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.
