Foot and Mouth Disease

ETIOLOGY  Classification of the causative agent

Virus family Picornaviridae
Genus Aphthovirus.
Seven immunologically distinct serotypes A, O, C, SAT1, SAT2, SAT3, Asia1
Temperature  Resistance to physical and chemical action
  Preserved by refrigeration and freezing and progressively inactivated by temperatures above 50°C
pH Inactivated by pH 9.0
Disinfectants Inactivated by sodium hydroxide (2%), sodium carbonate (4%), and citric acid (0.2%). Resistant to iodophores, quaternary ammonium compounds, hypoclorite and phenol, especially in the presence of organic matter
   

EPIDEMIOLOGY

  1. One of the most contagious animal diseases, with important economic losses
  2. Low mortality rate in adult animals, but often high mortality in young due to myocarditis
Hosts    Bovidae (cattle, zebus, domestic buffaloes, yaks), sheep, goats, swine, all wild ruminants and suidae. Camelidae (camels, dromedaries, llamas, vicunas) have low susceptibility
Transmission     1. Direct or indirect contact (droplets)
2. Animate vectors (humans, etc.)
3. Inanimate vectors (vehicles, implements)
4. Airborne, especially temperate zones (up to 60 km overland and 300 km by sea)
 
Sources of virus		  

  1. Incubating and clinically affected animals
  2. Breath, saliva, faeces, and urine; milk and semen (up to 4 days before clinical signs)
  3. Meat and by-products in which pH has remained above 6.0
  4. Carriers: particularly cattle and water buffalo; convalescent animals and exposed vaccinates (virus persists in the oropharynx for up to 30 months in cattle or longer in buffalo, 9 months in sheep). African Cape buffalo are the major maintenance host of SAT serotypes
Occurrence  FMD is endemic in parts of Asia, Africa, the Middle East and South America (sporadic outbreaks in free areas) For detailed information on occurrence, see recent issues of World Animal Healt

DIAGNOSIS

Incubation period is 2-14 days

Clinical diagnosis

Cattle

  • Pyrexia, anorexia, shivering, reduction in milk production for 2-3 days, then
  • smacking of the lips, grinding of the teeth, drooling, lameness, stamping or kicking of the feet: caused by vesicles (aphthae) on buccal and nasal mucous membranes and/or between the claws and coronary band
  • after 24 hours: rupture of vesicles leaving erosions
  • vesicles can also occur on the mammary glands
  • Recovery generally occurs within 8-15 days
  • Complications: tongue erosions, superinfection of lesions, hoof deformation, mastitis and permanent impairment of milk production, myocarditis, abortion, death of young animals, permanent loss of weight, loss of heat control (‘panters’)

Sheep and goats

  1. Lesions are less pronounced. Foot lesions may go cularsis. Lesions in dental pad of sheep. Agalactia in milking sheep and goats is a feature. Death of young stock

Pigs

  1. May develop severe foot lesions particularly when housed on concrete. High mortality in piglets a frequent occurrence

Lesions

  1. Vesicles or blisters on the tongue, dental pad, gums, cheek, hard and soft palate, lips, nostrils, muzzle, coronary bands, teats, udder, snout of pigs, corium of dewclaws and interdigital spaces
  2. Post-mortem lesions on rumen pillars, in the myocardium, particularly of young animals (tiger heart)

Differential diagnosis

Clinically indistinguishable:

  • Vesicular stomatitis
  • Swine vesicular disease
  • Vesicular exanthema of swine

Other differential diagnosis:

  1. Rinderpest
  2. Mucosal disease
  3. Infectious bovine rhinotracheitis
  4. Bluetongue
  5. Bovine mammillitis
  6. Bovine cular stomatitis
  7. Bovine viral culars

Laboratory diagnosis

Procedures

Identification of the agent

  1. ELISA
  2. Complement fixation test
  3. Virus isolation: inoculation of primary bovine thyroid cells and primary pig, calf and lamb kidney cells; inoculation of BHK-21 and IB-RS-2 cell lines; inoculation of mice

Serological tests

1. ELISA     (prescribed tests in the Manual)
2. Virus cularsisd test

Samples

  1. 1 g of tissue from an unruptured or recently ruptured vesicle. Epithelial samples should be placed in a transport medium which maintains a pH of 7.2-7.4 and kept cool
  2. Oesophageal-pharyngeal fluid collected by means of a cular cup Probang samples should be frozen to below -40°C immediately after collection

Special precautions are required when sending perishable suspect FMD material within and between countries.

PREVENTION AND CONTROL

Sanitary prophylaxis

1. Protection of free zones by border animal movement control and surveillance
2. Slaughter of infected, recovered, and FMD-susceptible contact animals
3. Disinfection of premises and all infected material (implements, cars, clothes, etc.)
4. Destruction of cadavers, litter, and susceptible animal products in the infected area
5. Quarantine measures (Code Chapter 2.1.1.)

Medical prophylaxis

Inactivated virus vaccine containing an adjuvant. Immunity: 6 months after two initial vaccinations, 1-month apart, depending on the antigenic relationship between vaccine and outbreak strains