Ecology of Emerging Viral and Bacterial Diseases in Wildlife
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.
Baylisascaris Nematode in Raccoons— Baylisascaris procyonis is an intestinal nematode commonly found in raccoons ( Procyon lotor) that can cause fatal larva migrans. This disease is characterized by enlargement of the liver, fever, cough, and abnormally large amounts of globulins in the blood in birds and mammals, including humans. The B. procyonis parasite has been found in isolated regions in the Appalachian Mountains and, more recently, in Atlanta, GA. NWRC researchers collaborated with scientists from the Southeastern Cooperative Wildlife Disease Study (within the College of Veterinary Medicine at the University of Georgia) to investigate the distribution and prevalence of B. procyonis in selected populations of raccoons in Georgia.
The researchers examined intestinal tracts of 312 raccoons from 25 Georgia counties for B. procyonis. B. procyonis was detected in Clarke County where 12 of 116 (10.3%) raccoons were infected. In addition, Toxascaris leonina, a morphologically similar nematode, was found in three raccoons from Clarke County and Morgan County. The researchers also genetically compared worms from Georgia, Kentucky, and Texas; sequence analysis confirmed that the Georgia samples were B. procyonis. These data indicate that the distribution of B. procyonis within Georgia is increasing dramatically, and that only limited genetic variation is present in the rRNA and ITS ( internal transcribed spacer) gene regions among B. procyonis from the southern United States.
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.
Ring-Billed Gull Movements in Response to Egg Oiling—Overabundant populations of ring-billed gulls in the Chicago, IL, lakefront area are a potential hazard to aviation and have led to numerous swim bans due to concerns over fecal pollution of the water. At the request of Chicago city officials, APHIS Wildlife Services implemented the Chicago Ring-Billed Gull Damage Management Project in 2006 to prevent increases in the local population of ring-billed gulls, reduce the severity of conflicts with gulls, and evaluate if the majority of gulls on Chicago lakefront are from local colonies.
In 2007, Wildlife Services field operations staff oiled 53% of the estimated number of nests at two local colonies and found that oiling eggs with food-grade oil was a successful method of preventing gull production. In 2008, Wildlife Services increased gull population management efforts and oiled 80% of the nests in the two Chicago nest colonies, totaling 57,590 gull eggs in 22,136 nests. Without this project, Wildlife Services estimates that the Chicago hatch-year gull population would have increased by an additional 22,000 to 44,000 gulls beginning in July 2008, based on a fledge rate of one to two birds per nest. Significantly fewer gulls were observed on most of Chicago's beaches in 2008, which likely contributed to a reduction in conflicts, including a 33% decrease in the frequency of swim bans on Chicago's beaches (without canine harassment) in comparison to 2006.
To observe gull movements in the region, NWRC scientists partnered with Wildlife Services field personnel to mark and observe 5,968 gulls in Chicago and 5,617 gulls in northwestern Indiana throughout the summer of 2008. The researchers did not observe any movement of marked after-hatch year gulls between Chicago colonies; after-hatch-year gulls nesting in Chicago, IL, and East Chicago, IN, tended to use beaches nearest to their nest colony. Recognizing this and the fact that gull use of beaches remained relatively stable throughout the swim season, it appears that gulls nesting outside of Chicago do not move into the city in significant numbers to use beaches during the swim season, and thus are not likely to contribute significantly to the conflicts on Chicago's beaches during the swim season. Oiling the eggs with food-grade oil proved to be an effective method of reducing Chicago's hatch-year gull numbers without resulting in the abandonment or relocation of nest colonies.
More on Avian Influenza Information--APHIS Wildlife Services
Avian Influenza Information from APHIS Veterinary Services
Wildlife Services' National Wildlife Disease Program Emergency Response
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