Introduction
- This collection of "Frequently Asked Questions" has been
compiled during the UK Foot-and-Mouth Disease (FMD) outbreak, Spring 2001. These questions
were asked by farmers, vets, electricians, receptionists, bankers, scientists, journalists
and many other people from diverse walks of life. Although all the individuals had a great
wish for accurate information, the overall level of knowledge tended to be basic and
scanty (there were a minority of notable exceptions where people had an excellent grasp of
the issues - particularly some journalists), whilst some people were working from entirely
inaccurate information. This section (indeed the whole of the WILDPro FMD Module)
aims to equip all those affected by Foot-and-Mouth Disease with the scientific background
to the disease and the management options, and so to clarify some of the misconceptions
that have arisen.
- Information within WILDPro is entered under a strict policy that
original sources are respected and referenced wherever possible. We strive to maintain a
non-judgmental position, properly reflecting areas of difference in opinion and explaining
the issues involved.
- The information within this section has specifically brought together for
UK Vets and Farmers prior to 6th June 2001, and the issues are discussed with respect to
the UK situation. Comments refer specifically to the vaccines that would be used in the UK
(should the current policy alter), and risk assessment and legislation information refers
specifically to that of the UK Government.
- The other sections within the WILDPro Module are written to be
of relevance worldwide.
Disinfection
(For more detailed information and source references see: Quarantine and Disinfection, Literature
Reports: Disinfection, Literature Reports: Quarantine, MAFF: Biosecurity - advice for
cattle and sheep farmers, MAFF: Restocking Form A premises: A farmers guide,
MAFF: Guidance on the Storage, Handling and Movement of Animal Manures and Slurries, MAFF: Silage and hay-making, and grassland management, during Foot
and Mouth disease restrictions: guidance for farmers, MAFF: Measures
to Allow Movement of Big Bale Silage within a Protection Zone, MAFF: Advice and precautions for zoos, wildlife parks
etc)
What is the best way for farmers to protect their stock?
- The best way for farmers to protect their stock and minimise
further spread of the disease (particularly in an infected area) is by strict control of
all movement (animals, people, vehicles and any materials) onto and off the farm, combined
with rigorous disinfection. When moving items or people ONTO the farm, assume that the
world outside is "infected" and the farm is "clean". When moving items
or people OFF the farm, assume that the farm is "infected" and the world outside
is "clean".
What are the important factors for disinfection?
- For confidence that disinfectants will work to effectively kill
FMD virus, they must:
- be an approved disinfectant (see MAFF Guidelines link above)
- never be mixed with one another. Disinfectants active against FMD
virus are often acids or
alkalis (which depend on their pH for their action against the virus) and mixing would
prevent their action against the virus.
- be used on clean surfaces (they are deactivated by organic matter)
- be used at the correct concentration
- have the right amount of detergent added (if appropriate)
We wash our vehicles through a ford/splash every day. Does this
clear the vehicles of the virus?
- Washing vehicles through a ford or splash may remove
gross contamination from your vehicle. However, it will not kill the virus and will not
necessarily remove all the virus from your vehicle. Additionally, live virus may be
carried downstream from the ford or water splash.
What are the main danger areas for persistent viral contamination on the farm?
- The virus survives in the environment quite well, especially in
dung and slurry, and can remain active inside buildings for long periods (months). The
virus has spread through hay contamination and can remain active on pasture for some time.
(see MAFF Guidelines link above)
What the best way to deal with substances that may be contaminated?
- After a farm has been infected, anything that cannot be
disinfected properly must be burned or buried with the animals. Treatment/disposal of
slurry will need to be undertaken. MAFF have developed strict guidelines for disinfection
of infected premises, for the treatment of manure and slurry, for making hay and bringing
in and using of big bale silage. (see MAFF Guidelines link above)
How long should a farm be left empty before re-stocking
- When restocking, sufficient time must be left between cleaning and
disinfection and restocking. MAFF guidelines should be followed. (see MAFF Guidelines link
above.) Officially, a premises must be left at least
21 days following approval of full cleaning and disinfection before restocking. Initially
it is advisable to re-stock with only a few animals to act as sentinels. A longer period
before restocking may be suggested or required if the disease is persistent in the local
area. If a farm becomes re-infected, the entire cleaning and
disinfection process must begin again. It was suggested following the 1967-68 outbreak
that a longer period be left before restocking where sheep were involved due to
difficulties in clinical diagnosis. During the 1967-68 outbreak there were a number of
cases of disease recurrence following stocking. These were thought to be due to either:
- Infection from surrounding premises still with active virus
infection (possibly airborne)
or
- Active virus still being present on the farm premises (e.g. in
hay).
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Spread of the Disease
(For more detailed information and source references see: Foot-and-Mouth
Disease, FMD Virus, Literature Reports: FMDV Transmission,
Literature Reports: FMDV Definitive Host Species, Literature Reports: FMDV
Paratenic Host Species, Literature Reports: FMD Disease Duration to Recovery in
Individual Animals, Literature Reports: FMD Incubation Period, Literature
Reports: FMD Time Course / Persistence of Disease, Computer modelling)
How long is an animal infectious?
- In livestock, after an animal becomes infected, the virus
multiplies in the body for several days, and is released from a variety of body systems,
including the lungs (air), mouth (saliva), skin (epithelium), urinary (urine), intestinal
(faeces), mammary (milk) and reproductive systems (semen / vaginal secretions). This is
the time that the animal is most infectious. After a few days the body begins to produce
antibodies which then appear to minimise virus production and the virus infection
"burns itself out" (usually a few days after antibodies first become active). At
this point the infected animal is usually reported to stop producing enough virus to
infect other animals. The chronic signs seen so frequently after FMD Virus infection
(lameness, infertility, poor milk yield, weight loss) are due to damage done to the body
in the early stages of viral multiplication before antibodies to the virus can be
produced, and / or due to secondary infection.
What are the distances the virus can travel on the wind?
- The distance virus can travel on the wind and still cause
an infection depends on environmental factors such as humidity, wind speed etc., the
amount of virus produced, and the type and number of potential hosts downwind of the
virus-producing animals. The virus seems to travel particularly long distances over water
(up to 250km/156 miles) has been reported) although not nearly so far over land. Pigs
produce much more virus than do cattle or sheep, while cattle are the species most likely
to be infected by breathing in airborne virus. A recent study indicated that small numbers
of sheep or cattle (e.g. ten infected animals) would not be infective more than about 100
metres (110 yards) downwind and even for 100 cattle or sheep producing virus, only cattle
would be likely to be infected as little as 700 m (half a mile) downwind. At the other end
of the scale, 1000 fully infective pigs could theoretically infect cattle 300 km downwind.
Cattle are the domestic species infected most easily by wind-borne virus (pigs are least
likely to be infected by this route). Larger herds appear to be more likely to become
infected by such virus, probably because they breath in a larger total amount of air and
there is more chance that one of them will inhale an infective dose (once one animal is
infected the virus will then multiply in that animal and quickly spread to the other
animals in the herd).
How does the virus spread through so many farms and herds
so quickly and can it establish itself permanently?
- Animals with active infection, with or without clinical signs, are
the major source of continuing spread of the virus. They can produce massive amounts of
virus. Having multiplied in one animal's body the virus must find a susceptible host in
order for FMD to continue to spread. The major route of spread within a herd or flock is
by direct contact, e.g. infected animals breathing out virus and the animals next to them
breathing it in. A major way in which the virus is spread from one farm to another is by
animals which are not visibly diseased being moved. However indirect contact is also
important (airborne spread between herds occurs less often). FMD can survive for some time
in the environment, particularly when attached to animal debris, so long as it is not
exposed to acid or alkaline conditions. In this way, FMD virus moves from the infected
animal to the external environment and then on to another susceptible animal. It will then
remain active in a region so long as there are a progression of susceptible animals, that
is it will become endemic (particularly if wildlife become infected and spread virus between
different farms or areas). New born animals may then become infected with FMD virus as
they lose any antibody immunity gained from their mother, and other individuals may become
infected as their natural immunity (caused by previous exposure to the virus) wears off.
What are carrier animals and what role do they play in outbreaks?
- The issue of carrier animals has been generally greatly
over-exaggerated. Carrier animals are those individuals in which virus can be detected
more than 28 days after infection. The virus has been recovered from the throat of
Domestic sheep for up to nine months post infection and from Domestic cattle for 3 years.
Numerous scientific experiments under biosecure conditions over the decades have failed to
demonstrate transfer of virus from carrier livestock to susceptible animals. There is some
epidemiological (field) evidence suggesting that carriers may be sources of infection for
other livestock occasionally.
Which species other than cattle, sheep, pigs and goats can get
and spread FMD?
- A wide variety of species can be infected naturally
with FMD, mostly cloven-hoofed animals such as deer and antelope but also hedgehogs and
Asian elephants, among others; infection in humans is extremely rare. Hedgehogs with
clinical disease develop severe foot problems and are unlikely to move long distances.
Almost any animal - bird, mammal, insect etc. can spread FMD mechanically. Among wild
animals, scavenging animals such as crows, seagulls, foxes and rats may be most likely to
spread the virus in this manner, although movement of people and their vehicles is thought
to play a much larger role.
Do small numbers of pet animals such as sheep really pose a risk
to other animals?
- FMD is transmitted by three main routes: direct contact between
infected and susceptible animals, indirect contact (e.g. movement of infected milk or
faeces from infected animals) and windborne spread. Small numbers of llamas, pet sheep and
other ruminants are unlikely to become infected by windborne spread unless they are
directly downwind of infected pigs and would be extremely unlikely to infect other animals
downwind of them. A single pet pig on the other hand, might produce enough virus to infect
cattle five kilometres downwind in good conditions for wind-borne spread.
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Vaccination
(For more detailed information and source references see: Vaccination Overview, Literature Reports: Vaccination
Regimes, Literature Reports: Vaccine Developments, MAFF: Approach to
Vaccination of Animals in Zoos)
Will vaccination work for a hill sheep flock where a few animals might not be
found at the time of vaccination?
- In order to protect a herd of animals against FMD virus it is not
absolutely necessary to vaccinate 100% of the animals, although as many animals as
possible in an area should be vaccinated. (To have herd immunity, 80 - 85% should be
protected / immune). This should be easily achievable in the domestic sheep, pig, and
cattle herds of infected areas within the UK as the vaccines can be distributed promptly
and maintained under the optimal conditions (cool but not frozen) to retain maximum
activity.
Can animals carry FMD virus after vaccination?
- Vaccinating an animal does not make it a carrier
(the vaccine uses an inactivated (dead) virus). In vaccinated animals which have
ALSO been exposed to FMD virus, samples taken from the back of the throat have been
positive for virus infection in the days immediately after infection and it has been shown
that they may pass virus to other animals for a few days after infection. Vaccinated
animals may also become long-term carriers. However, there is NO evidence that vaccinated
animals which become carriers pass infection to susceptible animals.
Is there a test that can distinguish between infected animals and vaccinated
animals?
- Both infected and vaccinated animals will produce antibodies which
protect the animals from further attack by the virus. New serological tests which have
been validated on tens of thousands of animals are reported to reliably distinguish
between those herds which have been vaccinated and have had no exposure
to virus, and those which have been exposed to virus and consequently developed
antibodies. These tests are under consideration by the OIE, but at present ruminants with antibodies to FMD virus cannot be traded
internationally and under the present regulations a country such as the UK, if using
vaccination alongside stamping out, would not regain its FMD-free status until either three
months after the slaughter of the last diseased or vaccinated animal or twelve
months after the slaughter of the last diseased animal if vaccinated animals were not
culled.
Can vaccination cause the virus to mutate or cause disease?
- The vaccines that would be used in the UK are killed
vaccines which are manufactured to very high safety standards. There is NO live virus in
vaccines produced to European industry standards. Vaccination does not cause the virus to
mutate and does not cause disease.
What are the vaccines and how are they given?
- Vaccines should always be used as detailed by the
manufacturer. The vaccines, which all use killed not live virus, are designed for use in
domestic cattle, sheep and pigs and work fast and well in all these species. The vaccines
come in two forms - "oil emulsion" (given by intramuscular injection and used in
cattle, sheep and pigs) and "aluminium hydroxide - saponin" (given by
subcutaneous injection and used in cattle and sheep). In emergency situations high potency
vaccines may be used which increase the speed and level of protection. Immunity begins to
develop a few days after a single vaccine dose and for one-off Emergency Vaccination with
a high potency vaccine (with all susceptible animals being vaccinated), one dose may be
considered sufficient. With conventional lower potency vaccines, or if the risk of
exposure to FMD Virus was considered likely to be long-standing, a second booster dose may
be recommended after 2-4 weeks and again at 6 months (usually pigs and cattle) or 1 year
(sheep). (In endemic regions regular booster vaccinations are used). The precise
vaccination regime to be recommended would depend on the species to be vaccinated, the
vaccine used and the level of risk of exposure to the virus.
Can the vaccines be given to zoo animals?
- There is a long history of zoo animals of many different
susceptible species being vaccinated, for example within continental Europe.
Whilst it is likely that the vaccines
would provide protection to non-domestic (wild) susceptible species, they are not
tested in these species and as a result it is not known whether they reach a strong immune
status after vaccination. As the "oil emulsion" preparation can be given by
intramuscular injection, it could be administered by dart.
Can free-living wild animals be vaccinated?
- Vaccinating free-living susceptible wild animals (e.g.
deer and wild boar) would be impractical. Unlike rabies,
there is no oral vaccine for FMD and injecting e.g. all the wild deer, even using dart
guns, would not be possible. However, vaccinating farm livestock in an area would protect
wild animals indirectly by reducing the amount of virus in the area and decreasing the
risk of spread from wild to domestic animals.
Are there enough vaccines to vaccinate all Domestic animals in the UK?
- Vaccines are usually made to order in an emergency
situation, with protection for the specific virus strain. Vaccine could be made available
extremely quickly from the emergency antigen banks to start emergency vaccination in the
UK of animals in high-risk areas. It would be physically impossible to vaccinate the whole
population of UK livestock in one or even a few days and more vaccine could be made
available to complete the vaccination programme. Enough virus antigen of the correct type
to protect animals against the type of FMD virus causing this outbreak is held in the EU
Emergency Vaccine Bank and the International Vaccine Bank to produce 5.5 million
cattle-doses (11 million sheep doses) of highly potent emergency vaccine.
Who makes the vaccines and how does one get permission to use a
vaccine?
- There are three major vaccine manufacturers in Europe,
Merial Animal Health Ltd., Bayer, and Intervet. In the UK, the use of vaccines is strictly
restricted by law. In addition, the UK Government itself must seek permission from the EU
Commission before it can implementing a vaccination programme.
What is the EU Policy on vaccination?
- The EU policy is basically one of non-vaccination.
However, leeway is given allowing the use of emergency vaccination in some circumstances.
Would we still need to cull animals if we vaccinated?
- Vaccination alone is not enough to control and eliminate
FMD. However, vaccination used alongside the slaughter of infected and in-contact animals,
quarantine and disinfection would reduce the number of animals becoming infected and could
greatly reduce the amount of culling needed to eliminate the disease.
Will vaccinating stop us exporting meat or livestock for several
years?
- No. Vaccination, alongside "culling" of infected animals
and "dangerous contact animals", quarantine and disinfection is widely
recognised as allowing the disease to be brought under control in an area more quickly.
Under the present rules for international trade, FMD-free status and the export of meat
and livestock could re-start just twelve months after the last infected animal was
slaughtered. If vaccinated animals were also slaughtered, FMD free status could be
regained as early as three months after the last diseased or vaccinated animal was
slaughtered.
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Computer Models and Changing Policy
(For more detailed information and source references see: Computer Models, Control Options for Stopping
FMD Virus Spreading, Assessing the Costs (Actual and Potential)
and Consequences of FMD and its Control)
Are Computer models of FMD spread worth using?
- Computer models of FMD spread can provide useful information to
assist decision making. It is important to use the best, most accurate models of FMD
spread available, which allow for different species (including wild species) producing and
being exposed to virus, different methods of spread (direct / indirect contact, airborne)
and different environmental conditions which. Models are only as good as the data entered
into them and good surveillance information, giving data showing the present extent of
infection in wild as well as domestic animals is necessary for models to give accurate
forecasts. It is also important to remember that answers from computer models, however
sophisticated, should never be used as the sole means of making major decisions. Computer
models can assist in making a professional judgement, but must never replace that
judgement.
If vaccination works, why can't we just get on and vaccinate?
- Much of the policy of an FMD free country with an export market
(here the UK) in dealing with an outbreak of FMD is focused around minimising the time to
regain OIE FMD-free status. In order to do this OIE rules must be followed. Whilst these
rules remain unchanged (e.g. the validity of new serological tests differentiating between
vaccinated and infected animals are not accepted) if vaccine is used a longer time period
during which meat and animals cannot be exported, and the associated losses, must be
accepted.
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Laboratory Tests
(For more detailed information and source references see: Diagnosis, Surveillance and Carriers, Literature Reports: FMDV Detection and Identification,
Literature Reports: FMD Detailed Clinico-Pathological Findings)
What samples are needed for the diagnosis of FMD?
- FMD is usually diagnosed by detecting virus or virus antigen. The
best sample for this is material from fresh lesions, because this contains large amounts
of virus and positive results can be confirmed just a few hours after the test is set up
at the laboratory. Antigen can also be detected in samples of milk and of whole
heparinised blood, in the early stages of infection. The sample most useful for detecting
virus in subclinically infected sheep (and in carrier animals) is cells and fluid
(oesophageal -pharyngeal fluid sample) taken from the back of the throat using a metal cup
on a rod - a probang cup. Just a nasal swab is needed for a new test which has recently
been developed but is not yet used in the UK. As the disease progresses and the animal's
immune system responds the amount of virus decreases (some may be left in the back of the
throat (pharynx area) of carriers). In the later stages of disease and after the period of
clinical signs, clotted blood samples are taken and the serum separated for the detection
of antibody.
How are cases of FMD confirmed and how long does this take?
Cases of FMD are usually confirmed by the
detection of virus or virus antigen in samples taken from mouth or foot lesions, although
blood and milk may also be used. If there are large quantities of virus in samples from
lesions, confirmation using an ELISA (to detect the presence of virus antigen) may take only a few hours once
the sample has reached the laboratory and been set up. However, if the initial test
results are negative, attempts will be made to grow the virus in tissue culture cells to
increase any virus present before re-testing, and this may take several days.
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Environmental Damage
(For more detailed information and source references see: Quarantine and Disinfection, Literature
Reports: Disinfection, Environment Agency:
Advice on the use and disposal of disinfectants, Environment
Agency: Guidance on ash disposal arising from Pyres and mobile incinerators, Environment Agency: Licensed Landfill Sites that are Suitable for the
Disposal of Carcasses, Environment Agency: Advice on disposal
of manure, slurry and dirty water, Environment Agency: Risks From BSE Via
Environmental Pathways)
What are the effects of disinfectants used in FMD control on the
environment?
Disinfectants are chemicals which kill organisms that
cause disease. They can also kill useful, valuable and / or rare organisms. Hence our
rivers and waterways, and thereby our water sources for human use, can be seriously
damaged by disinfectants. Care should be taken with their use and their disposal. The Environment Agency states on their website that "All
disinfectants pose a potential pollution risk, particularly to rivers, streams and their
associated wildlife, and those with a phenolic content can be particularly persistent.
Sensible precautions, however, will minimise the risks."
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Wildlife and Pets
(For more detailed information and source references see: Wildlife, Zoos, Pets and other Animals, Literature
Reports: FMDV Definitive Host Species, MAFF:
Advice and precautions for zoos, wildlife parks etc, MAFF: Approach to Vaccination of Animals in Zoos)
Does FMD affect any UK wildlife species?
FMD virus is highly infective and all cloven-hooved
animals appear to be susceptible, including deer and wild boar. Severe disease has also
been reported in hedgehogs in Britain. Numerous other animal species have been infected
experimentally with FMD virus, including cats, dogs, rats, mice, moles and water voles,
but it would appear that for many species infection occurs only as a result of massive
virus exposure or if injected with the virus.
Would it be possible to control the disease in wild animals?
Control of any disease in wild animals is difficult once
it becomes established. Many wild animal populations are too widely dispersed for the
virus to pass to sufficient new animals, so that FMD would be likely to die out in the
population over a period of time. However, FMD has been known to persist in wild animal
populations, including deer, and to return from wild populations into domestic stock. The
best way to control disease in wild populations is to stop the disease getting into the
population in the first place.
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