THE word botulism is derived from the Latin word botulus, meaning sausage, due to the spores’ resemblance to a sausage under a microscope.
Some early descriptions of botulism date from as far back as 1793 in Germany.
The occurrence of the disease is mainly related to two factors: the sensitivity of the animal species and in Zimbabwe the Mashona prototype cattle in particular are less vulnerable but also susceptible to the disease according to the type and amount of botulinum toxin ingested.
Botulism under the microscope
The toxins are absorbed and transported to sensitive neurons via the blood, where they then act at neuro-muscular junctions, resulting in motor paralysis without interference in functional sensory function. Primarily, the toxins affect the peripheral nervous system, where they block the process of synapse release of acetylcholine, which prevents the passage of nerve impulses to the muscle, causing flaccid paralysis.
Clinical signs of botulism in cattle usually appear three to 17 days after the ingestion of toxic material.
Botulism causes a progressive paralysis and animals die of respiratory failure from paralysis of the breathing muscles.
The symptoms exhibited by stricken cattle are muscular weakness – kuneta mumabvi – starting in the hind quarters and moving forward.
This can be followed by a paralysis of the jaw and throat muscles which manifest in the animal’s inability to chew or swallow feed. The animal may even fail to drink water due to its inability to swallow.
Affected cattle tend to have a stiff gait (walk) and drool saliva from their mouth – kubuda rute in Shona, caused by the tongue hanging out of the mouth of the affected animal.
The animals are usually found in a sitting position, unable to rise; their breathing becoming progressively more audibly laboured.
They frequently extend their hind legs behind them, in a ‘frog-legged’ position to make breathing easier.
The animal remains recumbent due to paralysis, but will retain consciousness until death occurs one-to-three days later.
Cattle can also die from dehydration as they are unable to drink water on their own.
While water can be given through stomach tubes, it is not a common practice, and certainly not many rural Zimbabwean farmers will have the requisite skills, mechanisms and veterinary equipment to carry out this procedure.
According to the World Health Organisation (WHO), cases of botulism in cattle have been described in several countries around the world, predominantly resulting from ingestion of the toxin in contaminated food or water or by osteopathy practiced in animals.
Osteopathy is the consumption of bones practiced by some animals when there is a shortage of calcium and phosphorus in their feed.
In European countries, Australia, Brazil, SA, and the Gulf Coast region of the US, where phosphorus deficiency is a common condition, osteophagia is the main risk factor for the occurrence of the disease in extensive farming systems.
Animals in feedlots are also susceptible to botulinum toxicity due to the risk of intoxication through contaminated and wrongly conserved feed containing decomposed organic matter or small carcasses.
Other scenarios such as the intake of water in the presence of animal carcasses or the consumption of cereals such as corn, hay and silage wrongly conserved or that contain the remains of carcasses of animals have also been described as factors leading to the onset of the disease.
It is important, therefore, to provide your heard with nutritional supplements of protein and phosphorus in order to reduce incidents of bone-chewing among grazing cattle.
The veterinary laboratory’s detection of botulinum toxin in cattle liver, ruminal contents or bovine intestinal samples is a gold standard for the confirmation of the disease’s diagnosis.
When analysing sanitary indicators, such as the absence of vaccination in conjunction with inadequate feed conservation, the risks for botulism in the herd increases considerably and consequently causes significant economic losses.
The use of vaccine protection against botulism can be very effective, however, some factors can minimise this efficiency, such as the amount of ingested dose of the neurotoxin, because even animals that are vaccinated may develop the disease if exposed to large enough amounts of it, or when the source of the toxin is not identified and removed from the area, keeping the animals exposed to the potential for ingesting it.
When vaccination of the herd with bivalent toxoids C and D is carried out in conjunction with a reduction in the exposure of the bovine to botulinum neurotoxin, then the rate of protection against the disease may reach 96 percent.
For this, the protocol of vaccination with two doses is recommend — the primo-vaccination followed by booster vaccination between four to six weeks.
For vaccines with bivalent toxoids C and D, according to the protocol of vaccination, each animal receives two doses.
Under conditions similar to the present outbreak, the best conduit for containment of this disease is to immediately identify and withdraw the feed in which the botulinum neurotoxin is present.
It is important to note that new cases may occur up to 18 days after the removal of contaminated feed.
In this way, vaccination can be considered a viable prophylactic, sanitary and economical option.
However, adequate sanitary schedule and planning is necessary for its execution, considering the risks and the time necessary for the cattle to acquire adequate immunological protection.
So, if you notice that your cattle seem to have an unusual liking to strange things, even bones lying around in the veld, you should know that your area is deficient in phosphorous and hence you need to provide your cattle with supplements such as mineral licks.
Unfortunately, in terms of treatment, there is not much that can be done to an animal severely affected by botulism.
But do not ignore easy preventative measures because you believe your cattle are ‘hard Mashona type’. Dzinofa kuti fii! They will die, as the many reports I have recently received confirm.
The most reliable way of dealing with this deadly disease is to prevent it.
This is done through annual vaccines, usually in areas where the disease is known to be endemic.
Animals that have not been previously immunised should be given two injections at four-to-five weeks intervals.
Thereafter, annual vaccinations are required.
Other management practices that can reduce the risk factor for botulism is by controlling rodents, vermin and other pest animals in order to reduce the risk of spreading decomposed material and preventing your animals from straying or grazing in the vicinity of animal carcasses.
Preventative measures farmers can practice include protecting the harvest and storage of feeds from contamination.
Preventing rats and other vermin from access to feed and the prudent inspection of the cattle’s drinking water sources for organic matter contamination is also important in preventing the occurrences of the disease.
Dr Tony Monda holds a PhD in Art Theory and Philosophy and a DBA (Doctorate in Business Administration) and Post-Colonial Heritage Studies. E-mail: tonym.MONDA@gmail.com