Horse Disease Surveillance
This Factsheet was written with the help of specialists at the Ontario Animal Health Surveillance Network (OAHSN). The OAHSN group has specialists in veterinary diagnostics, disease investigation, epidemiology, meat inspection, technology transfer and policy development that collect information related to animal health.
Table of Contents
The horse population is very mobile, moving between shows, racetracks and breeding facilities. This can result in a high exposure to disease.
During the first months of 2009, import restrictions were placed on:
Horse owners should remember to incorporate biosecurity measures into their daily procedures to prevent diseases from entering their premises.
Under the authority of the Health of Animals Act and Regulations, the Canadian Food Inspection Agency (CFIA) monitors and acts to prevent the introduction or presence of certain animal diseases in the domestic population (1). The Act divides the diseases of concern into three categories:
Table 1. Reportable Diseases and their Canadian Disease Status
(* see section on this disease in this Factsheet for details)
This group includes dourine, western and eastern equine encephalitis (WEE and EEE), West Nile virus (WNv), glanders (Burkholderia mallei), hendra virus and Japanese encephalitis. Canada is free of all of the above diseases with the exception of West Nile virus, EEE and WEE, which occur sporadically.
The annually notifiable diseases are the more common endemic diseases that occur in many jurisdictions of the world. They include botulism, equine coital exanthema (genital horse pox or equid herpesvirus type 3 (EHV-3)), horse mange (Psoroptes equi), equine viral arteritis virus and strangles (Strep. equi).
Anthrax, caused by the spore-forming bacterium Bacillus anthracis, occurs sporadically in Canada (2). Cases occur from Alberta through to western Ontario, with repeated outbreaks in the Mackenzie Bison Range in the Northwest Territories and in Wood Buffalo National Park in northern Alberta. Although all mammals are susceptible to anthrax, it is primarily a disease of herbivores. Cattle, sheep, goats and horses are highly susceptible. Horses have been reported with anthrax in 2006 (four cases in Saskatchewan and three in Manitoba, one of which was a donkey), in 2005 (two in Manitoba) and in 1999 (one in Alberta) (3,4).
The weather during the 2008 haying season was very unpredictable for farmers. A number of horse owners purchased or produced round-bale silage. Unfortunately, a number of outbreaks of botulism in horses were traced to the feeding of round-bale silage without vaccination. While the quality of forage in round-bale silage can be very high, the presence of the botulinum toxin is still unpredictable, so use caution when feeding silage to horses. See the OMAFRA InfoSheet Botulism in Horses and Haylage, if you are contemplating using silage, and talk to your veterinarian about vaccinating your horses for botulism.
In Ontario, 16 mares and one stallion were identified as being potentially infected with CEM as a result of insemination with potentially imported, infected semen in the 2008 breeding season. This was part of a large North-American-wide investigation. As a precaution, the CFIA quarantined animals on the farms, and these measures remained in place until all potentially exposed mares and their foals tested negative for CEM. Rounds of sampling are continuing, and all test results to date have been negative (5).
Effective January 19, 2009, the CFIA implemented a requirement for additional certification for the import of live horses from the U.S. In addition, as of January 29, 2009, new import requirements for horse germplasm (semen and embryos) were implemented.
In Canada, horse owners voluntarily pay to have their horses tested when proof of negative status is needed for movement to shows and other horse events. Private veterinary practitioners collect samples and submit them to private laboratories accredited for EIA testing by the CFIA. EIA-positive horses must be reported to the CFIA, and disease control measures are implemented. Since 2006, the competitive ELISA has been used for surveillance testing rather than the agar gel immunodiffusion (AGID) or Coggins test.
From 1998 to 2008 inclusive, 1,728 positive samples were detected from 826,866 samples submitted. The focus of EIA infection in Canada is in the provinces of Saskatchewan, Alberta and British Columbia, where all but 31 cases occurred over the 11-year period. In the same period, only four cases of EIA were found in the 297,855 samples submitted from Ontario (6).
EVA is occasionally diagnosed in Ontario. In 1999, an EVA-like syndrome - including a skin rash, urticaria-like reaction of the limbs, trunk, brisket, inguinal area and scrotal area, or mammary glands, along with any of the following signs: nasal and ocular discharge, fever, petechiae and oral lesions - was reported in horses in one of nine barns at an Ontario racetrack and in two training facilities (7). All of the standardbred horses that were reported to have been clinically sick and in barns affected by this EVA-like syndrome had titres greater than 1:4, while only 26% of the comparison group had an antibody titre greater than 1:4.
Summaries of neurological cases from all provinces were not available. The Ontario cases are presented in Table 2. In 2008, Quebec confirmed 19 cases of EEE in horses and, on one farm, three emu were confirmed to have died of EEE; a further 13 were suspected of dying of EEE.
In Ontario, WNv and EEE virus in horses are identified by IgM positive, IHC and/or PCR by the Animal Health Laboratory, University of Guelph. Eastern equine encephalitis virus (EEEV) rRT-PCR was adopted from the published procedure described by Lambert AJ et al. (8). Some cases may not be recorded when samples are submitted to other laboratories.
Table 2. Surveillance in Ontario 2000 - 2008
Since the outbreak of EHV-1 neurological form (nEHV-1) in a large group of horses in Findley, Ohio, in 2003, other outbreaks are being reported from across North America.
The neurological signs range from mild ataxia to complete paraplegia, often ending in death or euthanasia. It is recognized as a newly emerging mutant of the virus. In March 2008, an outbreak occurred in a boarding facility in Saskatchewan where 15 horses were infected. This is just one of the sporadic outbreaks occurring across the world equine community.
The development of a PCR test now allows for the identification of the nEHV-1 strain. This has and will provide laboratories and veterinarians with the tool to recognize the nEHV-1 strain more readily and more frequently. The increased detection may not mean an increased incidence of the disease but merely that "the more you look, the more you find." The Animal Health Laboratory, University of Guelph, has demonstrated nEHV-1 in three horses since late 2007 through 2008 (9).
There were 53 cases of rabies in horses in the 11-year period 1998-2008. Manitoba, Saskatchewan and Ontario had 19, 16 and 16 cases each, respectively (10).
The "Arctic Fox Strain" of rabies is now referred to as "Ontario Fox Strain" or "Eastern Fox Variant." The Ontario Ministry of Natural Resources operates a wildlife oral rabies vaccination program. It has greatly reduced the prevalence of rabies in Ontario and virtually eliminated it in foxes. Only one laboratory-confirmed case in a fox has been reported to date (July 16, 2009) this year. However, rabies still occurs in skunks and spill-over species from skunks, e.g., in three sheep this year. A new Ontario-developed, oral rabies vaccine (ONRAB) appears to successfully vaccinate skunks, raccoons and foxes, and should decrease the prevalence of rabies in wildlife in Ontario even further.
The raccoon rabies strain, which entered Ontario in a small location adjacent to New York State in July 1999, appears to have been eliminated. The bat strain of rabies is endemic in Ontario. No vaccine development is planned.
From January 2000 to March 2007 inclusive, three humans died from rabies in Canada and a fourth died as a result of being mauled by a rabid horse.
Strangles, caused by the bacterium, Streptococcus equi, is a highly contagious and serious infection of horses and other equids. It is endemic in most horse populations.
There are no requirements for horse owners to report or quarantine horses or barns, except in the case of racing facilities. Racetrack officials may restrict horse movement when strangles is diagnosed or suspected. The organism can be isolated from the nose or lymph nodes of affected animals and can be found in the guttural pouch of carrier animals. For more information on strangles and biosecurity to prevent the introduction of strangles, see the Health Management section under Horses.
Be aware of which diseases are reportable and/or notifiable. The best way to prevent disease in your horses is to work closely with your veterinarian and to establish good biosecurity protocols.
For more information:
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