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Foot and mouth disease (FMD)

This disease can affect all pigs. The key clinical signs include lameness vesicles and blisters; salivating pigs. This disease is notifiable – contact your vet and local authorities if you believe this disease is affecting your herd.

Background and history

FMD is a vesicular disease. There are four vesicular diseases of pigs which are difficult or impossible to differentiate clinically: FMD, swine vesicular disease (SVD), vesicular exanthema (VES) and vesicular stomatitis (VS). Of these, FMD is the most widespread and important with SVD being of secondary importance in some regions (e.g. the EU).

This disease should always be considered if sudden widespread lameness appears. In all countries it is notifiable and must be reported to the authorities with all speed.

FMD is the most important restraint to international trade in animals and animal products. Consequently, large sums of money have been invested in control and eradication programmes and also into research. As a result more is known about the FMD virus than about almost any other animal infection.

It generally produces severe disease in pigs.

If you live in an FMD fringe area that is also free of SVD you should be aware of what early clinical signs would make you suspicious and what you should do if you suspected them in your herd. If you farm in an endemic area or a fringe area in which SVD is present then you should try to be more knowledgeable.

If you farm in an FMD-free country that takes sound precautions against its entry, the risk to your herd is negligible (unless you farm in California where vesicular exanthema may pose a very small risk).

Among farm animals, pigs, cattle, sheep, goats and deer are susceptible. In addition, wild and domestic cloven hooved animals such as hedgehogs and rats are also susceptible as are elephants.

Clinical signs

  • Sudden widespread lameness.
  • Affected pigs salivate.
  • Blisters or vesicles are evident on the skin of up to 30mm in diameter. Common sites are:
    • top of the claws;
    • heels;
    • nose;
    • tongue;
    • lips;
    • teats of recently farrowed sows.
  • Within 24 hours many of the vesicles will have burst.
  • On the lips and teats they may leave shallow erosions but on the coronets of the feet secondary infection and trauma may convert them into raw jagged-edged ulcers.
  • Chomping of jaws.
  • Inappetence.
  • Depression.
  • Fever of about 40.5º (105ºF).
  • Thimbling (complete loss of hooves).
  • Abortion in sows.
  • Death in severe cases.

Sows

  • Abortion.

Piglets

  • Increased morality (this is often the first sign).
  • Cardiac arrest.

Boars

  • May stop serving sows.
  • Lameness.

The early signs of swine vesicular disease (SVD) when it is severe, are indistinguishable from FMD so you should suspect it too.

FMD in the US

Near the coast of California where FMD and SVD are extremely unlikely, vesicular exanthema could be a possibility. In Georgia, the Carolinas or Central or South America and it is summer/autumn time perhaps you should think of VS. The clinical signs of all four diseases are almost indistinguishable.

Diagnosis

Rapid accurate diagnosis is essential.

FMD cannot be distinguished from SVD on clinical grounds, or from VES in California, although SVD is often much milder. To differentiate these diseases and confirm the presumptive diagnosis, samples have to be sent to a laboratory capable of making a diagnosis.

There are not many of these. The main one is the World Reference Laboratory at Pirbright near London in England. There is also one on Plum Island off the coast of NY in the USA and one near Melbourne in Australia.

The samples sent are blood and pieces of the skin that overlay the blisters plus vesicular fluid if this is available. Once the samples have been received by the laboratory diagnosis is fairly rapid.

Tests called ELISAs are used for virus identification and if it is FMD they also indicate what serotype it is. The virus may also be grown in cell culture and the identification confirmed by other tests. A molecular genetic test called a PCR (polymerase chain reaction) may also be used to 'fingerprint" the virus. The gene (genome or RNA) of FMD repeatedly undergoes minor changes as the virus spreads through animal populations so by identifying the precise sequence in the gene the laboratory staff are able to make an assumption where it may have come from by the most recent isolate with a similar sequence.

Causes

FMD is cause by a picornaviridae aphthovirus. There are 7 main serotypes: A, O, C, SAT 1, SAT 2, SAT 3 and Asia 1. There are also many strains within serotypes. Careful selection of the strains for incorporation in vaccines is essential to ensure they are effective.

Over 60 subtypes of virus have been identified and new subtypes continue to develop.

Prevention

Vaccination

  • In endemic and high risk areas routine vaccination may be practised mainly to protect the breeding stock.
  • Most FMD vaccines are produced in cell suspension cultures and inactivated by ethylenamine derivatives. An adjuvant is added to make them more potent. Oily adjuvants are used in swine.
  • Vaccination in pigs is problematical. This is because protection is short-lived lasting only about six months. It is also partly because there are seven serotypes of FMD and protection against one leaves animals susceptible to the others. Vaccines must be multivalent (several serotypes) in most endemic regions.
  • Since FMD is largely a winter disease, vaccination should be carried out in the autumn.

Precautions

  • Countries in free and fringe areas apply strictly enforced national preventative measures against the introduction of infection. The main features of these measures are control over the importation of cloven-hoofed animals and of meat from such animals from counties in which FMD occurs.
  • The virus does not survive rigor mortis but it can persist in bone marrow and lymph nodes of infected carcasses for several weeks.
  • If the disease does enter a free or fringe area, a slaughter policy is implemented, all diseased and in-contact animals being slaughtered. A standstill on animal movement is imposed and tracings are carried out to check possible spread of the disease through previous contacts. Ring vaccination may be used around the affected region.
  • If you farm in an FMD-risk region you should take strict precautions against the contamination of your herd. If you have a cattle or goat herd or a flock of sheep as well as a pig herd you should also adopt preventative measures for them and keep a wary eye for the appearance of typical clinical signs.
  • Unfortunately, none of the measures described prevent the windborne spread of FMD. Infected pigs can produce huge quantities of infective virus as aerosols. In dry weather when there are strong thermals the aerosol virus is rapidly inactivated so the wind does not carry infective aerosols very far. Strong winds, hills and objects such as high buildings and trees create turbulence and disperse the plume of airborne virus as they would a plume of smoke from a bonfire. In humid overcast weather with a steady light wind blowing over flat countryside infective virus may survive long enough to infect other herds up to 60km (36 miles) distant. Over water, given the same climatic conditions, infective virus has been shown to travel up to 300km (180 miles) so siting your pig herd on an island in a lake is not going to stop it. Windborne infection is impossible to guard against. Even if your pig herd is in closed buildings, the aerosol virus can get in through the ventilation system and you may carry it in from outside on your boots or clothes.
  • If vaccination is permitted and the pig herd is in a high-risk area you should consider routine vaccination to reduce the susceptibility of your herd.

Basic biosecurity

Basic biosecurity measures are important in helping to minimise the spread of disease. The following procedures could help to reduce the risk:

  • Standardise pig movements and keep to an absolute minimum.
  • People and vehicles are a potential source of potential contamination.
  • Only allow essential visitors on to the farm and provide your own boots and clothing at the entrance.
  • If visitors do not shower ensure hands are washed.
  • Limit the movement of people between buildings as much as possible.
  • Place foot dips at all entrances, service and feed delivery points. Use an approved disinfectant at the correct dilution.
  • Review all cleaning and disinfection procedures. Only allow cleaned and disinfected vehicles to visit your farm.
  • Adopt special precautions at loading ramps. Provide designated boots and overalls for use on the loading ramp only. Disinfect all loading areas before and after use. Check drainage is away from the farm.
  • Clean all pens thoroughly. These should be disinfected and dried between pig groups.

Use the following protocol for cleaning swine facilities:

  • Soften dirt and manure in heavily soiled areas using a low-pressure water spray. Leave to soak for a few hours.
  • Once softened, use high-pressure sprays (750 psi to 2,000 psi preferred) to remove all the dirt and organic material.
  • Start at the back of the pen or building and work toward the front.
  • Spray the ceiling first, then the walls and finally the floor.
  • Use sprayers and nozzles that allow you to wash hard-to-reach areas, including the undersides of troughs, feeders and flooring when possible.
  • Once the pen is clean, rinse all surfaces to remove accumulated aerosol organic material.
  • Spray on surfactant or emulsifying agent to remove any residual organic materials.
  • Rinse all surfaces.
  • Thoroughly disinfect (NOTE: Disinfectants only work on clean surfaces).
  • Disinfectants work best at temperatures above 18°C (65°F), but not above 43°C (110°F).
  • Follow the manufacturer’s application instructions for the product.
  • Apply the disinfectant with pressure (ideally through pressure washer) to force disinfectant into pores, cracks and crevices. Fog or aerosol application is a second alternative.
  • Move from back to front and from top to bottom of the room.
  • Allow the building time to dry.
  • Leave rooms vacant for as long as the production system will allow before repopulating.

Treatment

There is no treatment. Animals should be culled.