Entomologic Investigations during an Outbreak of West Nile Virus Disease in Maricopa County, Arizona, 2010

Abstract

Abstract. Entomologic investigations were conducted during an intense outbreak of West Nile virus (WNV) disease in Maricopa County, Arizona during July 31-August 9, 2010. The investigations compared the East Valley outbreak area, and a demographically similar control area in northwestern metropolitan Phoenix where no human cases were reported. Five mosquito species were identified in each area, and species composition was similar in both areas. Significantly more Culex quinquefasciatus females were collected by gravid traps at Outbreak sites (22.2 per trap night) than at control sites (8.9 per trap night), indicating higher Cx. quinquefasciatus abundance in the outbreak area. Twenty-eight WNV TaqMan reverse transcription-polymerase chain reaction-positive mosquito pools were identified, including 24 of Cx. quinquefasciatus, 3 of Psorophora columbiae, and 1 of Culex sp. However, Cx. quinquefasciatus WNV infection rates did not differ between outbreak and control sites. At outbreak sites, 30 of 39 engorged Cx. quinquefasciatus had fed on birds, 8 of 39 on humans, and 1 of 39 on a lizard. At control sites, 20 of 20 identified blood meals were from birds. Data suggest that Cx. quinquefasciatus was the primary enzootic and epidemic vector of this outbreak. The most important parameters in the outbreak were vector abundance and blood meal analysis, which suggested more frequent contact between Cx. quinquefasciatus and human hosts in the outbreak area compared with the control area.

Avian Hosts of West Nile Virus in Arizona

“…Interestingly, 5% of the bloodmeals identified in our study and one conducted earlier in the summer pertained to bird species that were not permanently resident in the Phoenix suburban area. 20 The retrospective and prospective measurements of the mosquito inoculation index values for common bird species in suburban Phoenix produced markedly different results. This index expresses the relative number of infectious Cx.…”

“…Godsey and others 20 also identified bloodmeals from Culex mosquitoes collected 6 weeks earlier at random locations throughout the outbreak region during the first week of August. These data provide an alternative opportunity to retrospectively assess the important WNV amplifiers among the bird population.…”

“…From the mosquito feeding index data that we collected and from the earlier work, 20 doves and chicken are clearly selected as hosts by Culex mosquitoes in suburban Phoenix. The extraordinarily high number of dove infections would indicate doves as candidate free-ranging bird sentinels.…”

“…quinquefasciatus reached 0.33 (N = 39), compared with 0.03% (N = 113) in September (onetailed Fisher's exact test P 0.001). 20 However, no greattailed grackle bloodmeals were identified in August.…”

Neuroinvasive Arboviral Disease in the United States: 2003 to 2012

“…30,31 Similarly, large outbreaks in Arizona in 2010 and north Texas in 2012 were likely due to a confluence of favorable weather and environmental conditions resulting in an abundance of susceptible vertebrate hosts and vector mosquitoes. [32][33][34][35][36][37] Eastern equine encephalitis virus is an alphavirus. It is maintained in enzootic cycle between birds and mosquitoes by Culiseta melanura, which breeds in a specific hardwood swamp environment.…”