LIMITED VACCINATION SCHEME TO CONTROL AND ERADICATE FOOT AND MOUTH DISEASE FROM THE CYNEFIN SHEEP OF WALES WITH SPECIAL REFERENCE TO THE BRECON BEACON NATIONAL PARK.

 

 

INTRODUCTION

 

Vaccination of cynefin (hefted sheep) on common land against FMD

 

There is an emergency in the Brecon Beacons National Park. The sheep on the Brecon Beacon, Pen y Fan, and on the sugar loaf to the south, are being slaughtered now as a result of the outbreaks in Libanus and Crick Howell. The proposed vaccination programme needs to be urgently considered as it is makes slaughtering out the hefted sheep completely unnecessary.

 

Where common land is wholly or partly within infected areas or where a piece of the common land is in an infected area, as with the Brecon Beacons National Park, vaccination of the sheep on the common land is proposed. Also the vaccination of all sheep waiting to go up to the common land from their holdings and tack. Also the vaccination of any other receptive domestic stock on the common land such as cattle and goats of which there are small numbers. There is no veterinary need to kill vaccinated animals, indeed the intention is to preserve them.

 

The sheep on the Welsh common land, upland for the most part, are called cynefin literally sheep that have their own habitat. The sheep in the West of Britain and the rare breeds derive from the sheep successive peoples brought with them when they migrated here: the Celts, the Romans, the Vikings and later imports. In the hefted sheep (which are genetically often local strains) knowledge of the heft on the common land is passed from ewe to ewe lamb. The hefted flocks have passed this knowledge down since the days when a shepherd lived with his flock on the mountain and cared for and protected them.

 

The modern sheep also need attention to their welfare- shearing, dipping, foot trimming and foot bathes, vaccination against environmental or enzootic infections and lower winter pastures where they may be fed in bad weather and lamb in the spring. Some ewes are sold to lowland farmers to crossbreed for hybrid vigour and the making of larger lambs.

 

These sheep altogether form an irreplaceable heritage and the basis of pastoral farming in the West. This farming is based on grass- as pasture, silage, haylage and hay. The cynefin are responsible for the appearance of our landscape and its biodiversity; the open mountain and moor where people like to roam freely for recreation, and the fields with their hedgerows and trees in areas below 300m which appeal to the eye of tourists, as well as providing a diversity of habitats for wildlife.

 

The sheep on an area of common land such as the Brecon Beacons National Park are essentially one flock. They are in direct contact or indirect contact with all the other sheep. A virus infection such as FMD can spread among this population.

 

 

FMD vaccine

 

The vaccine proposed is the killed (inactivated) vaccine- the modern vaccine of the type that has been in use for about 45 years. Despite the fact there are 7 serotypes of FMD in the world a

 

monovalent vaccine can be used because the infecting strain of virus, serotype O subtype PanAsia has been isolated and the VP1 protein sequenced early in this epidemic. The serotype O vaccine contains the Manisa strain and from the sequence data can be anticipated to produce cross-reacting neutralising antibody. The Dutch have proved this as they had no further outbreak with our virus 5 days after completing vaccination.

 

The killed vaccine does not infect the vaccinated animal. The vaccine acts as an antigen stimulating the immune system to produce a virus specific response- the protective neutralising antibody. Either a high payload vaccine where one dose is required for primary vaccination, oil-adjuvanted if this is available, could be used or a commercial vaccine requiring 2 doses separated by 3 weeks. The aim of vaccination is to raise a good level of protective antibody in sheep.

 

It is proposed to administer vaccine without waiting for the results of a baseline blood drawn from every animal at the time of vaccination. Rather than attempt to detect and cull infected animals, or antibody positive animals (absurd in the circumstances of the proposed vaccination programme) it is proposed to rely on the vaccination programme to control FMD infection on the common land. Killing hefts and contiguous hefts of sheep will lead to a permanent loss of sheep from the common land. The aim of this proposal is to prevent that.

 

There are some 8 million cattle doses of killed serotype O vaccine held in Europe, equivalent to about 24 million sheep doses. This is in addition to the 500,000 cattle doses the UK holds. USA also has a stockpile of vaccine. Clearly there are enough doses of vaccine available for a vaccination campaign of sheep on a large scale.

 

Merial have told me their commercial vaccine costs about 50p a shot. This is clearly an economic option compared to the indefinite continuation of this epidemic and the cost it is imposing on the British economy.

 

 

Efficacy of vaccine for sheep

 

The response of sheep to oil-adjuvanted vaccine given IM is nearly 100%. Sheep respond well to vaccination. The vaccine protects against disease. The vaccinated sheep is less likely to become a carrier if infected than unvaccinated sheep so less carriers are generated. Sheep may also be protected against infection if good levels of antibody are raised. Failed vaccinations will leave only a small number of sheep still receptive to infection.

 

Dr Donaldson has recently written that the emerging serological evidence suggests that infection has progressed slowly through sheep flocks during the UK epidemic. The PanAsia virus is better adapted to sheep than other strains of FMD. Little attention has been paid to vaccinating sheep during this epidemic- I have heard members of the Science Committee say that it is not possible for various reasons. However I and other sheep farmers think it is possible to vaccinate over 80% of sheep on an area of common land. Subclinical infection is thought to be endemic in parts of the UK sheep flock. Since sheep hitherto have been significant in spreading FMD virus in this epidemic, (in contrast to the 1967  1968 epidemic with an O1 strain but not the Pan Asia subtype which first emerged in India in ~1990) it would seem to be logical to vaccinate sheep.

 

 

 

 

There is much less experimental work on sheep than cattle. The one small study I have seen shows sheep respond better to vaccination than cattle. Though a small % of partially vaccinated sheep could be infected by contact with 2 acutely infected piglets (serotype O Campos subtype) none

became carriers. Vaccination was more successful in preventing infection in sheep than in cattle. (Studies on the persistence of FMD virus in Bovines, Ovines and Llamas, Fondeveila N et al, ~1994).

 

Experimental work has put a question mark beside the vaccination of cattle. (Transmission of FMD by vaccinated cattle following natural challenge, AI Donaldson et al. Res. Vet. Science, vol 46 p9-14, 1989.) However in practice, in natural farm environments, vaccination programmes of cattle alone have led to the control and eradication of FMD virus in both epidemic and endemic infections.

 

Human vaccines are also imperfect yet may work very well in the field and have given spectacular success in eliminating small pox. Poliovirus is also due for elimination from the world in the next 2 years or so. There are 3 serotypes of poliovirus. Poliovirus is in the same virus family as FMD, the Picornaviridae. Humans shed virus for 6 months or more and the virus is hardy in the environment and stable at acid PH. It can be isolated from sewage. The virus has been eradicated from populations by vaccination with killed vaccine. No attempt has been made to sterilise the environment nor to restrain humans to biosecure locations. Yet outbreaks of poliovirus infection are controlled by vaccination and the virus is eliminated from populations.

 

 

Herd immunity

 

The goal is to vaccinate more than 80% of all receptive domestic stock on common land, to get as near to 100% as possible.

 

At least 80% of animals must be fully vaccinated and protected in order to halt the spread of FMD. The chain of acute infections that comprise this epidemic will be broken. There will be insufficient numbers of unvaccinated animals to spread the virus during the acute infection phase- an acutely infected unvaccinated animal will be very unlikely to contact another unvaccinated receptive animal. This is the principal of herd immunity by vaccination to control and eradicate a virus infection from a population.

 

 

Carrier animals and vaccination

 

All vaccinations can be overcome with exposure to a sufficiently large dose of virus, in humans and in animals. However sheep infected subsequent to making a good response to vaccination have never been implicated in the spread of FMD.

 

Sheep with a good level of protective antibody may be infected if exposed to a large dose of virus such as from an acutely infected pig, see above. Pigs shed 1000-fold greater concentration of virus than sheep or cattle. In the vaccinated sheep the acute infection will remain localised to the mouth and upper respiratory tract by the pre-existing protective antibody in the blood that prevents viraemia and consequent spread of virus throughout the body infecting organs such as muscle and mammary gland. A low concentration of virus is shed, probably complexed to antibody rendering

 

 

the virus less infectious. It is shed in saliva or respiratory droplets at too low a concentration to infect another vaccinated animal (or an unvaccinated animal).

 

 

Elimination of FMD virus from the common land

 

On the common land vaccinated sheep are unlikely to be exposed to a large dose of infectious virus sufficiently large to infect a vaccinated sheep.

 

Pigs are not on the common land (few have been infected in this epidemic). The virus in this our current epidemic, the serotype O Pan Asia subtype, is shed in lower concentration by infected animals including sheep and cattle than previous strains of FMD. This has resulted in a revision of the risk of airborne spread in our epidemic. Insufficient numbers of sheep and cattle have been acutely infected simultaneously to generate a plume of virus aerosol to infect animals 200 m away; 100 infected cattle or sheep are required to infect cattle 0.2 km distant, and 1000 infected cattle or sheep to infect sheep 0.2 km distant. (Relative risks of the uncontrollable (airborne) spread of FMD by different species, AI Donaldson et al, Vet. Record, vol. 148, p602 604, 2001). Infection on the common land will be by direct contact with another infected sheep or by contamination of pasture mainly by other infected sheep, an indirect contact.

 

Unvaccinated stock animals and wild receptive animals should form no more than 20% of the total receptive animal population on the common, preferably less. In this way FMD infection will also be eliminated from the wild animal population such as deer as well as the domestic stock.

 

Degradation of the virus contaminating the environment will inevitably take place. The amount of time this will take is not accurately known but 6 weeks is probably more than enough time. The uplands are acid and the virus is sensitive to both acid and alkali rapidly loosing infectivity when the PH drops below 6.

 

 

Unvaccinated carriers and elimination of virus

 

The acute phase of infection is cleared in 3 weeks. Some sheep remain carriers though for a shorter time than cattle. Carrier sheep have cleared infection from their body except for the oropharynx. This shed virus cannot be grown in tissue culture. The shed virus is not infectious unless neutralising antibody is first detached from the virus before inoculation of tissue culture. Sheep can carry the virus for up to 9 months (5%) but the majority of carrier sheep clear FMD virus by 3 months.

 

The subclinical spread of FMD infection in flocks of sheep will have generated many unvaccinated carriers. There is concern that infected vaccinated animals can become carriers though this is much less likely in sheep than cattle. Also vaccination at the time of exposure to infection or very early in the incubation period may also result in carriers. In any population of sheep that have been infected there are likely to be carriers.

 

The only examples of carrier animals transmitting infection to another animal are historical by contact in the field. The historical instances were circumstantial evidence for an outbreak starting by an unvaccinated carrier coming into contact with unvaccinated receptive domestic animals. Experimental conditions mimicking the natural environment have never succeeded in transmitting

 

 

infection from unvaccinated carrier animals to unvaccinated receptive animals. Vaccinated sheep have never been implicated in spreading FMD either in the field or experimentally.

 

It is believed that an unvaccinated carrier animal (sheep or cattle) can become infectious again as a rare event perhaps because of some stress- the one in a million chance. If carrier animals are surrounded by vaccinated animals during the period of carriage then the virus cannot be transmitted. This ensures elimination of FMD virus from the population.

 

After completing the primary course of vaccination there is an option to give one booster dose of vaccine. This can be given at 4 to 6 months of age to give one years coverage with protective antibody so that any carrier sheep in a vaccinated flock cannot transmit the infection during this time. There is no need to screen for carrier sheep. All carrier sheep will have cleared the virus by the time the vaccine induced antibody fades at about one year.

 

The 2002-generation of lambs will be unvaccinated, only their dams were vaccinated. By 6 months of age the maternal antibody they derived from colostrums will be gone. Monitoring later by checking all the next years lambs at 6 months of age for FMD infection will disclose whether FMD is eradicated.

 


 

Procedure

 

1) Apply vaccination to all sheep and any other receptive domestic stock, lambs calves and adults, gathering them into pens on the common land.

 

2) Ear tag with an individual number all stock with individual red ear tag number series for each common (1 to 99,999)* and a large hole in one ear.

 

3) Vaccinate IM with oil-adjuvanted vaccine immediately with a separate syringe and needle for each individual sheep or animal.

 

4) Draw blood with the same needle and syringe and record individuals heft and number on blood sample.

 

5) Release vaccinated ear tagged animals.

 

6) 3 weeks later gather and pen the hefted sheep on the mountain again and reapply vaccination to all stock on the common land or upland (unless high payload vaccine is used when one dose only is given).

 

7) Ear tag each individual vaccinated for a second time with a small red ear tag* punching a large hole in one ear and pitch-mark fleece or hide with indelible and highly visible colour*.

 

8) Any animals without the individually numbered ear tags used in 2) above go through the procedure 2) to 5) above.

 

9) Release twice vaccinated double ear tagged and pitch-marked animals (and any first vaccinated animals)

 

10) Catch any animals with unmarked fleece or hide in 3 weeks time and go through steps 7) to 9) above.

 

11) Give booster dose 4 to 6 months later and insert a third red ear tag* (possibly electronic tagging* could be done at this time)

* = Compliance with EU directives; that vaccinated animals are individually identifiable and fully vaccinated.

 

 

Notes on the procedure

 

The means of gathering handling and penning the animals should be such as to minimise the spread of virus from any infected animals at the time of gathering. This is an inherent hazard of interfering with hefted animals on the common.

 

There is no need to separate into the different hefts, no need to touch or examine any mouths. Smallish pens for about 200 animals could be erected on the common and the animals go through a race(s) for tagging, vaccinating and blood sampling.

 

Animals with virus in the bloodstream, asymptomatic viraemic animals, could be a source of infection to many other subsequent animals on a contaminated sharp. Thus the ear tagging should be as bloodless as possible and pliers could be dipped in glutaraldehyde between each animal. The blood sampling should use a different needle and syringe for each animal. This would also avoid contamination from a positive animal giving a low false positive for antibody or virus on the sample from a subsequent animal. One possibility to be considered is that the vaccine be given IM with the same needle and syringe for each animal as used subsequently for blood letting from a vein from that same animal. (The volume of vaccine is likely to be 1 or 2 ml and the volume of blood required about 8 ml; a 10 ml syringe could be used but if vacutainers must be used this would not be possible.)

 

The team doing the ear tagging, the vaccinating and the bleeding should be different for each pen.

 

Reliance on laboratory results at a later date for diagnosis is most appropriate as clinical diagnosis of FMD is unreliable. The samples taken at the time of the first dose of vaccine can be tested for antibody and the presence of FMD virus. The samples may simply be stored and a proportion only tested. They are there for later reference; a baseline sample can be essential in diagnosis of virus infection or for sero-epidemiology.


 

 

Rationale of vaccinating receptive animals to be released to the common land from their holdings

 

Many animals normally released to the common land to heft the ewe lambs for example, are still on their holdings or in tack. The harvesting of silage or hay and the preparation of pasture for winter are prevented. All these animals could also be vaccinated and released subsequently onto the common land.

 

The aim is to flood the common land with vaccinated animals (as near to 100% vaccinated as possible) to ensure unvaccinated animals and receptive wild animals are in the smallest minority that can be achieved. The common land can be reopened to walkers and other users such as pony trekking. It will not matter if virus contaminates the common land. Virus in the environment will degrade within one month (uplands are acidic).

Once released to the common land animals should remain there for at least one month, preferably 2 months. The common land and the holdings (to which tack animals can be returned) would be designated a vaccination zone complying with EU directives. The fully vaccinated animals can be moved from their holdings to the common land. Movement out of a vaccination zone is not allowed for one month after completion of vaccination. If we vaccinate now all fully vaccinated animals can be moved back to their holdings or to tack pastures in the autumn (November).

 

Procedure

 

-Vaccinate all the sheep and other receptive animals to be let out on the common as above steps 1) to 9)

-Then release to the common land when fully vaccinated.

-Give a booster as in step 11) above.

 

Notes on the procedure

 

There is no need to vaccinate fat lambs left behind on the holding. These could be moved to market by November and will not remain to be in contact with sheep and other animals returning from the common land. Similarly breeding ewes, which again could be sold before November in autumn sales.

 

All sheep remaining on the holding which will be there over winter and those to be mixed with the sheep returning from the common land in tack pasture will also have to be vaccinated. Only cattle going onto common land need be vaccinated, not cattle remaining behind on holdings. Cattle will be kept in from November and will not mix with sheep and be in contact with them.

 

As acutely infected animals will not be returned from the common land in the autumn (November) there should not be a resurgence of infection in November and December.

 

Rationale for monitoring eradication of FMD virus from vaccination zone

 

There are tests to detect infected animals and we will be expected to apply them in our effort to convince the OIE and our FMD-free trading partners that we have eradicated FMD. In the vaccination zone monitoring after stopping vaccination can prove the eradication of FMD from this zone. The last vaccination would be given in February 2002. The protective level of antibody will have declined significantly by July 2002 in the vaccinated animals and the last carrier sheep will have cleared infection by then. The 2002 lambs after screening can go into the human food chain.

 

Procedure for monitoring eradication of FMD from the vaccination zone with notes

 

Cattle on the holdings can be monitored clinically for infection. If there is any clinical sign of infection they should be tested on at least 2 occasions 5 days apart to make sure the evidence of infection is obtained before they are slaughtered and a test such as PCR applied. They will act as sentinel animals especially if mixed with sheep on the same pastures in April or May 2002.

 

 

The newborn lambs in the 2002 season will imbibe maternal antibodies in colostrum. These will be degraded by the lamb and by 6 months of age none or a trace will be detected if the lamb has remained uninfected. (Carrier animals do not transmit FMD infection to their newborns excepting Wild Cape Buffalo in South Africa that transmit the SAT serotypes and maintain FMD even in small isolated populations.) The lambs from vaccinated holdings can be checked for antibody before going for slaughter. If any give a high antibody result samples should be taken for virus detection. Every effort should be made in the laboratory to prove infection or rule it out. The spring crop of unvaccinated lambs will act as sentinel animals to detect residual FMD infection like the cattle.


 

Compliance with EU directives

 

1.                        Extent of geographical area in which emergency vaccination is to be carried out.

The common lands in the infected zones in Wales and the holdings that graze animals on the common land. This would be called the vaccination zone.

 

2.                        The species and age of animals to be vaccinated.

All sheep on the common land > 1week in age regardless of sex or gestational status. Any other receptive domestic species on the common land- goats and suckler cattle of which there are small numbers.

As above all those animals awaiting release onto the common land- in particular hefted sheep and their ewe lambs and cattle and goats. Any sheep to remain on the holding in winter or go into tack in the late autumn should also be vaccinated.

 

3.                        The duration of the vaccination campaign.

Initial immunisation course. This will be completed within 30 days or less. One booster by February 2002 optional. The reason for giving a booster is to give immunity for one year when all carrier sheep will have cleared the virus.

 

4.                        A specific standstill of vaccinated animals and their products.

No movement out from the vaccination zone until 30 days after the primary course of vaccination is completed. Movement within the vaccination zone may be allowed to remove rams from the common land.

 

5.                        The special identification and registration of vaccinated animals.

Each animal will have ear tagging and ear marking, also electronic tagging. The special registration will be through the electronic tagging and the computer print out of serum save or serology result per animal- this should record the individual number, the date, the common, where bled on the common or the holding, the heft or holding number and the sex.

 

6.                        Other matters appropriate to the emergency situation at the Brecon Beacons:

a)                       FMD may be endemic in hill flocks of sheep in parts of Britain. If the virus is spreading silently in the hill flocks then even after a negative test the animal may be subsequently infected. All the sheep on a common are directly or indirectly in contact with each other.

b)                       Denuding the common land of the hefted sheep flocks will end the ancient pastoral foundation of agriculture in the West of Britain (it is not suitable for arable crops). Nor are sheep suitable for intensive factory farming (overgrazing is a separate issue).

c)                       The ancient genetic lineages of British sheep going back 2000 years and the biodiversity of sheep will be gone forever. Suitable stock for the uplands and common land may not be available again should anyone be persuaded to camp on the mountain all summer with every flock to attempt to re-heft over some years.

d)                       Vaccination without slaughter will allow the survival of these flocks of special genetic stock adapted to local conditions and their special knowledge passed from ewe to ewe- the survival of the cynefin.

e)                       The landscape will change without any grazing and large areas could be difficult to manage, becoming impenetrable with dense scrubland changing to secondary woodland with loss of species and biodiversity and be unavailable for walkers or tourists to enjoy. Balanced grazing is required, with cattle or ponies and sheep.

f)                        Vaccination of all domestic stock on the common land will control and eradicate infection from wildlife such as deer as well as the hill flocks.

g)                       Resurgence of infection when sheep are brought down from common land is avoided (this is what happened at Crick Howell when 3000 sheep were brought down to 4 farms for shearing from the Sugar Loaf part of the Brecon Beacons National Park; the cattle went down with classical FMD a few days later on the 14-15 July).

h)                       The National Parks could immediately be re-opened for walkers and other recreational activities  biosecurity can be relaxed.

 

 

 

i)                         Welfare problems for farm animals can be avoided by releasing winter pastures from overgrazing and allowing the preparation of winter feed such as hay or silage by moving the hefted flocks waiting to go to the common land off these fields. Also the unvaccinated fat lambs remaining on the holdings can be sent straight to a designated abattoir from 30 days after the primary vaccination is completed. Ewes for breeding can be sold on the market 3 months after the primary course of vaccination is completed if their baseline blood before vaccination was antibody negative. Flocks of fully vaccinated sheep can be moved to biosecure tack not mixing or in contact with unvaccinated animals, and back to their holdings again in Spring 2002 for lambing. The EU will check that the movements of sheep and bovines within and out of the vaccination zone comply with their recommendations.

j)                         Eradication can be proven by testing the 2002 crop of unvaccinated lambs before they go to market, when they are about 6 months old. They will have cleared the maternal antibody by this age. Cattle and calves can also be screened on the holdings in the vaccination zone.

k)                       An exit strategy is proposed which can be applied to the upland areas of Britain as well as the Brecon Beacons. The rural population need a modus vivendi, a way to return to normality as far as possible whilst they live through the period of time when Britain is an FMD-infected country. The movement forward to a new agricultural policy needs to be controlled and managed positively.

l)                         Vaccination also allows the time for the re-opening export market to be anticipated as an FMD-free country- If the last vaccine doses are given in February 2002, the export market as an FMD-free country may be started in February 2003 according to OIE rules (provided there are no further outbreaks after Feb 2002).

 

 

 

 

Dr Ruth Watkins

BSc Hons, MBBS, MSc, MRCP, MRCPath

 

 

Clinical Virologist

18 July 2001