[Jacob-list] Vets opinion: vaccinations/FMD

[Thomas Simmons]

Forwarded with permission from a vet who has dealt with vaccinated 
animals and how to distinguish them from unvaccinated animals. Keep in 
mind that there are other tests not mentioned that have been developed 
for use in Africa, which typically deals with multiple strains at a time. 
But this is info from a vet who has dealt with the issue regularly and 
recently. 

>  > Date: 29 Apr 2001
>  > From: Steve Angus <SteveA at spc.int>
>  >
>  > FMD: telling the difference between vaccinated and infected animals
>  >
>  > ["Mason said veterinarians needed a vaccine that acted faster and also
>  > made it possible to pinpoint the difference between vaccinated animals
>  > and animals infected with the virus. The vaccine now available takes
>  > several days to take effect. Current [accepted] tests are unable to
>  > distinguish between cattle, sheep and pigs which have been vaccinated
>  > and those which have the disease." A quote from ProMED digest
>  > v2001.n095.]
>  >
>  > While working as the epidemiologist for the national veterinary
>  > epidemiology unit in Bolivia (Jan 98 to Dec 2000) I regularly spend my
>  > time investigating FMD outbreaks and surveying parts of the country
>  > for evidence of viral activity (i.e. evidence of recent past
>  > infection). In Bolivia there was sporadic vaccination against FMD
>  > which makes telling the difference between vaccinated animals and
>  > animals that had previously been infected critical to this work.
>  >
>  > There are a number of diagnostic tests which can be used to
>  > differentiate between infection and vaccination, most of which rely on
>  > the detection of antibodies for non-structural proteins. Although
>  > these tests do have the habit of showing up occasional false positives
>  > (mainly in older animals with a history of regular vaccination) it is
>  > possible to work around this problem by considering the epidemiology
>  > of FMD.
>  >
>  > FMD is not a disease of individual animals, rather herds of animals.
>  > Similarly animals are vaccinated on a herd basis, not as individuals.
>  > Hence, it is possible to tell whether herds of animals have been
>  > infected since it makes no biological sense that only 1 animal in an
>  > unvaccinated herd would be infected with FMD. In very extensive beef
>  > properties in South America a prevalence of about 15% was normal and
>  > in intensive dairy systems it could be over 80%.
>  >
>  > Identifying an infected vaccinated animal is very difficult and
>  > involves attempting virus isolation of probang samples from cattle
>  > tonsils.
>  >
>  > As to including a marker with the vaccine (something which will
>  > differentiate infection from vaccination) I accidentally came across a
>  > marker for vaccinated animals. Due to regulations and past history
>  > trivalent vaccine for types A,O and C were used in Bolivia. However
>  > virus type C had not been isolated from Bolivia or any of its
>  > neighboring countries for more than 6 years.
>  >
>  > Animals carrying antibodies to type C were invariably found to have
>  > been vaccinated as were animals with antibodies to all 3 virus types.
>  > Infected animals have type specific antibodies to the outbreak. Since
>  > any FMD vaccination program would be under strict ministry of
>  > agriculture control why would there not be a system of marking
>  > vaccinated animals, perhaps with distinctive ear tags as with S19
>  > brucellosis vaccination in many countries.
>  >
>  > This would save some of the problems created by individual animals.
>  > Alternatively ear punching could be used as a more permanent marker,
>  > but again animals are vaccinated on a herd basis and not as
>  > individuals and would presumably be under movement control so the
>  > occasional loss of an ear tag would be irrelevant.
>  >
>  > Should FMD virus remain in circulation in the wild deer population of
>  > the UK,  then vaccination will again become a very attractive option.
>  > Indeed, had the vaccine been used when the epidemic was first
>  > recognized to have been "out of control" at the beginning of March
>  > [2001] it may have saved the slaughter of more than 2 million head of
>  > livestock, a figure which could double before the end of the outbreak.
>  > All this at what cost economically and socially to the people of the
>  > UK?
>  >
>  > --
>  > Dr. Stephen D. Angus BVMS MSc PhD MRCVS
>  > Veterinary Epidemiologist
>  > Regional Animal Health Service
>  > Secretariat of the Pacific Community (SPC)
>  > Suva, Fiji
>  > <SteveA at spc.int>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.pairlist.net/pipermail/jacob-list/attachments/20010504/6df6ef7a/attachment.htm