PROJECT GOAL: Understand the ecological role of wildlife in transmission and movement of emerging viral and bacterial pathogens causing livestock and human disease in order to develop diagnostic, surveillance, and management methods to minimize the impact of those diseases on agricultural production and human health
Project Accomplishments 2010
Considerable concern exists worldwide about recent emerging infectious diseases. Seventy-five percent of these emerging infectious diseases are zoonotic, meaning that they are naturally transmitted between wildlife species and humans. Some zoonotic diseases carried by wildlife can also be transmitted to economically important domestic animals, such as avian influenza virus to poultry and pathogenic bacteria to cattle. Therefore, wildlife populations often play a key role in many diseases that directly impact humans and agriculture. The National Wildlife Research Center (NWRC) is at the forefront of monitoring, surveillance, and research for many of these diseases.
Raccoons and West Nile Virus—Raccoons (Procyon lotor) are considered a public health threat for a variety of zoonotic diseases. It is well established that raccoons are commonly exposed to West Nile virus (WNV) in several geographic regions of the United States, but little is known about their ability to serve as reservoirs for WNV and/or shed significant quantities of the virus. In a recent study, NWRC scientists experimentally infected eight raccoons with WNV to monitor morbidity and mortality rates, blood profiles, viral shedding, viral production in tissues, and pathology.
The results of this study suggest that raccoons are not an important host in WNV mosquito transmission cycles. Only 75% of the test animals developed detectable levels of virus in their blood. WNV was not detected in tissues tested or in any opportunistically collected urine samples. WNV fecal shedding was observed in the majority of inoculated individuals and typically began several days after the virus was detected in the blood. On occasion, fecal swabs contained relatively high WNV titers, suggesting that whole feces may contain much higher viral loads. Observations of high survival with little or no obvious signs of the disease in raccoons are consistent with those reported for some other mammalian species. Although raccoons are well documented to be commonly exposed to WNV in nature, their role in WNV transmission, if any, may more likely be associated with fecal contamination of the environment rather than with mosquito-host transmission cycles. Researchers surmise that, although raccoons are commonly exposed to WNV, they probably do not have a major involvement in WNV cycles.
Antibody Responses of Raccoons Naturally Exposed to Influenza A Virus— NWRC and Iowa State University scientists investigated the concentration of naturally acquired antibodies to influenza A virus in raccoons (Procyon lotor) over time. Seven wild raccoons, some of which had been exposed to multiple subtypes of influenza A virus, were held in captivity for 279 days, and scientists collected serum samples on 10 occasions during this interval. They then tested the serum samples for the presence of antibodies to influenza A virus. Although titer declines were noted in most animals over time, all animals maintained detectable antibodies for at least nine months.
These data indicate that naturally acquired antibodies to influenza A virus can remain detectable in raccoons for many months, with the actual duration presumably being much longer because all animals had been exposed to influenza A virus prior to the study. Surveillance programs using antibodies to detect recent influenza A virus activity should take into account that these antibodies may portray a historical perspective in mammalian wildlife and only occasionally represent recent exposures to influenza A virus. However, the longevity of these antibodies could be extremely useful to detect exposures months after outbreaks have occurred.
Low Pathogenic Avian Influenza in House Sparrows and European Starlings—Little is known about the role of songbirds (Order Passeriformes) in the ecology of the avian influenza (AI) virus. Many passerine species are abundant and widespread, and they commonly come into contact with free-ranging birds as well as captive game birds and poultry. In a recent study, NWRC scientists inoculated captive house sparrows ( Passer domesticus) and European starlings ( Sturnus vulgaris) with low pathogenic AI viruses to better understand the birds' responses to primary infection and their potential role in the transmission of this disease.
The results showed shedding of the virus for both starlings and sparrows; however, the shedding was low and short-lived with no transmission among cage mates. Antibodies were detected as early as three days post treatment, and 97% of inoculated birds developed antibodies within 28 days post treatment. Pre-existing immunity appeared to reduce shedding. Infectious low pathogenic AI virus was cultured from oral and cloacal samples, as well as from gastrointestinal and/or respiratory tissues from both species. These results suggest that passerines are not likely to be significant reservoirs of low pathogenic AI viruses in nature.