Scours
USING BIO-SECURITY TO COMBAT PROTOZOAN INFECTIONS
Calf scour is distressingly common, always expensive and all too frequently deadly.
It has been estimated that around 20 per cent of young cattle in the UK will suffer scouring to some degree, and tens of thousands will die as a result. Findings also indicate that each case of scour will cost on average more than £80 per sick calf treated. The problem is estimated to be costing the British cattle industry around £15 million per year.
These are stark figures, and ones which must cause concern, both in terms of stock health and welfare, and from an economic standpoint.
While there are many causes of calf scour, among the most significant are diseases caused by protozoa - minute single-celled parasitic organisms which are stubbornly resistant to most disinfection agents. The two major diseases which fall into this category are cryptosporidiosis, caused by Cryptosporidium parvum, and coccidiosis, chiefly caused by the Eimeria bovis or zürnii organisms.
These specific Eimeria organisms affect only cattle, while C parvum is non-host-specific, but in each case, infection is most likely to occur under similar conditions, and methods of prevention and control are also similar. The key word in tackling protozoan infections is bio-security.
In order to understand why this is so important, it is necessary to understand the conditions under which these protozoan parasites flourish, and something of their life cycle.
Briefly, the organisms inhabit the gut where, once fertilised, they create a protective membrane or cyst wall around themselves, thus becoming an oocyst. In this form they are passed out of the host in the faeces. Once on the ground the organism develops and divides within the protective cyst wall. Once 'ripe' it becomes capable of re-infecting any animal which swallows it. Back in the gut, the cyst wall dissolves, allowing the organisms to escape and repeat the cycle.
Infection with these organisms causes persistent diarrhoea, dehydration, weight loss and failure to thrive. In extreme cases, death is the outcome. Such infections also appear to be immunosuppressive, and increase a sufferer's susceptibility to other infections, for example, of rotaviruses or coronaviruses.
There is no specific treatment for the diseases caused by these organisms, and, as yet, no preventative vaccine for cattle. Avoidance of the problem is therefore a question of management - clearly it is essential to remove the environmental challenge in order to control the disease.
Because these diseases occur most often in situations where calves are crowded together, perhaps in dirty and wet conditions, attention to good management practices can pay dividends in terms of infection avoidance. A clean and healthy environment is essential. To achieve and maintain this is to achieve biosecurity.
Since the organisms spread by transmission of the oocysts from host to host, minimising the opportunities for this to happen is the first and best step in breaking the cycle of infection. The aim should be to reduce the number of oocysts ingested to the point where the level of infection does not adversely affect the health of the calf, and a certain level of natural immunity develops.
The most effective method of attaining this is by regularly emptying and thoroughly cleaning calf houses, and by using an all in/all out system which ensures a break in occupation.
From the moment of birth, calves should be kept in an environment which is as clean and dry as possible, where they mix as little as possible with other animals, and where feeding and cleaning programmes are strictly followed.
It should not be forgotten that, since cryptosporidium is non-host-specific, it can be carried by, and transmitted to, other animals. It is therefore very important that biosecurity regimes take this factor into account. For example, rats and mice droppings can contain infective oocysts, so effective rodent control in and around the calf houses is essential, using bait blox and sachets for safety in use.
Since man is also capable of transmitting and being infected by the organism, personal cleanliness is also essential. If the same stock person tends sick and healthy calves, the sick calves - which should also be housed separately - should be tended last. Scrupulous attention to the changing of clothes, use of foot dips and hand hygiene systems should also be observed at all times.
One of the most difficult problems to overcome in achieving biosecurity against these protozoa is the structure of the organism itself. In its oocyst form, it is resistant to most disinfectants, and has an incredible capacity for survival in all but the harshest weather conditions. Indeed, in favourable conditions, oocysts have been found to survive for years without losing their viability.
The only product which is fully effective in destroying these oocysts is the disinfectant coccidiacide Oo-Cide (Antec International) which has a formulation designed to penetrate the extremely dense outer walls of the organism. Thorough treatment of calf houses with Oo-Cide at terminal disinfection should result in the destruction of the oocyst population. This will provide the break in the cycle of infection and re-infection that is necessary before true biosecurity in the calf house can be established.
by Mark Blackwell MA VetMB MRCVS
Director, Marketing and International Sales, Animal Health Division, Antec International