Questions and Answers for Ontario Horse Owners

 

Q1. What is West Nile Virus (WNV)?

A1. West Nile Virus is a mosquito-borne disease that can cause inflammation of the central nervous system (encephalomyelitis).

Q2. Can I protect my horse from WNV?

A2. Yes. Two WNV vaccines are available for horses in Canada. The vaccines are safe and proven effective.

Q3. What is the WNV vaccination protocol?

A3. The initial vaccination for WNV requires two injections 3 - 6 weeks apart followed by an annual booster. For horses at higher risk, such as those travelling to areas where mosquitoes survive year-round and high performance horses, a booster every 4 - 6 months may be recommended by your veterinarian. For complete coverage, vaccinations should begin before mosquitoes are present. Talk to your veterinarian about a comprehensive vaccination program to protect your horse from WNV and other diseases.

Q4. If my horse is vaccinated for eastern equine encephalitis (EEE) or western equine encephalitis (WEE), will it be protected from WNV?

A4. No. EEE and WEE belong to another family of viruses for which there is no cross-protection for WNV. However, one of the manufacturers of the WNV vaccine does combine West Nile with EEE and WEE. Check with your veterinarian to confirm what vaccines have been used.

Q5. Can foals or pregnant mares be vaccinated?

A5. Vaccination protocols should be discussed with your veterinarian. The colostrum from a vaccinated mare does transfer protection from the mare to her foal. Booster pregnant mares annually 4 to 6 weeks before foaling. This enhances colostral concentrations of immunoglobulins that generally protect their foals against these diseases for 6 to 7 months. Start vaccination of foals from vaccinated mares at 3 - 4 months of age in order to avoid maternal antibodies. Foals should receive an initial series of 3 doses of killed-virus vaccine administered 4 to 6 weeks apart (3, 4, and 6 months of age). (Ref. AAEP Guidelines for Vaccination of Horses, 2005)

Q6. Can this vaccine be used for donkeys or mules?

A6. Use of the horse WNV vaccine for other members of the equine family, such as donkeys, mules or zebras, should be discussed with your veterinarian.

Q7. What other measures can I take to protect my horse?

A7. Horse owners are advised to eliminate potential mosquito breeding areas and reduce the risk of mosquito bites by refraining from outdoor activities during peak mosquito times of dusk and dawn, and using added protection such as flysprays, flymasks and flysheets.

Q8. How serious is WNV disease in horses?

A8. WNV infection can result in inflammation of the central nervous system (encephalomyelitis). Symptoms range from listlessness, depression, trembling, loss of appetite, stumbling, in-coordination, weakness, head tilting, and partial paralysis, to convulsions and even death. Fever appears in only approximately 25% of the cases. The disease can progress very rapidly with severe symptoms appearing within 12 hours. Mortality rates amongst horses showing clinical signs of disease are approximately 35%.

Q9. Can a horse with WNV be treated?

A9. There is no specific treatment for WNV. Since a virus causes the disease, antibiotics will be ineffective. Contact your veterinarian if any signs of nervous system disease are observed. Your veterinarian will use supportive therapy, such as good nursing care, intravenous (IV) fluids to prevent dehydration, and measures to prevent secondary infections. In addition, samples will be collected for further laboratory testing. If your veterinarian suspects rabies or equine encephalitis as a diagnosis, the Canadian Food Inspection Agency (CFIA) must be informed.

Q10. Are some horses more susceptible to WNV?

A10. Horses of all ages, breeds, and health status are susceptible to WNV.

Q11. Will an infected horse be quarantined or euthanized?

A11. There is no evidence that WNV can spread directly from horses to other species, including humans. Quarantine is not required. Most horses exposed to WNV will not show any signs of disease. The majority of horses with clinical signs will recover, particularly if the infection is diagnosed at an early stage. Euthanasia would be an option only if the horse were suffering and not expected to recover.

Q12. Can horses be infected with other mosquito-borne diseases?

A12. Yes. WNV belongs to a class of viruses called the arboviruses, which include eastern equine encephalitis (EEE) and St. Louis encephalitis, both of which have been diagnosed in Ontario in the past. These diseases are spread by biting insects such as mosquitoes, flies and ticks. Disease transmission and spread occurs when the insects are active. Birds are the natural hosts for these viruses. Eastern equine encephalitis was diagnosed in 11 Ontario horses in 2003 and two horses in 2004.

Q13. WNV the only cause of central nervous system disease in horses?

A13. No. Central nervous system disease in horses may arise from a variety of causes including viruses, bacteria, parasites, developmental abnormalities or trauma injury.

Q14. Is it easy to diagnose WNV infection?

A14. The symptoms of WNV are similar to rabies, eastern equine encephalitis (EEE), western equine encephalitis (WEE), equine protozoal myeloencephalitis (EPM), the neurological form of herpesvirus, and wobblers syndrome. Contact your veterinarian immediately should you observe any sign of central nervous system disease. Blood tests may be useful to determine the cause of infection. Should death occur, a complete post-mortem examination and follow-up testing to determine the cause of death is recommended. As required by the federal Health of Animals Act, horses suspected of having rabies must be reported to the Canadian Food Inspection Agency.

Q15. How widespread is WNV in Ontario?

A15. Widespread evidence of WNV has been found in birds and mosquitoes throughout Ontario since 2002. WNV in Ontario was the probable or confirmed diagnosis for 107 horse cases in 2002. Anecdotal evidence suggests that the number of horse infections is actually higher. Evidence confirms that WNV is endemic in Ontario and will be present in the horse population at varying levels each year.

West Nile Virus Cases in Horses 2001 - 2005

Year	Number of WNV Cases Confirmed or Probable	Region
2001	0
2002	107	4 - Brant 3 - Chatham-Kent 9 - Haldimand-Norfolk 4 - Halton 3 - Hamilton-Wentworth 6 - Lambton 1 - Middlesex 1 - Muskoka-Parry Sound 12 - Niagara 2 - Northwestern 1 - Ottawa 3 - Oxford 1 - Perth 6 - Toronto 5 - Waterloo 1 - Wellington 41 - Windsor-Essex 4 - York
2003	10	1 - Durham 1 - Eastern Ontario 2 - Essex 1 - Halton 2 - Niagara 1 - Peel 1 - Perth 1 - Peterborough
2004	9	1 - Brant 1 - Durham 1 - Elgin 1 - Lambton 1 - Muskoka 3 - Nipissing 1 - Sudbury District
2005 to Oct. 14	5	1 - Essex 2 - Lambton 1 - Niagara 1 - Waterloo

Q16. What other animals are affected by WNV?

A16. WNV infections have been reported in a wide range of animal and bird species, including horses, dogs, cats, deer, crows, chickens, geese, jays, raptors and owls. Horses and birds of the corvid family, including ravens, magpies, jays and crows, are particularly susceptible to WNV.

Q17. How do I know if WNV is in my region?

A17. Usually the first signs of WNV are unexplained wild bird deaths. The Ontario government conducts an active surveillance program for WNV. Test results for your area are available on the Ministry of Health and Long-Term Care web site or through your local public health unit. If you observe an unexplained bird death, contact your local public health unit.

Q18. Can animals or birds infected with WNV pass on disease to people?

A18. There is no evidence that WNV can pass directly from an infected animal or bird to a person. People and animals become infected after being bitten by a mosquito carrying WNV.

Q19. Is WNV expected to spread within Ontario?

A19. WNV is a mosquito-borne disease. Since it is considered endemic in Ontario, residents should anticipate WNV to be widely present in the province each year. WNV is a serious, emerging disease but the risk of humans or horses contracting the disease is still quite low.

Q20. When did WNV first appear?

A20. WNV was first detected in Africa in 1937 and appeared in the New York City area in 1999. Since then, the virus has spread widely throughout the United States and Canada. In 2001, the first signs of WNV appeared in birds and mosquitoes in Ontario. In 2002, WNV was detected in Nova Scotia, Quebec, Ontario, Manitoba and Saskatchewan.

Q21. Where can I find further information?

A21. For information on WNV and human health concerns, surveillance results and mosquito control, contact the Ontario Ministry of Health and Long-Term Care website or your local public health unit.

For further information on WNV and horses, contact the Ontario Ministry of Agriculture, Food and Rural Affairs, Agricultural Information Contact Centre 1-877-424-1300, or your veterinarian.

Related Links:

Canadian Cooperative Wildlife Health Centre
Health Canada
Ontario Ministry of Health and Long-Term Care -
INFOline at 1-877-234-4343 (Toll-free in Ontario only)
TTY 1-800-387-5559
Public Health Agency of Canada