Clinical Signs and Economic Significance

Coccidiosis primarily affects suckling piglets, and is seen more frequently in animals between 8 and 15 days old, although the disease may strike earlier (day 5) or later (up to the third week of age).

The initial clinical sign is pasty diarrhoea that changes to become more liquid. The faeces are white to yellow in colour, but can also be brownish or greyish, and are fatty or creamy. Blood is not present. The diarrhoea lasts for up to 5 or 6 days. Some piglets in infected herds have also been found to be constipated, excreting of dry, pellet-like faeces. The piglets usually continue to nurse, but develop a rough hair coat, become dehydrated, and have low weight gain. In a Danish survey, practitioners reported that the disease had only a slight impact on mortality, but lowered growth rates by 15% on average (Larsen 1996), i.e., approx. 500 g at weaning.

Diarrhoea can occasionally last until weaning, but usually, after three weeks of age, there is very little evidence of the clinical signs of the disease, even in the case of massive experimental infections. In practice, eventually Isospora suis can be detected in faeces at weaning, and in some cases there may still be mild diarrhoea. It is difficult, however, to confirm the role of Isospora suis as the etiological cause of the diarrhoea because other management and dietary factors are also involved. Isospora suis does not cause clinical signs in finishing pigs and breeding stock.

The severity of the diarrhoea varies from one litter to the next. Typically, piglets with diarrhoea and piglets with normal faeces will be found in the same litter, although usually morbidity is high. Mortality is low to moderate, although in some cases concurrent bacterial, viral or even other parasitic infections may result in high mortality and complicate a diagnosis. In such cases, the expense of therapeutic treatment is high.