Avian Cholera Detected at Rush Lake in Palo Alto County
Posted: April 24, 2008

Wildlife officials with the DNR are taking steps to prevent the further spread of avian cholera after the disease was detected at a wetland area in northwest Iowa.

DNR Wildlife officials report that avian cholera has been detected at Rush Lake in southwest Palo Alto County. Avian cholera is a contagious disease that can be harmful to domestic poultry and migratory waterfowl, but is not considered a high risk for humans. Standard disease protection procedures should be used when working with diseased animals, including wearing rubber gloves and washing skin thoroughly.

Since April 9th, a total of 213 ducks and geese, consisting of 16 species have been removed from Rush Lake in southwest Palo Alto County. Analysis of a sample of these by the National Wildlife Disease Center (NWDC) in Madison, WI, indicated that avian cholera was the cause of death. Since April 9th, DNR staff has surveyed Rush Lake and surrounding wetlands on a bi-weekly basis and has followed NWDC protocol regarding the retrieval and disposal of dead birds. This, combined with lowering water levels to make Rush Lake less attractive to waterfowl appears to be working, as the number of dead birds found has decreased significantly. DNR staff will continue to monitor Rush Lake and surrounding areas until no newly deceased birds are found.

Waterfowl most frequently become infected with avian cholera when feeding in waters contaminated with high numbers of the disease carrying bacterium or through direct contact with infected birds. The bacterium often enters the upper respiratory tract, but infection can also be through eye membranes or skin abrasions. Once infected, death can occur in as few as 6 to 48 hours. Field signs of an avian cholera outbreak include large numbers of many species of waterfowl dying in a relatively short period of time, the presence of lethargic birds, birds swimming in circles or in stationary positions with their heads held over their backs, and dead birds that otherwise appear to be in good physiological condition. Positive identification is made through inspection of internal organs and blood/tissue analysis by trained personnel.

Strategies to mitigate the impacts of an avian cholera outbreak include picking up and properly disposing of all infected birds and managing the habitat to make it less attractive to other waterfowl. Since high concentrations of the disease carrying organisms can contaminate water bodies for several weeks, ongoing surveillance and removal of dead birds is needed to end the outbreak.

Avian cholera most likely appeared in wild birds in the United States in the mid to late 1880’s. Recent research suggests that snow geese are probably an important carrier for the disease as outbreaks have followed that species’ migration paths and the bacterium has been identified on their breeding and wintering grounds. In certain areas of North America, avian cholera occurs almost annually and in especially hard hit areas, mortality has exceeded 75,000 waterfowl.

In Iowa, avian cholera was first reported in 1979-80 and in 1980-81 when 3,000 and 7,000 snow geese and mallards respectively died of the disease in the southwest part of the state. Since then, cholera outbreaks have been much less frequent and die-offs usually number in the hundreds.

Outbreaks most frequently occur when waterfowl concentrate during migration, and in Iowa, most outbreaks have occurred in late fall and early winter. Similar to other diseases outbreaks that are magnified by high numbers of animals occupying the same area at the same, the effects of avian cholera outbreaks can be reduced by providing additional high quality migration habitats that allow birds to disperse across the landscape during migration.

For additional information on the avian cholera outbreak in Palo Alto County, please contact Wildlife Biologist Bryan Hellyer at 712-837-4850. In addition, the DNR requests that any person observing more than five dead waterfowl species on any given wetland or lake reports their finding immediately to Guy Zenner or Alan Hancock at the IA DNR Waterfowl Research Station in Clear Lake, 641-357-3517.