Animals – Falling fowl of botulism

Botulism is a disease that presents as a flaccid paralysis of muscle groups in affected animals or persons. The disease is caused by the ingestion of the botulinum toxin which, in turn, is produced by a bacillus called Clostridium botulinum. This is a common bacterium in wetland ground and only grows in the absence of oxygen (anaerobic) and produces spores. The spores need warm water temperatures (25C to 45C), a protein source and anaerobic environment to produce the toxin. This environment is present in many wetlands with shallow stagnant ponds, with water fowl concentrated in smaller areas because of rapid evaporation of pond surfaces due to hot summer weather like we have now.

The birds defecate in the water and provide a protein source for bacteria and spores at the bottom of warm shallow ponds. The aeration in the sludge at the bottom is minimal and high temperatures further reduce the oxygen carrying capacity of the water. Dabbling water fowl have easy access to the toxin produced at the floor of the pond. Affected birds often have their wings spread flat on the water and are unable to fly. On land the birds stagger and use their wings for support like crutches spread out sideways. The bird’s call is quite often affected as well. The toxin works by blocking the release of the neurotransmitter Acetylcholine from the nerve endings (motor neurons) that lead to the muscle.

Acetylcholine is the chemical that gives the muscle cell the impulse to contract. In the absence of this chemical the muscle stays flaccid. This applies to all muscles of the body, respiratory muscles and the muscle groups of the heart included. Once the toxin has connected with the receptors at the motor neuron this will permanently inhibit the nerve endings from releasing Acetylcholine. The clinical effect is directly proportional to the number of motor neurons permanently blocked.

Recovery from this dilemma comes from the body’s ability to grow new motor neurons, a process that takes weeks to months. Laboratory diagnosis is tricky because confirmation of toxin presence in serum or tissue by ELISA or PCR tests is strongly influenced by sample quality and the gold standard of a mice inoculation test is not on offer in New Zealand laboratories. Therapy largely relies on taking the birds away from the pond to prevent drowning, to supply clean fresh water in shallow containers and to provide food and shelter from predation until symptoms subside.

Note: Botox is a very purified version of the botulinum toxin. The way it is used in cosmetic medicine relies on the very fact that it paralyses the muscle connected to the skin in order to reduce wrinkle formation. This effect is maintained until new motor neurons restore the function of the underlying muscle.