Botulism

Also known as

Ptomaine poisoning, food poisoning

Description

Botulism is a rapid onset, usually fatal disease caused by the botulinum toxin produced by the bacterium Clostridium botulinum. Signs are usually seen within 2–6 days after eating contaminated materia. High doses of the toxin will produce botulism within 12–24 hours. Lower doses of the toxin will produce signs of botulism within 7–20 days. In a herd outbreak, most deaths will occur within in the first week, but can continue for up to three weeks.

Botulism is characterised by a progressive muscle weakness (paralysis). Affected animals may be weak, stagger about, or go down. Cattle characteristically display flaccid paralysis and occasionally protrusion of the tongue.

Cattle are extremely sensitive to the effects of the toxin meaning that ingestion of very small amounts of toxin can result in clinical disease. The progression and severity of the disease depends on the amount of ingested toxin. When a large amount of toxin has been ingested, the animal may be found dead without having shown any signs of disease. Conversely if only a small amount of toxin is ingested the progression of the disease may take a more chronic course and clinical signs may be less severe.

Signs

• Hindlimb weakness
• Paralysis of muscles of the face, jaw or tongue
• Inabiity to eat or drink
• Drooling
• Overall paralysis
• Collapse (downer cattle)
• Respiratory failure
• Death

Cause

Botulism is caused by ingestion of pre-formed toxins of Clostridium botulinum where clinical disease varies from apparent sudden death to recovery after 14-21 days. Clinical signs are confined to the nervous system with muscle weakness affecting the hindlegs during the early stages with eventual recovery.

Common sources of toxin include animal carcasses, rotting organic material and poorly prepared silage. Most sporadic cases of botulism in cattle have been associated with poultry litter spread onto pasture. The feeding of ensiled poultry manure and bakery waste has caused very serious losses in cattle on individual properties. Bird carcases in silage clamps have been implicated in some sporadic cases of botulism.

Usually, weakness progresses over four to seven days to involve the forelegs, head and neck. Affected cattle have difficulty chewing and swallowing and there is paralysis of the tongue. Cattle must be euthanased at this stage for welfare reasons otherwise eventual involvement of respiratory muscles and diaphragm causes death.

Prevention

Vaccination is the most effective way to control botulism. However, the commercially available vaccines are difficult and hazardous to produce. Botulinum antitoxin has been used for treatment with varying degrees of success, depending on the type of toxin involved and the species of host however, such treatment is rarely used in cattle.

Vaccination with the bivalent (type C and D) botulism vaccine is the most effective long-term prevention strategy. A range of botulism vaccines is available and involves either an initial two-shot program, one month apart, or a single shot followed by an annual booster shot.

An alternative long-acting vaccine consists of an initial single shot followed by a booster shot every three years. Both vaccines provide a similar level of protection. Which vaccine to select will depend on cost and management practices.

All vaccines require booster shots to maintain immunity and a veterinarian should be consulted to determine if vaccinations are appropriate for particular cattle.

Supplementation with non-protein nitrogen (e.g. urea) and phosphorous is recognized as a management practice by some in helping prevent botulism in cattle, but little scientific research is found on this topic.

Careful disposal of all animal or bird carcases and poultry litter is essential to minimise the risk of botulism to livestock. Poultry carcases should be promptly removed and disposed of by incineration or rendering as required by the Animal By-Products (Enforcement) Regulations (NI) 2015.

Poultry litter should not be spread on agricultural land that is to be grazed, or from which silage or hay is to be harvested, in the same year. This is because fragments of carcases, containing botulinum toxins, may persist on pasture for a considerable time.

If litter must be spread, it should be deep-ploughed into arable ground. If this is not an option and litter must be disposed of by spreading on pasture, ruminants should not have access to the treated fields for at least several months.

However, there is no guarantee that the treated fields would then be safe for cattle and it is important to remember that fragments of carcases on pasture may be transported by scavenger animals and birds to neighbouring fields. Spreading litter on a windy day may also pose a risk of contaminating adjacent fields.

Treatment

Currently there is no effective treatment. Disease can be controlled by specific vaccination but it is not included in standard multivalent clostridial vaccines.