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What is Avian Botulism?

Avian botulism, limberneck or western duck sickness, is a paralytic disease in birds caused by ingesting a toxin produced by the bacterium, Clostridium botulinum. There are seven distinct types of toxin that have been identified, however waterfowl die-offs as a result of botulism are usually caused by type C toxin, type E can effect gulls and loons. Humans, dogs and cats are generally considered resistant to type C avian botulism.

Signs & Symptoms
Avian botulism affects the nervous system resulting in muscle paralysis. Signs include:

• Inability to sustain flight. Ducks can often be seen propelling themselves across the water using their wings, this symptom alone is not indicative to botulism as other diseases can cause this.
• Paralysis of the inner eyelid and neck muscles, resulting in an inability to hold the head erect. When birds reach this stage, they often drown. Those that do not drown will eventually die from respiratory failure as paralysis spreads.

Once these signs and symptoms are confirmed with the absence of obvious lesions, it is recommended to send sick or dead birds to the laboratory to test for avian botulism where they will use the mouse protection test.

What are optimum conditions for outbreaks in avian botulism?
C. botulinum is an anaerobic (oxygen-intolerant) bacteria that exists in dormant spores, resistant to extreme environmental conditions and able to remain viable for years. The spores are distributed in wetland sediments and also in the tissues of many aquatic invertebrates, mollusks, crustacea and vertebrates. The botulism toxin is not produced until the spores germinate when conditions are optimal.

Outbreaks usually occur during summer and fall when temperatures are at their highest (77-104^oF). Many environmental factors contribute to increased chances of outbreaks, such as:

• Elevated temperatures
• Decreased dissolved oxygen
• Presence of a food source (organic matter) for the bacteria
• Shallow water
• Water level fluctuations
• Poor water quality
• pH (5.7-6.2)

Decomposing carcasses can support toxin production and wetland flooding or draining with pesticide and agriculture pollution may kill aquatic life providing extra substrate for toxin production. Raw sewage and rotting vegetation are other potential energy sources for the bacteria to thrive.

Prevention & Control
Botulism spores are so dominant in the environment that the most feasible action to take is mitigating the environmental conditions that may cause outbreaks. These include

• Reducing organic inputs
• Proper removal and disposal of carcasses (incineration or burial)
• Improving water quality
• Aeration
• Increasing dissolved oxygen
• Reducing water fluctuations, either flooding or sharp water drawdowns.

Through AquaBio’s (ABET) natural remediation technologies, water quality can be drastically improved via on-site bioremediation and proper aeration.  These simple steps will greatly decrease the likelihood of serious outbreaks at treated sites.

References
http://www.nwhc.usgs.gov/publications/field_manual/chapter_38.pdf (http://www NULL.nwhc NULL.usgs NULL.gov/publications/field_manual/chapter_38 NULL.pdf) – US Geological Survey National Wildlife Health Center

http://www.archive.org/stream/avianbotulism00unitrich/avianbotulism00unitrich_djvu.txt (http://www NULL.archive NULL.org/stream/avianbotulism00unitrich/avianbotulism00unitrich_djvu NULL.txt) – US Fish and Wildlife Service

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