Exotic Diseases

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Species Infected

cattle, sheep, goats, pigs

occasionally humans, but clinically mild

does not infect horses

Clinical Signs

Cattle

• incubation 2-8 days
• first signs
• fever
• anorexia
• depression, drop in milk production
• then development of stomatitis¸ lip smacking
• ropey salivation
• vesicles full of clear, straw-coloured fluid
• vesicles rapidly enlarge and rupture within 24 hours
• epithelium desquamates
• concurrent development of vesicles on coronet, in cleft
• rupture leads to marked lameness
• secondary bacterial infection of deeper structures a common sequel
• teats may also be involved
• high morbidity
• up to 100%
• low mortality in adults
• may have sudden death in calves of up to 20%

Pigs

• important differences to the signs seen in cattle
• milder disease
• vesicular lesions small
• may get severe lameness with separation of corium
• high mortality amongst piglets
• myocarditis
• pancreatitis
• gastroenteritis

Sheep and Goats

• very mild disease but can be variable
• lesions uncommon in mouth
• tend to occur on gums and dental pad
• if occur on tongue appears as a blanching
• sloughing of epithelium without vesicle formation
• excess salivation is NOT a feature
• feet lesions more common
• generalised flock evidence for lameness may be only overt sign
• secondary bacterial infection could be mistaken for footrot
• teat lesions and mastitis
• abortions; lamb mortalities due to cardiac and skeletal myonecrosis

Lesions

• species differences
• cattle may be most spectacular
• pigs mild
• sheep primarily foot related

Pathogenesis

• main routes of infection are by ingestion and inhalation
• inhalation prime route for spread between cattle
• viraemia develops, lymphoid tissue localisation is then followed by epithelial sites of predilection
• vesicles become main but not sole source of infection
• carrier state can develop for prolonged periods after clinical disease

Aetiology

• Aphthovirus (Picornaviridae)
• 7 types and more than 60 subtypes
• new antigenic variants developing all the time
• little or no cross protection
• problems with vaccination programmes
• resistant to environmental influences
• survives for long periods in humid situations
• survives for long periods in animal products especially bone marrow, parenchyma
• sensitive to acid (pH 4.0) and alkaline (pH 11.0) conditions

Epidemiology

• humans important factor

1. Nature of virus

• highly resistant to inactivation outside of animal in temperate climates
• one of the most infectious of viruses
• extremely high replicative titres
• multiple antigenic subtypes

2. Nature of disease

• short incubation period leads to a rapidly propagating epidemic
• virus excretion occurs before lesions develop
• a carrier state can occur
• in recovered animals
• in vaccinated animals
• pigs represent the most dangerous species for spreading of disease as they show only mild lesions yet produce highest virus titres

3. Nature of host

• cattle most sensitive to infection
• pigs are link between infected garbage and other species
• cattle are therefore considered indicators of disease
• pigs are therefore considered amplifiers of infection

4. Nature of environment

• temperate climate, high humidity and low sunlight all assist virus survival
• virus is readily windborne and new outbreaks could be attributable to wind carriage

Differential Diagnoses

     1.  other vesicular diseases
     2.  rinderpest/peste de petits ruminants
     3.  bluetongue
     4.  mucosal disease
     5.  papular stomatitis
     6.  footrot
     7.  phototoxic dermatitis due to contact with plants from the family Umbelliferae