Defenders' Experts

Threats to Imperiled Species from Disease

Diseases are a conservation concern for many species of birds, mammals, amphibians and fish. Many of the most problematic diseases originated in other parts of the world and arrived here accidentally through travel and trade pathways, and these pose a particular threat because most species lack an immune response.

Broken Screens

This report about the regulation of live animal imports in the United States includes information about the threats of disease associated with live animal imports.
Learn more >>

About 10% of the imperiled animals in the United States face a major threat from diseases. For threatened birds, the number is closer to 40%, because avian malaria and avian pox have helped push many of Hawaii’s native birds to extinction.

The following are a few of the diseases that have impacted, or have the potential to impact America’s wildlife.

Avian Influenza

Avian Influenza (or “bird flu”) is a general name for dozens of strains of the type A influenza virus. The strains are denoted according to varieties of two proteins on the coating of the virus: there are 16 types of “H” and 9 types of “N.”

Most strains are not highly pathogenic and occur naturally in shorebirds, gulls, waterfowl, and other wild birds, often without causing any symptoms.

Other strains, including some that are highly pathogenic, are common in humans, swine, and domestic birds.

The most dangerous of these is the H5N1 strain, which has killed or led to the culling of over 220 million domestic birds in Asia, Africa and Europe.

There is great concern that this virus, which has killed over half of the 330 people is has infected, could evolve into a form that spreads more quickly among people. H5N1 has not been detected in North America, but scientists in Alaska regularly test wild bird, in order to provide advance notice to wildlife managers, public health officials, and agriculture officials if the virus does arrive here.

Additional Information

Host information from the Center for Infectious Disease Research and Policy at the University of Minnesota.
Information and Ongoing Research on Avian Influenza at the USGS Alaska Science Center

Avian Malaria

Avian Malaria is caused by a relative of the mosquito-borne protozoa (Plasmodium relictum) that causes malaria in humans. The birds of the Hawaiian Islands evolved in the absence of both mosquitoes and malaria, and the disease, which destroys the red blood cells, has had devastating impacts on the islands’ native birds. Hawaii’s forest birds only persist in the cooler reaches of the islands above 4,000 feet in elevation, above the mosquitoes’ range.

Additional Information

Information on the protozoa Plasmodium relictum from the Global Invasive Species Database.

Avian Vacuolar Myelinopathy

Avian Vacuolar Myelinopathy (AVM) is a neurological disease that affects bald eagles, American coots and several other species of waterfowl and birds of prey. The disease was first discovered in Arkansas in 1994, and is characterized by lesions on the brain and spinal cord that cause birds to lose muscle coordination. Scientists have not yet found an infectious agent for AVM and suspect that a toxin might be the cause.

Brucellosis

Brucellosis is a bacterial disease of wild and domestic ungulates. Brucellosis spreads when animals are congregated together, such as on winter feeding grounds, and it can cause joint inflammation and spontaneous abortion in infected animals. Humans can also contract the disease by drinking raw milk or from direct contact with infected animals or carcasses. Hundreds of bison have been killed outside the boundaries of Yellowstone National Park due to fears that bison might spread brucellosis to cattle, which were the original source of the disease in bison.

Additional Information

Chronic Wasting Disease

Chronic Wasting Disease is a fatal neurological disorder of elk, deer and moose. Abnormal proteins called prions transform the proteins in brain tissue, creating a “spongiform” network of diseased tissue. As it progresses, the disease interferes with balance, behavior and feeding, resulting in the characteristic “wasting.” Part of the family of “transmissible spongiform encephalopathies” that includes mad cow disease and scrapie in sheep, CWD is contagious among animals in close contact, such as at feeding stations or in captive herds. CWD has been found in ungulates in 13 states and two Canadian provinces.

Additional Information

Implications and challenges of CWD for wildlife managers - from the Chronic Wasting Disease Alliance website.

Batrachochytrium dendrobatidis (Bd)

Batrachochytrium dendrobatidis (Bd), also known as the amphibian chytrid fungus (or the amphibian chytrid), is a pathogenic fungus linked to the declines and extinctions in many amphibian populations worldwide. Although certain areas are still thought to be free of the fungus, Bd has been spreading geographically and taxonomically since its discovery in 1998. Not all amphibian populations are affected equally and some groups of heavily traded amphibians appear to even be resistant to Bd. The trade and/or release of such animals and/or Bd-contaminated water may introduce the pathogen into new areas. New findings show that Bd infections may be treatable through the application of antibiotics, however, this is not feasible on a large scale. A precautionary method regulating the trade and/or release of Bd-infected animals and water should be implemented to prevent further spread of Bd.

West Nile Virus

West Nile Virus is a mosquito-borne virus of Africa and Asia that first appeared in North America in 1999, and rapidly spread across the country from its entry point in New York. WNV occasionally causes serious or fatal illness in humans, and also infects 18 species of mammals and over 250 species of birds. Members of the corvid family – crows, jays and ravens—are particularly susceptible to WNV, with nearly 100% mortality among infected individuals. However, West Nile virus’ biggest danger is the threat it poses to species that are already at risk, particularly the sage grouse. Ten states have reported sage grouse deaths from WNV and there is no evidence that any infected birds have survived and developed immunity.

Additional Information

Lean Times for the Cock of the Plains - An article in the Spring 2005 issue of Defenders Magazine
West Nile Virus in Greater Sage Grouse - November 2006 USGS Wildlife Health Bulletin

Viral Hemorrhagic Septicemia

Viral Hemorrhagic Septicemia is a serious new disease of fish in the Great Lakes region. At least 23 species are vulnerable to infection, which causes lesions and bleeding internally and externally. VHS probably arrived in the Great Lakes via contaminated ballast water, a major invasive species pathway that also brought zebra mussels to the region.

Additional Information

Viral Hemorrhagic Septicemia (VHS) Briefing Paper - from the Michigan DNR (November 2006)

Whirling disease

Whirling disease is a parasite of Eurasian origin that was introduced to the U.S. in the 1950s and is widespread in the western states. It infects the brains and spinal cords of young trout and salmon, damaging the areas that control equilibrium in the water. Infected fish swim erratically, displaying the “whirling” behavior for which the condition is named.