Risk Factors Associated With West Nile Virus Mortality in American Crow Populations in Southern Quebec

Abstract

ABSTRACT:Soon after the appearance of West Nile virus (WNV) in North America, a number of public health authorities designated the American Crow (Corvus brachyrhynchos) a sentinel for WNV detection. Although preliminary studies have suggested a positive association between American Crow mortality and increased risk of WNV infection in humans, we still know little about dynamic variation in American Crow mortality, both baseline levels and mortality associated with WNV. We hypothesized that the complex social behavior of American Crows, which is shaped by age and seasonal factors, influences both baseline mortality and WNV mortality in American Crow populations. We examined American Crow mortality data from Quebec for the 2005 WNV surveillance year, which lasted from 5 June to 17 September 2005. The variables of interest were age, gender, body condition index, time of year, and land cover. We used a log-linear model to examine baseline mortality. Logistic regression and general linear regression models were constructed to examine variables associated with mortality due to WNV. We found that both age and time of year were key variables in explaining baseline mortality. These two variables were also risk factors for WNV mortality. The probability that a carcass tested positive for WNV increased with the age of the dead bird and as summer progressed. WNV-positive carcasses also had a lower body condition index than WNV-negative carcasses. We believe that the first major wave of American Crow mortality observed in the early summer of 2005 was the result of natural mortality among young American Crows. Because this mortality was not linked to WNV, it appears that American Crow may not be a good species for early detection of WNV activity. Our data also suggest that second-year American Crows play a major role in propagating WNV during their movements to urban land covers during midsummer.

Clinical Diagnosis of West Nile Fever in Equids by Classification and Regression Tree (CART) Analysis and Comparative Study of Clinical Appearance in Three European Countries

“…The peak of occurrence of WNF cases in the three countries was observed during September. This result is in accordance with previous studies on WNF and vector activity in temperate climates (Murgue et al., 2001; Zeller and Schuffenecker, 2004; Ludwig et al., 2010). Indeed, the study by Ludwig et al.…”

“…This result is in accordance with previous studies on WNF and vector activity in temperate climates (Murgue et al., 2001; Zeller and Schuffenecker, 2004; Ludwig et al., 2010). Indeed, the study by Ludwig et al. (2010) performed on American crow populations demonstrated that time of year was a significant risk factor and that end of summer and autumn were associated with a higher mortality rate owing to WNF.…”

Parasite–bird interactions in urban areas: Current evidence and emerging questions

“…We base our review on birds as hosts since they are the vertebrate group best studied in cities around the world, are ubiquitous, have been used to explore effects and responses to urban development, and exhibit a complex community system in cities. They are used as bio-indicators of environmental quality in cities (Chace & Walsh, 2006;Ortega-Álvarez & MacGregor-Fors, 2011) and as sentinels for diseases and pathogens (Ludwig, Bigras-Poulin, Michel, & Bélnger, 2010).…”

Systematic review of surveillance systems and methods for early detection of exotic, new and re-emerging diseases in animal populations

“…This category considered mathematical models that were used to explore epidemiological and disease data related to surveillance and/or to evaluate distinct health measures (n = 20) [27,32,49,50,53,61,72,79,96,101,103,[109][110][111][112][113][114][115][116][117]. We found a wide range of models, such as linear, logistic, binomial, Poisson, time series, or CART.…”