Ecological Routes of Avian Influenza Virus Transmission to a Common Mesopredator: An Experimental Evaluation of Alternatives

Abstract

BackgroundWild raccoons have been shown to be naturally exposed to avian influenza viruses (AIV). However, the mechanisms associated with these natural exposures are not well-understood.Methodology/Principal FindingsWe experimentally tested three alternative routes (water, eggs, and scavenged waterfowl carcasses) of AIV transmission that may explain how raccoons in the wild are exposed to AIV. Raccoons were exposed to 1) water and 2) eggs spiked with an AIV (H4N6), as well as 3) mallard carcasses experimentally inoculated with the same virus. Three of four raccoons exposed to the high dose water treatment yielded apparent nasal shedding of >102.0 PCR EID50 equivalent/mL. Little to no shedding was observed from the fecal route. The only animals yielding evidence of serologic activity during the study period were three animals associated with the high dose water treatment.Conclusions/SignificanceOverall, our results indicate that virus-laden water could provide a natural exposure route of AIV for raccoons and possibly other mammals associated with aquatic environments. However, this association appears to be related to AIV concentration in the water, which would constitute an infective dose. In addition, strong evidence of infection was only detected in three of four animals exposed to a high dose (e.g., 105.0 EID50/mL) of AIV in water. As such, water-borne transmission to raccoons may require repeated exposures to water with high concentrations of virus.

Low viral doses are sufficient to infect cottontail rabbits with avian influenza A virus

“…This is in contrast to raccoons (Procyon lotor), as free access to water pans spiked with 10 5 and 10 3.2 EID 50 / mL of IAV only resulted in transmission to a fraction of raccoons experimentally tested with the higher dose of water [16], thereby suggesting that raccoons require a higher inoculation dose for successful infection, presumably via the oral route, when compared to cottontail rabbits. Nonetheless, raccoons have been commonly shown to have antibody responses to IAV in multiple regions in their native range [7] as well as in introduced populations elsewhere [8], suggesting that a sufficient mechanism for their infection exists but may not be well described at this time.…”

“…The oral route of infection, although less efficient in this species, is likely to be a more probable natural infection route than nasal exposure. Nonetheless, inadvertent nasal exposures while utilizing a body of water have been suggested for other mammal species [16]. As has been suggested previously [18,19], cottontail rabbits should be taken into account in the biosecurity plans of poultry facilities.…”

“…The LP IAV used in this study, A/ Mallard/CO/P70F1-03/08(H4N6), which was grown and titered in SPF chicken eggs, has been described previously [16]. On day zero of the study, all cottontail rabbits were inoculated with their respective viral dose (approximately 10 2 , 10 3 , or 10 4 EID 50 ) diluted in 1 mL (oral route) or 250 µl (nasal route) of BA-1 diluent [21].…”

“…The objective of this study was to assess the efficacy of low infectious doses of IAV in cottontail rabbits by both the oral and nasal routes to further characterize the biosecurity risk that may be posed by this species. To accomplish this study, a LP H4 IAV was selected because it has been shown previously to replicate in multiple mammalian species and is a very common virus in wild bird populations in North America [14,[16][17][18]21].…”

Transmission of H6N2 wild bird-origin influenza A virus among multiple bird species in a stacked-cage setting

“…We hypothesize that the lack of contact transmission among cohoused ducks is due to the lack of large shared water resources conducive of oral-fecal transmission. For example, others have shown successful transmission among mallards in contact with a water source previously contaminated by experimentally infected mallards [18] and water-associated transmission has also been postulated for mammals [12]. Overall, the index mallards in the highdensity stack appear to have shed virus for insufficient time and in insufficient quantities to elicit transmission within this stacked cage setting.…”