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Viral Disease - Foot and Mouth Disease

Synonym

Aphthous fever, FMD

Etiology

Acute highly contagious febrile disease of cloven footed animals characterized by formation of vesicles in mouth and feet of cattle, sheep, goat and swine. Caused by Picorna virus group (Aphtho virus). Having Serotypes - O, A, C, and South African type SAT1, SAT2, SAT 3 and Asia 1 of which O, A, C and Asia 1 - prevalent in India.

Epidemiology

FMD affects all cloven-footed animals and it is rarely fatal except in very young animals. It is endemic in Africa, Asia, South America and parts of Europe. The disease can occur in any country but Japan, New Zealand and Australia are disease free.

Incubation period

Few hours to few days, Sheep: Incubation period is 3 to 8 days

Transmission

Ingestion of contaminated materials and direct contact with affected animals.

Pathogenesis

Virus invades the epithelial cells and multiplies, causing focal areas of inflammation Invades lymph and blood and it reaches epithelium of other mucous membrane producing vesicles.

{Inhalation/ingestion - oropharyngeal infection - Cuses viremia - epidermal cells - clinical signs and lesions enhanced by mechanical trauma}.

Clinical Signs

High temperature, Vesicles appear on mouth, Rupture leaving ulcer - refuses feed and water, Vesicles on cleft of feet leading to lameness, Also seen in lightly haired parts (Udder and teat), Produces smacking noise and in neonates, interstitial mononuclear and necrotic myocarditis.

Vesicles on the mucosa of lips, dorsum of tongue and palate in cattle and also in coronet, udder and teat, Lesions also seen - Rumen, reticulum and omasum, Haemorrhage and diffuse oedema in mucosa of abomasum and small intestine, Death may be due to gastroenteritis and myocardial lesions, In sheep: Oral lesions appear on the dental pad only.

Hyaline degeneration and necrosis of myocardial fibres and also in sketetal muscles - "Tigroid heart appearance". Secondary bacterial infections produces osteomyelitis and suppurative arthritis.

Secondary Effects

Mastitis

Anaemia

Disturbances in sexual function

Diabetes

Over growth of hair

Cardiac cicatrices

Panting

Dyspnoea

Delayed growth of young animals

Differential diagnostic list

Vesicular stomatitis

Vesicular exanthema

Swine vesicular disease

Rinderpest

Bovine viral diarrhea

Diagnosis

Clinical signs and lesions

Complement fixation test

Virus isolation and polymerase chain reaction

Treatment

no specific treatment is available

Prevention and control

vaccinating the animals,

Regular vaccination against FMD is a way of life for most of the world and vaccine production is a major industry. In the endemic countries, eradication does not seem possible within the foreseeable future and countries free of the disease may require regional vaccination during outbreaks.

To be effective, the program should consist of vaccination against a number of strains three times yearly. More frequent vaccination may be necessary in the face of outbreaks during optimum conditions for spread. Young animals with maternally derived antibodies do not respond to vaccination.

Vaccination of sheep and pigs is also used in control programs. In pigs a bior trivalent, inactivated, adjuvant vaccine gives h2 immunity for 6 months and some resistance for 12 months. Severe local reactions (abscesses and granulomas) at vaccination sites can be reduced by the inclusion of an oil-adjuvant.

However, vaccination of pregnant sows leads to a high rate of abortions and stillbirths. In sheep, monovalent or trivalent vaccines give immunity for 5-6 months but the sheep may act as inapparent carriers.


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