The Latest Information on West Nile Virus

By Teri Nilson Baird

I attended a most informative three-hour presentation by Dr. Michelle Kutzler of Oregon State University. Dr. Kutzler is the author of the study sponsored by the Alpaca Research Foundation, the Willamette Valley Llama Association, and the Southwest Washington Llama Association, which dealt with the safety of the [WNV] horse vaccine in camelids. I must emphasize that the efficacy of the vaccine is still unknown and a challenge study has not yet been done. 

A lot of information was exchanged this weekend between Dr. Kutzler and eight of our local veterinarians [front range Colorado area]. They were able to provide her with anecdotal evidence of their experiences and studies, and a lot of the blanks may begin to be filled in. 

To summarize the discussion at the meeting, we may not need to vaccinate all of our animals. Dr. Jeannie Rankin passed along to Dr. Kutzler the results of blood tests she had done on a herd that lost several alpacas. Seventy of the animals tested showed high titers for the virus but had no clinical symptoms. These animals are producing their own antibodies without vaccination, meaning they had also been exposed to the virus but did not become clinically ill. 

The eight local vets, with Dr. Kutzler's input, formulated a strategy for next year along the Front Range of Colorado and other areas previously affected. They will recommend blood testing (less expensive than vaccination) ten percent (or more if the owner desires) of each herd to determine probable antibody levels. Animals who have antibodies will have a natural immunity and therefore do not require vaccination. In fact, there is anecdotal evidence of two animals that experienced anaphylactic shock when vaccinated; these animals had not been tested for antibodies prior to administration of the vaccine. 

If animals do not show antibodies, the timing for vaccination should be April, May, and June for the three-course administration of the vaccine. Pregnant females should not be vaccinated in the first or last 60 days of pregnancy. This schedule should provide at least twenty weeks of immunity. The vaccine may be boostered again in September and twice the next year. This could be an expensive proposition, depending upon the number of animals in each herd and whether the price of the vaccine declines next year with competition from the other vaccine manufacturer. Oregon State University has not tested the last blood draws they did in October so we do not yet know about antibody titers beyond the twenty weeks. 

Unvaccinated animals that contract the disease (and are caught early in its course, before it crosses the blood-brain barrier) have the best chance of recovery if the vet sees the animal when the facial tremors begin. A treatment with plasma from vaccinated animals has proven to provide the best results, possibly within 48 hours. It is possible an immune booster may be used in conjunction with the plasma; discuss this with your veterinarian. Dr. Rankin is testing passive transfer of antibodies via colostrum through Oregon State Univ. as well, and has funding through Colorado State University for other WNV research. 

It appears that everyone learned a lot this weekend and I believe the Alpaca Breeders of the Rockies did many of us a great service by sponsoring Dr. Kutzler's trip to Parker, [CO]. It was productive to get our local veterinarians together, sharing their individual experiences, and then to have Dr. Kutzler pass some of the information along to the owners.