Table 1.
Species, number of individuals testing positive for influenza A virus matrix gene by rRT-PCR (Pos), number of individuals tested for AIV (Sampled), and point estimate of interval apparent prevalence (IAP) in breeding and overwintering seasons for each species across all three years of data used in this analysis.
Table 2.
Candidate set of models used to identify the relative influence of covariates on the probability an individual bird sampled during the breeding season tested positive for Avian Influenza Virus (AIV).
Figure 1.
Receiver operating characteristics (ROC) curve for assessing goodness-of-fit for the top model selected from the candidate set.
The area under the curve (AUC) is 0.76, suggesting a strong ability to discriminate between true and false signal and a good fit of the model to the data.
Figure 2.
Top model estimate of average predicted probability that an individual bird sampled from local watersheds during the breeding season tests positive for avian influenza virus.
The probability is an average across all three years of data for all waterfowl sampled within a given watershed. Note the strong latitudinal gradient with higher probabilities of testing positive in northern latitudes and decreasing probabilities in southern latitudes.
Figure 3.
Map showing the odds ratio for the overwintering season temperature effect from the top model fit to the data.
The sample size reflects the number of AIV samples collected within each of the 137 local watersheds used in this analysis and the colors reflect the mean odds ratio of testing positive for AIV, with red indicating that the odds of testing positive for AIV are nearly three times as likely than points colored dark green based on this variable.
Figure 4.
Map showing the odds ratio for the overwintering season interval apparent prevalence effect resulting from the top model fit to the data.
The sample size reflects the number of AIV samples collected within each of the 137 local watersheds used in this analysis and the colors reflect the mean odds ratio of testing positive for AIV, with red indicating the odds of testing positive are more than twice that of points colored dark green based on this variable.
Table 3.
Maximum likelihood estimates for covariate parameters in the global model examining the relationship between the probability a bird tested positive during the breeding season (April 1 to September 30) and the variables shown.
Table 4.
Maximum Likelihood estimates (p-values) for key model parameters when AIV data are restructured such that the timing of breeding (April 1 to September 30) and overwintering (October 1 to March 31) seasons differs from that used to generate the parameter estimates shown in Table 3.
Figure 5.
Map showing overlap in breeding relative abundance for mallard and gadwall species.
Note that the geographic distribution of gadwall breeding locations is contained almost entirely by areas where mallard breed, with similar areas of high- and low-breeding concentrations across the contiguous United States. The mallard tested positive at some of the highest rates and the gadwall was near the lowest in proportion of AIV positive tests, suggesting geographic overlap alone does not explain variations in species prevalence patterns.