West Nile virus cluster analysis and vertical transmission in Culex pipiens complex mosquitoes in Sacramento and Yolo Counties, California, 2011

Ethan Fechter-Leggett, Brittany M. Nelms, Chris Barker, William Reisen

Research output: Contribution to journalArticle

11 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)442-449
Number of pages8
JournalJournal of Vector Ecology
Issue number2
StatePublished - Dec 1 2012



  • Culex pipiens
  • Focus detection
  • Vertical transmission
  • West Nile virus

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Ecology

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