• Secondary Transmission Dynamics of the West Nile Virus in Mosquitoes

      Causarano, Jason; Centre for Biotechnology
      West Nile Virus (WNV) is a member of the genus Flavivirus and is transmitted by mosquitoes. It first appeared in North America in New York City in 1999 and was first detected in Windsor Ontario in an infected bird collected in early August 2001. Prior to WNV, flaviviruses were not of major concern in Canada as only 1 short outbreak had occurred in the country. The secondary transmission cycles of WNV are typically overlooked in regards to their role in maintenance and survival of the virus in nature. The first component of this thesis was to investigate transovarial or transovum transmission (TOT) of WNV in Ontario during the 2012 and 2013 epidemic seasons. 89 males from 7 different traps were tested from samples collected in 2012. During the 2013 season individuals across 9 different WNV vector species were collected throughout the Niagara region with 1023 tested for the presence of naturally occurring WNV TOT. None of the samples showed signs of TOT. A single gravid female Culex pipiens tested positive for WNV, but no viral RNA was found in any of her 270 offspring, highlighting the many difficulties in detecting this type of transmission in natural populations. Laboratory testing was conducted to further investigate secondary transmission of WNV. A novel method for infecting adult mosquitoes was developed during this process; it was found more individuals would feed on an infectious sugar meal (ISM) as opposed to an infected blood meal in the lab setting. The ISM showed rates of infection, dissemination, and transmission by the WNV vector Aedes albopictus that were similar to those observed in previous vector competence studies. The ease of infecting adults and the similar rates of infection to previous literature suggests that this method could be used to investigate vector competence of other species for WNV. The ISM was also successful in the infection of male Aedes albopictus and was used to investigate WNV venereal transmission (VT) within the species. Evidence showed that 45% of the uninfected virgin females were positive for WNV after mating with infected males, indicating for the first time that male Aedes albopictus could transmit the virus venereally.