Scientists Test Nature’s Own Filter To Detect Bird Flu Virus

Recent outbreaks of avian influenza, or bird flu, have become a worldwide concern in light of widespread mortality in domestic poultry and wild aquatic bird species. Scientists are equally concerned about the possibility of an avian influenza pandemic developing in humans.

The rapid spread of H5N1 - the highly pathogenic strain of bird flu - to new locations and species has necessitated development of detection and monitoring methods for birds and their aquatic habitats. Colorado State University researchers are travelling this summer to Vietnam, where severe outbreaks of H5N1 have occurred, to complete two separate studies on detecting avian flu viruses in water and in land bird species.

Southeast Asia is a focus of recurrent avian influenza, or AI, outbreaks in birds and humans including portions of northern and central Vietnam. In birds, AI viruses typically replicate in the intestinal tract and the viable virus is shed in the feces. Transmission occurs when contaminated water or other material is ingested by uninfected birds.

One method to detect the virus is by testing water in areas where outbreaks are common. While mechanical filters are effective at concentrating and detecting the virus in water, using a large number of the filters in the field can be costly.

Instead, Colorado State and U.S. Department of Agriculture scientists have been using a natural filter to detect and quantify AI viruses in water. Preliminary lab experiments by Kate Huyvaert, assistant professor in the Department of Fish, Wildlife and Conservation Biology at CSU, and Alan Franklin from the USDA's National Wildlife Research Center indicate that freshwater clams accumulate AI viruses in their tissues when they filter water contaminated with virus. This finding suggests that the bioaccumulation - or natural filtration - of viruses by mollusks may be a useful tool in detecting and monitoring AI viruses in the wild.

"What is really neat is that we are harnessing nature to learn about a virus that affects humans and wildlife," Huyvaert said. "Not only are clams cost effective, but we learn more about the ecological process of the virus interacting with other organisms."

This summer, researchers will put these ideas to test in a pilot study in northern Vietnam where they will expose Asiatic clams - these clams are widespread and commercially available in Asia and they have been used as biomonitors of heavy metals and other contaminants - to bodies of water where infections have been identified in birds that use the habitat.

Avian influenza has been studied extensively in domestic poultry and waterfowl, but information about the existence of the virus in wild land birds is still limited. In a separate study, CSU scientists will address this lack of knowledge by providing a baseline survey and characterization of avian influenza viruses carried by wild land birds in forests as well as the surrounding human-dominated landscape in northern Vietnam.

Specifically, Thinh Vu, a doctoral student at Colorado State, will study the prevalence of the virus in wild land birds and test his prediction that birds that live in the forest interior are less likely to carry the virus than birds whose habitats are located at the forest edge and in close proximity to humans and their domestic birds.

Preliminary lab results completed by Vu provide evidence that AI has been circulating in resident land birds in the region as well as aquatic birds. Land bird species are not considered by most scientists as important AI reservoirs; however, Vu thinks that may be in part because few studies have been completed on these species. Vu's research may support emerging evidence that indicates that land bird species could play a role in preserving and circulating AI in the environment.