Influence of body condition on influenza A virus infection in mallard ducks: experimental infection data.

Migrating waterfowl are implicated in the global spread of influenza A viruses (IAVs), and mallards (Anas platyrhynchos) are considered a particularly important IAV reservoir. Prevalence of IAV infection in waterfowl peaks during autumn pre-migration staging and then declines as birds reach wintering areas. Migration is energetically costly and birds often experience declines in body condition that may suppress immune function. We assessed how body condition affects susceptibility to infection, viral shedding and antibody production in wild-caught and captive-bred juvenile mallards challenged with low pathogenic avian influenza virus (LPAIV) H5N9. Wild mallards (n = 30) were separated into three experimental groups; each manipulated through food availability to a different condition level (-20%, -10%, and normal ±5% original body condition), and captive-bred mallards (n = 10) were maintained at normal condition. We found that wild mallards in normal condition were more susceptible to LPAIV infection, shed higher peak viral loads and shed viral RNA more frequently compared to birds in poor condition. Antibody production did not differ according to condition. We found that wild mallards did not differ from captive-bred mallards in viral intensity and duration of infection, but they did exhibit lower antibody titers and greater variation in viral load. Our findings suggest that reduced body condition negatively influences waterfowl host competence to LPAIV infection. This observation is contradictory to the recently proposed condition-dependent hypothesis, according to which birds in reduced condition would be more susceptible to IAV infection. The mechanisms responsible for reducing host competency among birds in poor condition remain unknown. Our research indicates body condition may influence the maintenance and spread of LPAIV by migrating waterfowl

Duration of viral shedding (A) and mean number of positive samples (B) for captive-bred and wild mallard treatment groups.

<p>Bars represent means ±1 standard error, letters identify significant differences among wild mallard treatment groups (Mann-Whitney rank sum, alpha = 0.05). The mean number of positive samples was calculated from the 4 sampling days between 1–5 dpi.</p

Viral shedding profiles (log₁₀ GEC/140 µl of swab sample fluid) for all infected mallards with detectable viral RNA using matrix gene RRT-PCR.

<p>A: captive-bred (n = 9), B: wild normal (n = 10), C: wild lean (n = 10), D: wild poor (n = 6).</p

Breast condition score for wild mallard treatment groups at capture vs. LPAIV H5N9 challenge.

<p>Bars represent mean condition score ±1 standard error (n = 10), asterisks represent significant within group differences (paired t-test, alpha = 0.05).</p

Group mean daily (±1 SD) viral genome load (log₁₀ GEC/140 µl swab sample fluid) for mallards inoculated with LPAIV H5N9.

<p>Mean genome load is calculated using only infected mallards (birds that seroconverted or shed detectable viral RNA≥3 dpi). Minimum and maximum values are reported for the number of birds <i>(n)</i> with detectable viral RNA on the given day.</p

Serological status (mean ± SD) of mallards before and after LPAIV H5N9 challenge using ELISA and HI tests.

*<p>Bold numbers indicate days after LPAIV H5N9 inoculation.</p>1<p>The ELISA scores represent the signal to noise (S/N) ratio where values ≤0.50 are considered seropositive.</p>2<p>The hemagglutination inhibition (HI) values represent the mean titer (log₂) of sera samples.</p>3<p>Before LPAIV H5N9 inoculation.</p>4<p>Mean (±1 SD) test scores include all infected birds in each treatment.</p

Regression analysis for the calibration of the number of IAV matrix gene copies (circles) and plaque forming units (triangles).

<p>The standard curve was generated using a log₁₀ dilution series of quantified RNA runoff transcripts or known concentrations of LPAI H5N9 stock virus.</p

Short Report: Antibody Prevalence of Select Arboviruses in Mute Swans (\u3ci\u3eCygnus olor\u3c/i\u3e) in the Great Lakes Region and Atlantic Coast of the United States

Mute swans (Cygnus olor) are an invasive species in the United States. The dramatic increase in their populations in localized areas has led to various problems, among them competition with native species and attacks on humans by aggressive swans. However, very little is known about the ability of these swans to transmit pathogens to humans, domestic birds, or wildlife or participate in enzootic maintenance. To learn more about select pathogens that mute swans may harbor, a survey was conducted from April of 2011 to August of 2012 in the Great Lakes region and localized areas of the Atlantic coast, which revealed serologic evidence of arbovirus exposure in mute swans. Of 497 mute swans tested, antibodies were detected for eastern equine encephalitis (4.8%), St. Louis encephalitis (1.4%), West Nile (1.2%), and Turlock (0.6%) viruses. Samples were also tested for evidence of antibodies to La Crosse virus, but none were positive

Body condition for wild mallard treatment groups throughout the study.

<p>Data points represent mean condition (±1 standard error), A = start of diet manipulation, B = LPAIV H5N9 inoculation.</p