Botulism in animals: a rare disease with serious consequences
What is botulism?
Botulism is caused by a paralysing neurotoxin produced mainly by the bacterium Clostridium botulinum. It is the most powerful natural toxin known to date: a few micrograms can be lethal to humans or animals.
In France, animal botulism mainly affects domestic and wild birds, and cattle.
Are the toxins responsible for cases in humans and animals the same?
The toxins involved largely differ:
- In humans, the most common forms, often associated with food contamination, are caused by type A and B toxins and, to a lesser extent, type E and F toxins.
- In animals, it is mainly type C and D toxins and C/D and D/C mosaics that are responsible, with type E being very rare.
Botulism caused by type E toxins is rare in France in both humans and animals.
Is botulism transmissible from animals to humans?
The risk of transmission of botulism between animals and humans is low, and the toxins involved are generally different. There are currently no known cases of direct transmission of botulism between animals and humans.
However, people in certain professions and activities who are particularly exposed, such as farmers, slaughterhouse workers, fishermen, hunters or those responsible for collecting wild animal carcasses, must comply with appropriate hygiene and personal protection measures, such as wearing gloves and protective clothing.
Is there a risk of contamination from consuming animal products?
In the UK, beef and poultry-based foods are very rarely the cause of human botulism. Compliance with processing and storage rules (hygiene during slaughter, cooking, cold chain, use-by date) effectively prevents the risk.
If type E botulism is suspected in a body of water, consuming raw fish (ceviche, marinades, etc.) from that environment should be avoided.
What are the consequences of botulism in animals?
Botulinum toxin prevents the transmission of nerve signals, causing flaccid paralysis of the muscles. The affected animal becomes unable to move, feed or even breathe, leading to death.
In livestock farms, mortality can reach 100%, resulting in significant economic losses. In wildlife, thousands of birds can die during an episode of botulism, with a significant impact on biodiversity.
How do animals become infected?
Food, drinking water and litter can carry the bacterium and/or the toxin. Biosecurity breaches are often identified as the cause of an outbreak. Clostridium botulinum bacteria can persist in the environment in the form of spores for several years, leading to recurrent outbreaks in livestock.
In wildlife, the factors that trigger an outbreak are not yet fully understood, but annual recurrences are often observed. It is recommended that carcasses be disposed of quickly. This is because the maggots present on the carcasses can concentrate large amounts of botulinum toxin. Birds that feed on these maggots are then exposed to the toxin and die, causing the cycle to spiral out of control and mortality to skyrocket.
Is botulism common?
Animal botulism remains relatively rare in France, with an average of ten outbreaks per year in cattle, thirty in poultry and twenty in wild birds confirmed in laboratories. However, these figures are probably underestimated, as not all cases are systematically reported or analysed in laboratories.
Are there any treatments for botulism?
In poultry, antibiotic treatment with β-lactams eliminates the form of the bacterium that produces the toxin and thus stops the clinical signs. However, it does not eliminate spores, and clinical signs are likely to reappear once treatment is stopped.
A vaccine exists but is not authorised for sale in France. Its use may be considered under temporary authorisations for use. The vaccine is used in cattle farms in the event of outbreaks in order to vaccinate animals that do not show clinical signs and to prevent recurrences.
Is botulism seasonal?
Outbreaks of botulism mainly occur in wildlife during the summer. Summer conditions (heat, low water levels, reduced oxygen in the environment, etc.) are conducive to the development of the bacterium. Climate change could increase the frequency of botulism cases in the coming years.
This seasonality is also observed in poultry farms, although outbreaks can be detected throughout the year. It is much less pronounced in cattle farms.
ANSES is the national reference laboratory (NRL) for avian botulism. As such, it develops and validates methods for detecting and characterising Clostridium botulinum strains.
It participates in the investigation of animal botulism outbreaks, in conjunction with managers and stakeholders in the field.
It conducts research projects to improve the prevention of animal botulism episodes, in particular by studying the reservoirs of the bacterium, the routes of contamination, host/pathogen interactions and means of control.
Lastly, the Agency carries out risk assessments and issues recommendations to professionals, public authorities and consumers to prevent botulism in animals and humans.