Analysis of Culex and Aedes mosquitoes in southwestern Nigeria revealed no West Nile virus activity.
BACKGROUND
Amplification and transmission of West Nile virus (WNV) by mosquitoes are driven by presence and number of viraemic/susceptible avian hosts.


METHODS
In order to predict risk of WNV infection to humans, we collected mosquitoes from horse stables in Lagos and Ibadan, southwestern Nigeria. The mosquitoes were sorted and tested in pools with real-time RT-PCR to detect WNV (or flavivirus) RNA using WNV-specific primers and probes, as well as, pan-flavivirus-specific primers in two-step real-time RT-PCR. Minimum infection rate (MIR) was used to estimate mosquito infection rate.


RESULTS
Only two genera of mosquitoes were caught (Culex, 98.9% and Aedes, 1.0%) totalling 4,112 females. None of the 424 mosquito pools tested was positive for WNV RNA; consequently the MIR was zero. Sequencing and BLAST analysis of amplicons detected in pan-flavivirus primer-mediated RT-PCR gave a consensus sequence of 28S rRNA of Culex quinquefasciatus suggesting integration of flaviviral RNA into mosquito genome.


CONCLUSIONS
While the latter finding requires further investigation, we conclude there was little or no risk of human infection with WNV in the study areas during sampling. There was predominance of Culex mosquito, a competent WNV vector, around horse stables in the study areas. However, mosquito surveillance needs to continue for prompt detection of WNV activity in mosquitoes.
Department of Biological Sciences, Faculty of Basic and Applied Sciences, Osun State University, PMB 4494, Oke-Baale, Osogbo, 230212, Osun State, Nigeria.
Waidi Folorunso
WF
Sule
Department of Veterinary Microbiology and Parasitology, Faculty of Veterinary Medicine, University of Ibadan, Ibadan, Nigeria.
Daniel Oladimeji
DO
Oluwayelu
D000330:Aedes; D000818:Animals; D003465:Culex; D005260:Female; D006736:Horses; D006801:Humans; D007303:Insect Vectors / Q000821:virology*; D009549:Nigeria; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014901:West Nile Fever / Q000517:prevention & control* / Q000635:transmission; D014902:West Nile virus / Q000302:isolation & purification*
Mosquitoes; WNV-RNA; infection risk; real-time RT-PCR; southwestern Nigeria