FOOT AND MOUTH DISEASE

This is a highly contagious acute febrile disease of cloven footed animals. It is characterized by vesicle formation on the tongue, mouth and in the rumen, teat and mammary gland and feet especially on the margin of the hoof in young animals. Degenerative changes occur in skeletal muscles; also extensive involvement of the cardiac muscle resulting in death. Human infection has been recorded but it is rare.
Etiology
It is caused by picorna virus (small RNA). There are 7 strains of the virus made of 3 standard or European strain and they are types O, A, C. others are African strains SAT1, SAT2 and SAT3 (sudan African territories type). The 7th strain is the Asian one found in far East. Each strain is made of many substrain which are antigenically different.
Distribution
Foot and mouth is widely distributed throughout the world and has been reported in almost all countries except Newzealand. The disease is endemic in Philipines, Africa, Europe, South America and Asia. The disease was last reported in USA and Australia about 75 years ago.
Epidemiology
Foot and mouth disease virus is found in body fluids, for example, milk, urine, faeces, saliva, blood and semen. The virus is most stable between PH 7.4 and 7.6 and rapidly destroyed by acid or alkali. It survives below 40C and may be stored for many years at temperature below freezing. It is resistant to heat. Most field strains are inactivated by heating at 560C for 30 minutes but a number of laboratory strains have shown ability to resist even 80oC for several hours. The disease spreads extremely readily when atypical type of virus appears in an area which it has not been affected before and so spread proceeds very rapidly. In the tropics, it is likely that spread takes place mainly by direct contact between animals. All formites are infective and contaminate the environment of an infected animal. Airborne spread can take place in temperate countries over considerable distances. In the tropics, airborne spread is likely to be limited to the night time when humidity is high. Since the virus can survive on material commonly found close to the animals like hair, straw, water and feed. Movement of material can lead to spread of the disease.

The milk of infected cow may contain high titres of the virus and provides another source of indirect infection. The virus will survive in tissues of animals slaughtered for meat although it is inactivated in muscles following rigor mortis. Bone marrow and lymphnodes will remain infective and responsible for movement of the virus on a scale. This is probably infrequent occurrence in tropical countries but may in the future have important effect on prospects of establishing trade in carcass meat from tropical areas to more temperate regions and countries where the disease has been controlled. Some animals with inapparent or mild infection will act as carriers for susceptible animals while ungulates act as carriers for domestic stock but transmission can occur when they come in contact.
Clinical signs
The severity of foot and mouth disease varies widely according to the virus strain involved and immune status of the animals affected. The disease is non-fatal. In severe disease, the typical picture are as follows:
High fever
Dejection
Anorexia and acute stomatitis
Abundant foamy salivation and characteristic smarking of the lips
Vesicles appear on the buccal mucosa, tongue and dental pad. These rupture leaving raw painful surfaces.
Vesicles appear on the feet at the same time. When this ruptures, the animal is in pain and lame. Vesicles may appear on the mammary gland, prepuce, vulva, gums and cheek.
There is fall in milk production.
Pregnant animals may abort.
In young animal, there is skeletal and cardiac muscle degeneration leading to death.
Immunity
About 3 days after the appearance of lesions, antibody can be detected in the serum and the antibody increases rapidly to a peak from 3-4 weeks. With the declining titres, antibody will persist for 2-4 years or even longer but no cross immunity with different strains. Immunity duration against heterologous strain or subtype is difficult to predict since it depends on the antigenic relationship between new strain and original infecting strain. After vaccination, immunity reflects the efficiency of the vaccine used but is in all cases less than that following recovery from the infection. Where vaccination operations are performed, revaccination is required to be done at intervals which depend on the exposure to the infection which animals are likely to encounter.
Diagnosis
This is based on clinical signs, low mortality, pathology and high morbidity.
Guinea pig inoculation: There is intra-dermal injection into the foot pads of the guinea pig. After some days, this leads to development of vesicles in foot pads.
It can be diagnosed using large animal inoculation.
Differential diagnosis
PPR
Goat and sheep pox
Rinderpest
Blue tongue
Orf
Prevention and control
The policy to be adopted by a country in relation to foot and mouth disease is indicated by its initial status. If the country is free from the disease, the policy should be directed at preventing its importation and in addition, defining the measures to be taken should the disease be imported. First of all, the control of importation must cover large animals from areas where the disease exist. If importation of such animal is of vital importance for livestock improvement or for other reasons, the importation should be only allowed under strict regulation covering test of the animal for carrier virus and for presence of antibody in serum and with appropriate quarantine at the country of origin and on arrival in importing country. If possible, importation should be limited to young stocks which have not been vaccinated so that if antibody is found, there is evidence of exposure to the virus. Unvaccinated animals are preferred as they are less likely to be in a state of inapparent infection. Prohibition of importation of animal products is the next measure to be applied. The principal risk attach to carcass and offals. The risk from banned and free packed meat and cooked meat is minimal. Pork and mutton represent a slightly greater hazard than beef and less likely to be imported as free packed products.
If outbreak occurs, all infected herds should be slaughtered and animals deeply buried or incinerated. Infected premises should be disinfected. In endemic areas, animals should be vaccinated annually. It is essential to use polyvalent vaccine or vaccine containing organisms against the type prevalent in the country. In case of outbreak, herds should be placed on quarantine. There should be no movement of animal to and from the herd. Animals in herd should be vaccinated. There should be no movement of personal, utensils and materials from infected to free premises. Avoid purchasing animals from infected herd. Animals dying of this disease must be buried or incinerated.
Treatment 
Broad spectrum antibiotics should be administered.