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What is coccidiosis?

Please note that as of 31ˢᵗ July 2020, Elanco no longer owns Vecoxan (diclazuril).

Coccidiosis is a disease of the intestinal tract caused by single celled intracellular parasites of the genus Eimeria. It affects several different species, both farmed and wild, with young stock such as lambs and calves being at highest risk of disease.1 In studies, 100% of sheep housing and 60% of pastures were contaminated with the pathogenic sheep species and another showed up to 100% prevalence in beef and dairy herds.2

There are over 20 different species of coccidia in cattle and sheep which are host specific with no cross infection between different host species.

It is important to note that not all species of coccidia are pathogenic:

In lambs, only two are known to cause disease:

  • Eimeria ovinoidalis.
  • Eimeria crandalis.

It is important to understand when faecal egg testing: a single high oocyst count does not in itself confirm coccidiosis and further investigation to identify the species of Eimeria is often necessary.

Coccidial infections are not always obvious or easy to see. Despite this the parasite is very prevalent in the environment and nearly all cattle and sheep have some coccicial oocysts in their faeces.2 It is also very difficult to destroy (even with disinfectants) and can survive in the environment for up to two years: this means it is almost impossible to eliminate coccidia at farm level.

How do animals become infected?

Contaminated water and feed troughs and the skin of dams’ udders are common routes for the spread of coccidiosis and infection is by the faecal-oral route: once oocyts (eggs) are passed out they can be eaten by the same or new animal. As a rule, whilst adult animals may be the initial source of infection, heavy contamination comes from naïve lambs and calves themselves which, after contracting the initial infection, can go on to excrete millions of oocysts into their environment.

Subsequent groups of naïve young animals then entering that same environment are exposed to a far higher challenge, and are far more likely to suffer significant gut damage, production losses and disease.

How the damage is done

As it progresses through its life cycle this parasite reproduces within the cells that line the gut causing the cells to rupture and damaging the villi (finger like projections that increase the surface of the gut to maximise absorption of nutrients). This damage reduces the amount of nutrients absorbed, causing ill health, poor growth rates and leaving them susceptible to other diseases. However, the obvious signs of disease (such as diarrhoea) do not appear until after a significant level of damage has already happened, leading to reduced growth rate and economic loss.3



The consequences of this lifecycle being allowed to continue can be devastating. A single ingested oocyst can lead to the destruction of 32 million intestinal cells (and result in serious gut damage) and lead to the production of a further 16 million oocysts to further contaminate the environment.2