Foot and Mouth Disease

foot mouth ds

 

If we talk about diseases that have significantly affected cattle industry over centuries, Foot-and-mouth disease (FMD) would be one. It is highly contagious viral disease of domestic and wild cloven-hooved animals. Cattle are usually the main host, apart from other susceptible hosts including swine, sheep, goat, buffalo, deer, antelope, wild pigs, elephant, giraffe, and camelids. So far no zoonotic link has been established.

All you need to know about the causative agent and the disease:

The virus belongs to Aphthovirus genus of Picornaviridae family. There are seven immunologically distinct serotypes: A, O, C, SAT1, SAT2, SAT3, and Asia1 which do not confer cross immunity. The disease is difficult to control because mutation from error-prone RNA replication, recombination, and host selection generate constant new FMDV variants.

The interval between exposure to infection and the appearance of symptoms varies between 24 hours and 10 days, or even longer depending on the degree and duration contact. The average time, under natural conditions, is 2 to 5 days.

Spread of infection occurs by:

  • Movement of infected animals and the direct contact between the infected and susceptible animals
  • Feeding of contaminated animal products to susceptible livestock, particularly pigs
  • Indirect contact, i.e., contact with virus from infected animals transported mechanically by persons, livestock vehicles, fomites, or possibly by wild animals and birds.
  • Virus in dried blood, milk, meat, faeces, saliva and carcasses can be stable and serve as a potent source of infection.
  • Airborne spread of the disease can take place and under favourable weather conditions the disease may be spread considerable distances by this route (60 Km overland and 300 Km over sea).

The disease is generally mild in adult cattle, but pregnant cows may abort. Although morbity is high; mortality is low in adult animals and high in young calves.

Symptoms

  • Pyrexia
  • Vesicular lesions on the mouth, tongue, feet, snout and teats of infected animals
  • Drop in milk production
  • Weight loss
  • Loss of appetite
  • Smacking of the lips, grinding of the teeth and drooling
  • Lameness

Complications: tongue erosions, superinfection of lesions, hoof deformation, mastitis, permanent impairment of milk production, abortion, permanent loss of weight, loss of heat control (‘panters’) and poor young calves may die from myocarditis.

Lesions: 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 inter-digital spaces  Erosions on rumen pillars at post mortem. Gray or yellow streaking in the heart from degeneration and necrosis of the myocardium in young animals of all species (‘tiger heart’)

Treatment

No treatment given as such, affected animals usually recover within 8-15 days. However, considering the loss of production and infectiousness of the disease, culling is usually the best option to be adopted.

Prevention

  • Regular coordinated mass vaccination
  • Control of animal movements
  • Quarantine practices
  • Strict zoo-sanitary measures
  • Biosafety and Biosecurity
  • Export restrictions are often imposed on countries with known outbreaks.
  • Infected carcasses must be disposed of safely by incineration, rendering, burial or other techniques. Milk from infected cows can be inactivated by heating to 100°C (212°F) for more than 20 minutes. Slurry can be heated to 67°C (153°F) for three minutes.

 

Vaccination with one serotype does not protect the animal against other serotypes, and may not protect the animal completely or at all from other strains of the same serotype. Currently, there is no universal FMD vaccine. Vaccines widely used are of inactivated type. To be effective, vaccines must include the viral types and subtypes that prevail in field.

-Dr. Sudha Kripal

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