Zoonoses: Botulism
Botulism is a disease caused by ingestion of the toxin produced by the bacterium Clostridium botulinum. There are several different types of toxin. The bacteria are widespread and their toxins can affect most animals and birds, including people. It is commonly found in the gut of poultry and wild birds, and in the litter in poultry houses. Problems with intoxications are sporadic in wild birds, but can cause paralysis with high numbers of birds dying. Intoxications in cattle have been associated with the grazing of land on which poultry litter has been spread.
Botulism in Cattle, Sheep and Goats
There has been a recent marked increase in the reported incidence of suspected cattle botulism in England and Wales. From 1997 – 2002 an average of four botulism incidents occurred each year but this rose to 20 in 2003, 20 in 2004, 20 in 2005 and there have been 29 up to end of November in 2006. Botulism in cattle in UK is considered to be caused mainly by Clostridium botulinum toxin types C and D. A large proportion of the suspect incidents have been associated with direct or indirect contact with broiler poultry litter. A similar pattern of a recent rise in incidents and apparent association with broiler litter has also occurred in N.Ireland.
Botulism in cattle usually presents as a progressive flaccid paralysis, which begins as an unsteady gait. It develops over a period of several hours and leads after several days to recumbence and usually the paralysis is ultimately fatal. Some animals are found dead or recumbent when they had been observed apparently normal a few hours earlier. A small proportion of animals may recover but many affected cattle are euthanased to avoid welfare problems.
Cases of botulism in cattle are usually diagnosed on the basis of the clinical signs and by the elimination of other conditions. It can be very difficult to obtain positive confirmation that botulism exists. Tests are available that can detect the toxin in the serum of affected animals, however, in cattle especially the concentration of toxin in the blood of affected cows is usually too low to be detected. Hence most of the cases investigated are classified as suspected rather than confirmed botulism.
Cases of suspect botulism which are brought to the attention of the Veterinary Laboratories Agency are investigated on behalf of the Food Standards Agency as suspect food safety incidents and appropriate steps are taken to protect the food chain.
Advisory Committee on Microbiological Safety of Food (ACMSF)
The ACMSF set up an ad hoc group to consider “Botulism in Cattle” in 2004. The group produced a draft report which was put out to public consultation in spring 2006.
Following consideration of the responses to the consultation the report was published in December 2006 and was accepted by the ACMSF at its meeting on 28 September 2006.
In May 2007 the Ad-Hoc Group on Botulism in Cattle was reconvened. The original terms of reference of the Group were revised to consider the potential health risks associated with botulism or suspected botulism in sheep and goats (in addition to cattle), particularly in relation to the spreading of poultry litter in agricultural land, and to report back with recommendations to the ACMSF.
The ACMSF concluded that current restrictions on food produced from clinically affected sheep and goats should remain in place. However, based on current scientific evidence it considered the restrictions on unaffected animals from farms where there have been cases of botulism in sheep and goats to be over-precautionary, primarily because the botulinum toxin types in animals (C and D) have rarely been associated with disease in humans. In addition, there is little evidence of any human cases of botulism have been caused by consumption of meat and milk. The ACMSF therefore recommends that in the absence of other signs, there should be no restrictions on the sale or consumption of milk or meat from healthy sheep and goats from affected farms.
Following public consultation, the ACMSF report was published in 2009 and is available below:
Following ACMSF recommendations the Food Standards Agency has amended its advice on the management of outbreaks of suspected botulism in sheep and goats. The change brings the FSA’s advice in to line with the current advice on botulism in cattle, which was amended in 2006.
Botulism in Wild Birds
Wild birds can be affected by botulism. Cases are seen in hot weather and associated with decaying plant and animal matter and poor oxygenation of the water. This allows development of the bacterial spores. Birds with botulism suffer from a flaccid paralysis, swim in circles and eventually drown. Often many birds of different species in the same location die. The disease can be spread between ponds and lakes on bird's feet so often several ponds in an area can be infected. We have seen a number of botulism outbreaks associated with the hot summer of 2006. Deaths of wild birds are investigated by the Veterinary Laboratories Agency as part of our scanning wildlife surveillance. Further information on Veterinary Surveillance and wildlife.
Further information
Page last modified: 19 May 2009
Page last reviewed: 15 January, 2007