Picornaviridae

Aphthoviruses

Foot and Mouth Disease Virus

Introduction

• Affects all cloven hoofed animals, cattle, sheep and pigs and others.
• 1967 + 2001 major outbreaks in UK.
• Controlled by slaughter policy in UK.
• Still widespread in many parts of world especially S. America, far East.
• Very infectious virus.

Clinical

• Foot and Mouth disease is not a high fatal disease - approximately 5% mortality, usually young animals, older animals recover but stop giving milk yield - i.e. production losses are important factor.
• It is very debilitating and animals take weeks or months to recover.
• Economic impact as stops export of cattle and cattle products.
• Fairly easy to diagnose in classical form - difficult in sheep.
• Animals froth at mouth, usually in more than one animal (one animal may be just sore mouth from another cause).
• Lameness in a number of animals.
• Characteristic lesions in mouth that are short lived.
• Incubation from two days up to 3 weeks in sheep.

Pathology

Gross

1. Initially - hyperaemia of mucosa (e.g. catarrhal inflammation) then within 12 hours produces fluid filled vesicles on dorsum of tongue, may be other places.
2. Small vesicle coalesce to produce big ones -i.e. Bullae.
3. Very quickly rupture; epithelium appears dirty grey in colour because of necrosis - sloughed skin, very good for diagnosis.
4. Leave painful, hyperaemic epithelium.
5. Looks like "ulcer "with ragged edge but not a true ulcer as stratum germinativum retained and will rapidly heal completely in about 2 weeks unless becomes secondarily infected.

• Also produces sores in interdigital cleft, at coronet and bulbs of heals.
  • These feet lesions often take a long time to heal as secondary infections may ensue and produce true deep ulceration.
• Teats on animals that are suckling may also develop vesicles.

• Sheep develop very few vesicles in mouth but foot lesions can be dramatic - like a whole flock with foot rot. N.B. Can also be very mild!
• Coronets are very red with vesicles and sores.

• Pigs have vesicles on snout, which are quickly eroded - hard to look at pig’s tongue.
• Hoof lesions like other species; hoof may come off, known as "thimbling".
• Lesions will heal eventually but is very painful (Often need euthanasia)

Microscopic lesions

• Degeneration of prickle cells.
• Cells "balloon" as fill with fluid and then die to produce vesicle containing straw coloured or clear fluid.

Diagnosis

Definitive diagnosis.

N.B. Notifiable Disease.

• Inform MAFF (and police) as soon as suspect clinical diagnosis.
• MAFF will take specimens of fluid from vesicle. Suck out fluid with syringe.
• Skin that has sloughed off vesicle also good for diagnosis.
• If the above two are not available can use scraping of base of erosion.

• May see animals that have discoloration of tongue due to having had FMD. In these cases take scraping of retropharyngeal region, put scrapings in transport medium.

1. Atigen capture ELISA
2. PCR
3. Culture (need ph7 buffered transport media)
4. Antibody capture ELISA

• In foot and mouth disease usually use ELISA to provide quick diagnosis - especially if have vesicular fluid.

Enteroviruses

Swine Vesicular Disease Virus

Caused by an enterovirus. (picorna virus)

May produce vesicles in mouth that are indistinguishable from foot and mouth disease.

Swine vesicular disease produces sporadic large outbreaks; approximately 5% have lesions in mouth, foot lesions much more common.