Foot-and-Mouth Disease (FMD)

Also known as

Hoof-and-mouth disease

Description

Foot-and-mouth disease (FMD) is an infectious and sometimes fatal viral disease that affects cloven-hoofed animals, including domestic and wild bovines. Susceptible animals include cattle, water buffalo, sheep, goats, pigs, antelope, deer, and bison.

This virus causes a high fever lasting two to six days, followed by blisters inside the mouth (on tongue and lips) and on the feet—between the toes--(and sometimes on the teats of cows) that may rupture and cause a sore mouth and lameness.

Clinical signs can range from mild or unnoticed to severe: signs are more severe in cattle and in confined pigs than in sheep and goats.

Clinical signs in cattle include depression and fever, followed by blister (vesicle) development on the tongue, hard palate, dental pad, lips, gums, muzzle, coronary band, interdigital cleft (between the toes), and teats of cows. Acutely affected individuals may salivate profusely, stamp their feet, and prefer to spend time lying down rather than stand.

Ruptured blisters in and around the mouth can come together and form large erosions, but these heal rapidly, roughly 7 to 11 days after the blister formation. Feet blisters take longer to heal and are susceptible to bacterial infection, leading to chronic lameness. Secondary bacterial mastitis is common in cows due to infected teat blisters and resistance to being milked or nursed by their calves, due to the pain. After blisters develop, cattle are reluctant to eat or move, and quickly lose weight.

Lactating cows suffer dramatic drop in milk production, which can persist even after recovery. The health of young calves, lambs, and piglets may be compromised by lack of milk if dams are infected.

Blisters may also appear above the hooves, and at pressure points on the skin. Ruptured blisters can result in extreme lameness and reluctance to move or eat. Secondary bacterial infection of ruptured open blisters, can also occur.

The incubation period for FMD virus is one to 12 days. The first sign is high fever that declines rapidly after two to three days. Blisters inside the mouth cause excessive secretion of stringy or foamy saliva and drooling. Adult animals may suffer weight loss and may not regain weight for several months.

Mature males may have swollen testicles. Though most animals eventually recover, FMD can lead to myocarditis (inflammation of the heart muscle) and death, especially in newborn animals.

The disease is rarely fatal in adult animals, but there is often high mortality in young animals due to myocarditis or from lack of milk when the dam is infected by the disease. Death can occur before development of blisters due to inflammation of the heart muscle. Myositis (inflammation and weakness of muscles) may also occur in other sites.

Some infected ruminants have no obvious signs but remain carriers--and may still be able to transmit the virus to other animals. Though the majority of affected animals recover, the disease often leaves them weakened and debilitated.

The severity of clinical signs depends on the strain of virus, the exposure dose, the age and species of animal and the host immunity. Morbidity (number of animals affected in a group) can reach 100% in susceptible populations. Mortality is generally low in adult animals (1–5%), but higher in young calves, lambs and piglets (20% or higher).

FMD has been eradicated in many countries with diligent government programs because it has severe impacts on livestock and is highly infectious and contagious. It can be spread by infected animals to uninfected animals not only by direct contact but also through contact with contaminated farming equipment, vehicles, clothing, and feed. It can also be spread by predators.

Once it appears in a region, containment of this disease requires considerable efforts in vaccination, strict monitoring, limiting movement of animals, trade restrictions, quarantines, and culling of  animals in that area.

FMD must be reported to the World Organization for Animal Health (OIE), as indicated in the Terrestrial Animal Health Code. This was the first disease for which the OIE established control programs and official status recognition. Member countries can also apply for official endorsement of their national control programs.

Currently, the World Organization for Animal Health categorizes countries as being in one of three disease states with regard to FMD: FMD present in that country 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. Many nations, including Canada, the U.S. and the UK, work hard to maintain their current FMD-free status. Some countries such as Brazil and Argentina, with large beef-exporting industries, practice vaccination in some areas, but have other vaccination-free zones within their country.

Reasons for restricting export from countries using FMD vaccines include the fact that routine blood tests relying on antibodies cannot distinguish between an infected and a vaccinated animal. This problem severely hampers screening of animals used in export products, risking spread of FMD to importing countries.

A widespread preventive vaccination program would also conceal the existence of the virus in a country. From there, it could potentially spread to countries that don’t have vaccine programs. Also, an animal infected shortly after being vaccinated can harbor and spread FMD without showing signs, hindering containment and culling of sick animals.

This highly contagious disease has serious consequences if it is introduced into a country that is FMD-free. A number of outbreaks in FMD-free countries have had large socio-economic impacts. The 2001 outbreak in the United Kingdom caused losses of more than 8 billion pounds (more than $10 billion U.S. dollars).

Outbreaks have continued to occur in countries that were earlier considered to be free of this disease. FMD occurred again in the United Kingdom in 2007, and Taiwan reported several outbreaks beginning in February 2009. In 2010 both Japan and the Republic of Korea experienced large FMD outbreaks which required extensive programs to control. The 2010–11 Korean outbreak is estimated to have cost that government some 3 trillion (about 2.7 billion U.S. dollars).

To minimize risk, most countries have preventative programs. In Australia, both the government and industry engage in significant planning and preparedness--involving the coordinated control of FMD by eleven countries in the Southeast Asia region.

However, FMD remains endemic in most of these eleven countries. Australia also maintains a strong biosecurity program at the border to minimize FMD risks, and also undertakes extensive preparedness activities to ensure that the disease can be contained and controlled as quickly as possible if it were to enter the country.

Accurate diagnosis is very important. In cattle and pigs, the clinical signs of FMD are indistinguishable from those of vesicular stomatitis, and in pigs indistinguishable from signs of swine vesicular disease and vesicular exanthema.

Laboratory confirmation is essential for diagnosis of FMD and should be performed in specialized laboratories that meet OIE requirements for Containment Group 4 pathogens. Countries lacking access to a national or regional laboratory meeting these guidelines should send specimens to an OIE FMD reference laboratory. The tissue of choice for sampling is blister tissue or fluid.

Signs

• Fever
• Blisters in the mouth and on the feet and teats
• Drop in milk production
• Loss of appetite
• Weight loss
• Lameness

Cause

The disease is caused by a virus of which there are seven types, each producing the same signs, and distinguishable from one another only in the laboratory.

The organism causing FMD is an aphthovirus of the family Picornaviridae. The seven types (A, O, C, SAT1, SAT2, SAT3, and Asia1) are endemic in different countries. Each one requires a specific vaccine to provide immunity to a vaccinated animal. Immunity to one type does not protect an animal against other types.

All seven of the serotypes have also been found in wildlife, although wild animals do not play a significant role in the maintenance and spread of the disease. To date, the only confirmed reservoir in wildlife is African buffalo.

Like other RNA viruses, the FMD virus continually evolves and mutates, so one of the difficulties in vaccinating against it is the huge variation between, and even within, serotypes. No cross-protection is seen between serotypes (a vaccine for one will not protect against any others) and in addition, two strains within a given serotype may have major genetic differences.

This means FMD vaccines must be highly specific to the strain involved. Vaccination only provides temporary immunity that lasts from months to years.

The FMD virus can be transmitted in a number of ways, including close contact, animal-to-animal spread, long-distance aerosol spread and fomites (inanimate objects, typically feed and motor vehicles, the clothes and skin of animal handlers). Standing water, and uncooked food scraps and feed supplements containing infected animal products can harbor the virus, as well. Cows can also become infected with FMD from the semen of infected bulls.

Humans may spread the disease by carrying the virus on their clothes and bodies, and other animals that are not susceptible to the disease (such as birds, dogs, cats) may aid in spreading it. This was the case in Canada in 1952, when an outbreak flared up again after dogs carried off bones from dead animals. Wolves are thought to play a similar role in the former Soviet Union.

The virus is transmitted via direct or indirect contact with infected secretions and excretions (including semen and milk), and can also be carried by air currents over land or water. The virus can enter the body via inhalation, ingestion, or through skin wounds and mucous membranes. Breeding is a possible route of transmission for the SAT viruses in African buffalo populations.

FMD is found in all excretions and secretions from infected animals. Some can breathe out a large amount of aerosolized virus, which can infect other animals via the respiratory or oral routes.

One way for the disease to be introduced into a previously FMD-free area is for a susceptible population, such as pigs, to be given imported food derived from an infected animal (meat, offal, milk). The virus then spreads readily from those pigs, since pigs can exhale up to 3,000 times more virus than cattle. Thus the virus could be spread to cattle via aerosol.

Airborne spread of the disease is fairly common, and under favorable weather conditions the disease may be spread considerable distances by this route. FMD virus was reported to travel over water 155 miles from Brittany, France, to the Isle of Wight, UK, in 1981, but it usually travels no more than about 6 miles over land.

FMD is not considered a public health problem for humans, but there are reports of people who work in FMD vaccine laboratories who developed antibodies to the virus. There are a few reports of people with laboratory-confirmed cases of clinical illness between 1921 and 1969. The disease in people is usually short-lived and mild, however, with symptoms including vesicular lesions and influenza-like illness.

The incubation period of FMD is variable and depends on the host, environment, route of exposure, and virus strain. After infection with FMD virus, the average incubation period for sheep and goats is 3 to 8 days, about 2 days for pigs, and 2 to 14 days in cattle. The incubation period can be as short as 18 hours for host-adapted strains in pigs, especially under intense direct contact in confined pigs.

The virus survives in lymph nodes and bone marrow at neutral pH, but is destroyed in muscle when pH is less than 6.0 (such as after death--after rigor mortis). The virus can persist in contaminated feed and the environment for up to one month, depending on temperature and pH conditions.

Animals pick up the virus either by direct contact with an infected animal or by contact with feed or other things which have been contaminated by an infected animal, or by eating or coming into contact with some part of an infected carcass. Outbreaks have been linked with importation of infected meat and meat products.

The virus may be present in milk and semen for up to 4 days before the animal shows clinical signs of disease.

The significance of FMD is related to the ease with which the virus can spread by any infected animals newly introduced into a herd (carrying virus in their saliva, milk, semen, etc.); contaminated pens/buildings or contaminated animal transport vehicles; contaminated materials such as hay, feed, water, milk or biologics; contaminated clothing, footwear, or equipment; virus-infected meat or other animal products (if fed to animals when raw or improperly cooked); infected aerosols (spread of virus from an infected property via air currents).

Animals that have recovered from infection may sometimes carry the virus and initiate new outbreaks of the disease.

The primary site of infection and replication of the virus is in the mucous membranes of the throat. The virus may also enter through skin lesions or the GI tract. Once distributed throughout the lymphatic system, the virus replicates in the tissues of the mouth, muzzle, teats, feet, and areas of damaged skin.

More than 50% of ruminants that recover from illness and those that are vaccinated and have been exposed to FMD virus can carry virus particles in the back of the throat—for up to 3.5 years in cattle, 9 months in sheep, and more than 5 years in African buffalo.

The virus is present in the milk of dairy cows before clinical signs develop, so there is opportunity for virus to spread farm to farm and from cow to calf via raw milk. It may survive pasteurization depending on the method used; the lipid (fat) component of milk protects the virus during heating. FMD virus survives up to 20 weeks on hay or straw bedding, in dry fecal matter for up to 14 days in summer, in a fecal slurry for up to 6 months in winter, in urine for 39 days, and in soil for 3 (summer) to 28 (winter) days.

Prevention

Control measures include quarantine and destruction of both infected and healthy livestock, and export bans for meat and other animal products to countries not infected with the disease.

The initial measures described in the Global Foot and Mouth disease control strategy are early detection and warning systems and implementation of effective surveillance in accordance with guidelines detailed in the OIE Terrestrial Code. The implementation of FMD control strategy varies from country to country.

It is essential for livestock owners and producers to maintain sound biosecurity practices to prevent introduction and spread of the virus, since FMD is one of the most difficult animal diseases to control. Because it occurs in many parts of the world, there is always a chance of its accidental introduction into an unaffected country.

Export restrictions are often imposed on countries with known outbreaks. FMD outbreaks are usually controlled by quarantines and movement restrictions, euthanasia of affected and in-contact animals, and cleansing and disinfection of affected premises, equipment and vehicles.

Infected carcasses must be disposed of by incineration, rendering, burial or other effective techniques. Milk from infected cows can be inactivated by heating to 100°C (212°F) for more than 20 minutes. Manure slurry can be heated to 67°C (153°F) for three minutes to kill the virus.

Rodents and other animals that might spread the disease should be killed to prevent them from mechanically disseminating the virus.

Vaccination can be used in endemic regions, to reduce the spread of FMD or protect specific animals, but FMD vaccines must closely match the serotype and strain of the infecting strain. Vaccination with one serotype does not protect animals against other serotypes, and may not protect completely (or at all) from other strains of the same serotype. Currently, there is no universal FMD vaccine.

Current global status of FMD distribution shows geographic areas of “hotspots” where FMD prevalence is highest over long periods of time. These are commonly located in poor countries where veterinary services and resources are inadequate to control or eradicate FMD. Trade and movement restrictions of animals and animal products has not completely prevented introductions of FMD into FMD-free areas.

These viral incursions into countries or regions where FMD is not already present are usually controlled by slaughter of all infected and susceptible animals, restriction of animal and vehicle movement around infected premises, proper carcass disposal, and environmental disinfection, without the use of vaccines.

Inactivated virus vaccines are limited in their use, because they protect for only 4–6 months against the specific serotype(s) contained in the vaccine. They protect animals from clinical illness but not viral persistence in the throats of those animals; therefore, vaccination can induce a carrier state.

Additionally, it is difficult to distinguish infected animals from vaccinated animals unless purified killed vaccines are used. For these reasons, vaccination is used more in enzootic countries to protect valuable animals, particularly high-yielding dairy cattle, from clinical illness because the slaughter of all at-risk individuals may be economically unfeasible and might cause food shortages.

Rapid disease reporting is essential to control FMD outbreaks in non-endemic countries. Veterinarians who encounter any vesicular (blister-causing) disease in the U.S. should immediately inform their state or federal veterinary authorities. After an outbreak, tracing is done through to help identify the source of disease introduction.

In countries where mass slaughter is not possible, strict quarantining and movement restriction should be enforced. However, quarantine may not be long enough to prevent carrier animal movement after an outbreak. When mass euthanasia is performed, infected carcasses must be disposed of via incineration, burial, or rendering--on or close to the infected premises.

Scavengers and rodents should be killed to prevent mechanical dissemination of virus. Buildings should be cleaned with a mild acid or alkali disinfectant and fumigation, and people who have come into contact with the virus may be asked to decontaminate their clothing and avoid contact with susceptible animals for a certain period of time.

In some regions, FMD persistence in wildlife populations, such as the wild African buffalo, can make FMD eradication impossible. Control measures, such as fencing of wildlife reserves to prevent contact with domestic livestock, have helped limit the spread of virus in certain areas. A twice-yearly vaccination of livestock in a buffer zone around certain wildlife reserves may also help prevent outbreaks.

Treatment

Treatment is generally not given. Affected animals will usually recover. However because of the loss of production and the highly contagious nature of the disease, infected animals are usually killed.

There is no specific treatment for FMD, but supportive care may be allowed in countries where FMD is endemic and infected animals are not being destroyed in a control program.