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Foot and mouth disease (FMD) (Epidemiology (Sheep/cattle mainly infected…
Foot and mouth disease (FMD)
Aetiology
Picornavirus (7 serotypes, no cross-immunity between them)
Highly infectious vesicular disease of even-toed ungulates (cattle, sheep, goats, pigs and others)
Not generally fatal, but causes severe production/trade losses and animal welfare compromise
Pathogenicity
Survives at pH 6.7-9.5 if at 4 degrees Celsius or lower
Replication in pharynx, then viraemia, then replication in epithelium (epithelial cell lysis causes vesicles)
Clinical signs (vesicles develop within 2 days of exposure)
Cattle
Drooling, lameness, inappetence/lethargy, vesicles on feet, buccal mucosa, tongue, teats & nasal passages. Vesicles rupture approx. 24 hrs after forming.
Sheep/goats
Many subclinical. Main clinical sign is lameness (+/- vesicles at coronary band and sometimes buccal mucosa).
Pigs
Lameness, blanching of skin at coronary band with vesicles (+/- on teats, mouth and snout) progressing to recumbency, ulcerations and claw sloughing.
Epidemiology
Sheep/cattle mainly infected by inhalation
Pigs mainly infected by ingestion (swill feeding) and are MAJOR AMPLIFIERS
Virus shed in vesicular fluid, ocular secretions, saliva, urine, faeces, milk and semen (everywhere!)
Incubation period usually 2-4 days (1-14d) with shedding up to 4 days before clinical signs
Peak transmission 0-4 days after onset of clinical signs
Spread via swill feeding, animal-to-animal, contiguous premises and aerosol (pigs)
Vaccinated animals may shed the virus (but are protected from clinical disease) for up to 1 week
Swill feeding is most likely means of entry into Australia
Diagnosis
Principles
Detect Ag (PCR, Ag ELISA, virus isolation)
Detect Ab (Ab ELISA)
Virus removed from blood 3-4 days after onset of clinical signs. Ab titre rises approx. 4 days after onset of clinical signs.
Samples
Vesicular fluid (placed in red tube) and epithelium (placed in buffered phosphate saline with 50% glycerol). Used for PCR, Ag ELISA, virus isolation.
Blood samples (red tube). Used for PCR, Ab ELISA.
Oral/nasophargyeal swabs. Used for PCR, Ag ELISA, virus isolation.
Sample packaging/transport
All samples should be labelled and stored in an insulated, cool box
Inform lab that they are coming
"Triple pack" to prevent spillage
DDx (cattle)
Vesicular stomatitis
Refer to Blisters assignment
Malignant catarrhal fever
Fatal disease of cattle (1-3 yrs) caused by a group of herpesviruses (mainly ovine herpesvirus). Causes erosions/ulcers in the oral cavity.
BVDV (mucosal disease)
Cytopathic BVDV causing oral erosions in PI calves (6 mths to 2yrs)
IBR
BHV-1 may cause necrotic oral lesions in calves
Papular stomatitis
Parapox virus causing papules of the muzzle, nostrils, buccal cavity and udder.
Ageing lesions (cattle)
Accurate to 5 days (and less so to 7 days), but cannot age beyond 7 days. Mouth lesions most accurate.
Day 1: epithelial blanching with vesicle formation
Day 2: ruptured vesicles, raw epithelium, clear demarcation, no fibrin
Day 3: loss of sharp demarcation, less red. Fibrin.
Day 4: lots of fibrin, epithelial regrowth.
Day 7: scar tissue, healing. Some fibrin.
DDx (sheep)
Scabby mouth
Parapox virus causing vesicles on lips/muzzle/buccal cavity.
Bluetongue virus
Abrovirus (culcoides spp) causing stomatitis and oral mucosal erosions. Sometimes lameness.
DDx (pigs)
Swine vesicular disease
Vesicular exanthema
Vesicular stomatitis
Phototoxic dermatitis
Prevention/control/eradication in Australia
Prevention
Training vets/industry to recognise CS
Raising awareness of swill feeding risks & banning swill feeding
National/industry biosecurity measures
Control in outbreak
Emergency vaccination (delays/prevents further spread). Generally done using 'ring vaccination' +/- suppressive vaccination.
Eradication
Stamping out with vaccination (all vaccinated animals would have to be destroyed eventually)
Stamping out without vaccination
AUSVETPLAN
For all diseases in EADRA, there is a preferred approach to an outbreak. Outlines the steps/procedures undertaken in the event of an FMD outbreak in Australia.
Phases of an EAD response
1: Investigation/alert
Steps of outbreak investigation
Farm visit, info/sample collection, communication with LLS, EAD hotline and diagnostic labs.
Initial quarantine/movement control
State CVO notified, then national CVO within 24 hrs
2: Operational
CCEAD/NMG convened, AUSVETPLAN implemented, response structure is established (LCC, FCPs, SCCs, NCCs)
Restricted/control areas established
3: Proof-of-freedom
Monitoring, surveillance and research provide evidence that regions are free of disease
Key step in removing restrictions and progressing towards disease control (eradication vs containment)
4: Stand-down
If EAD not confirmed, people/agencies contacted during investigation/alert phase are notified
Operations are systematically wound up
CCEAD and NMG conclude activities and arrange a final report