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Foot and Mouth Disease
FMD
Aphtosa, Aphtous Fever


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Vesicular lesions of the muzzle...
Pathogenic Agent
  Picornavirus, genus aphtovirus, 7 types and several subtypes
Etiology
  FMD, highly contagious and one of the most feared diseases, is endemic to Asia, Africa, parts of Europe and South America. Because the disease is easily transmitted and spreads rapidly, outbreaks cause enormous financial losses in terms of production and export revenue, and costs of eradication and vaccination programs.
Cloven hoofed livestock such as cattle, pigs, sheep and goats as well as several wild animals (deer, water buffaloes, bears, antelopes, llamas, camels, giraffes, elephants, rats, hedgehogs) of all ages and sexes are susceptible to infection. Men in very rare cases may develop very mild forms of disease. Horses are resistant.
FMDV is resistant to cold temperatures and survives even freezing, but it is susceptible to pH less than 5, sunlight, heat and dryness.
Transmission is either via aerosol from animal to animal, or contaminated personnel, equipment or feed. Wind may spread the virus over long distances. Occasionally, it is imported to FMD-free countries by contaminated frozen meat or garbage. Several outbreaks could be traced to consumption of uncooked waste (swill feeding) from ships or airplanes originating from FMD-infected countries. Even contaminated biologicals (MLV vaccines against hog cholera, Rinderpest or insufficiently inactivated FMD vaccines) have been a source of infection in the past.
In cattle, the primary site of infection are mainly the nostrils, following inhalation of aerosols. The virus replicates there, gains access to the bloodstream and infects the epithelium of mouth, feet, rumen and teats as well as the heartmuscle especially in young animals. Large amounts of virus are shed before clinical signs develop and thereafter.
Morbidity approximates 100%, mortality ranges from 5% (adults) to 75% (young stock). Surviving animals remain virus carriers for up to two years. These carrier animals will shed the virus without showing any clinical signs.

Clinical Signs
  Following an incubation period of 2 to 21 days (in most cases 3 to 5 days), infected animals develop fever, depression, nasal discharge and anorexia. Excessive lip smacking, which is one ot the pathognostic symptoms to be heard, and salivation due to vesicular lesions of the tongue, buccal and oral cavity are characteristic signs. Blisters (0,5 to 3 cm in diameter) may also appear on the muzzle, teats, udder, pili of the rumen, interdigital area and coronary band. They contain a straw colored fluid, are painful and cause anorexia and lameness in affected cattle.
Two to 3 days after appearance the blisters rupture, leaving denuded areas, erosions and painful ulcers.
Frequently, the healing is delayed by secondary bacterial infection of the wounds. Severe forms of mastitis, bronchopneumonia and lameness may occur subsequent to the initial viral infection. Abortion and weight loss as well as a drastic decline of milkproduction are common.
Calves up to 6 months and piglets up to 2 months frequently develop fatal
myocardial degeneration and die within a few days without showing any other clinical signs.

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...of the tongue...
Diagnosis
  The following signs should be considered as possible FMD infections: highly contagious diseases among cattle and pigs, vesicular lesions, erosions and ulcers of the oral cavity, throat, teats, coronary band and interdigital area, lameness, fever, abortions, sudden drop of milk yield and sudden death of calves, lambs or piglets. Contact state authorities immediately.
Collect and submit samples of vesicular fluids, tissue samples of the blisters, blood serum and esophageal secretions in suitable containers to confirm the clinical findings. Tissue culture,
ELISA, virus neutralization, complement fixation, or agar-gel precipitation are used for detection and typing of virus and antibodies.

Differential Diagnosis
  Vesicular stomatitis, bovine papular stomatitis, bovine herpes mammilitis, bluetongue, severe cases of IBR, BVD/MD, pseudocowpox, rinderpest, malignant catarrhal fever in cattle, SVD (swine vesicular disease) in pigs and footrot in sheep
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...and of the interdigital area
Control
  Prevention

The International Animal Health Code of the OIE contains the criteria for a country or zone to be listed as FMD free. There are free countries with and without vaccination.
Free countries maintain their status by prohibiting or restricting the introduction of animals and animal products from countries in which FMD exists. Any way these countries are always under a very high risk of infection. It is commonly practiced that such countries put contingency plans into place to be prepared for an accidental outbreak. Computer programs have been developed to simulate possible outbreaks and to evaluate the economic effects of eradication by compulsory slaughter, vaccination programs or different combinations respectively. The consequences of a wrong decision can be economically devastating.
FMD infected countries try to control the disease by

Eradication

Eradication programs are favored in countries with a low incidence of disease. The success depends on the thoroughness that is paid to the following points:

  • immediate slaughter of all infected and suspicious cloven hoofed animals and those who had contact with them
  • safe discarding of carcasses e.g. in rendering plants where the complete carcasses may be autoclaved at temperatures above 121C
  • restricted areas with a radius of 2 miles (3 km) where all animal movement is strictly prohibited and even movement of humans is restricted
  • quarantine zones with a radius of 10 to 15 miles (16 to 24 km) of the outbreak
  • setting restricted areas and quarantine zones geographical parameters, such as main roads, rivers, sea or lakes, meteorological parameters, such as winddirection, temperature, and bright sunshine as well as socio economical behavior of people must be taken into consideration
  • traffic through the quarantine zone must be reduced to a minimum
  • cleaning and decontamination of the premises
  • no possibly contaminated material may leave the premises nor the quarantine zone
  • burning of all contaminated objects that cannot be thoroughly disinfected
  • restocking of the premises after 30 days with test animals such as cattle, pigs or wild animals, which are monitored for clinical signs of FMD
  • final permission for restocking after 30 days of careful monitoring
  • prohibiting or restricting the introduction of animals and animal products from countries in which FMD exists

Vaccination

Regular vaccination programs in a form of a blanket vaccination are favored in countries with a high incidence of disease, where eradication does not seem possible in the near future. The enormous number of animals saved from stamping out and the prevention of losses due to clinical disease may outweigh the costs of vaccination programs. However, in very rare cases and depending on the quality of the vaccine, unexpected expenses may be caused by the occurrence of adverse reactions to vaccination (especially in pigs) and immunity breakdowns of individual animals.
There is no cross immunity among the different strains of FMD virus.
Vaccination programs include

  • regular basisimmunization consisting of 2 shots 3 to 6 weeks apart of all cattle
  • good farm and vaccination management
  • monitoring of vaccination programs by state authorities
  • administration of killed vaccines, approved by the OIE laboratory, WRL (World Reference Lab) Pirbright, UK and covering the strain of FMD causing the outbreak
  • typing of field virus in case of a new outbreak and administration of vaccine from locally isolated virus strains or covering the strain with a high probability


Treatment

Treatment is prohibited in several countries, because eradication programs demand the slaughter of affected animals. Treatment must be avoided even in countries where it is not prohibited, because treated animals shed high amounts of virus and are a very high risk for all remaining animals. If allowed, systemic antimicrobial drugs, mild disinfectants, immunomodulators and protective dressings are recommended to prevent secondary bacterial infection, alleviate the signs and strengthen the immune system.

References
  Literature
  •  
  • Blood D.C., Radostis O.M., Veterinary Medicine, 1989
  • Fraser, C.M. et al., The Merck Veterinary Manual, 1991
  • Mayr, A., Medizinische Mikrobiologie, Infektions- und Seuchenlehre, 1984
  • Mayr, A., Scheunemann, H., Infektionsschutz der Tiere, 1992
  • Smith, B. P., Large Animal Internal Medicine, 1990

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