Re: Report of Horse Death, possibly resulting from WNV Equine Vac cine

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> A very sad case, to be sure. I notice the horse received 3 immunizations
at
> the same time. How was hypersensitivity to the other 2 ruled out, in
order
> to implicate the WNV vaccine?

It wasn't. The positive serology and postmortem findings indicate West Nile
virus infection as the cause of symptoms. I don't think this owner is
trying to say the vaccination per se was the cause of death.

Had the horse received these before, perhaps?

Probably. They are very common vaccinations.

> Also, could this have been a tragic coincidence of the onset of WNV
symptoms
> from a mosquito exposure appearing at the time of the vaccination?

Since the serology was drawn within 24 hours of the vaccinations, and PRC
testing of the CSF was also positive, odds are the WNV exposure occurred at
least several days prior to the vaccination, if not longer.

Or are
> you saying that perhaps the vaccination made an incipient case of WNV
worse?

That, I think, is the big question.

> I'm no vet, but it also strikes me odd that the symptoms and damage were
> neurological. Do reactions to vaccines cause nuerological symeptoms so
> quickly?

I think everyone is assuming that the neurological symptoms were caused by
the active West Nile Virus infection, rather than a vaccine reaction,
although I suppose that, or a combination of the two, is possible. There is
not much information available on neurological sequelae to vaccination in
horses. I'm sure it's rare, but not nonexistent.
>
> This is way out of my area of expertise, but I am interested because WNV
is
> well established here on Long Island and it will be a continuing problem
for
> horse owners for the forseeable future. We had the dubious distinction of
> the first equine cases in North America. I have directed increased
mosquito
> prevention efforts toward areas where we have lost horses, but my first
> priority has to be human health. There does not appear to be a close
> relationship between human WNV illness here and equine cases. For
instance,
> we had 24 horse cases in Suffolk in 1999, but no humans, while in 2002, we
> had 6 humans, but only 2 horses (horse vaccine was used in 2002).

Unfortunately, the effectiveness of the vaccine remains unknown since
neither the vaccinates nor the unvaccinated horses became symptomatic in Ft.
Dodge's challenge trials. So many factors to consider here - the mosquito
control efforts, increasing numbers of naturally immune horses from prior
exposure, ? variations in mosquito species from year to year, etc..

 In
> addition, horses get sick later in the year than humans.

Not necessarily. Here in PA this year, the first equine case predated the
first human one (although not by much; 8/21 vs 8/31). Before intensive bird
and mosquito surveillance was in place, a positive horse was often the first
indication the virus was active in an area (that happened here in PA, in
several counties in NJ and this year a horse was the first detection of
virus activity in North Dakota - early July). This year, equine cases
predated humans in many of the states hardest hit:

S. DAKOTA: First activity noted in a positive bird sample, followed three
days later by report of the first two positive horses

MINNESOTA: Again, first four equine cases reported within days of first bird
positives

LOUISIANA: Positive equine cases January, February and May, first human not
until June

TEXAS: First positive birds reported June 18th, first equine case euthanized
on June 29th

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Received on Wed Oct 23 14:46:48 2002