Wellness Tips

West Nile Virus Information Sheet

1. How is the virus transmitted?

  1. Migratory birds, primarily Blue Jays and crows, are reservoir hosts.
  2. Mosquitoes are vectors as they become carriers once they take a blood meal from an infected bird.
  3. Humans and horses are dead-end hosts, becoming infected with the virus once an infected mosquito takes a blood meal.

**Horses can NOT pass the virus from one horse to another, nor can humans**

2. What are the symptoms of the virus in horses?

The virus causes an encephalitis, an inflammation of the brain. The incubation period (the time it takes for symptoms to show) is 5 to 15 days. Clinical signs include:

**Be aware that there are several other diseases with symptoms like these**

3. Is testing for the virus available?

Yes. The test requires a blood sample and costs $134.00 plus GST (subject to change).

4. How is the virus treated?

As with all other viruses, there is no ‘cure’. We can only treat symptomatically. This would probably include intravenous fluid therapy, non-steroidal anti-inflammatory medication and other supportive therapy as needed. Prognosis is guarded in most cases; some horses may fully recover if diagnosis and treatment begins early. Older horses usually develop severe encephalitis which can be fatal.

5. How can we protect our horses from the virus?

By vaccination. There is a new vaccine available that has, to date, received limited testing showing favorable results. Further trials remain in progress. The vaccine requires an initial inoculation and a booster in 3 to 6 weeks. Annual vaccination is strongly recommended. Horses vaccinated with the West Nile Virus vaccine may not be eligible for export to countries that require negative serological test results for WNV. It is advisable to bank serum samples prior to vaccination when exporting to such countries.

The cost of the vaccine is $40.00 plus GST per dose (subject to change). The sale of this vaccine requires strict record keeping; we must have the full description of each horse being vaccinated and a valid client-patient-veterinarian relationship.

6. Can pregnant mares receive the vaccine?

Yes. There are no safety concerns in pregnant mares to date.

7. How old does a horse need to be to receive the vaccine?

Foals in our area should be 3 to 5 months of age. A booster is required in 3 to 6 weeks. If the mare has not been vaccinated, the foal should receive a second booster in another 3 to 6 weeks.

8. Why should a veterinarian administer the vaccine?

The vaccine is currently available on a conditional license. This requires the veterinarian to be accountable for every dose of vaccine. We are required to keep a record of the client and the horses receiving the vaccine. Another reason why your veterinarian should vaccinate your horse is because full licensing of the vaccine is dependent on it’s performance. Adverse vaccine reactions due to improper injection technique and vaccine handling can hinder this process.