Difference between revisions of "Foot and Mouth Disease"
Jump to navigation
Jump to search
| Line 65: | Line 65: | ||
====Epidemiology==== | ====Epidemiology==== | ||
| − | + | *'''Highly contagious''' virus that is spread by '''aerosol''', '''saliva''', '''infected swill''', '''direct contact''', and '''fomites''' | |
| + | *'''Pigs''' produce '''3000 times more aerosol virus''' than cows | ||
| + | *Cows are much more susceptible to infection than pigs | ||
| + | **Persistent infection of cattle can occur in unkeratinized lesions, but subclinical carriers do not usually transfer infection | ||
| + | **Subclinical '''buffalo''' CAN transmit the disease | ||
====Diagnosis==== | ====Diagnosis==== | ||
Revision as of 19:20, 22 October 2008
 |
This article is still under construction. |
|
Morphology
- Very small (25nm) RNA virus
- 12 capsomeres (1 per vertex)
- 5 subunits per capsomere
- 1 molecule of virus protein (VP) per subunit
- 4 virus proteins (VP1-VP4)
- VP1 is the attachment protein
Antigenicity
- FMDV was the first animal virus in which serotypes were isolated
- To date, there are (important in bold):
- Oise (O)
- Allemagne (A)
- C (also German)
- South African Territories (SAT) 1, 2, and 3
- India (Asia-1)
- Each serotype has at lease three subtypes
- Serotype and subtype can be quickly identified by ELISA using guinea pig antisera
- All isolates are virulent
Hosts
- Cloven-hoofed animals, EXCLUDING the horse
- Cattle
- Sheep
- Goats
- Pigs
- Deer
- Elephants
- Wild ruminants: buffalo, kudu, impala, etc
Pathogenesis
- Primary replication in the upper respiratory tract, tonsils, or upper alimentary tract
- Aerosol excretion during this incubation period
- Viremia
- Virus targets stratum spinosum of stratified squamous epithelia and mucus mebranes
- Secondary vesicles appear after incubation of 2-14 days
- Appearance of lesions by age:
- 0-2 days: unruptured vesicles
- 1-3 days: newly ruptured vesicles with adherent epithelia at margins
- 3-7 days: ruptured vesicles, loss of epithelia, no marked fibrous margin
- 7-10+ days: open lesions with marked fibrous margin
- In the young, without maternal antibody, virus will localize in the heart and cause death by myocarditis
- FMDV causes loss of condition and productivity but is NOT typically fatal
Pathogenesis by species
- Pigs and Sheep:
- Lesions less obvious, but vesicles around nose, mouth, and coronary band
- Lesion at coronary band means infection is usually less than a week old
- Lesions grow down claw at a rate of 1mm per week
- Cattle
- Lesions are seen inside mouth, around muzzle, in the interdigital cleft, around coronary band, and on teats
- Excessive salivation, anorexia, secondary mastitis
- PM: lesions in oesophagus and forestomachs
Epidemiology
- Highly contagious virus that is spread by aerosol, saliva, infected swill, direct contact, and fomites
- Pigs produce 3000 times more aerosol virus than cows
- Cows are much more susceptible to infection than pigs
- Persistent infection of cattle can occur in unkeratinized lesions, but subclinical carriers do not usually transfer infection
- Subclinical buffalo CAN transmit the disease
Diagnosis
Control
- Recovered animals show immunity ONLY to the subtype of first exposure, and even this is relatively short-lived
- Re-exposure to the original serotype after immunity as waned will still result in virus excretion, even without clinical symptoms
- Infection by a second serotype will result in clinical disease
- For these reasons, vaccination is not practiced in the UK
- Further, vaccination would mean a loss of meat export markets