title: West Nile virus cluster analysis and vertical transmission in Culex pipiens complex mosquitoes in Sacramento and Yolo Counties, California, 2011.
abstract: West Nile virus (WNV) is now endemic in California, with annual transmission documented by the statewide surveillance system. Although much is known about the horizontal avian-mosquito transmission cycle, less is known about vertical transmission under field conditions, which may supplement virus amplification during summer and provide a mechanism to infect overwintering female mosquitoes during fall. The current study identified clusters of WNV-infected mosquitoes in Sacramento and Yolo Counties, CA, during late summer 2011 and tested field-captured ovipositing female mosquitoes and their progeny for WNV RNA to estimate the frequency of vertical transmission. Space-time clustering of WNV-positive Culex pipiens complex pools was detected in the northern Elk Grove area of Sacramento County between July 18 and September 18, 2011 (5.22 km radius; p<0.001 and RR=7.80). Vertical transmission by WNV-infected females to egg rafts was 50% and to larvae was 40%. The estimated minimal filial infection rate from WNV-positive, ovipositing females was 2.0 infected females/1,000. The potential contribution of vertical transmission to WNV maintenance and amplification are discussed.
authors.affiliation: Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
authors.forename: Ethan
authors.initials: E
authors.lastname: Fechter-Leggett
authors.forename: Brittany M
authors.initials: BM
authors.lastname: Nelms
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Barker
authors.forename: William K
authors.initials: WK
authors.lastname: Reisen
mesh_terms: D000818:Animals; D002140:California / Q000453:epidemiology; D003465:Culex / Q000821:virology*; D005260:Female; D018445:Infectious Disease Transmission, Vertical; D014901:West Nile Fever / Q000635:transmission*; D014902:West Nile virus / Q000472:pathogenicity*