Vet's Voice: Coccidiosis caused by host-specific protozoan organisms

Photo courtesy of Texas A&M Veterinary Medical Teaching Hospital Coccidiosis is a disease of ruminants (and other animals) caused by host-specific protozoan organisms.


What is coccidiosis?

Coccidiosis is a disease of ruminants (and other animals) caused by host-specific protozoan organisms. It is characterized by severe diarrhea in young stock.

In ruminants, coccidiosis commonly is caused by Eimeria species, each of which cause disease of varying severity.

The life cycle of this protozoan is complicated. Ruminants ingest the infective organism, where it replicates in their intestines, and they release more into the environment when they pass feces. The cycle then is repeated once another animal ingests the organism. Once an animal ingests the organism, it can take one to four weeks for the animal to become ill, depending on the species with which it was infected.

The protozoan is hardy and can survive in the environment for several months.

Who is at risk?

While all ruminants have Eimeria present in their GI tracts, it is most commonly young animals that show clinical signs. In cattle, disease commonly is seen in calves 3 weeks to 6 months old. It is most prevalent in feedlot calves, as well as dairy calves taken from hutches into group calf pens. In sheep, lambs typically show signs when they are less than 6 months old. Those most commonly infected are lambs that are intensively reared and suckling lambs on pasture at high stocking rates. Goat kids are the most susceptible to coccidiosis of all the ruminant species, with infection usually occurring 2-3 weeks after weaning. As host-specific organisms, Eimeria organisms cannot be transmitted from one species to another.

Coccidiosis is a disease closely related to management. This can be improved by changes in housing, stocking rate, and good hygiene. Clinical disease is typically triggered by stressful events such as weaning, shipping, changes in feed, or extreme weather conditions.

What does coccidiosis in ruminants look like?

Disease presents similarly in all ruminant species but clinical signs can vary in severity. Animals with mild to moderate coccidiosis typically have diarrhea, reduced weight gain, and are in poor condition. More severe disease can result in profuse bloody diarrhea and severe dehydration. Although you may see diarrhea in calves, lambs, and kids around and after weaning, some animals may show very few signs but still can harbor the protozoan. These animals may appear normal, but are actually of greater economic loss versus those who show clinical signs due to reduced weight gain and poor feed conversion.

A specific subset of coccidiosis, nervous coccidiosis, is occasionally seen in calves. This disease can occur after apparent resolution of scours and presents as episodes of neurological signs including seizures, muscle tremors, and extreme sensitivity to touch. Treatment involves supportive care under the guidance of a veterinarian, but is rarely successful. Nervous coccidiosis occurs primarily in weaned beef cattle, and has not been reported in small ruminants.

How is coccidiosis diagnosed?

A veterinarian may suspect coccidiosis in young animals with scours that have just experienced a stressful event. Confirmation of coccidiosis can be achieved with microscopic evaluation of feces and identification of organisms seen. Quantity of organisms does not correlate to severity of disease. Because infected animals do not shed Eimeria organisms for very long, feces must be collected and examined early in the diarrhea episode.

How can coccidiosis be treated and prevented?

Because this parasite is a protozoan and not a worm or bacteria, it cannot be eliminated using dewormers or antibiotics. Treatment for clinical coccidiosis involves supportive care (i.e. fluid therapy) and isolation of the scouring animal from the rest of the herd. Anticoccidials during acute disease have limited therapeutic benefit, but are most useful when used as a control measure to prevent an outbreak in the herd.

The best way to control coccidiosis is prevention of clinical disease. It is important to realize that healthy animals can maintain small numbers of Eimeria organisms in their intestinal tract and that the presence of these organisms is not inherently dangerous.

There are three components to controlling coccidiosis in ruminants: improved hygiene, killing oocysts in the environment, and preventative coccidiostat administration. As it takes several days for organisms shed in feces to become infective, cleaning manure from stalls and pens daily can decrease exposure to the organism.

Decreasing stocking rates, elevating feed bunks off the ground, and routine water trough cleaning also can aid in reducing exposure.

Sunlight and drying is one of the best ways to rid the environment of the coccidial organism. Coccidiostats (i.e. amprolium, decoquinate, monensin, and others) can be administered in feed or water around the time of weaning. This administration will help prevent clinical disease while allowing the animal to mount its own protective immune response to the organism. Vaccinations exist, but there is minimal evidence that they are effective.

As you wean calves this fall, work with your veterinarian on developing an appropriate herd plan to include coccidiostats in your feeding program and make any improvements to the environment to help to prevent coccidiosis.

This article was written by fourth-year veterinary students at the College of Veterinary Medicine, graduating as veterinarians in May 2018 under the mentorship of Dr. Meredyth Jones.

Photo courtesy of Texas A&M Veterinary Medical Teaching Hospital

Coccidiosis is a disease of ruminants (and other animals) caused by host-specific protozoan organisms.

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