Protozoa

Coccidia (Eimeria species), Cryptosporidium and Giardia

Coccidia

Coccidia are a type of microscopic parasites known as protozoa. The main coccidia that trouble sheep and goats are the Eimeria species, causing the disease known as coccidiosis.

They develop in the intestinal tract of sheep and goats, and produce eggs (oocysts) that pass in the dung onto the pasture where they take several days to develop (‘sporulate’), after which time they can infect grazing stock.

Image: Nodules from Coccidia in small instestine of sheep (Source: Dr R Woodgate, Department of Agriculture & Food WA)

Several species of Eimeria affect sheep and goats. These parasites are usually acquired in the first few months of life and small numbers are carried by most young animals, usually causing no ill-effects. However, with stress and overcrowding, particularly under damp unhygienic conditions, disease may occur. It is most commonly seen in young stock just before weaning, or in lambs or kids, or hoggets in feedlots, and other situations where stock are confined at very high stocking rates. Coccidiosis in young animals is usually associated with very cold conditions and poor pasture nutrition resulting in a reduced milk supply from the ewe or doe, forcing the lambs or kids to graze close to the ground.

Sheep rapidly develop strong and lifetime immunity to coccidia, so coccidiosis is uncommon in adult animals. However, goats do not develop such a strong immunity and infection is commonly seen in goats of all ages.

Affected animals scour (brown-red, liquid and foul smelling), have characteristic hollow flanks and hunched appearance, and are depressed. Deaths occur in severe cases. Although the organisms are microscopic, aggregations of some species of Eimeria may cause white nodules in the gut of affected hosts.

Diagnosis and treatment

Most sheep and goats are infected with coccidia in the first few weeks to months of life without showing signs of infection. Coccidiosis is usually suspected when severe scouring is seen in lambs or kids at a younger age than usual for worm problems, or in sheep or goats in situations of very high stocking rates and often under nutritional stress. Affected stock fail to respond to drenching for worms (unless significant worm burdens are also present).

Laboratory diagnosis is not definitive, as there is little relationship between the number of coccidial oocysts present in the faecal sample, and the occurrence and severity of disease. Large numbers (100,000 oocysts/gram faeces) of oocysts may be found in unaffected animals, and alternatively, disease may occur in animals with few oocysts in the faeces. Despite this, there is a general correlation between detection of high levels of oocysts in faecal counts and the incidence of disease.

If you submit samples for a worm egg count, the lab will usually report the presence of coccidiosis in their report. The coccidia eggs (oocysts) can be seen under the microscope and are classified as low, medium or high numbers.

The great majority of affected animals recover without help, although some may suffer severe weight loss and some may die. Treatment of affected individuals is not usually undertaken on a mob or herd basis and registered treatments must be obtained from a veterinarian. Effective prevention can be provided by pre-treatment or in-feed products, but is only justified where there is an on-going history of disease. Attention to hygiene (feedlots) and nutrition is a more sustainable approach.

Young animals with severe coccidiosis may need electrolytes and supportive treatment.

Preventive products are usually mixed in feed or pellets. This is often done when there is a high risk, such as in lamb feedlots, cattle feedlots or goats grazing with high stocking density. Talk to your vet or nutritionist to decide on the best approach for your stock.

Cryptosporidium and Giardia

The role of other common microscopic water-borne protozoans, such as Cryptosporidium and Giardia, has only recently been investigated in Australia. It appears that infection with these organisms are relatively common in sheep and goats, but scouring as a consequence is far less common than for coccidiosis, and occurs mostly in animals up to a week old resulting in a reduction in body weights.

In goat kids, particularly neonates (in their first two weeks), but up until weaning, ‘crypto’ can cause a severe infectious gastroenteritis, especially if they are housed under moist unsanitary conditions or are artificially reared.

Of concern regarding these parasites is the potential for human infection. However, this is a relatively minor risk, as only some species of Cryptosporidium or Giardia carried by sheep or goats appear to infect humans, and by far the majority of cases in people are due to between-person contact. However, Cryptosporidium outbreaks in children have been associated with patting lambs and kids.

The diagnosis of disease due to Cryptosporidium and Giardia is based on testing a faecal sample, but using a test different from the worm egg count. It seems that these parasites are not likely to be significant causes of scouring in sheep or goats in Australia, and treatment or prevention is not considered necessary. Access of kids and lambs under 30 days of age to adequate quantities of colostrum will help to prevent them from acquiring the infection in early life.

Crytosporidium oocyst excretion increases in the week before and after lambing in ewes, or kidding in does.

Dogs may also become infected. Only a few antimicrobial agents have shown activity against Cryptosporidium infection in man or animals.