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Within this genus, there are more than ten species of coccidia that are known to infect sheep or goats. Not all of the species are pathogenic or have the same level of pathogenicity. In fact, only a few are usually responsible for disease outbreaks.

Coccidia are host-specific, meaning the species of coccidia that affect poultry do not affect sheep and goats [5]. Even sheep and goats are affected by different species of coccidia. Attempts to cross-contaminate sheep and goats have failed.

A noteworthy exception is Toxoplasma gondii, which causes coccidiosis in cats and can cause abortion in sheep, goats, and people. Sheep and goats serve as an intermediate host for Toxoplasma gondii. Toxoplasmosis is a common cause of abortions in ewes and does in the U.S.

 

Life cycle
Coccidia have a very complicated life cycle [5], with many stages of development [6]. As with other internal parasites, there is a free-living stage which takes place outside of the animal and a parasitic phase which takes place in the intestines of the host.

 

The egg-like structure of coccidia is called an oocyte. It is passed in the feces of infected sheep and goats. When first passed, the oocyst is not infective. It must undergo a period of development called sporulation (hatching) . Sporulation requires oxygen and moisture. The time required for development is temperature-dependent. In general, the warmer the weather, the faster the development, unless the temperature is high enough to kill the organism.
 

After sporulation, the oocysts are very resistant to environmental conditions and cannot be killed by ordinary disinfectants. Extreme desiccation or direct sunlight are the only environmental factors which are detrimental to sporulated oocysts. In fact, a sporulated oocyst may survive for a year or longer if it is protected from direct sunlight.

When a sheep or goat ingests a sporulated oocyst, sporozoites are released and enter the cells lining the small intestines. The entire life cycle takes about 14 days. The damage done to the host is essentially that of intestinal cell destruction. The host cells affected most often are epithelial cells lining the gut which transport nutrients and fluids into the body.

 

Transmission

Lambs and kids between the ages of 1 and 6 months are most commonly affected by coccidia. In a survey conducted in the UK, 4 to 8 week old lambs were the most likely to be affected and 4 week old lambs were the most vulnerable to clinical disease. Many disease outbreaks occur shortly after weaning, as this is a very stressful period in the lamb or kid's young life. Bad weather may also trigger disease outbreaks.

Almost all sheep and goats are exposed to coccidia. Sheep and goats routinely ingest oocytes each day through feces, contaminated feed and water, or by licking themselves or another animal. Mature animals are largely immune to the effects of the parasite, but they serve as a reservoir of infection.

Coccidiosis is mainly associated with intensive production systems in which sheep and goats are housed in barns and dry lots. Fecal material is more concentrated in these production environments than if the livestock are kept on pasture. At the same time, outbreaks of coccidiosis are not uncommon in pasture rearing environments. Some pasture rearing situations can mimic confinement situations.

Clinical signs

As with most diseases, there are clinical and sub-clinical forms of coccidiosis. Sheep and goats with subclinical disease do not show obvious signs of the disease. They appear outwardly normal, but suffer from reduced feed consumption, feed conversion, and growth performance. Most cases of coccidiosis are subclinical and from an economic stand point, subclinical coccidiosis is probably the most costly.
 

Clinical coccidiosis can be deadly and usually requires prompt treatment. The first sign of coccidiosis is that lambs and kids may not be thriving as well as expected. Lambs may appear open fleeced. Kids may have a rough hair coats. Dirtiness around the tail may be observed, a result of mild diarrhea.

Soon, lambs and kids begin to lose their appetite and become weak and unthrifty. Lambs and kids may become anemic and strain to pass feces. As the disease condition worsens, affected lambs and kids may experience severe diarrhea, with streaks of blood, followed by severe dehydration and death.
 

Diagnosis

Diagnosis of clinical coccidiosis is based on flock history and observation of clinical signs, usually diarrhea. Fecal testing is of limited diagnostic value. While a oocyst count of 5,000 is considered clinically significant, not all coccidia are disease-causing or equally pathogenic. In addition, lambs and kids may become clinically-parasitized before shedding any oocytes.  Therefore, a negative fecal test does not rule out coccidiosis, anymore than a positive test is indicative of disease.

There are many other disease conditions that cause symptoms similar to coccidiosis: some worms, overeating disease, salmonellosis, E. coli scours, crptosporididium, and viral infections. Parasitized lambs and kids often suffer from mixed parasitic infections.

Treatment

For sheep and goats exhibiting clinical signs of coccidiosis, there are several treatment options (in the U.S.), including sulfa drugs, tetracyclines, and amprolium [7]. Conventional anthelmintics (dewormers) have no effect on coccidiosis.
 

Amprolium (Corid®) can be used as both a treatment and preventative for coccidiosis. It is sold in liquid or powder form. When coccidia ingest Corid®, they experience a thiamine deficiency and die from malnourishment Though rare, polioencephalomalacia (thiamine deficiency) has been reported as a side effect of treatment with amprolium [4].
 

Many sulfanamide medications can be used to treat coccidiosis. Sulfa medications are sold in liquid or powder form. Sulfa medication can be bitter tasting, so products may include flavoring, or jello can be added to reduce the bitter taste and promote adequate consumption by the animals.

 

Whenever medications are administered in the water, it is important that the medicated water be the only source of water. One of the limitations of water treatments is that there is no guarantee that every animal will receive the necessary amount of the medication. This is particularly true of an animal that may already be feeling poorly due to coccidia infection. For this reason, it is usually better to individual treat each animal with the medication.  Severely parasitized animals should be penned separately, drenched individually with the medication, and receive necessary supportive treatment.

 

All medications used to treat coccidiosis are not FDA-approved for use in sheep and goats. As a result, extra-label drug use by a licensed veterinarian is required. Producers must understand that just because a product can be purchased over-the-counter doesn't mean it can be used legally without the advice of a veterinarian. Further, while Corid® may be purchased OTC, sulfa drugs must now be obtained from a veterinarian, as a result of the 2017 Veterinary Feed Directive, which transitioned water soluble antibiotics from OTC to Rx.