Foot & Mouth Disease

FMD- ulceration of the oral cavity and other places such as the
ruminal mucosa. Also presents as digital dermatitis.

Foot and mouth disease is from the family of viruses known as picornaviruses which are positively stranded rRNA viruses. FMD presents similar to a lot of other disease such as Malignant Catharral Fever, and Mucosal Disease. Therefore, it is very important to be able to differentiate FMD from these other diseases. 

Distribution 

• Worldwide with seven serotypes. There are different viral pools and evolving FMD genotypes. Cycles of emergence and spread usually affect several countries within a region. 
• Asia, South Africa, Europe and parts of South America are usually affected. 

Organism

• Serotype protection is not crossprotective. Protection against one serotype does not give you protection from another. 
• Affects cloven animals.
• Type A serotypes- posseses 32 different subtypes. This shows that even the different stains of the virus have much variation within them. This means that vaccinations are harder to construct as you cannot aim that at a serotype only. 
• Most isolated serotypes are type O. 
• The virus remains undetected in nearly half of FMD cases.
• The virus spreads easily across countries.

Clinical Signs 

• 2-12 day (36 hours) incubation period. 
• Fever, and vesicles which progress to erosions.
• Abortion.
• Death in young animals.
• Two weeks recovery period unless secondary infection complications.
• Cows- drooling, ropey thick saliva. Depressed and sick looking. 40.5 degree rectal temperature. Uncomfortable on the feet. 
• Sheep- mild clinical signs. Fever, oral lesions and lameness. Diagnosis and prevention of spread is difficult as hard to detect signs.
• Pigs- more severe foot lesions than in cattle around the coronary band, heel and interdigital space. Snout vesicles, oral lesions less common and drooling is rare. 

Diagnosis

• Clinical signs.
• Lab-> virus isolation from a tissue culture, antigen detection by ELISA or PCR, and antibody detection via ELISA or SNT.
• Virus isolation takes 1-4 days for a result whereas ag-ELISA and RT-PCR only takes four-five hours. 

Epidemiology

• Transmitted by inhalation of droplets/aerosol. Oral infection is  poor route of infection in ruminants, but pigs are initially infected orally from swill feeding. Virus excretion is for a period of 6 days, and the incubation period is around 7 days.
• Epidemiological factors include- viral serotype, viral multiplication, virus production, viral stability, infective doses and carrier states. 
• Virus stability- inactivated below PH 6.5 and above PH 11. Survives in milk and milk products, bone marrow and the lymph glands. 5 weeks survival in saliva at 4 degrees such as in winter.
• Period of FMD excretion related to the onset of clinical signs. 
• The respiratory infective dose for a cow is 12iu, and for a pig 20iu. The oral infective dose for a cow is 1 million iu, whereas for a pig it can be as small as 8 thousand iu. 
• Method of spread may be direct animal contact, or people, AI, movements of animal or equipment, and transport to name but a few methods.

Control and Eradication 

• Prevent disease reintroduction.
• Promote early detection.
• Prevent disease spread.
• Eliminate disease rapidly.
• Measures may or may not include vaccination.
• Eradicate disease and keep UK 'free' status- causes least disruption, minimise number of animals slaughtered, minimise environmental damage, and minimise the burden to the taxpayer. 

Control Strategies:

• Nothing.
• Prophylactic vaccine- regular vaccination of country regions with the serotype(s) present in that area. This reduces levels of disease.
• Stamping out- slaughter of infected animals/suspect infected, slaughter of animals exposed to FMD and slaughter to prevent spread.
• Stamping out with vaccination to kill (suppressive)- number of animals culled exceeds disposal capacity and vaccinate to slaughter. This reduces the amount of virus circulating and reduce the risks of spread.
• Stamping out with vaccination to live (protective)- outbreak not contained by stamping out so vaccinate to live. Defined category of animals identified for protection (geographic or species) and protect zoo animals and rare breeds. 

Other Control Strategies

• Restrict and control movements via license.
• Identify disease through reporting and surveillance and vet inspection.
• Cull animals on dangerous contact farms/on confirmed infected farms within 24 hours of the first report. 
• Rapid carcass disposal.
• Cleaning, disinfection and restocking.
• Implement strict biosecurity measures.
• Serosurveillance, epidemiology, enforcement and vaccination. 

Vaccination can be used to prevent disease spread, buffer pressure on disposal capacity, reduce livestock losses, and reduce the economical costs of the outbreak.