Avian cholera, also known as fowl cholera, is caused by the bacterium Pasteurella multocida and is one of the most common diseases among wild North American waterfowl and domestic poultry (turkeys).  Different strains of the bacteria may infect many bird and mammal species; however, avian cholera in wild birds is primarily caused by one strain, Type 1. The species of birds most commonly affected are ducks and geese, coots, gulls, and crows.  Humans are not at a high risk for infection with the bacterial strain causing avian cholera.

The bacteria can be transmitted by bird-to-bird contact, contact with secretions or feces of infected birds, or ingestion of food or water containing the bacteria. Aerosol transmission may also occur. The bacteria may survive up to 4 months in soil and water.

The bacteria kill swiftly, sometimes in as few as 6 to 12 hours after infection. Live bacteria released into the environment by dead and dying birds can subsequently infect healthy birds. As a result, avian cholera can spread quickly through a wetland and kill hundreds to thousands of birds in a single outbreak. Avian cholera often affects the same wetlands and the same bird populations year after year.

Because this disease is highly contagious and can spread rapidly, prompt action is needed to prevent and minimize the spread of the disease. Careful carcass collection and disposal helps reduce the amount of bacteria in the environment.

Birds may show the following signs when infected with the bacteria: lethargy, convulsions, swimming in circles, throwing the head back between the wings, erratic flight, such as flying upside down or trying to land a foot or more above the water, mucous discharge from the mouth, soiling or matting of the feathers around the vent, eyes, and bill, pasty, fawn-colored or yellow droppings, or blood-stained droppings, or nasal discharge.