Differential Impact of West Nile Virus on California Birds

Abstract

The strain of West Nile virus (WNV) currently epidemic in North America contains a genetic mutation elevating its virulence in birds, especially species in the family Corvidae. Although dead American Crows (Corvus brachyrhynchos) have been the hallmark of the epidemic, the overall impact of WNV on North America's avifauna remains poorly understood and has not been addressed thoroughly in California. Here, we evaluate variation by species in the effect of WNV on California birds from 2004 to 2007 by using (1) seroprevalence in free-ranging birds, (2) percentage of carcasses of each species reported by the public that tested positive for WNV, (3) mortality determined from experimental infections, and (4) population declines detected by trend analysis of Breeding Bird Survey (BBS) data. Using Bayesian linear models, we extrapolate trends in BBS data from 1980 to . We attribute significant declines from expected abundance trends in areas supporting epiornitics to WNV transmission. We combine risk assessed from each of the four data sets to generate an overall score describing WNV risk by species. The susceptibility of California avifauna to WNV varies widely, with overall risk scores ranging from low for the refractory Rock Pigeon (Columba livia) through high for the susceptible American Crow. Other species at high risk include, in descending order, the House Finch (Carpodacus mexicanus), Black-crowned Night-Heron (Nycticorax nycticorax), Western Scrub-Jay (Aphelocoma californica), and Yellow-billed Magpie (Pica nuttalli). Our analyses emphasize the importance of multiple data sources in assessing the effect of an invading pathogen.

West Nile Virus–related Trends in Avian Mortality in California, Usa, 2003–12

“…Human incidence was high in many areas such as Tehama County in the north (17.8 cases/ 100,000 people) and San Bernardino County in the south (11.5/100,000). The populations of many bird species subsequently declined throughout the US and California because of WNV (LaDeau et al 2007;Wheeler et al 2009). …”

“…American Crows (Corvus brachyrhynchos), Western Scrub-Jays (Aphelocoma californica), Yellow-billed Magpies (Pica nuttalli), and Common Ravens (Corvus corax) are the most common corvid species reported and tested in the DBSP. These species rapidly develop symptoms, elevated viremia, and usually die within 1 wk after experimental infection (Komar et al 2003;Weingartl et al 2004;Wheeler et al 2009;Ernest et al 2010). American Crow abundance, high visibility, susceptibility, and widespread periurban distribution make them an ideal natural surveillance indicator to track WNV activity (Eidson et al 2001).…”

“…They are a preferential host of Culex pipiens complex mosquitoes (Hamer et al 2009), and WNV spread in northeast and northcentral US has been attributed to American Robins (Kilpatrick et al 2006;Hamer et al 2009). Peridomestic House Finches (Haemorhous mexicanus) and House Sparrows (Passer domesticus) serve as reservoir and amplifying hosts in California Wheeler et al 2009;Molaei et al 2010) and have been associated with human WNV disease outbreaks (Kwan et al 2012), especially in the western US.…”

“…Although studies have used data from the DBSP (e.g., Reisen et al 2004Reisen et al , 2013Crosbie et al 2008;Wheeler et al 2009;Ernest et al 2010;Kwan et al 2010;Carney et al 2011;Healy et al 2015), an overview and summary of WNV-infected dead birds has not been presented since the detection of WNV in California.…”

Overwintering site of Culex pipiens pallens in an urban environment of Saitama Prefecture in Japan

“…In the United States, a West Nile fever epidemic has been ongoing since 1999, and patients have exceeded 30,000, with more than 1,200 fatalities in the last 11 years (CDC, 2011). West Nile virus (WNV) is maintained in nature by many species of birds as amplifying hosts, and the virus has been detected in more than 326 species of birds in the United States, although there are great di erences in the viremia level among bird species (CDC, 2009;Wheeler et al, 2009). WNV has also been detected in 64 mosquito species, including genera Culex, Aedes, Anopheles, Coquillettidia, Culiseta, Deinocerites, Mansonia, Orthopodomyia, Psorophora and Uranotaenia in the USA (CDC, 2006;White et al, 2001;Nasci et al, 2001).…”