We have recently been presented with the expected challenge of interpreting serologically positive rails from west nile virus (WNV) vaccinated institutions and how this impact's their movement to Guam which is still considered a WNV naive areas similar to Hawaii.

The most recent discussions among zoo vets regarding this virus was that birds were THOUGHT to be viremic for only 10- 14 days after to exposure to the virus (whether live virus or even possibly killed virus from the equine vaccine product currently being used- see comments below). However, there is just not enough scientific data out there to guarantee this right now. Furthermore, serologic monitoring of exposure to WNV is complicated with birds that have a history of vaccination and any vaccinated bird would/ could complicate potential future diagnosis of a natural infection.

With the help of the SSP pathologist, Dr. Scott Terrell, and his involvement with the Zoo WNV Surveillance program, we have been discussing this issue with the DAWR team while in Guam. These discussions warranted further inquiries with the investigators at the CDC who have the cutting edge information regarding these arboviruses and this is what we have found:

The philosophy surrounding Guam should differ from that of California or any other mainland state prior to introduction of the virus. Before Ca had WNV, we could assume it was eventually going to get there by natural routes, so they could be less conservative with movements of birds and vaccinations. In Guam, we are fairly certain that WNV is not present (150 birds tested at DAWR- all negative for EEE, WNV, SLE, and Japanese Encephalitis), therefore we should make every effort not to introduce the virus onto the island in any way, shape, or form (this includes animals vaccinated with the killed virus vaccine, see below)

The horse vaccine is a killed product, but according to investigators at CDC, this does not mean it is safe from post- vaccine shedding. Even if 99.9% of the vaccine is killed, there is still the possibility of that 0.01% living vaccine reverting to virulence in a susceptible species (such as a crow or horse) and causing infection or viremia and potentially being a source of introduction. With this conservative approach, any bird vaccinated on the mainland with the equine product could theoretically be a source of infection.

There is still alot unknown about the persistence of the virus in tissues of birds and other animals. It is theoretically possible for an animal exposed to WNV to start shedding virus again at some later date. In all likelihood that bird is safe and develops lifelong immunity BUT there is too much unknown at this time to say that definitively.

A bird that was actually sick due to WNV and survived is also not safe. There is evidence that the virus can persist long term in tissues such as the skin and could be a source of infection for insects or other birds at some later date.

So what does this mean:

1. Any bird that had been naturally infected and survived WNV infection is not a candidate for relocation

2. Any bird that has naturally seroconverted is not a candidate for relocation

3. Any bird vaccinated with the equine product is not a candidate for relocation

4. Only seronegative birds placed in mosquito proof housing immediately following serologic testing should be considered.

I can appreciate that this is the most conservative recommendation but it is the position of the CDC's arboviral experts at this time and a philosophy that I feel we should adopt until we have more definitive information about this disease and its impact in rails. Therefore, as if the above information does not reinforce this, vaccination of rails against WNV is not recommended for institutions participating in repatriation of rails to Guam.

Please email me directly if you have any concerns or questions.

Deidre K. Fontenot, DVM

Veterinarian, Animal Programs

Disney's Animal Kingdom

1200 N. Savannah Cir. E

Bay Lake, FL 32830

Office (407) 939-6238, FAX 407-939-6391