Coccidiosis is the most common cause of pre-weaning scour in piglets. In calves, lambs and poultry, the protozoa Eimeria is the causative species of coccidiosis. In piglets, however, the intracellular protozoan Isospora suis is the key culprit, and hence the term isosporosis can also be used to describe the disease.
Oocysts of I. suis are often ubiquitous in the immediate environment on a pig unit, having been excreted by previous litters of piglets. These sporulate after between 12 hours and three days and when ingested by a piglet go on to release sporozoites inside the small intestine. These enter the cells of the intestinal mucosa and continue to multiply, the sheer numbers of which cause damage to the intestinal mucosa, resulting in a loss of functional epithelial tissue.
In just 5-7 days from ingestion of a single oocyst, new oocysts will rupture from the intestinal cells into the lumen and pass out in the faeces, perpetuating the cycle. This 5-7 day pre-patent period is relatively short (compared to that of Eimeria in other livestock species). So although clinical coccidiosis – for which the main sign is diarrhoea – can affect piglets up to 15 weeks of age, it is most common at 8-15 days of age, and hence is frequently referred to as “10-day scour”.
Typically, mortality is low, around 5% or less, but morbidity is high, around 70%. Coccidial infection also predisposes piglets to secondary enteric infections such as E. coli or rotavirus, which can increase pre-weaning mortality rates by up to 30%.
For diagnosis, faecal samples should be taken from apparently healthy piglets as well as those that have started scouring. Recommended sampling is 5-10% of litters and 3-5 piglets per litter. Results from these should be evaluated along with herd history and clinical signs (see Table 1).
Control
The reduced performance of piglets infected with I. suis is the direct result of damage to the resorptive surface of the gut due to the multiplying parasites. So to minimise production losses from coccidiosis, metaphylactic treatment (i.e. before the onset of clinical signs) is recommended for all at-risk piglets.
In the past, without the availability of a licensed coccidiocide, pig units have often controlled coccidiosis using offlabel products such as Baycox 2.5% solution (toltrazuril). But since this is designed for mass water medication in poultry, only after dilution in a large volume of water, it is not recommended to give this directly by mouth. There is also anecdotal evidence that farmers are inaccurately dosing using this formulation: it has a lower concentration of the active ingredient, so sometimes repeat dosing has been carried out, probably in an effort to compensate for under-dosing. However, following the licensing of the ready-touse suspension Baycox 50mg/ml (toltrazuril), effective dosing and administration is now readily available: piglets require a single oral dose of 20mg/kg between days 3 and 5 of life.
Sulphonamides are sometimes used to treat coccidiosis. However, in a recent comparative study*, sulphadimidine did not improve performance of piglets with clinical coccidiosis, and in fact gave similar results to the control group. The trial involved experimentally infecting piglets with I. suis, and then comparing the effects of administering either a single dose of toltrazuril or three daily doses of 200mg/kg sulphadimidine, in the pre-patent period.
Oocyst excretion was markedly reduced and significantly controlled in the toltrazuril-treated group (see Figure 1) and no diarrhoea was seen. However, diarrhoea was seen from five days post-infection in the sulphadimidine-treated group and the control group. Histopathology also showed necrosis and atrophy of villi in the small intestines in all groups except the toltrazuril-treated group.
Over a four-week period, toltrazuriltreated piglets gained significantly more weight compared to the other groups and histopathology showed villi were significantly longer at 11 days post infection.
In addition to chemotherapy, coccidiosis control requires attention to hygiene and management to reduce the disease challenge. As well as regular disinfection, pig farmers can also reduce the disease pressure by reducing the stocking density of pens and improving ventilation.
Even at sub-clinical levels of coccidial infection, piglets will still suffer intestinal damage and performance setbacks. So where oocysts have been detected, even with no scouring present, treatment with a coccidiocide of all at-risk piglets can still be economically beneficial.
Coccidiosis is an insidious disease, and taking preventive control is imperative to safeguard piglet weight gains and feed conversion efficiency, and achieve uniformity of body weights at weaning. Now, with the advent of a ready-to-use licensed product, pig farmers can conveniently protect their profits.
* Mundt, H. C. (2007) Efficacy of various anticoccidials against experimental porcine neonatal isosporosis. Parasitol. Res. 100: 401-411.
