Commonly seen in young foals, this infection can be fatal if left untreated.

UC Davis Center for Equine Health

Parasites in the genus Cryptosporidium are an important source of gastrointestinal disease in humans and animals globally. These highly contagious parasites infect the intestine and cause diarrhea and weight loss. 

Cryptosporidiosis, associated specifically with Cryptosporidium parvum, is most commonly seen in foals one to four weeks of age. Foals that are immunocompromised (especially those with severe combined immunodeficiency syndrome) or stressed are particularly at risk of infection. Foals become infected by ingesting the parasite (in the oocyst stage) in contaminated food or water.

The parasite can be transmitted from horses to humans in contaminated water, soil, or surfaces, and can survive in the environment for long periods.

Diarrhea, dehydration, and weight loss are clinical signs of cryptosporidiosis in foals. Subclinical infection may be common in adult horses and foals that otherwise appear healthy.

Cryptosporidiosis is diagnosed by identification of cryptosporidium oocysts in fecal samples by staining, immunofluorescence assay, or flow cytometry. The parasite can also be identified by enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR).

There is no specific treatment, including antibiotics, for cryptosporidiosis. Therapy for sick foals is largely supportive, often involving fluid replacement.

Many horses recover fully, but cryptosporidiosis can be fatal if left untreated. The disease is serious in immunocompromised foals.

Cryptosporidiosis can be challenging to prevent and control. There are no vaccines currently available for cryptosporidiosis. Oocysts shed in feces are very hardy and can survive for extended periods in the environment. They are also resistant to many disinfectants.

Good biosecurity protocols, including isolation of infected foals and disinfection of contaminated areas, are the best ways to prevent Cryptosporidiosis.

Related: Flexural Limb Deficiencies in Foals

Printed with the kind permission of the UC Davis Center for Equine Health. The UC Davis Center for Equine Health is dedicated to advancing the health, welfare, performance and veterinary care of horses through research, education and public service.