Written for warmwell in September 2007
FMD Vaccine and virus challenge at the time of vaccination
By Dr Ruth Watkins BSc Hons, MSc, MBBS, MRCP, MRCPath.
When a killed vaccine is used in an outbreak situation including FMD - and FMD vaccine provides solid protection from infection with one dose of the high potency vaccine - there are occasional instances when either the vaccinee has been exposed to virus just before vaccination or in the first few days afterwards.
If the vaccine is given around the time of infection particularly in the few days after exposure, it can modify the infection. The immune response to the vaccine somewhat precedes that to the virus which is more slowly getting underway early in infection because the vaccine is a relatively large dose of highly immunogenic adjuvented virus protein (the structural virus proteins but not the non-structural virus proteins are included in the vaccine). The high potency vaccine is designed to produce a good level of protective anitbody by 10 days after the inoculation is given.
If the incubation period should be changed by prolonging it, or the exhibition of any symptoms and signs should be diminished, and virus clearance delayed, this is quite normal in human and animal virus infections when killed vaccines are used. It is not an attribute special to FMD vaccine. To suggest that "this is what happens with foot and mouth vaccine" just displays ignorance of infectious disease in general and vaccination in particular. (This is one of the problems of scientists in labs; they usually have no specialist training generally in infection or virology, nor any experience in the field. Their focus is narrow upon their subject of research, valuable illuminating and relevant though this might be).
If vaccination was used on a farm where there was - unknown to the vets- infection early in the incubation period, or exposure a few days after vaccination so that a few infections modified by vaccine occurred, this farm would be detected on screening during surveillance. All animals infected by the virus make antibodies to the non-structural proteins and so the the antibody test to these would be positive (The test is negative if the animals are only vaccinated as they can only have antibodies to the proteins presented in the vaccine, the structural proteins.). The test for anitbodies to non-structural proteins is validated on a herd or flock basis.
All the animals on the farm where any tested positive to non-structural antibodies would be culled as the premises would be classified as an infected premise on screening. (As per EU Directive Article 57 paragraph 3 p 29)
Even so, the virus infection would be limited to that farm.. 5 days or so after vaccination antibodies to disease have developed so the virus cannot continue the chain of infection. It will not be able to spread -neither on that farm nor into the vaccinated neighbouring farms
It might be thought then, that killing the animals on such a farm to be entirely gratuitous. However FMD can give rise to an infectious carrier state particularly in cattle when the virus may be shed from the oropharynx intermittently making it hard to reliably detect such animals. The antibody test to distinguish animals infected by virus may not be relied upon to clearly discriminate infected from vaccinated animals on a single animal basis with reliable accuracy in every individual case. Also a farm on which there have been infections must be cleaned and the dung appropriately disposed of.
FMD vaccinated animals on uninfected farms are the ones that should not be destroyed. The possession of protective neutralising antibody prior to infection changes the whole outcome if a vaccinated animal should be exposed to FMD. If a vaccinee should somehow come across the virus (which is unlikely in a vaccinated herd unless there is exposure to infected deer or fomites) it is either completely protected against infection ( the commonest case - which is why FMD vaccine is so good) or, if infection should occur, it would be limited and the animal does not become an infectious carrier.
Antibody to killed vaccines will eventually fade, and become undetectable, so that if FMD remained in the environment vaccination would have to be boosted perhaps annually or maybe more frequently in pigs. In actual practice of using FMD vaccination to control an outbreak this rarely proves necessary as the infection has been eliminated by one round of vaccination.
( In poor countires where FMD is unchecked infected animals can have complications and sustain injury such as myocarditis - particularly associated with serotype O - and oxen for example can be rendered useless from this complication of FMD infection. Vaccinated animals do NOT sustain injury from myocarditis.)
The rules in the UK on FMD vaccination have clearly been formulated to make it as unlikely as possible that we should use vaccination. They are bureaucratic rules to protect the UK and EU meat industry. Unfortunately, the stakeholders meetings on the subject of vaccination held around the country took place not to consult and listen but rather to be able to say that consultation has taken place. There is no obligation on the officials to take any notice whatsoever of anything said or submitted by those who disagree with the policy.
September 17 ~ Vaccinated animals can be moved within national borders
Some farmers are under the misapprehension that animals can never be moved once vaccinated except to slaughter. Under the present Article 63 of the EU Directive they cannot be exported - (even though there is no valid scientific or veterinary reason why not) - but there is no ban on vaccinates moving freely within the UK once FMD status has been regained. Although with vaccination to live this is supposed to take six months, there is provision under Article 62 " .. to withdraw the restrictions applied in accordance with this Directive after the clinical and serological survey provided for in Article 56 and the measures provided for in Article 57 have been completed and confirmed the absence of foot-and-mouth disease virus infection." - a let-out clause that seems to allow for some degree of common sense.
The mindset that balks at vaccination is, in any case, likely to have to shift very soon. French Agriculture Minister, Michel Barnier, very concerned about the seriously escalating cases of Bluetongue throughout Northern Europe (See Bluetongue page) is now calling on the EU Commission for a community-wide vaccination programme against Bluetongue and for support to be given towards the urgent supply of relevant vaccines before the originally expected time of Summer 2008.
With such acceptance of vaccination for Bluetongue as we are seeing in France and much of Europe now, the mindset is certainly changing - and if for Bluetongue then it would be illogical for the outdated rules on FMD vaccinates to continue for much longer within the EU.
September 17 ~ Although the paragraphs on meat from the vaccination zone make one's head spin, they are not quite as complicated as they seem.
Under the present Directive , vaccination to live ("protective emergency vaccination") means that animals from around the outbreak are vaccinated and allowed to live out their “normal” life. 30 days following vaccination, fresh meat produced from vaccinated cattle, sheep and goats, deboned and matured, can be marketed with a health stamp inside the EU. Pig meat may be refused for six months by Member States who wish to do so, otherwise heat treated pig meat products can be marketed within the EU. However, within the country itself, things are simpler. Article 58, once disentangled of its legalese, says provided that fresh meat is properly identified, contains no part that could harbour virus (Annex 8) and kept separately from unvaccinated meat, meat and milk can be sold freely inside and outside the vaccination zone.
Milk has to be pasteurised or sterilised - which it already is.
It should be added that an EU Discussion document (not online) from last October said:
"...the OIE has recently stated in two letters that their own experts and those at the world reference laboratory, consider that there should be no reason to identify/label products from vaccinated animals, and that FMD vaccination does not differ from those vaccines already largely used against other diseases that may affect the same animals, without any adverse effect on consumers...."
".....correct, informative and trustworthy information must be communicated from everyone involved: scientists, veterinarians, government and national food safety authorities, farmers, industry, retailers, multinational food chains and consumer organisations."
September 17 ~ Misinformation about vaccinates
It has been worrying to hear uninformed comment, about how vaccinated animals can get infected, being aired in the press and online. "One in five vaccinated animals carry and display signs of the disease" said a Surrey farmer - wholly erroneous information - but which is likely to be believed because it was on a BBC page on Saturday.
Vaccination may not be a silver bullet - but it is very close to being one. Ruth Watkins has written for warmwell a careful explanation of vaccine and virus challenge. Dr Watkins' is one of most knowledgeable virologists in the UK on this subject. She now farms - not as a hobby but with absolute commitment - and her life outside the confines of the lab gives her a special perspective. Without attempting to gloss over the realities, she shows that the present vaccines are excellent:
"The possession of protective neutralising antibody prior to infection changes the whole outcome if a vaccinated animal should be exposed to FMD. If a vaccinee should somehow come across the virus (which is unlikely in a vaccinated herd unless there is exposure to infected deer or fomites) it is either completely protected against infection ( the commonest case - which is why FMD vaccine is so good) or, if infection should occur, it would be limited and the animal does not become an infectious carrier." (see article)Delaying vaccination - holding on to see if we can manage without it for the sake of the livestock trade - did NOT work in August. Gambling yet again - when the animals infected in Egham had old lesions meaning that the virus could be incubating in other animals anywhere in the region of Egham or beyond - is inexplicable.
Of course we must work on getting the EU's arcane and unfair rules changed but right now - vaccination works. It deprives the virus of the ability to spread - and FMD dies. The alternative of waiting and hoping - and killing - has been shown to be far, far worse. As we saw so often in 2001, the culling of livestock all together can terrify and stampede them - with the distressing and avoidable consequences of Saturday's miserable fiasco.
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