Disease Monitoring
Diseases of wildlife are certainly not new; they have been recognized for centuries. References to wildlife diseases were recorded more than 2,000 years ago in the Bible, as well as in the writings of Homer and Aristotle. Historically, disease played an important part in the natural population cycle. In modern situations, however, wildlife is more concentrated and disease outbreaks spread more rapidly. Also, the lack of predators means that wildlife that die from disease are not removed from the environment, but rather remain as a source of further contamination. Large disease outbreaks can no longer be left to simply run their course, so during times of heavy wildlife concentrations, such as during the fall waterfowl migration, it is important that we monitor the refuge for diseased animals and dispose of any that we find.
Avian Botulism Outbreak
In October of 1997, avian botulism killed about 5,600 birds at the Chautauqua Refuge. Dead birds were initially reported by a volunteer on the refuge's Lake Chautauqua on October 2. Refuge personnel collected the birds and sent them to the National Wildlife Health Center, of the U.S. Geological Survey, in Madison, Wisconsin. Early tests ruled out other infectious diseases, and botulism was confirmed in later tests. A wildlife disease specialist from the center went to the refuge to conduct further tests.
A bacteria (Clostridium botulinum) produces a toxin that, when ingested, causes avian botulism, type C. This bacteria is commonly found in soils and mud along lakes and rivers. When water levels drop, temperatures rise, and oxygen is no longer present, the bacteria reproduce, generating the toxin. Waterfowl and shorebirds are affected when they ingest toxin while feeding in these areas. The disease can spread quickly when healthy birds feed on maggots on infected carcasses, prompting our extensive efforts to remove dead birds. Maggots concentrate the toxins to the point where the ingestion of as few as two maggots can kill an otherwise healthy bird.
The Refuge staff received assistance from the Illinois Department of Natural Resources, which provided personnel and an airboat, and from personnel at Mark Twain National Wildlife Refuge. Most of the birds collected (about 3,500) were green-winged teal. Other species affected included mallards, pintails, Canada geese, shorebirds, and blue-winged teal. Carcasses were buried to prevent spread of the disease.
Lake Chautauqua is about 3,200 acres in size, although due to lowered water levels, only about 200 acres were open water at the time of the outbreak. The remainder was moist soil areas and vegetation. Managers let as much water as possible into the lake from a nearby creek in an effort to dilute the toxin and cover exposed mud flats. Personnel in airboats also hazed the birds to keep them away from the lake.
Avian botulism can affect any bird species, although it is most often seen in waterfowl and shorebirds. The disease is not always fatal, but smaller species such as teal are generally at greater risk. Birds die when they lose control of muscles enabling them to fly or breathe, and they can drown when they can no longer hold their heads up. Type C, or avian botulism is rarely a threat to humans, who are more often affected by Type A, B, or E, sometimes found in improperly canned food.
Monitoring for new outbreaks will occur whenever conditions are right for the spread of the toxin. While outbreaks cannot be prevented, rapid response by flushing the pools with fresh water and removal of dead birds will prevent further spread of the disease.
