Difference between revisions of "Foot and Mouth Disease"
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− | {{ | + | {{unfinished}} |
− | |||
− | == | + | {{toplink |
+ | |linkpage =Viruses | ||
+ | |linktext =VIRUSES | ||
+ | |sublink1=Picornaviridae | ||
+ | |subtext1=PICORNAVIRUSES | ||
+ | |pagetype =Bugs | ||
+ | }} | ||
+ | <br> | ||
− | + | ====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==== |
+ | *Clinical signs for provisional diagnosis | ||
+ | *Confirmed by '''ELISA''' for virus '''antigen''' | ||
+ | **ELISAs are serotype-specific | ||
+ | *Should soon be replaced by immunochromatography-bedside ELISA to allow on-farm diagnosis | ||
+ | *'''Virus isolation''' can also be performed in kidney culture cells, and then serotyped by ELISA | ||
+ | *Serology for virus '''antibody''' can determine past infection | ||
+ | **ELISAs used to detect subclinical carrier sheep | ||
+ | **Cannot be done on vaccinated animals | ||
+ | *RT-PCR has been suggested for on-farm diagnosis, but has flaws: | ||
+ | **RNA is readily degraded by tissue enzymes | ||
+ | **RNA must be purified before converting to DNA for PCR | ||
+ | **False positives can occur easily by contamination with previously amplified DNA | ||
− | + | ====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 | |
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Revision as of 19:27, 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
- Clinical signs for provisional diagnosis
- Confirmed by ELISA for virus antigen
- ELISAs are serotype-specific
- Should soon be replaced by immunochromatography-bedside ELISA to allow on-farm diagnosis
- Virus isolation can also be performed in kidney culture cells, and then serotyped by ELISA
- Serology for virus antibody can determine past infection
- ELISAs used to detect subclinical carrier sheep
- Cannot be done on vaccinated animals
- RT-PCR has been suggested for on-farm diagnosis, but has flaws:
- RNA is readily degraded by tissue enzymes
- RNA must be purified before converting to DNA for PCR
- False positives can occur easily by contamination with previously amplified DNA
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