As a general rule, animals with high burdens of infection or low levels of resistance – especially young animals – will display clinical signs. The clinical signs of coccidiosis are loss of appetite, diarrhoea (from green and slimy to bloody), dehydration, straining – which can lead to rectal prolapse – abdominal pain, wasting and death. The damage to the gut allows for secondary bacterial infections to occur.
Cases of subclinical coccidiosis are also very common and, whilst often going unnoticed, they account for as much as 61% of total losses related to coccidiosis.1
Coccidiosis should be suspected in animals of the right age group showing the typical clinical signs, and confirmed by analysis of faecal samples. It is important to understand though that 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. Always seek veterinary advice and have a confirmed diagnosis of coccidiosis before recommending a treatment.
Understanding the role of maternal immunity
Young animals initially acquire a degree of immunity against coccidiosis from antibodies absorbed from colostrum. As this initial protection wanes, lambs and calves are particularly susceptible to infection. In lambs this is usually from 4 to 8 weeks of age, and in calves most commonly between 3 weeks and 6 months of age.
The diagram below show the relationship between age, infection pressure, immunity and clinical coccidiosis in lambs.
Risk factors that trigger coccidiosis
So, whilst most animals have some coccidia not all farms see clinical disease. The outcome of infection is a balance between the infection pressure, immunity and various stress factors that may lower the animal’s ability to cope with infection. These range from overstocking and re-housing to poor hygiene and bad weather.