Advances in detection methods mean that cases of leukemia in horses are being diagnosed more frequently, though it is a rare disease.
The criteria in testing horses is not as clear-cut as it is for dogs and cats. The two main types of leukemia found (myeloid and lymphoid) are fairly straightforward to differentiate in dogs and cats but not so in horses.
Ontario Veterinary College researcher Dorothee Bienzle said difficulties in making a diagnosis can result in animals that die without a diagnosis.
“Equine leukemia is a rare and terrible disease which is challenging to diagnose,” she said.
In a recent three-month study, Bienzle with the help of graduate veterinarian Carina Cooper, compiled information from the last 16 years of cases of equine leukemia that came through the OVC. Over half of the 16 diagnoses have occurred in the last two years due to recent advances in detection.
“New technologies such as flow cytometry and immuohistochemistry, pioneered at OVC, had been fundamental to the increase in definitive diagnoses of equine leukemia in the past two years,” she said.
Acute Myeloid Leukemia (AML) and Acute Lymphoid Equine Leukemia (ALL) tend to have a grave prognosis with survival of days or weeks. There is a third type of leukemia, called Myelodysplastic Syndrome (MDS), which dogs, cats, humans and horses can have. This is also a cancer of bone marrow seen in the more elderly. MDS typically progresses at a slower rate. The current treatment for MDS in equines is corticosteroids and the survival rate can be months to years allowing life as a companion animal during that time.
Hematology results of the study by Bienzle and Cooper showed all cases as having atypical white blood cells in circulation, and in most cases there was high Serum Amyloid A (SAA), which is a protein produced in the liver that will rise in response to inflammation. Anemia, low neutrophil and low platelet counts are reasons to test further for equine leukemia.