive measures and sustainable intervention approaches.