Importance
Foot and mouth disease (FMD) is a highly contagious viral disease of livestock. It can rapidly spread through a region if control and eradication practices are not implemented upon its detection. Weight loss, poor growth, permanent hoof damage, and chronic mastitis are just some of the sequelae of infection. The detection of Foot and mouth disease (FMD) in a country impacts international trade and embargoes could cause significant economic losses.

 

A virus of the family Picornaviridae, genus Aphthovirus.
Foot and mouth disease virus (FMDV) is icosahedral in shape, nonenveloped, and measures 27nm in diameter. The genome is approximately 8 kilobases of single-stranded RNA.
Seven serotypes of FMDV have been identified (O, A, C, SAT1, SAT2, SAT3 and Asia1) and are distributed in different geographic regions.

Temperature: Preserved by refrigeration and freezing and progressively inactivated by temperatures above 50°C
pH:    Inactivated by pH <6.0 or >9.0
Disinfectants: Inactivated by sodium hydroxide (2%), sodium carbonate (4%), and citric acid (0.2%). Resistant to iodophores, quaternary ammonium compounds, hypoclorite and phenol, especially in the presence of organic matter
Survival: Survives in lymph nodes and bone marrow at neutral pH, but destroyed in muscle when is pH <6.0 i.e. after rigor mortis. Can persist in contaminated fodder and the environment for up to 1 month, depending on the temperature and pH conditions

In susceptible populations, morbidity can be 100%. Mortality is generally less than 1% but can be up to 40% in younger animals or outbreaks situations.

FMD is endemic in parts of Asia, Africa, the Middle East and South America (sporadic outbreaks in free areas)

Bovidae (cattle, zebus, domestic buffaloes, yaks), sheep, goats, swine, all wild ruminants and suidae. Camelidae (camels, dromedaries, llamas, vicunas) have low susceptibility

Under natural conditions, the most common form of transmission is by aerosol, with infectious particles exhaled by an animal in the acute phase of the disease being carried on the air to the respiratory tract of a susceptible animal.
The incubation period from point of contact to observable disease is 2-8 days.The virus first replicates in the pharyngeal tissue and/or lung. Twenty-four to 72 hours later, there is a high titered viremia, with dissemination to and replication in stratum spongiosum at multiple epithelial sites.
Vesicles develop as the virus grows within a group of contiguous epithelial cells, rupturing them, and creating a large lake of fluid within the epithelium. This vesicular fluid contains abundant viral particles and the virus persists in the surrounding cells for 3-8 days, diminishing at about the same time antibodies develop.
This photomicrograph depicts Foot and mouth disease virus (stained black-brown) within epithelial cells surrounding a vesicle.
Replication in mammary gland epithelium occurs as well, and the virus can be detected in milk for at least 10 days post-exposure at which point antibodies have been produced which neutralize the virus.

Recovery generally occurs within 8-15 days
Complications: tongue erosions, superinfection of lesions, hoof deformation, mastitis and permanent impairment of milk production, myocarditis, abortion, death of young animals, permanent loss of weight, loss of heat control ('panters')

Sheep and goats
Lesions are less pronounced. Foot lesions may go unrecognised. Lesions in dental pad of sheep. Agalactia in milking sheep and goats is a feature. Death of young stock

Pigs
May develop severe foot lesions particularly when housed on concrete. High mortality in piglets a frequent occurrence

Vesicles or blisters on the tongue, dental pad, gums, cheek, hard and soft palate, lips, nostrils, muzzle, coronary bands, teats, udder, snout of pigs, corium of dewclaws and interdigital spaces
The characteristic lesions of foot-and-mouth disease are single or multiple vesicles/bullae from 2 mm to 10 cm in diameter. Early lesions range from a small pale area to a fluid-filled vesicle, sometimes coalescing with adjacent lesions to form bullae. Once vesicles rupture, red, eroded areas or ulcers will be noted. These may be covered with a gray fibrinous coating; a demarcation line of newly developing epithelium may be noted. Loss of vesicular fluid through the epidermis may lead to “dry” lesions. These will appear necrotic instead of vesicular and are more common in the oral cavity of pigs. Lesions also occur at the coronary band and can progress to the skin and hoof. Coronitis may be seen on the hooves and pigs may slough their claws in severe cases. In younger animals, gray or yellow streaking in the myocardium, also called “tiger heart” lesions, may be seen and are caused by zones of degeneration and necrosis in the tissue. Vesicular lesions may also be found on the ruminal pillars.

The incubation period is 2-21 days (average 3-8) although virus is shed before clinical signs develop. The rate of infection (morbity) can reach 100%, however mortality can range from 5% (adults) to 75% (suckling pigs and sheep). Recovered cattle may be carriers for 18 to 24 months; sheep for 1 to 2 months. Pigs are not carriers.

FMDV can be identified using enzyme-linked immunosorbent assay (ELISA), complement fixation, and virus isolation. Virus isolation is done by inoculation of primary bovine thyroid cells and primary pig, calf and lamb kidney cells, inoculation of BHK-21 and IBRS-2 cell lines, or inoculation of mice. ELISA and virus neutralization tests can be used to detect antibodies in serum. Virus isolation and identification must be performed on the initial case. Subsequently, antigen or nucleic acid detection can be used to diagnose additional cases in an outbreak.

Notification of authorities
A quick response is vitally important in containing an outbreak of Foot and mouth disease (FMD). State and federal veterinarians should be immediately informed of any suspected vesicular disease.
Quarantine and Disinfection
Suspected animals should be quarantined immediately and the premises should be disinfected. Sodium hydroxide (2%), sodium carbonate (4%), citric acid (0.2%), and Virkon-S® are effective disinfectants. Other disinfectants (e.g., iodophores, quaternary ammonium compounds, phenols) may be less ideal because they can be rapidly inacti- vated in the presence of organic matter.
Vaccination
Foot and mouth disease (FMD) vaccines, whether used prophylactically or for control of an outbreak, must closely match the type and subtype of the prevalent FMDV strain. With seven serotypes, and more than 60 subtypes of FMDV, this task is one of the biggest challenges in Foot and mouth disease (FMD) vaccination. Currently, there is no universal vaccine against FMD. The U.S., Canada, and Mexico maintain the North American Foot and mouth disease (FMD) Vaccine Bank, which contains vaccine strains for the most prevalent circulating serotypes in the world. The decision to use vaccination in control and eradication efforts is complex and depends upon scientific, economic, political, and societal factors specific to the outbreak situation. The final decision to use vaccination as an aid in controlling an outbreak of Foot and mouth disease (FMD) in the U.S., Canada, or Mexico would be made by the Chief Veterinary Officer in each country.