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Questions and answers on chronic botulism
Updated BfR FAQ, 10 February 2012
Since the mid 1990s, reports have appeared in scientific publications on so-called visceral or chronic botulism in cattle populations. This is a disease the causes of which are as yet unknown and which was initially observed in high-performance cattle but also in calves. The disease is documented with a wide range of clinical symptoms. The clinical pictures described have not been scientifically verified yet. It is assumed that the cause is a toxicoinfection with Clostridium (C.) botulinum. However, this cause has not been conclusively proven to the present day.
In humans too, chronic syndromes are observed. It affects farmers and their families in whose facilities cattle have contracted the disease. The cause of the typically non-specific symptoms in affected humans has not been established to date.
The Federal Institute for Risk Assessment (BfR) has systematically assessed the available scientific data and comes to the conclusion on the basis of the latest knowledge that fresh meat and raw milk do not entail any risk of triggering the clinical syndrome of “botulism” in humans. What follows below is a list of questions and answers compiled by the BfR.
- What is chronic (visceral) botulism?
- What is acute botulism?
- What are the causes of the disease referred to as visceral or chronic botulism?
- How prevalent is chronic botulism in animal populations?
- Are there laws against affected cattle being slaughtered and processed into food?
- Can foods such as milk or meat cause acute or chronic botulism in humans?
Since approximately the end of the 1990s, scientific publications have reported on an aetiologically uncertain disease in cattle which is usually referred to as visceral or chronic botulism. The disease is characterised by a wide range of clinical symptoms. These include indigestion, abomasal displacement, emaciation, downer cow syndrome, foot and joint diseases, paralysis, taut abdominal wall, raised abdomen, difficulties swallowing as well as acute febrile mastitis (inflammation of the lactiferous glands). The disease was first found in high-performance cattle, although calves too were affected.
In addition, it has been suspected for some years now that farmers and their families who spend time in facilities in which cattle are ill with chronic botulism could contract the disease as well.
Acute botulism denotes the illness caused by “Botulinum neurotoxins“. Botulinum neurotoxins are produced by bacteria of the species Clostridium botulinum and can cause nausea, diarrhoea, and constipation as well as neurological symptoms with paralysis including respiratory paralysis. Both animals and humans can be affected by the disease. In Germany, approximately 20 persons come down with botulism per year.
Acute botulism in humans is predominantly a food-borne disease. It has always been associated with the consumption of processed food products in which bacteria had the opportunity to multiply and produce toxins under anaerobic conditions.
Another form of food-borne botulism is infant botulism. In the leaflet entitled “Hinweise für Verbraucher zum Botulismus durch Lebensmittel (104.2 KB)” (in German only), the BfR has summarised how the risk of contracting the disease can be reduced.
There is no scientific explanation as yet as to what causes the disease. Some scientists assume that the underlying cause is a toxicoinfection with Clostridium (C.) botulinum. When a toxicoinfection is contracted, bacteria colonise the intestine where they release toxins which are then absorbed by the body. This hypothesis has not been confirmed to date. Other scientists postulate a multifactorial scenario, i.e. they believe that various factors are involved in the development of the disease. Research projects focusing on this issue are currently conducted at various scientific institutions.
Botulism in domestic animals, even in its classic acute form, is subject neither to registration nor reporting requirements. In consequence, there are no scientifically collected data about the number of ill cattle or about the affected cattle populations.
In principle, only healthy animals may be slaughtered and processed into food. If animals do not show any symptoms of disease but come from a farm in which animals have been affected by it, the farmer has an obligation to inform the abattoir accordingly. In such cases, the competent veterinarian initially verifies that the animal is indeed healthy.
High hygienic standards for the slaughter of cattle additionally ensure that pathogenic microorganisms are not transmitted to the meat.
Having evaluated the available data, the BfR has found no indication that raw milk or fresh meat pose any risk of causing acute botulism in humans: a number of scientific publications deal with the subject of “Presence of botulinum toxins in the milk of dairy cows with clinically acute botulism.” There is no indication that toxins are excreted with the milk. In one study, dairy cows were artificially contaminated; no toxin was detected in the milk of the infected animals. Even for cattle suffering from acute botulism, no instances of botulinum toxin detection in the flesh of such animals have been described in the scientific literature. As regards the research methods for detecting the toxins, however, significant improvements are needed.
For so-called chronic botulism, the possible transmission paths have not been established.