West Nile Virus Has Reached California

[By Douglas Novick, DVM]

Make Sure Your Horse is Vaccinated Against This Deadly Disease

 West Nile Virus is a viral brain infection that came to the United States in 1999. It causes severe neurological symptoms and kills over 30% of horses that contract it.  Mosquitoes spread it with birds being the natural host for the disease. In 2002 it spread across to the country with nearly every state except California affected. 

As of August 20, 2003 it reached California.  The spread is rapid.  In the last week of July it was being seen in North Dakota and Minnesota.  In the first week of August a dramatic outbreak occurred in Colorado and it was being seen in New Mexico.  By the second week of August it was being found in horses in Utah.  Now it is in California

I urge all my clients who have not vaccinated their horses to immediately vaccinate their horses.  I urge all clients who have not had their horses vaccinate against West Nile Virus within the past 8 weeks (June 27, 2003) to follow the recommendations of the staff at the UC-Davis Veterinary School and  re-vaccinate their horses

Things you need to know

How serious is the disease? In 2002 there were approximately 15,000 confirmed cases in horses in the U.S. of which over 5000 horses died. 

In 2003 there were over 4000 cases in horses and over 8000 cases in people.

Does the vaccine work?  A challenge study in which vaccinated horses were injected with live virus showed that the vaccine was 95% effective in preventing the disease.  Results in affected areas confirm the effectiveness of the vaccine.  Less than 5% of the confirmed cases were from vaccinated horses.  Furthermore, if a vaccinated horse does get West Nile disease, they only have a 5.8% mortality rate vs. a 30% death rate in horses that were un-vaccinated and come down with the disease.

How often should I vaccinate my horses?  In April 2003 the staff at UC-Davis Veterinary School issued updated recommendations.  The staff currently recommends the following:

Does this mean I am going to have to vaccinate my horses every 8 weeks?  No. The purpose of the extra booster for horses vaccinated before well before the first case of the year is seen in California is to maximize the protection between the time of the outbreak and the end of November when the mosquito season ends.   

Is it contagious?  No.  One horse cannot give it to another horse.  Horses and man are called dead-end host for the disease.  The virus can cause disease in horses, but cannot reproduce enough to have a mosquito bite a horse and transfer virus to another animal or person.  Birds are the natural host for the disease with mosquitoes biting birds then biting either other birds or other animals such as horses.   However, if a horse does come down with the disease in your barn, it means that mosquitoes in your area are potentially carrying the disease.  You personally need to be careful.  People should apply daily a DEET containing mosquito repellent to themselves.  You can help your horse by applying fly spray daily or applying an every two-week fly repellent such a Liberty that we keep in stock for this purpose.

Other places on the Internet to look for Information about West Nile Virus

California West Nile Surveillance Center:  http://westnile.ca.gov/

If you see a dead bird call (877) WNV-BIRD to have it tested for West Nile Virus

US Geological Survey West Nile Maps: http://westnilemaps.usgs.gov/

US Geological Survey National Wild Life Health Center West Nile Page: http://www.nwhc.usgs.gov/research/west_nile/west_nile.html

Dr. Douglas Novick is an equine veterinarian practicing in the San Francisco Bay Area. His practice is limited to the treatment of horses with special interests in equine lameness, equine dentistry and reproduction. He is also the first veterinarian in Northern California to implant horses with ID Microchips with optional freeze brands as a method of preventing horse theft.


See more at www.novickdvm.com


(C) 2004 Douglas Novick, DVM- This article is copyrighted. It is licensed for personal use only. Any re-use, duplication, re-transmission via electronic or other means without the expressed written permission of the author, Douglas Novick, is strictly forbidden.