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  Discussion on Research Summary: Prediction of risk of West Nile based on dead bird surveillance
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Moderator:
DrO

Posted on Wednesday, May 23, 2007 - 10:16 am:

Some states have a active dead bird surveillance program that monitors for the prevelance of WNV infection in the birds. This has been found to be one of the best ways of estimating risk of exposure to WNV of you and your horse. Unfortunately many states do not have active reporting programs. In the WNV article there is a link to a map maintained by the U.S. Department of the Interior that shows reported activity for WNV and other mosquito borne viruses of concern to horse owners. If your area is not reporting you might check with your state veterinary office or public health department for more information.
DrO

Vector Borne Zoonotic Dis. 2006 Spring;6(1):1-6.
Prediction of equine risk of West Nile virus infection based on dead bird surveillance.

Roberts RS, Foppa IM.
Department of Epidemiology, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carol ina, USA.

Since the introduction of West Nile Virus (WNV) to the United States in 1999, the efficacy of dead bird surveillance for the prediction of human and veterinary WNV infection has been an issue of debate. We utilized South Carolina's Department of Health and Environmental Control surveillance data from 2003 to determine whether dead bird surveillance accurately predicts equine WNV infection on a county level. We adjusted for human population density as a potential confounder of an association between WNV-positive dead bird counts and mammalian WNV risk. We found a strong positive association between avian risk of WNV death and subsequent equine mortality due to WNV in South Carolina even after adjusting for human population density. Sensitivity of dead bird surveillance as a predictor of future equine WNV risk was far superior to mosquito surveillance (95% vs. 9.5%, respectively). A Poisson regression model of the equine WNV rate as a function of WNV-positive dead bird rate, adjusting for population density and taking into account effect modification by population density shows a good fit with the data. Unlike most previous studies, we control for potential confounding of the dead, WNVpositive bird-equine WNV infection association by human population density. Yet, the positive association between dead bird surveillance and equine WNV risk remains strong and statistically significant, indicating that dead bird surveillance remains a valuable tool of WNV surveillance.
Member:
christel

Posted on Wednesday, May 23, 2007 - 10:53 am:

Hi DrO, thanks for that info.
When WN raised its ugly head and came into being here in the states, I did vaccinate and continue to do so. My county in the panhandle of Texas had approximately 15 cases the first year. We have had no positive cases since.
My question- my local vets seemed to think that in a couple of years horses would create their own immunity to WN. Do you think they have done this? Since no horses have been found in the last couple of years to be positive, it seems maybe they were correct. Will be interesting, we have had an extremely wet winter and spring, the mosquitos are out in big numbers here.
I have read recently that Oregon is preparing for the WN onslought, do you know if this the first year they are experiencing this?
Thanks DrO, as always I appreciate your thoughts.
Chris
Member:
hpyhaulr

Posted on Wednesday, May 23, 2007 - 1:12 pm:

The summer of 2005 Frank lost 3 of his mares across the road to WNV, only his stallion survived. That is good enough to scare the daylights out of us...I would vaccinate ME if I could!!!And yet, noone I know of has sighted any dead birds which were not road kill....(sorry to be so blunt). We have mosquitoes here with call signs.... take no chances, take no prisoners. We are located in SC, very close to the NC border by Rockingham (NASCAR people know where 'the ROCK' is). Very concerned about the mosquito immunity issue..how long does it take for the mosquitoes to develop their immunity to the HORSE'S immunization?
Moderator:
DrO

Posted on Wednesday, May 23, 2007 - 10:30 pm:

Chris, I don't know any work to suggest that exposure to natural disease is consistent enough to maintain a protected status in horses. In fact just the opposite. In areas where this disease has been endemic for decades (Africa, Middle East, Southern Europe) they still had episodic equine WNV epidemics before the vaccine. Here is one of many such reports:
West Nile virus in Morocco, 2003.
Schuffenecker I, Peyrefitte CN, el Harrak M, Murri S, Leblond A, Zeller HG.
Centre de Reference des Arbovirus, Institut Pasteur, 21 Ave Tony Garnier, 69365 Lyon cedex 07, France. schuffenecker@cervi-lyon.inserm.fr

West Nile virus (WNV) reemerged in Morocco in September 2003, causing an equine outbreak. A WNV strain isolated from a brain biopsy was completely sequenced. On the basis of phylogenetic analyses, Moroccan WNV strains isolated during the 1996 and 2003 outbreaks were closely related to other strains responsible for equine outbreaks in the western Mediterranean basin.

Cyndy, I am uncertain what you mean by the mosquitos developing immunity to the horse's immunization? The vaccine does not work by protecting the horse from mosquito bites but by killing the virus introduced by the mosquito. It is unlikely the virus will overcome the vaccine anytime soon but as new strains develop there may be some antigenic drift, so not impossible.
DrO
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