Multi-Year Comparison of Community- and Species-Level West Nile Virus Antibody Prevalence in Birds from Atlanta, Georgia and Chicago, Illinois, 2005-2016

Abstract

West Nile virus (WNV) is prevalent in the United States but shows considerable variation in transmission intensity. The purpose of this study was to compare patterns of WNV seroprevalence in avian communities sampled in Atlanta, Georgia and Chicago, Illinois during a 12-year period (Atlanta 2010-2016; Chicago 2005-2012) to reveal regional patterns of zoonotic activity of WNV. WNV antibodies were measured in wild bird sera using ELISA and serum neutralization methods, and seroprevalence among species, year, and location of sampling within each city were compared using binomial-distributed generalized linear mixed-effects models. Seroprevalence was highest in year-round and summer-resident species compared with migrants regardless of region; species explained more variance in seroprevalence within each city. Northern cardinals were the species most likely to test positive for WNV in each city, whereas all other species, on average, tested positive for WNV in proportion to their sample size. Despite similar patterns of seroprevalence among species, overall seroprevalence was higher in Atlanta (13.7%) than in Chicago (5%). Location and year of sampling had minor effects, with location explaining more variation in Atlanta and year explaining more variation in Chicago. Our findings highlight the nature and magnitude of regional differences in WNV urban ecology.

Figure 1.

Total (A) and WNV–positive (B) sample composition of birds captured and sampled for WNV antibodies in Atlanta, Georgia, 2010–2016. (C) Estimated WNV seroprevalence (±SE) for each species sampled in Atlanta.

Figure 2.

Total (A) and WNV–positive (B) sample composition of birds captured and sampled for WNV antibodies in Chicago, Illinois, 2005–2012. (C) Estimated WNV seroprevalence (±SE) for each species sampled in Chicago.

Figure 3.

(A) Estimated WNV seroprevalence in birds by sampling location in Atlanta, Georgia, 2010–2016. (B) Estimated WNV seroprevalence in birds by year in Atlanta, Georgia, 2010–2016. Bars represent the estimate; lines represent the 95% CI of the estimate. Sampling location maps and descriptions can be found in the referenced Atlanta-specific studies (see Background).

Figure 4.

(A) Estimated WNV seroprevalence in birds by location in Chicago, Illinois, 2005–2012. (B) Estimated WNV seroprevalence in birds by year in Chicago, Illinois, 2005–2012. Bars represent the estimate; lines represent the 95% CI of the estimate. Sampling location maps and descriptions can be found in the referenced Chicago-specific studies (see Background).

Figure 5.

Fixed effect predictions of a single resident bird testing positive for WNV antibodies in Chicago, Illinois, 2005–2012 (A, C, and E) and Atlanta, Georgia, 2010–2016 (B, D, and F). (A and B) Predicted effect of month on a single bird of any age in any year testing positive for WNV. (C and D) Predicted effect of age on a single bird of any species in any year testing positive for WNV. (E and F) The predicted interaction between month and age for a single resident bird in any year testing positive for WNV (black line indicates adults; gray line indicates hatch year birds). Predictions were generated from a binomial generalized linear mixed effects model with WNV antibody positive as the response term, total monthly trapping effort was included as an intercept offset, month, age, and a month-by-age interaction were fixed effect terms, species was a crossed random effect, and year and location were nested random effect terms. Solid lines represent the average prediction, and shaded regions (or bars) indicate the 95% CI of the prediction. AHY indicates hatch year bird; HY indicates hatch year bird.