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Coccidiosis: its commonalities and differences across livestock species

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01 August 2010, at 12:00am

Coccidiosis is an insidious enteric disease, with diarrhoea the most obvious clinical symptom. It is the most common cause of pre-weaning scour in piglets, and one of the most common enteric diseases affecting lambs and calves. 

In all species, coccidial infection – both at sub-clinical and clinical levels – will compromise digestive efficiency and live weight gains, and make animals more susceptible to secondary infections. So to ensure the future performance potential of the animal is achieved, the best strategy is to adopt a preventive approach to the disease, to safeguard health and consequent long-term performance. 

Protozoa are the causative agents of coccidiosis: Eimeria spp. are the culprits in calves, lambs and poultry; and there are many different species: all are hostspecific, but not all are pathogenic. 

In piglets, Isospora suis is responsible for coccidiosis and hence the term isosporosis is also sometimes used. Coccidial infections arise when sporulated oocysts of Eimeria or Isospora are ingested and go on to cause significant damage to intestinal cell walls as they reproduce through the different life-cycle stages (see Figure 1).  

The age at which a young animal is likely to suffer coccidial infection depends on when it first encounters coccidial oocysts in the environment and the level of the burden ingested. It is important to also consider the prepatent period of the protozoan species, i.e. the time for completion of one lifecycle – from ingestion of an oocyst to shedding further oocysts. 

For example, in housed cattle, E. bovis and E. zuernii often cause coccidiosis in calves at between three and 12 weeks of age, depending on the specific rearing practices on the farm and when calves first enter a high-risk area for oocysts. Since the timing of a coccidiosis outbreak will vary from farm to farm, so will the timing of any preventive action taken. 

In piglets, the pre-patent period is only 5-7 days, so outbreaks of clinical coccidiosis (onset of diarrhoea) typically occur at 8-15 days of age (see Table 1).

Reducing spread of infection 

In all species, damage to the animal’s gut occurs when sporulated oocysts are ingested and then release sporozoites which enter intestinal cells and multiply rapidly through a number of stages. Each causes damage to the intestinal mucosa, resulting in a loss of functional epithelial tissue. After the pre-patent period, oocysts rupture from the intestinal cells and are passed back into the environment in the animal’s faeces. 

A single oocyst can multiply dramatically in number: in calves up to 24 million oocysts can be produced in three weeks from one oocyst, and in lambs up to 16 million can be produced in two weeks. When these are shed into the environment, all incontact animals are at risk of infection. 

Since oocysts are also extremely resistant, surviving from year to year, they will remain in the environment, on grassland and in sheds, to re-infect future generations of livestock. Disease transmission occurs mainly through the faecal-oral route from contaminated bedding, pastures, feed or water troughs. 

So key to reducing the disease challenge is to stop oocyst excretion and break the cycle of infection. This can be achieved effectively using the coccidiocide toltrazuril (Baycox 50mg/ml) which destroys Eimeria and Isospora at all stages during their intracellular development, including asexual multiplication and sexual reproduction. 

This prevents oocysts from being produced, and stops the damage to the intestinal cells. However, since the extracellular sporozoites and merozoites are not killed, these stages of Eimeria and Isospora can still attach to the mucosal cells that line the gastrointestinal tract, a process that is key for host recognition and immunity to develop. 

Treating animals with a coccidiocide once a clinical outbreak of the disease has occurred will stop further reproduction of coccidia and damage to the gut; however, future performance will have been compromised. So the best strategy is to adopt a preventive approach with metaphylactic treatment, i.e. before the onset of clinical signs but after exposure to the challenge. 

So the animal needs to have ingested some oocysts and for the reproductive cycle to have started. This means the actual timing of dosing, with any coccidiocide, is essential for success. Treating coccidia-naïve animals with a coccidiocide will not have any benefit. 

To determine the optimal treatment time, review the disease history on the unit. For example, in calves, a single oral dose should be given approximately one week before the expected onset of clinical symptoms. Typically, this is around 14 days after they enter a high-risk environment, but will vary from unit to unit.

Similarly with lambs, specific management practices will affect optimal treatment timing. In piglets, where early management practices are very similar and there is a short prepatent period, then preventive treatment with a single dose of Baycox 50mg/ml can be routinely carried out at day 3 to 5 of age.

An integrated approach 

In addition to chemotherapy, coccidiosis control requires attention to hygiene and management to reduce the disease challenge. For example, ensure clean bedding and water troughs, lower stocking densities. 

Farmers who have witnessed clinical outbreaks of coccidiosis are more likely to adopt a preventive strategy. The bigger challenge for the veterinary professional is to motivate pre-emptive action on farms where the disease is present at sub-clinical levels. 

However, with today’s economic pressures, the typically more intensive rearing practices, and constant timepressures on stockmen, vets should discuss with their clients how financial benefits can still be made by preventing sub-clinical levels of coccidial infection, to safeguard animal health and boost performance levels. And that’s relevant across all livestock species.