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West Nile virus emergence and persistence in Los Angeles, California, 2003-2008

Jennifer L Kwan1, Susanne Kluh, Minoo B Madon

  • 1School of Veterinary Medicine, University of California, Davis, CA, USA.

The American Journal of Tropical Medicine and Hygiene
|August 5, 2010
PubMed

Insights

West Nile virus (WNV) invaded Los Angeles in 2003, with Culex pipiens quinquefasciatus as the primary vector. Spatial analysis revealed transmission clusters, leading to major epidemics in 2004 and 2008.

Area of Science:

  • Veterinary Public Health
  • Epidemiology
  • Arbovirology

Background:

  • West Nile virus (WNV) emerged in Los Angeles in 2003, exhibiting cyclical patterns of amplification, decline, and resurgence over five years.
  • Understanding WNV transmission dynamics is crucial for public health interventions.

Purpose of the Study:

  • To analyze the enzootic transmission patterns of West Nile virus in Los Angeles from 2003 to 2008.
  • To identify the primary vectors and spatial spread of WNV.
  • To investigate the enzootic amplification preceding major WNV epidemics.

Main Methods:

  • Tracking WNV transmission via mosquito abundance and infection rates (Culex pipiens quinquefasciatus, Cx. tarsalis).
  • Monitoring bird populations through seroprevalence in peridomestic passerines, dead bird surveillance, and sentinel chicken seroconversions.
  • Utilizing spatial scan statistics on mosquito infection and dead bird data to identify transmission clusters.

Main Results:

  • Culex pipiens quinquefasciatus was identified as the primary WNV vector; gravid traps proved most effective for monitoring viral activity.
  • Spatial analysis delineated three main WNV transmission clusters, originating in the Los Angeles Basin and spreading to the San Fernando and Santa Clarita valleys.
  • Major WNV epidemics occurred in Los Angeles in 2004 and 2008.

Conclusions:

  • Culex pipiens quinquefasciatus is a key WNV vector in Los Angeles.
  • Spatial and temporal analyses are effective tools for understanding WNV epidemiology.
  • The study provides insights into WNV amplification patterns preceding epidemic outbreaks.

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