By Nathalie Fouché, DrMedVet, Dipl. ECEIM, of the Swiss Institute of Equine Medicine, and Vince Gerber, DVM, PhD, Dipl. ACVIM, ECEIM, FVH, of ISME, WEVA treasurer and junior-vice president.

Although many horses are exposed to the bacteria Leptospira interrogans, only a few develop clinical disease. The presence of circulating antibodies against different forms (serovars) of these bacteria suggest anywhere from 10% (in a Canadian study) to 33% (in an Australian survey) to more than 50% of healthy horses (in Swiss research) are exposed to Leptospira species.

The main health concerns associated with Leptospira species are abortion in pregnant mares and equine recurrent uveitis. However, foals can also develop disease, although in much lower numbers, due to exposure to the bacteria. Acute renal (kidney) disease and respiratory failure in foals have been described in the literature due to leptospirosis infection.

“Foals presented with acute renal injury due to leptospirosis usually show nonspecific clinical signs,” said Nathalie Fouché, DrMedVet, Dipl. ECEIM, of the University of Bern, in Switzerland, who recently reviewed the clinical records of these cases. “Those foals are unwilling to nurse, obtunded (lacking alertness), and might have a high rectal temperature.”

If foals are presented to a clinic early, when clinical signs are first noted, they are often excessively quiet and might not yet show signs of associated dehydration. The veterinarian will need to examine blood work results to gain more information about the foal’s state: “Foals will have abnormally high concentrations of the body waste compounds urea and creatinine in the blood, which reflects insufficient filtering of the blood by the foals’ kidney,” Fouché said.

Further diagnostic steps include urinalysis and identification of Leptospira species in the urine by PCR. Blood work performed on two occasions can reveal an increase in antibodies against the bacteria.

Affected foals should ideally be treated in a hospital. They most importantly need intravenous fluid therapy and antibiotics, as well as nursing care until clinical signs resolve.

“We usually see approximately one Leptospira-affected foal annually at the Swiss Institute of Equine Medicine (ISME) equine hospital in Bern,” said Fouché. “The foal we had last year, did not respond well to intravenous fluid therapy alone and needed hemodialysis to reduce the concentrations of urea and creatinine in his blood. After this therapy, the foal recovered well and was discharged a few days after presentation to our hospital. Renal replacement therapy is not yet routinely performed in horses. However, it is a good option to treat affected foals that do not respond to intravenous fluid therapy alone.”

If the diagnosis is made early in the course of the disease and intensive care and treatment are implemented immediately, the foal has a fair to good chance to make a full recovery.