Print PageAvian influenza viruses are known to productively infect a number of mammal species, several of which are commonly found on or near poultry and gamebird farms. While control of rodent species is often used to limit avian influenza virus transmission within and among agricultural operations, few studies have investigated the potential role of these species in outbreak dynamics.
We used three approaches to evaluate whether small mammals pose a transmission risk during an avian influenza outbreak. First, we trapped and sampled synanthropic mammals on a gamebird farm in Idaho, USA that had recently experienced a low pathogenic avian influenza outbreak. Second, we trapped mammals on a virus-free farm in Colorado, USA in spring, summer, and fall to characterize the synanthropic mammal community. We used these data to develop population estimates for different species on the farm and on an adjacent field. Finally, we experimentally infected groups of naïve Norway rats and wild-caught house mice with five different low pathogenic avian influenza viruses that included three viruses derived from wild birds and two viruses derived from chickens.
Results/Conclusions
Each of six house mice (Mus Musculus) caught on the outbreak farm were presumptively positive for influenza A antibodies while individuals of all other species were negative. The most common species on the virus-free farm were house mice, deer mice, and Norway rats. Movements between the farm and the adjacent field were limited, but exchanges did occur.
Experimental infections of mice showed virus replication was efficient in animals inoculated with viruses derived from wild birds and more moderate for chicken-derived viruses. Mean titers (EID50/mL equivalents) across all lung samples for seven days of testing ranged from 103.89 (H3N6) to 105.06 (H4N6) for the wild bird viruses and 102.08 (H6N2) and 102.85 (H4N8) for the chicken-derived viruses. In general, viral replication was lower for rats and replication rates were similar for wild bird and chicken-derived viruses. Regression models indicated differential replication between sexes for both mice and rats, with significantly (p < 0.05) higher concentrations of RNA found in females compared with males.
This study provides evidence that wild house mice can be naturally exposed to avian influenza viruses and that these viruses can replicate efficiently without adaptation. Further investigation is warranted to determine the generality of sex-based replication rates.
