Foot and mouth disease sometimes referred to as hoof and mouth disease is an infectious and fatal viral disease that affects cloven-hoofed animals, including domestic and wild bovid. The virus causes a high fever for two or three days, followed by blisters inside the mouth and on the feet that may rupture and cause lameness.
Foot-and-mouth disease has severe implications for animal farming, since it is highly infectious and can be spread by infected animals through aerosols, through contact with contaminated farming equipment, vehicles, clothing or feed, and by domestic and wild predators.
Its containment demands considerable efforts in vaccination, strict monitoring, trade restrictions and quarantines, and occasionally the elimination of animals. The virus responsible for the disease is a picornavirus, the prototypic member of the genus Aphthovirus. Infection occurs when the virus particle is taken into a cell of the animal. The cell is then forced to manufacture thousands of copies of the virus, and eventually bursts, releasing the new particles in the blood. The virus is genetically highly variable, which limits the effectiveness of vaccination.
In the early stage, the disease manifests itself among cows through a rise in temperature and the animal becomes dull. A milking cow will show a sudden drop in yield. Blisters begin to develop, usually within a few hours, most frequently on the upper surface of the tongue and the bulbs of the heels. Feeding and cuddling may cease and the animal is ‘tucked up’ with staring coat.
If at pasture, the animal will be away from the rest of the herd, and probably lying down. There is quivering of the lips and uneasy movement of the lower jaw, with copius, frothy saliva around the lips that drips to the ground at intervals a smacking sound is produced by partial opening of the mouth.
About the same time there is evidence of pain in the feet. The animal lies down constantly and, when forced to move, walks very tenderly, occasionally shaking a leg as if to dislodge some object wedged in the hoof. Lameness usually gets worse, until the animal can only hobble when moving on hard or uneven surfaces. Loss of condition is marked, partly on account of the fever and partly because the mouth is so painful that the animal is afraid to eat. Cows and heifers may develop blisters on the teats and resent any attempt at milking.
If the mouth is examined in the early stages, blisters on the dental pad, inside the lips, and sometimes on the muzzle, will be found, as well as those on the upper surface of the tongue. At first the blisters are seen as small raised areas, whitish in colour and containing fluid: they quickly increase in size until they may be as big as half a walnut.
Two or more blisters may join to form a larger one, sometimes covering half the surface of the tongue. Later, the blisters burst and collapse, leaving the ‘skin’ loose and wrinkled, with a dead appearance. On handling, the ‘skin’ is easily removed, leaving a raw surface underneath. When the blisters have burst the temperature falls, pain decreases and the animal may start to eat again.
The blisters develop on the feet about the same time as in the mouth, or a little later; they rarely appear first. Most commonly they occur at the bulbs of the heels, at the front of the cleft of the hoof, and in the cleft itself. They usually burst fairly quickly through movement of the feet, and then appear as a ragged tear exposing a raw surface.
The chief symptom is a sudden among sheep and goats is severe lameness, affecting one or more legs. The animal looks sick, lies down frequently and is very unwilling to rise.
Usually, the disease affects all four feet, and when the animal is made to rise, it stands in a half-crouching position, with the hind legs brought well forward, and seems afraid to move. Mouth symptoms are not often noticeable. There are blisters on the feet at the top of the hoof, where the horn joins the skin in the cleft of the foot. They may extend all round the coronet, and when they burst the horn is separated from the tissues underneath, and the hair round the hoof is damp. Unless complicated by foot rot, the foot is clean and there is no offensive smell. Blisters in the mouth, when they do develop, form on the dental pad and sometimes the tongue.
The chief symptom in pigs is sudden lameness. The animal prefers to lie down and when made to move squeals loudly and hobbles painfully, though lameness may not be so obvious where the pigs are on deep bedding or soft ground. The blisters form on the upper edge of the hoof, where the skin and horn meet, and on the heels and in the cleft. They may extend right round the hoof head, with the result that the horn becomes detached.
At a later stage new horn starts to grow and the old hoof is carried down and finally shed. The process resembles the loss of a fingernail following some blow or other injury. Mouth symptoms are not usually visible, but blisters may develop on the snout or on the tongue. It is important to note that the disease known as Swine Vesicular Disease, has identical symptoms to Foot and Mouth disease.
Therefore anyone who sees vesicular disease in pigs must report the sighting and treat the condition as suspected Foot and Mouth disease until laboratory tests prove otherwise. The virus is present in great quantity in the fluid from the blisters, and it can also occur in saliva, milk and dung. Contamination of any objects with any of these discharges is a danger to other stock. At the height of the disease, virus is present in the blood. Infected animals begin by excreting the virus a few days before signs of the disease develop. Pigs in particular produce large numbers of virus particles.
Airborne spread of the disease can take place and under favourable weather conditions the disease may be spread considerable distances by this route. Animals pick up the virus either by direct contact with an infected animal or by contact with foodstuffs or other things which have been contaminated by such an animal, or by eating or coming into contact with some part of an infected carcass. In the past, outbreaks of the disease have been linked with the importation of infected meat and meat products.
The disease is spread mechanically by the movement of animals, people, vehicles and other things which have been contaminated by the virus. Trucks, Lorries, market places, and loading ramps – in or over which infected animals have travelled – are dangerous until disinfected. Roads may also become contaminated and virus may be picked up and carried on the wheels of passing vehicles.
The boots, clothing and hands of a herdsman who has attended diseased animals can spread the disease and dogs, cats, poultry, wild game and vermin may also carry infection. Humans can be infected with foot-and-mouth disease through contact with infected animals, but this is extremely rare. Some cases were caused by laboratory accidents. Because the virus that causes FMD is sensitive to stomach acid, it cannot spread to humans via consumption of infected meat, except in the mouth before the meat is swallowed.
In the UK, the last confirmed human case occurred in 1966, and only a few other cases have been recorded in countries of continental Europe, Africa, and South America. Symptoms of FMD in humans include malaise, fever, vomiting, red ulcerative lesions (surface-eroding damaged spots) of the oral tissues, and sometimes vesicular lesions (small blisters) of the skin.
Like other viruses, the FMD virus continually evolves and mutates, thus one of the difficulties in vaccinating against it is the huge variation between, and even within, serotypes. There is no cross-protection between serotypes (meaning that a vaccine for one serotype will not protect against any others) and in addition, two strains within a given serotype may have nucleotide sequences that differ by as much as 30 percent for a given gene. This means FMD vaccines must be highly specific to the strain involved. Vaccination only provides temporary immunity that lasts from months to years.
Currently, the World Organisation for Animal Health recognizes countries to be in one of three disease states with regards to FMD: FMD present with or without vaccination, FMD-free with vaccination and FMD-free without vaccination. Countries designated FMD-free without vaccination have the greatest access to export markets, so many developed nations, including Canada, the United States, and the UK, work hard to maintain their current status.
There is no viable treatment for the disease. Affected animals always recover on their own. However, because of the loss of production and the infectious state of the disease, infected animals are usually culled. Vaccination can be used to reduce the spread of FMD or protect specific animals. Vaccines are also used in endemic regions to protect animals from clinical disease. FMDV vaccines must closely match the serotype and strain of the infecting strain.
Vaccination with one serotype does not protect the animal against other serotypes, and may not protect the animal completely or at all from other strains of the same serotype.