The foot and mouth disease (FMD) virus is capable of rapidly infecting large numbers of animals, but death rates are generally low. Animals with FMD usually recover uneventfully but the highly infectious nature and rapid spread of the virus has a profound negative economic impact. Part of the economic impact stems from production losses in intensive production systems, such as the dairy industry, where cattle may experience chronic mastitis, poor growth, and permanent hoof damage. An FMD outbreak leads to economic sanctions, including the loss of export markets. In addition, an outbreak of FMD can also negatively impact the tourism industry as restrictions are placed on the movements of people and animals. This was the case in the 2001 outbreak in the UK.
FMD virus is a member of the Picornavirus family. There are seven immunologically distinct serotypes and over 60 sub-types. The seven serotypes are O, A, C, SAT 1, SAT 2, SAT 3 and Asia 1. Strains of FMD Type O are of most concern for disease spread into new areas. In addition to the 2001 UK outbreak Type O has been responsible for recent FMD incursions in previously unaffected regions worldwide. In 2010/2011 these have included Mongolia, parts of eastern Africa, Japan, the Korean peninsula, Israel and Bulgaria.
FMD is not considered zoonotic by the CDC, meaning transmission from animals to people is exceptionally rare. There has only been one confirmed case of FMD in a human which occurred in 1966 in Great Britain. FMD is NOT the same as Hand, Foot and Mouth disease in humans.
According to the World Organisation for Animal Health (OIE), the incubation period (time between infection and appearance of clinical signs) is 2-14 days. The clinical signs of FMD can vary with the species infected.
For example, cattle have prominent oral lesions, while swine have severe foot lesions. Sheep often have mild, if any, clinical signs of FMD. The clinical signs of FMD include:
- blisters/vesicles of the muzzle, nose and/or tongue
- blisters/vesicles of the foot in between the digits or at the hoof/ foot junction (coronary band)
- blisters/vesicles of the teats
- anorexia (unwillingness to eat)
- excessive salivation
- decreased milk production
- death in newborn animals due to inflammation of heart muscle (myocarditis)
Click here to view photos of typical FMD lesions.
FMD is usually transmitted through direct contact with or inhalation of the virus. FMD outbreaks can be difficult to control as the disease can be spread by carrier animals. Carriers are animals that can shed the FMD virus more than 28 days after infection. As a result, seemingly healthy animals can spread the disease rapidly.
Cattle are considered to be a sentinel species because they consistently show textbook clinical signs of FMD. Cattle are an important carrier of FMD and may shed the virus for up to 2 years. Pigs are considered amplifiers of the disease because they shed large amounts of virus into the air. Thus, enhancing the spread of the virus. However, pigs do not shed the virus after active infection and are not carriers. Sheep and goats are considered maintenance hosts of the disease because they often only have very mild clinical signs. Sheep and goats may shed the virus for up to 6 months.
Routes of initial infection can include:
- improperly sterilized garbage or illegally imported meat used as pig feed
- contact with contaminated clothing, shoes and/or equipment
- contact with live animal carrier including birds and rodents
- contaminated artificial insemination products
- windborne (1981 Isle of Wight outbreak)
- deliberate act of bioterrorism
There are several diseases that mimic the clinical signs of FMD including vesicular stomatitis, swine vesicular disease, foot rot (sheep, cattle), traumatic stomatitis and chemical/thermal burns. Therefore, it is imperative that any animal exhibiting any of the clinical signs of these diseases be reported to state or federal veterinary officials immediately for proper quarantine and testing.
FMD Surveillance and Biosecurity
Since 1870, the United States has experienced 9 FMD outbreaks. The largest of these outbreaks occurred in 1914 when FMD entered the Chicago stockyards. The virus spread rapidly across the US and infected 3,500 livestock herds and cost $4.5 million to eradicate. The last outbreak in the United States occurred in California in 1929. Currently, the US is considered free of FMD without vaccination by the World Organisation for Animal Health (OIE). The OIE has four categories of FMD free countries: FMD free country without vaccination, FMD free country with vaccination, FMD free zone (within a country) without vaccination and FMD free zone (within a country) with vaccination. Countries must meet certain criteria in order to maintain FMD free status including having a record of regular and prompt animal disease reporting, have an effective surveillance system and demonstrate that all FMD prevention measures are in place.
It is estimated that an outbreak of FMD in the U.S. could result in a loss of billions of dollars for agriculture and related industries. With FMD endemic to many areas of the world, it is difficult to predict when and where the disease may first enter the country. APHIS has banned the import of all animal and animal products from FMD endemic areas. Successful control of an outbreak of FMD would depend on promptly reporting clinical signs consistent with FMD to the state or federal veterinary authorities and rapid confirmation of the diagnosis so control measures could be put in place.
In the case of a positive FMD diagnosis, the United States will begin an eradication plan that would include stamping out and/or ring vaccination procedures.
Using this eradication procedure, all premises with infected livestock shall be placed under quarantine with animal movement restrictions. All infected and in contact animals are to be slaughtered with government compensation. Carcasses, manure and bedding are to be incinerated. The premises and all contaminated equipment must be disinfected with sodium hydroxide, sodium carbonate or citric acid.
- Difficult or impossible to carry out in the event of widespread infection
- Huge amounts of money required for farmer compensation
- May necessitate slaughter of more animals than necessary
- Regain OIE FMD free status 3 months after last case
In animal dense areas, ring vaccination strategies may be used in addition to stamping out procedures. In this method, a group of animals around the premises is vaccinated and acts as a barrier to further FMD spread. The animals within the ring are then subject to stamping out procedures.
- Must have correct strain of FMD virus for the vaccine to be effective
- Appropriate vaccines may not be available immediately (stored at North American FMD Vaccine Bank on Plum Island)
- May contain outbreak to a smaller area
- If used in conjunction with stamping out, can regain OIE FMD free status 3 months after slaughter of last vaccinated animal
- If not used in conjunction with stamping out, can regain OIE FMD free status 12 months after last case and last vaccination
In order to protect the herd from becoming infected with an exotic animal disease such as FMD, producers are urged to take the following measures:
- Isolate incoming animals from the rest of the herd and monitor for clinical signs of disease
- Follow an All In/All Out strategy of animal management and disinfect the facilities between groups
- Require visitors to wear clean boots and coveralls before coming in contact with the herd
- Do not allow visitors who have been out of the country and in contact with animals or animal facilities, including zoos, to be in contact with the herd for five days
- Properly clean and disinfect livestock trucks and trailers before entry into the farm
- Dispose of carcasses promptly and correctly
- Discourage employees from bringing food onto the farm (that may have been illegally imported)
- Do not allow employees to have contact with any swine or cattle outside the herd
- Have an effective rodent and insect control program
- Always report any suspected disease to a veterinarian immediately
Historical FMD Outbreaks
United Kingdom, 2001
On February 20, 2001, a pig was diagnosed with FMD at a slaughterhouse in Essex. Although this was the first animal diagnosed with the disease, it was not believed that the slaughterhouse in Essex was the source of the outbreak. The animal was traced to Burnside Farm in Northumberland where up to 90 percent of the herd was exhibiting the severe foot lesions characteristic of FMD. No report had been made to local veterinarians.
Burnside Farm was a pig finishing unit that was licensed to use processed garbage (food scraps) as feed. Processed garbage has been boiled to an internal temperature of at least 212o F in order to kill harmful pathogens before use as feed. After a careful inspection of the feed storage facilities at Burnside Farm, it was determined that the pigs were fed unprocessed garbage that was contaminated with the FMD virus.
Although FMD was diagnosed on February 23, 2001, at Burnside Farm, further investigation and dating of the skin lesions placed the actual date of exposure between January 26 and February 7. The delay in diagnosing FMD allowed the disease to become an epidemic across the UK. The disease began to spread through the movement of infected pigs from Burnside Farm to the slaughterhouse. From there, the virus was carried mechanically (on clothes, equipment, etc.) through various areas of Essex. The disease also spread through airborne transfer from Burnside Farm to a neighboring sheep farm. The infected sheep were sold before an FMD diagnosis was made and spread the disease throughout England, Scotland and Wales.
A total of 2,026 cases of FMD were confirmed between February 20 and September 30, 2001. According to the OIE, over 6 million cattle, sheep, swine and goats were slaughtered to stop the spread of the disease. In all, this epidemic is estimated to have cost the UK economy £7 billion.
On March 19, 1997, a sow at a farm in Hsinchu was diagnosed with a strain of FMD that infected swine only. The cause of this outbreak remains unknown, however, the farm was located near a port city with a thriving pig smuggling industry and illegal slaughterhouses. It is likely that the FMD was introduced through contaminated meat scraps or the introduction of smuggled swine into the herd.
Once the index case was diagnosed, the disease spread rapidly through the swineherds in Taiwan. There are several reasons why the disease spread so rapidly:
- very high swine density
- garbage feeding
- hog farms close to slaughterhouses
- frequent social farm visits
- incomplete diagnostic laboratory capability
- no vaccination program
In addition to these problems, swine vesicular disease (SVD) was endemic to Taiwan. The clinical signs of this disease are virtually indistinguishable from FMD. To further complicate matters, laboratory analysis was often not employed to diagnose SVD. Therefore, it is likely that several reported cases of SVD were actually FMD. Also, once FMD was confirmed, there was a considerable delay between diagnosis and the implementation of depopulation and disposal. Finally, the indemnity payments offered to farmers for swine infected with FMD were often more than the market value of the pig leading many farmers to intentionally introduce FMD onto their farms.
These factors contributed to the rapid spread of FMD across Taiwan and the destruction of over 3.8 million swine at an estimated cost of US $6.9 billion. Prior to this outbreak, Taiwan had been the leading exporter of pork to Japan. The disease devastated the Taiwanese pig industry and eliminated the export market.
United Kingdom, 1967
On October 25, 1967 a farmer at Bryn Farm in Shropshire reported a lame sow to a local veterinarian. She was diagnosed with FMD. It is believed that the sow contracted FMD from eating swill that contained legally imported lamb from Argentina contaminated with the virus. The farm was placed under quarantine and a ban on animal movement was put into effect. The infected pigs generated a plume of FMD virus that spread to the nearby Ellis Farm.
Two cows from the Ellis Farm had already been shipped to the market prior to the ban on animal movement. Although the disease was reported quickly and animal movement restricted, 442,285 animals were slaughtered. The outbreak cost an estimated £370 million. It is believed that the FMD virus was spread through wind, birds and rodents.
This outbreak caused the government to place tighter controls on imports from countries with FMD and improve animal hygiene and health.