West Nile Virus Activity in a Winter Roost of American Crows (Corvus brachyrhynchos): Is Bird-To-Bird Transmission Important in Persistence and Amplification?

Abstract

Since its emergence in North America, West Nile virus (WNV) has had a large impact on equines, humans, and wild bird communities, yet gaps remain in our understanding of how the virus persists at temperate latitudes when winter temperatures preclude virus replication and host-seeking activity by mosquito vectors. Bird-to-bird transmission at large communal American Crow roosts could provide one mechanism for WNV persistence. Herein, we describe seasonal patterns of crow and Culex mosquito abundance, WNV infection rates, and the prevalence of WNV-positive fecal samples at a winter crow roost to test the hypothesis that bird-to-bird transmission allows WNV to persist at winter crow roosts. Samples were collected from large winter crow roosts in the Sacramento Valley of California from January 2013 until August 2014, encompassing two overwintering roost periods. West Nile virus RNA was detected in local crow carcasses in both summer [13/18 (72% WNV positive)] and winter [18/44 (41% WNV positive)] 2013-2014. Winter infections were unlikely to have arisen by recent bites from infected mosquitoes because Culex host-seeking activity was very low in winter and all Culex mosquitoes collected during winter months tested negative for WNV. Opportunities existed for fecal-oral transfer at the overwintering roost: most carcasses that tested positive for WNV had detectable viral RNA in both kidney and cloacal swabs, suggesting that infected crows were shedding virus in their feces, and >50% of crows at the roost were stained with feces by mid-winter. Moreover, 2.3% of fecal samples collected in late summer, when mosquitoes were active, tested positive for WNV RNA. Nevertheless, none of the 1,119 feces collected from three roosts over two winters contained detectable WNV RNA. This study provided evidence of WNV infection in overwintering American crows without mosquito vector activity, but did not elucidate a mechanism of WNV transmission during winter.

Influence of Host Ecology and Behavior on Campylobacter jejuni Prevalence and Environmental Contamination Risk in a Synanthropic Wild Bird Species

“…We hypothesized that C. jejuni prevalence would be higher in nestlings than adults, due to a less-developed immune system and high exposure to social sources of infection from parents and nest mates (32). We also predicted that overall C. jejuni prevalence in feces would be highest at the peak of the communal roosting season, when thousands of crows spend each night in close proximity and up to 58% of crows have visible fecal staining on their feathers from roost mates perched on higher branches (31). For nestlings, we predicted that the shared nest environment would drive transmission, with nest mates tending to be either all uncolonized or all colonized with a similar strain of C. jejuni.…”

“…In addition to the high prevalence of C. jejuni infection, American crows exhibit social behavior and movement patterns that may influence the risk of transmission from crows to domestic animals or directly to humans (30). Each winter, crows form large communal roosts that may facilitate both within-species transmission and amplify crossspecies transmission risks in areas surrounding the roost (31).…”

Low heterozygosity is associated with vector‐borne disease in crows

“…Adults (n = 58) were captured adjacent to a >7000-bird communal roost, composed of both migrants and residents (Hinton et al 2015, Townsend et al 2018b, during the winter roosting periods (January to March of 2014 and 2015) using a net launcher (Coda Enterprises) or drop-in trap (Taff et al 2016). 1; Townsend and Barker 2014, Wheeler et al 2014, Hinton et al 2015, Taff et al 2016). Adults were sampled, marked with a numbered USGS band and a unique color band, and released.…”

“…antibody by plaque reduction neutralization test (PRNT). We used qRT-PCR with primers and probe specific for the envelope region of the WNV genome (Lanciotti et al 2000), a ViiA 7 Real-Time PCR system (Life Technologies), and SensiFAST One-Step reagents (Bioline, Taunton, MA; testing procedures described in Wheeler et al 2014, Hinton et al 2015. 1; Wheeler et al 2014, Hinton et al 2015 were tested for the presence of the virus.…”

Potential for Waterborne and Invertebrate Transmission of West Nile Virus in the Great Salt Lake, Utah

“…American crows (Corvus brachyrhynchos) dying from WNV also have been reported in winter in the northeastern United States (9) and in California (10).…”