Horse Disease Surveillance Report

Reportable Diseases in Canada

No cases of contagious equine metritis, dourine, piroplasmosis (babesiosis), or glanders have been reported.

Rabies:

There were no cases of rabies in Ontario horses during 1997 or 1998. However, one rabid horse was detected in Manitoba and two in Saskatchewan in 1998.

The wildlife vaccination program of the Ontario Ministry of Natural Resources has virtually eliminated rabies in foxes. However, skunks remain as a reservoir of the virus.

Equine Infectious Anemia (EIA):

In 1997, 111 cases of EIA were detected from a total of 68,347 samples.

In 1998, 96 cases of EIA were detected from a total of 66,177 samples. Only one case of EIA was detected in Ontario in 1997 and 1998. The main focus of infection was detected in Saskatchewan, Alberta, and British Columbia. There are approximately 700,000 horses in Canada. Therefore, roughly 10% of the horse population is annually being monitored for EIA. Some of these samples will be duplicate samples.

Non Reportable Diseases in Ontario

Epizootic lymphangitis of horses, horse pox, Japanese encephalitis of horses, and Venezuelan equine encephalitis have not been known to occur in Canada.

Eastern Equine Encephalitis (EEE):

In September, 1997, a 20-year-old Quarter Horse mare from Orillia became stiff and reluctant to move. The horse assumed lateral recumbency 4 hours later, with seizures and opisthotonus beginning after another 12 hours. The horse was unresponsive to antibiotics and anti-inflammatory drugs after another 12 hours and was euthanized. The horse had been vaccinated for rabies routinely. The EEE antibody titres for the single sera were determined by arbovirus reference centers to be HI titre > 1:640; IgM capture ELISA - positive; neutralization titre to EEE of 1:5. These serological results suggest recent infection with EEE. This is the third incident of sporadic EEE infection in horses in Ontario since 1992. EEE was diagnosed in two horses in the fall of 1992, and in two horses in the fall of 1994 (5 others died in the 1994 outbreak but were not tested). Before 1992, EEE had not been diagnosed in horses in Ontario since 1938.

Equine Viral Arteritis:

An EVA-like outbreak affected horses in one barn at a Standardbred track and at two training facilities. The clinical signs reported by practitioners included edema of the limbs, trunk, brisket, inguinal and scrotal areas and a skin rash. No mortalities were observed. Single serum samples from 67 horses were obtained. Of the 67 horses, 74% of controls were negative for antibodies to EVA while 26% of the controls were positive. Of the 27 horses who were reported to have been sick, 100% were positive for antibodies to EVA. Age of the horse was not a factor as to whether the horses had antibodies to EVA. The results are statistically significant that the disease syndrome was associated with high convalescent EVA titres (when compared with the non affected comparison groups). However, it may have been more conclusive if acute and convalescent samples had been submitted to the laboratory.

Leptospirosis abortions:

Two abortions caused by leptospirosis were diagnosed on separate facilities in eastern Ontario in late 1998. Titres to the serovars Leptospira pomona, grippotyphosa and bratislava indicated recent infections. Leptospiral infection, as a cause of abortion in horses, has been previously reported from Kentucky, Louisiana and Ontario.

Rhinopneumonitis in yearlings:

Vaccinated Standardbred yearlings were diagnosed with viral-induced respiratory disease. The yearlings had four fold changes in antibody titre to equine herpesvirus subtype 1 and 4 (EHV 1&4). The laboratory test used can not differentiate between subtypes EHV 1 and 4. The horses had been vaccinated with a killed herpesvirus EHV subtype 1 and 1b vaccine. The vaccine did not provide protection from this virus outbreak.

Equine herpesvirus (EHV) has been diagnosed as the cause of still births in four thoroughbred foals and one Standardbred near-term foal in the first six weeks of 1999. From 1992 until Jan. 1st 1999, 37 abortions had been diagnosed as caused by EHV by the Animal Health Laboratory.

Equine Rhinovirus:

Antibodies greater than or equal to 1:128 to rhinovirus were detected in 78% of 95 horses sampled in a survey of respiratory disease in Standardbred horses in Ontario. (The 1:128 antibody titre level was chosen as an arbitrary level of active immunity). Rhinovirus is a common pathogen of horses and is common in most adult horses in Ontario.

Ulcerative stomatitis of unknown origin was investigated in a group of horses. The horses were EIA negative, vesicular stomatitis negative, but had seroconversions to influenza AE2. It is unknown whether there is a relationship between the oral lesions and the four fold change in titre to influenza AE2.

Strangles:

References:

1. Roger R., Rivard G., CAHNet Bulletin, Winter 1998-99, Edition #2

2. Animal Health Laboratory Newsletter, Animal Health Laboratory, University of Guelph, March 1998

3. Animal Health Laboratory Newsletter, Animal Health Laboratory, University of Guelph, December 1998, Vol. 2, No.4

4. Animal Health Laboratory Newsletter, Animal Health Laboratory, University of Guelph, March 1999, Vol. 3, No.1

5. Salsberg, E. B., Personal Communication, Canadian Food Inspection Agency, 174 Stone Road West, Guelph

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