Information Sheet: (FMD) Foot and Mouth Disease

(FMD) or aphthous fever is an acute, highly infectious disease affecting cattle, swine, sheep and other cloven-hoofed livestock. It is a serious livestock disease and can have a devastating economic impact when outbreaks occur in areas that are usually free of FMD. It is estimated that the world-wide losses by FMD equal or surpass the losses produced by all other infectious or parasitic diseases of cattle combined.

FMD is a viral disease that most commonly affects cattle and swine. Other species can be infected with FMD, but in these other species the disease tends to be milder. FMD is endemic in Africa, Asia, South America and parts of Europe. Australia, New Zealand, Canada and Mexico are considered free of FMD. Western Europe was FMD free until the most recent outbreak. The United States has been free of FMD since 1929.

FMD results when a susceptible animal ingests or inhales the virus. The virus spreads locally and is distributed in the circulatory system. The primary target tissues are the mucosa membranes of the mouth, pharynx, coronary band of the foot, the digestive tract and the udder. Two days after exposure the animal develops a fever, becomes depressed, goes of feed and develops vesicles (blisters). These vesicles rupture in 48 hours and the underlying tissue will slough and have deep erosions that often take weeks to heal. There can be secondary bacterial infections. FMD has a high morbidity (close to 100%) but low case mortality (2% in adult animals and 20% in young stock). The primary impact of FMD is the ability of the virus to rapidly spread in susceptible livestock and the economic impact of weight loss, decreased milk production, mastitis and abortions that are observed in infected animals.

The FMD virus is highly contagious. Fluid from the ruptured vesicles contains large numbers of the viruses and will directly infect other animals. The virus can be spread by aerosol, with infected animals breathing on other animals and the wind can carry the virus up to 150 miles. FMD viruses can survive for very long periods in frozen meat and bone, in uncooked processed meats and fomites such as bedding, mangers, clothing, shoes, hides, milk (even pasturized milk) and frozen bull semen. FMD is rapidly inactivated by high or low pH and sunlight but is very resistant to common disinfectants, normal environmental conditions and drying. Humans are not usually affect by FMD but they are often involved in the spread of the disease by transporting the virus in uncooked foods or clothing or through the movement of infected animals. Humans can carry the virus in our respiratory tract for 28 hours.

Outbreaks of FMD occur when the virus passes from endemic areas into animals in "free" areas. Often these outbreaks are initiated when swine are fed contaminated meat scraps. The common sources of contaminated meat are carrier sheep and process meat. Before the disease is identified, these swine have contact with other animals and the disease is quickly spread. In the most recent outbreak in the UK the movement of sheep from farm to markets and to international export was responsible for the rapid spread of FMD.

When these outbreaks happen it is important to quickly identify if FMD virus is involved. Other vesicular diseases can look similar to FMD and a correct and accurate diagnosis is vital. FMD has seven types (A; O; C; South African Territories 1, 2, and 3 and Asia 1) and more than 60 subtypes. The subtypes can change their antigenic markers and there is marked difference in virulence between subtypes. Some subtypes show an adaptation to species specific hosts and may be less able to infect other species. Identification of type and subtype is vital because there is little cross protection provided by vaccination between subtypes. If part of the control program involves vaccination it must be done with the correct type and subtype.

In endemic areas FMD vaccine is routinely used. The correct type and subtype must be used. Often a multi valent killed vaccine is used. To be effective this vaccine must be given 2-3 time yearly and in some cases all livestock including sheep, pigs and cattle must be vaccinated. Half of the animals infected with FMD remain carriers. The vaccine does not prevent the carrier state. Vaccination is sometimes used to form a "ring" around outbreaks. There are problems with the use of vaccination to control an outbreak; the correct type and subtype must be used, all livestock must be vaccinated, veterinary personnel involved with the vaccination program may inadvertently spread the disease with contaminated clothing or vehicles.

Prevention of FMD in free areas is centered on keeping the disease out. This requires the complete embargo of animals and animal products from infected areas. This embargo should extend to all material that may come into contact with infected livestock such as bedding, feeds, handling equipment and vehicles used to move susceptible animals. Food waste from ships and aircraft, particularly meat scraps and undercooked processed meats can carry the virus. These waste products should not be fed to swine. Personal clothing can carry the virus from endemic area to susceptible livestock. Semen from an infected bull can infect a cow bred using that semen. Physical barriers can be important. The Darien Gap is a tract of impassable land between Colombia and Panama and acts as a physical barrier to prevent the spread of FMD from South America to Central America.

An outbreak of FMD in the United States would have huge economic costs. Our control program would require a stop of all livestock movement and slaughter all infected and exposed animals. Because of the number of animals moving daily, it may be difficult to isolate an outbreak. A large scale outbreak could halt all livestock movement for several weeks. This would have a direct impact on all the industries dependent on livestock production and the consumer. Some agricultural experts have estimated that the effects of control efforts necessary to stop a major FMD outbreak could start a major recession. The USDA and state veterinarians have increased surveillance to reduce the chance FMD could enter the United States.

The information in this document has been reviewed by the Veterinary Staff at AzVDL.
If you have questions of FMD please contact me at:
The Arizona Veterinary Diagnostic Laboratory, telephone 520-621-2356 ext 18
or see the USDA web site http://www.aphis.usda.gov/oa/fmd/index.html.