During recent years, there has been a progressive increase in the incidence of botulism in cattle and sheep in Northern Ireland, with the number of confirmed cases having increased from 15 per year in 2009 to over 60 confirmed cases in 2015.
Over the last year, the UFU Animal Health and Welfare committee has had several meetings with DARD and poultry processors in order to investigate the reasons behind this increase and to ascertain what farmers can do to protect livestock.
As explained to the committee, there are three main reasons for the increase, namely the move from a bioassay test to an ELISA test which has doubled the number of suspected cases that are confirmed as positive, a greater awareness of farmers resulting in an increase in the number of animals being submitted for post mortem and to a lesser extent, the possibility of an increased use of poultry litter for fertilizer increasing the risk of carcasses being spread on agricultural land.
As explained to the committee, botulism is caused by a clostridial bacterium (Clostridium botulinum) which produces a neurotoxin called botulinum. The botulinum toxin is widely regarded as the most potent, naturally occurring toxin known to mankind, with a single gram, effectively distributed having the power to kill over one million people. The botulinum toxin causes severe flaccid paralysis in both humans and animals.
It is for this reason, that it is used in some treatments such as Botox to reduce the appearance of wrinkles or Neurobloc to treat cervical dystonia (a painful condition in which your neck muscles contract involuntarily causing your neck to twist uncontrollably).
In livestock, clinical signs are characterised by: muscle tremors, muscle weakness starting in the hindquarters before progressing forwards, inability to chew or swallow, drooling, laying down, and sudden death. The progression and severity of the disease will depend upon the amount of toxin ingested. However, if you suspect any possibility of botulism, you are advised to move animals to alternative grazing and contact your vet as soon as possible who may be able to provide antitoxins.
Treatment won’t reverse any paralysis that has already been caused, but it will stop it from getting worse and in many cases the animal will gradually improve as the muscle tissue is replaced over the following weeks and months.
The Clostridium botulinum bacteria itself is an obligate anaerobic bacteria, meaning that normal levels of atmospheric oxygen are poisonous to the cells. As such, the bacterium is only able to produce the neurotoxin under anaerobic conditions. Whilst the toxin is resistant to the enzymes in the gastrointestinal tract and thus can be absorbed into the body causing illness and fatalities in both humans and animals, the toxin is rapidly destroyed at temperatures above 100°C and therefore poses a negligible food safety risk provided that food is properly cooked.
The bacterium is divided into four Groups (I-IV). Typically, most human outbreaks of botulism are caused by Group I or II. Group III organisms mainly cause disease in animals and Group IV has not been shown to cause any disease in humans or animals. These Groups are further subdivided into seven serotypes (A-G) based on the antigenicity of the toxin produced.
Only types A, B, E and F cause disease in humans with A, B and E typically associated with foodborne illness (mainly home-canned goods that haven’t been properly heated) and type E which is specifically associated with fish products. Type C is mainly associated with birds causing Limberneck and type D causes the disease in other mammals and livestock.
Clostridium botulinum is most commonly found in oxygen-poor environments with low acidity. As such, its habitat is fairly ubiquitous, being found in soil, wetlands and marine habitats throughout most of the world. Additionally, organic matter and carcasses can provide suitable substrates for multiplication of the bacteria and resultant toxins. Many of these environments are home to numerous invertebrates that are resistant to, and can accumulate high levels of the botulinum toxin.
Outbreaks of botulism in wildlife and livestock occasionally result from consumption of these toxin-laden invertebrates. Animals that die subsequently become infested with maggots that then perpetuate the outbreak in what is described as a “carcass-maggot cycle”. There is also evidence that direct ingestion of contaminated organic matter (such as silage or straw containing dead rats or kittens etc) can result in cases of botulism.
In addition to natural infection sources, outbreaks of botulism occasionally occur in commercial poultry. Where these cases occur, they tend to be rare and frequently reoccur on the same farm due to poor husbandry. The disease tends to be most severe in pen-reared pheasants where mortality can reach up to 100%. Often the source of the toxin in these outbreaks is difficult to isolate leading to speculation that botulism in poultry is a “toxico-infection” where C. botulinum is able to reproduce in the intestine with subsequent toxin production and ingestion which leads to fatalities.
At this stage, the evidence remains unclear as to what factors (if any) cause C. botulinum to proliferate in the intestine and produce toxins. However, numerous studies have shown that healthy birds do not harbour C. botulinum serotype C in their ceca and that C. botulinum has not been recovered from the environment of poultry houses that did not have a history of botulism. These findings suggest that C. botulinum is neither frequent nor widespread in poultry populations and is more likely to be introduced due to sporadic infection of new flocks introduced to farms.
Given that Northern Ireland’s 17 million chickens currently produce over 260,000 tonnes of poultry litter per year and that the industry only had around 60 botulism cases in 2015, this confirms that, in reality the risk from poultry litter is extremely low and that the vast majority of growers are acting responsibly. However, given the toxicity of a single gram of botulinum, EU regulations 1069/2009 and 142/2011 enforce strict rules on carcass disposal of all animals including poultry.
Furthermore, whilst the spreading of poultry litter is legal, the spreading of litter containing carcasses is illegal. The UFU Poultry committee is adamant that all responsible bird keepers should be walking their houses several times per day to ensure the removal of all dead stock and that following the removal of each bird crop, all house doors should be kept closed until the litter is being removed. Furthermore, when litter is being removed, it should be loaded directly onto a covered vehicle. At no time should it be accessible to foxes, dogs, crows or other scavengers that may carry carcases onto adjacent pasture.
Additionally, DARD’s advice that all litter should be deep ploughed into arable ground. If this is not an option, it should not be spread on land that is to be grazed or from which silage or hay is to be harvested in the same year. If a farmer wishes to store poultry litter in a field heap, the NIEA must be notified (02892623188) and the heap must be covered with an impermeable membrane within 24 hours of placement in the field.
The litter must be spread at the time of next application in the field and the storage must be no longer than 180 days. All of these precautions are in place because legislators at EU and NI level are aware that even a small fragment of carcass may persist on pasture for a considerable period of time which may provide a suitable breeding ground for naturally occurring, soil dwelling C. botulinum.
In addition to these precautions, DARD request that where you believe a neighbour may be in breach the current legislation and is spreading litter that contains carcasses, report the individual to DARD (03002007842) and they will come out and take enforcement action against the individual if carcasses are found.
In the event of loss of livestock, all farmers will have public liability insurance which will cover death as a result of botulism. If the farmer in question refuses to accept liability, unfortunately the only option remaining is to pursue damages via a civil case through the courts. In such cases, the judge is likely to look for ‘probable cause’. Given the many environmental sources of botulism, proving probable cause can be difficult. However, having established a burden of proof, (e.g. DARD inspectors having found evidence of carcasses being spread) a judge is more likely to rule in the claimant’s favour.
In summary, the UFU acknowledges that whilst the number of cases of botulism occurring each year remains low, we are concerned by the current upward trend in the number of cases. As such, the UFU would like to remind farmers to act responsibly towards one another and for all parties to play their part in order to prevent loss of livestock.
This ranges from growers regularly walking their houses to remove fallen stock and ensuring effective storage of litter, to farmers spreading litter ensuring that whenever they can they plough it in, or where this isn’t possible to have a discussion with your neighbour in order to mitigate risks (in such cases, vaccination of your own and your neighbours herd/flock may be advisable), and finally for DARD/NIEA to ensure that swift and robust action is taken against farmers who are flaunting the current legislation in order to protect farmers from losing livestock through no fault of their own.