MORPHOLOGICAL AND MOLECULAR IDENTIFICATION OF CULICOIDES SPECIES, THEIR HOST PREFERENCE AND INVOLVEMENT IN THE TRANSMISSION OF FILARIAL PARASITES IN BENUE STATE, NIGERIA

Abstract

Culicoides (biting midges) are small blood-sucking dipteran flies inhabiting various regions of the world. They are biological vectors of numerous economically important pathogens, especially filarial nematodes and a serious source of annoyance to humans and animals. Despite their importance and status as neglected vectors, there is limited information on morphology and molecular identification of Culicoides species in Nigeria, especially Benue State. Therefore, this study was aimed at identifying Culicoides species, their host preference and their possible involvement in filarial worm transmission in Benue State, Nigeria. A purposive sampling technique was used for the collection of adult Culicoides species in thirty locations across the three geopolitical zones (Benue South, Benue Northeast, and Benue Northwest) in Benue State, Nigeria. In weekly overnight collections using two CDC black-light suction traps, Culicoides species were trapped between January and December, 2018 and corresponding environmental data recorded. The trapped Culicoides were morphologically identified using a stereomicroscope to determine their sex and parity status. Polymerase chain reactions were carried out and characterisation of dominant species was achieved using sequence analysis targeting the ITS1 gene. Their sources of blood meals were investigated using mitochondrial MT-cyt b gene and their role in the transmission of filarial parasites was probed using Cox-1 gene. Data were analysed using descriptive statistics and correlation coefficient at α0.05. A total of 30,163 Culicoides species were trapped, with the highest collection of 13,700 (45.4%) recorded for Benue South geopolitical zone. There was positive association between rainfall and the number of Culicoides species trapped (r = 0.96), while the number of catches correlated negatively with wind speed and temperature (r = -0.1586 and r = - 0.4789) respectively. Twenty-one species were morphologically identified. Females represents 87.9% (n = 26,502) of the total collection of which 31.4% (n = 8,314) were parous. The two dominant species were Culicoides imicola (37.6%) and C. oxystoma (13.8%). Culicoides indistinctus (0.2%) identified in this study area is a new species reported in Nigeria. The Nigerian C. imicola and C. indistinctus strains were 95.8% and 97.3% related to French strains respectively, while C. oxystoma was (95.2%) related to Israeli strains. Cattle (60%), humans (37%) and dogs (3%) were their preferred hosts. The filaria, Onchocerca gutturosa was found in C. imicola and C. oxystoma that fed on cattle, while Mansonella perstans was obtained only from C. oxystoma that fed on humans. Culicoides imicola and Culicoides oxystoma were dominant species while Culicoides indistinctus was identified for the first time in Nigeria. The potential roles of Culicoides in the transmission of filarial parasites of humans and animals were confirmed. Hence, control of Culicoides is recommended.