Foot and mouth disease (FMD)

FMD is an acute viral and extremely contagious disease of cloven footed animals such as cattle, sheep, goats, pigs and antelope. It is manifested by vesicles and erosions in the muzzle, nares, mouth, feet, teats, udder and pillar of the rumen. There are three main strains of viruses causing FMD, namely A, O and C. Three additional strains, SAT 1, SAT 2 and SAT 3 have been isolated from Africa and a further strain ASIA-1 from Asia and the Far East.
Transmission:
Direct and indirect contact with infected animals and their secretions including saliva, blood, urine, faeces, milk and semen, aerosol droplet dispersion, infected animal by-products, swill containing scraps of meat or other animal tissue and fomites and vaccines.
Antemortem findings:
Before vesicle formation:Incubation is 1 - 5 days or longer Morbidity: Nearly 100 % Mortality: variable depending on the strain of virus and its virulence and susceptibility of host; 50 % in young animals, 5 % in adults Fever up to 41.7°C Dullness Lack of appetite Drastic drop in milk production. Uneasiness and muscle tremors.
Vesicle formation:Smacking and quivering of lips Extensive salivation (Fig. 45) and drooling Shaking of feet and lameness The vesicles and later erosions are commonly found on the muzzle, tongue, oral cavity, teat and on the skin between and above the hoofs of the feet. In more chronic cases in cattle the hoof become loose and the animal may walk with characteristic “clicking” sound (Slippering).
Some strains of FMD, particularly in swine, sheep and goats cause erosions instead of vesicles.
Postmortem findings :Necrosis of heart muscle(tiger heart), usually only in young acutely infected animals.Ulcerative lesions on tongue, palate, gums, pillars of the rumen and feet.
Judgement :
In countries or in zones within a country free or nearly free of FMD diseased or suspect animals are prohibited to be admitted in an abattoir or slaughtered. If FMD is suspected on postmortem examination the carcass and viscera are condemned and appropriate action recommended by the regulatory authorities of the country must be taken. In countries where this disease is present, the judgement should be in accordance with the current animal health requirements, and consisted with effective public health protection. Particular attention should be paid to secondary bacterial infections and general findings. Sanitary measures should be taken to comply with national animal health policy.
Remarks : Latent infections with Salmonella organisms were reported in animals affected with FMD.
Differential diagnosis in bovine and ovine species : Vesicular stomatitis, allergic stomatitis, feedlot glossitis, photosensitization, bluetongue, rinderpest, infectious bovine rhinotracheitis, malignant catarrhal fever, bovine papular stomatitis, bovine viral diarrhoea, pseudocowpox, ovine pox, contagious ecthyma, footrot, mycotoxicosis and increased salt in concentrate.Discussion : In order to prevent the spread of the virus in the abattoir, the equipment and room should be disinfected with 2 % NaOH (caustic soda). In some countries sodium carbonate (Na2CO3) is used. The vehicle conveying diseased animals should also be disinfected and abattoir personnel leaving the abattoir should pass through a footbath with 1 % solution of NaOH.The virus of FMD can survive in meat and meat products for a considerable length of time. Outside the pH range of 6 – 9, viral infectivity is destroyed. A bovine carcass matured at above +2°C produces a drop in the pH of muscle tissue to between 5.3 – 5.7 within 24 hours of slaughter. This is caused by the formation of sarcolactic acid. Quick freezing of the meat arrests acid production and consequently the virus remains infective for about 6 months. In salted meat at 4°C, the virus is still infective in bone marrow and lymph nodes for 6 months. In blood clots in large vessels of cattle and swine, the virus is infective for 2 months. The virus is inactivated by ultraviolet rays, acetic acid, 2 % lye and ethylene oxide. At high temperatures, the virus is only active for a short period. 2 % NaOH solution inactivates the virus in 1 – 2 minutes. In dry refuse in stalls, the virus remains infective for 14 days, 3 days on soil surfaces in summer compared to 39 days in fall. It is also infective for 39 days in urine and for 20 weeks on hay dried at 22°C. The virus can be destroyed with 0.5 % citric or lactic acid, by cooking meat to an internal temperature of 69°C and by pasteurization processes of milk.