Foot and Mouth Disease
Foot and Mouth disease (FMD) is one of the most infectious viral diseases known. It is a disease of cloven-hoofed animals, such as cattle, pigs, sheep, goats and water buffalo. The virus is capable of rapidly infecting large numbers of animals, but death rates are generally low. Animals with FMD usually recover eventully 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 tourist industry as restrictions are placed on the movements of people and animals. This was the case in the 2001 outbreak in the UK.
http://fazd.tamu.edu/fmdwebportal
http://www.aphis.usda.gov/
http://www.oie.int/eng/info/en_fmd.htm
March 5, 2001
Contact: Stephen M. Apatow
SierraEquest Online: Emerging Infectious Disease Network
Eastern United States: (203) 668-0282
Western United States: (775) 884-4680
Major risk for livestock producers/animal health workers relates to lack of direct experience or recognition and handling of foot and mouth disease
According to the 1994 USDA:APHIS:VS paper "Foot and Mouth Disease - Sources of Outbreaks and Hazard Categorization of Modes of Virus Transmission:"
Foot and Mouth Disease (FMD), a highly contagious viral disease affecting primarily cloven-hoofed animals, continues to be a concern in the United States even though the last outbreak in North America was eradicated in 1954 (Mexico). The Economic consequences of an unchecked outbreak in the United States would be great -- estimated in 1979 to be more than $12 billion in the first 15 months.
Livestock animals in this country are highly susceptible to FMD viruses. If an outbreak occurred in the United States, this disease could spread rapidly to all sections of the country by routine livestock movements unless it was detected early and eradicated immediately. -- USDA:APHIS Fact Sheet on Foot and Mouth Disease
According to the paper, since the last U.S. outbreak was in 1929, few livestock producers or animal health workers have direct experience in the recognition and handling of the disease.
Challenges of FMD in Ecosystem
Results of Hazard Categorization for Live Animals
Of the 99 animals identified as possible sources of FMDV, 31 were categorized as high hazards, 50 as moderate, and 18 as low. Some of these animals are discussed below.
Wild Bovidae
Although there have been few confirmed primary outbreaks caused by wild game, circumstantial evidence suggests that such animals may be a source of outbreaks among cattle in countries where wild game and domestic cattle often share grazing land and watering holes. In a large survey conducted between 1965 and 1969, 1,323 samples of serum were collected randomly from 39 species, primarily in Zimbabwe (formerly Rhodesia). Significant FMDV antibody titres were found in 16 species, all cloven-hoofed animals. Of particular interest is the African buffalo; of the 116 animals tested, 77 had positive antibody titres. African buffalo often do not show clinical signs and may carry the virus for long periods (5 years). A study in an area in which FMD had not been recorded for 25 years found 14 of 34 buffalos with significant antibody titres. In addition, recent studies involving nucleotide sequencing of the virus support the belief that wild bovids, particularly African buffalo, may play a role in the transmission of FMDV to cattle.
Suidae
Domestic pigs were assigned a high hazard category. They play an important role in the epizootiology of FMD as initiators and amplifiers. They can act as initiators of FMD by the consumption of infected garbage. Pigs serve as amplifiers of the virus because they can excrete aerosols that contain up to 3,000 times more virus than produced by an equal number of cattle or sheep. Many outbreaks linked to airborne spread are thought to have originated from domestic pigs. One characteristic that distinguishes pigs from cattle and sheep is that they appear to harbor the virus only during clinical stages of the disease and therefore do not act as carriers. Some other species of Suidae have been known to become infected and show clinical signs of FMD, but it is not known if other such species can carry the virus subclinically. Information is also lacking on transmission of virus from other Suidae.
Cervidae
Most deer, including white-tailed and mule deer like those found in North America, were assigned a high hazard category because of demonstration of FMDV transmission. At least one white-tailed deer remained a carrier of FMDV for 11 weeks after infection (Table 12). Exotic deer, including red, sika, and fallow, have been gaining popularity for use on deer farms or game ranches. Such deer have been found to both acquire and transmit FMDV under natural conditions. There is no information on transmission from other cervids such as moose and elk. Accordingly, those cervids were placed in the moderate hazard category.
Llamas
Llamas were categorized as high hazard animals based on the results of experimental transmission of FMDV under "natural" conditions, although such experimental work in llamas has yielded somewhat inconsistent results. One experiment showed that FMDV was transmitted from cattle to llamas, from llamas to swine, and from llamas to other llamas. Responses in the llamas ranged from generalized infection with mucosal lesions (oral and lingual) and severe lameness to no clinical signs. No virus was isolated from the oesophageal-pharyngeal (OP) fluid of infected animals after 7 days post-inoculation or post-contact.
In another study, none of 20 llamas exposed to pigs infected with FMDV types A or C developed clinical signs or yielded any virus from OP fluid or blood. Two of 10 llamas exposed to pigs infected with FMDV type O did develop mild lesions. After removal of the pigs, additional susceptible llamas and other domestic livestock were placed in contact with the initial group of 30 exposed llamas; all of the secondary exposure group llamas remained healthy and were negative for FMDV antibodies. The authors concluded that llamas are resistant to FMDV infection and that they harbor the virus in their OP region only for a short time.
Humans
Humans may acquire FMDV through various routes, the most important of which has probably been ingestion (drinking infected milk). Airborne virus has also been linked with several human cases, as has direct contact with infected animals. However, the number of documented cases in humans is relatively small (only in about 40 cases has FMDV been isolated), indicating that humans are quite resistant to FMDV infection and that it is not a public health problem. Whether or not one considers FMD to be a true zoonotic disease, humans can play a role as carriers or transmitters of FMDV and were categorized as a high hazard. Virus has been recovered from the nasal passage up to 36 hours after exposure. It is reported that virus can be isolated from humans with vesicles up to 14 days after the onset of disease. However, the most important form of transmission from humans to animals is mechanical, because virus can persist on clothing or shoes for at least 9 weeks.
Invertebrates
Although the role of flies and ticks in the epizootiology of FMD is not usually large, it has been demonstrated that ticks and some species of biting flies can transmit the virus through bites. Ticks, flies, and biting flies were categorized as high hazards, based either on transmission capability or long carrier status (whether mechanically or biologically). Houseflies can carry FMDV both externally and internally; whether they can transmit the virus is unknown. It is unlikely that the virus multiplies in the cells of invertebrates. However, experimental transovarial infection of a portion of a population of Dermacentor ( Anocentor ) ticks has been reported. FMDV has also been transmitted to cattle experimentally by inoculating them with ground-up earthworms. Given the artificial nature of transmission and given that infected earthworms are not known to have been associated with any outbreaks, earthworms were placed in the moderate rather than the high hazard category.
In response to the need for educational resources on Foot and Mouth Disease, SierraEquest Online has constructed an information site which includes: Photos (FMD in cattle, pigs sheep), OIE: AETIOLOGY - Foot and Mouth Disease,
USDA:APHIS: Fact Sheet: - Foot and Mouth Disease, Centers for Epidemiology & Animal Health (An OIE Collaborating Center), Center for Emerging Issues, current North American Advisories and more. To access this resource, visit the:
Emerging Infectious Disease Network (EIDNet)
Topic: Foot And Mouth Disease
Links are provided as an information service. They do not constitute an endorsement of any non-affiliated organizations, businesses, products or content of these pages by the Cooperative Extension Service, CU Livestock-Poultry Health, or Clemson University.