False positive rabies result determined for a Perth County horse

Huron Perth Public Health

It turns out a horse from Perth South that recently tested positive for rabies, was not rabid after all.

The Canadian Food Inspection Agency (CFIA) has completed further testing on a sample from the horse in Blanshard Ward and it has been reclassified as rabies negative.

“This was very unexpected and a first for Ontario,“ says Dale Lyttle, Senior Public Health Inspector at Huron Perth Public Health (HPPH). “Upon receipt of a positive rabies result in an animal, decisions need to be made quickly to protect the health of any individual that has been exposed.”

Follow up with the CFIA lab and Ministry of Health representatives indicated that the initial test strongly suggested a low-level positive result. Due to the fatal nature of rabies virus infections, and because human exposures were reported, a positive result was issued. When the CFIA conducted additional tests to determine the type of rabies virus strain within the sample, no such virus was detected. Following additional testing, the CFIA has determined that the initial result was a false positive. HPPH has followed up with the individuals who were determined to have exposures to the horse.

Lyttle says the test that is used by the CFIA to determine if a sample contains the rabies virus has been internationally accepted as a primary diagnostic test for rabies for over forty years. According to the CFIA, this is only the second sample out of approximately 32,000 samples in the past 10 years that has been reported as a false positive.

The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) has been in contact with the farm owner regarding ongoing management of the other animals on the farm that were in  contact with the horse in question following the reclassification of the test result.

“We continue to be very confident in the reliability of the test used to detect rabies,” says Lyttle. “Rabies is almost always fatal, which is why public health is required to thoroughly investigate all human exposures.”