Difference between revisions of "Foot and Mouth Disease"

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Also known as: '''''FMDV —  FMD'''''
 
  
−
== Introduction ==
+
FMD
 +
FMDV
  
−
This [[:Category:Apthoviruses|Apthovirus]] is a small (25nm) +ss RNA virus, unenveloped and has 7 serotypes, namely '''Oise (O), ''''''Allemagne (A), ''''''C (also German), '''South African Territories (SAT) 1, 2, and 3 and Asia-1.
+
====Morphology====
 +
*Very small (25nm) +ss RNA virus, unenveloped
 +
*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
  
−
This disease affects all '''cloven-hoofed animals, '''namely cattle, sheep, goats, pigs, deer, elephants and other wild ruminants such as buffalo and kudu etc. It does NOT affect the horse. The main presentation of the disease is the formation of '''vesicles'''.
+
====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'''
  
−
The disease is NOTIFIABLE in the UK and any animals with the disease, or in contact with the disease have to be destroyed.
+
====Hosts====
 +
*'''Cloven-hoofed animals, EXCLUDING the horse'''
 +
**Cattle
 +
**Sheep
 +
**Goats
 +
**Pigs
 +
**Deer
 +
**Elephants
 +
**Wild ruminants: buffalo, kudu, impala, etc
  
−
The virus replicates primarily in the upper respiratory tract, tonsils, or upper alimentary tract and there is '''aerosol''' excretion during this incubation period. This is then followed by a viremia. Virus targets stratum spinosum of stratified squamous epithelia and mucus membranes and secondary '''vesicles''' appear after incubation of 2-14 days. Lesions also affect the feet with cutaneous erosions in interdigital cleft, at coronet and bulbs of heals . These feet lesions often take a long time to heal as secondary bacterial infections may ensue and produce true deep ulcerative dermatitis. In the young, without maternal antibody, virus will localize in the heart, particularly the wall of the left ventricle, resulting in multi-focal necrosis of the myocardium and subsequent death. Persistent infection of cattle can occur in unkeratinized lesions, but subclinical carriers do not usually transfer infection except for subclinical buffalo that can transmit the disease.
+
====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 [[Cavity & Gingiva - Pathology#Foot and Mouth disease|'''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
 +
*'''Lameness'''
 +
**Also produces cutaneous erosions in interdigital cleft, at coronet and bulbs of heals
 +
**These feet lesions often take a long time to heal as secondary bacterial infections may ensue and produce true deep ulcerative dermatitis
 +
*'''Teats''' on animals that are suckling may also develop vesicles
 +
*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
  
−
FMDV causes loss of condition and productivity but is NOT typically fatal. Approximately 5% mortality (usually young animals); older animals recover. The virus is highly contagious and spread is by aerosol, direct contact, saliva, infected swill and fomites. Pigs produce 3000 times more aerosol virus than cows, but cows are much more susceptible to infection than pigs.
+
=====Pathogenesis by species=====
 +
*'''Pigs''' and '''Sheep''':
 +
**Lesions less obvious, but vesicles around nose, mouth, and coronary band
 +
**Pigs have vesicles on snout, which are quickly traumatised to leave an eroded lesion
 +
**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
  
−
In 1967 and 2001 there were major outbreaks in the UK. The disease is still widespread in many parts of world especially S. America and far East.
+
====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
 +
*1967 + 2001 major outbreaks in UK
 +
*Still widespread in many parts of world especially S. America, far East
 +
*Foot and Mouth disease is NOT a highly fatal disease: approximately 5% mortality (usually young animals); older animals recover
  
−
== Clinical Signs ==
+
====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
 +
*May see animals that have discoloration of [[Oral Cavity - Tongue - Anatomy & Physiology|tongue]] due to having had FMD
 +
**In these cases take scraping of retropharyngeal region, put scrapings in transport medium and send for testing
  
−
Main clinical signs include pyrexia, depression, separation away from the herd, drooling, excess salivation, anorexia pain while eating as well as smacking of the lips. Lameness is also a key clinical sign and in pigs may often be the first noticeable sign as mouth lesions in this specie are less severe.
+
====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
  
−
Lesions in the mouth and on the tongue have the following characteristics depending on age of lesions.
+
=====Prevention in the UK=====
−
: At 0- 2 days there will be unruptured vesicles.
+
*Imported stock must come from virus-free countries that DO NOT vaccinate
−
: At 1-3 days newly ruptured vesicles with adherent epithelia at margins will appear.
+
*Meat imported from endemic countries must be de-boned
−
: By 3-7 days there will be ruptured vesicles, loss of epithelia, no marked fibrous margin.
 
−
: At days 7-10+ open lesions with marked fibrous margin will be present.
 
  
−
'''Teats''' on animals that are suckling may also develop vesicles.
+
=====In an Outbreak=====
 +
*ANY sign of lesions in a susceptible animal is '''NOTIFIABLE''' to the Divisional Veterinary Officer and local police
 +
*Once diagnosis is confirmed, all animals on the premises must be '''slaughtered and incinerated'''
 +
*Further disinfection of the premises
 +
*Movement is controlled within a 10-mile radius
 +
*Follow-up serology must be performed to ensure no spread has taken place
 +
*'''Ring vaccination''' with relevant subtype to create a barrier of immune animals (although this was not done in the 2001 outbreak)
  
−
In pigs and sheep, lesions are less obvious, but vesicles around nose, mouth, and coronary band are present. Pigs have vesicles on snout, which are quickly traumatised to leave an eroded lesion. Presence of a lesion at '''coronary band''' means infection is usually less than a week old. The lesions grow down the claw at a rate of 1mm per week.
+
=====In Endemic Areas=====
 +
*Disease cannot be prevented by slaughter due to large numbers of carrier stock
 +
*Annual '''Inactivated whole virus vaccination''' using local subtypes
 +
**Inactivated by azuridines, using alhydrogel adjuvant for cows, and oil for pigs
 +
**Attenuated virus reverts to virulence
 +
**Subunit vaccines ineffective
 +
**Expensive
 +
**2 initial injections at 4 months (if dams vaccinated), followed by boosters every 6-12 months
 +
**Induces virus-neutralizing antibodies
 +
*Vaccination DOES NOT render meat harmful to consumers, but does affect when it can be exported
  
−
In cattle, lesions are seen inside mouth, around muzzle, in the interdigital cleft, around coronary band, and on teats. There will be excessive salivation, anorexia, secondary mastitis and on PM there will be lesions in oesophagus and forestomachs.
+
====Pathology====
 +
=====Gross=====
 +
#Initially - hyperaemia of mucosa (e.g. catarrhal inflammation) then within 12 hours produces fluid filled vesicles on dorsum of [[Oral Cavity - Tongue - Anatomy & Physiology|tongue]], may be other places
 +
#Small vesicle coalesce to produce big ones -i.e. Bullae
 +
#Very quickly rupture; epithelium appears dirty grey in colour because of necrosis - sloughed skin, very good for diagnosis
 +
#Leave painful, hyperaemic epithelium
 +
#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
  
−
== Diagnosis ==
+
=====Microscopic lesions=====
 +
*Degeneration of prickle cells
 +
*Cells "balloon" as fill with fluid and then die to produce vesicle containing straw coloured or clear fluid
  
−
Clinical signs are enough to make a provisional diagnosis. This must be confirmed by [[ELISA testing|'''ELISA''']] for virus '''antigen. '''ELISAs are serotype-specific. This method is soon to 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 and ELISAs are used to detect subclinical carrier sheep. This cannot be done on vaccinated animals.
 
  
−
RT-PCR has been suggested for on-farm diagnosis, but has flaws such as, 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.
+
====For more information====
−
 
+
[http://www.defra.gov.uk/footandmouth/ DEFRA]
−
Samples should be taken from the vesicle itself and include the vesicle fluid as well as the tissue. These should be placed in transport medium and sent for testing.
+
[[Category:Apthoviruses]][[Category:Cattle]][[Category:Sheep]][[Category:Goat]][[Category:Pig]]
−
 
 
−
== Control ==
 
−
 
 
−
Recovered animals show immunity ONLY to the serotype of first exposure, and even this is relatively short-lived, therefore re-exposure to the original serotype after immunity has waned will still result in virus excretion, even without clinical symptoms. Infection by a second serotype will result in clinical disease. It is for these reasons, that '''vaccination is not practiced''' in the UK. Further, vaccination would mean a loss of meat export markets.
 
−
 
 
−
===== Prevention in the UK =====
 
−
 
 
−
Imported stock must come from virus-free countries that DO NOT vaccinate. Any meat imported from endemic countries must be de-boned.
 
−
 
 
−
ANY sign of lesions in a susceptible animal is '''NOTIFIABLE''' to the Divisional Veterinary Officer and local police. Once diagnosis is confirmed, all animals on the premises must be '''slaughtered and incinerated''' and the premises fully disinfected. Movement is controlled within a 10-mile radius and follow-up serology must be performed to ensure no spread has taken place on any nearby farms. '''Ring vaccination''' with relevant subtype to create a barrier of immune animals (although this was not done in the 2001 outbreak) can be used. There is to be no movement on or off the farm as soon as a case is suspected.
 
−
 
 
−
'''In Endemic Areas''' disease cannot be prevented by slaughter due to large numbers of carrier stock. Annual '''inactivated whole virus vaccination''' using local subtypes is used. This vaccine is inactivated by azuridines, using alhydrogel adjuvant for cows, and oil for pigs. Subunit vaccines are ineffective. The course involves 2 initial injections at 4 months (if dams are vaccinated), followed by boosters every 6-12 months, which induces virus-neutralizing antibodies. Vaccination DOES NOT render meat harmful to consumers, but does affect when it can be exported.
 
−
 
 
−
== References ==
 
−
 
 
−
Andrews, A.H, Blowey, R.W, Boyd, H and Eddy, R.G. (2004)'''Bovine Medicine '''(Second edition), ''Blackwell Publishing''
 
−
 
 
−
Brownlie, J (2007) '''Virology Study Guide, '''''Royal Veterinary College.''
 
−
 
 
−
Radostits, O.M, Arundel, J.H, and Gay, C.C. (2000) '''Veterinary Medicine: a textbook of the diseases of cattle, sheep, pigs, goats and horses '''''Elsevier Health Sciences''
 
−
 
 
−
Taylor, D.J. (2006) '''Pig Diseases''' (Eighth edition)'' St Edmunsdbury Press ltd''
 
−
 
 
−
 
 
−
{{review}}
 
−
 
 
−
{{OpenPages}}
 
−
 
 
−
[[Category:Apthoviruses]] [[Category:Oral_Diseases_-_Cattle]] [[Category:Oral_Diseases_-_Sheep]] [[Category:Oral_Diseases_-_Goat]] [[Category:Oral_Diseases_-_Pig]] [[Category:Dermatological_Diseases_-_Cattle]] [[Category:Dermatological_Diseases_-_Sheep]] [[Category:Dermatological_Diseases_-_Goat]] [[Category:Dermatological_Diseases_-_Pig]] [[Category:Oral_Cavity_-_Vesicular_Pathology]] [[Category:Integumentary_System_-_Viral_Infections]] [[Category:Viral_Myositis]]
 
−
[[Category:Expert Review - Farm Animal]]
 

Revision as of 12:15, 25 May 2010


 This article is still under construction.


FMD FMDV

Morphology

  • Very small (25nm) +ss RNA virus, unenveloped
  • 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
  • Lameness
    • Also produces cutaneous erosions in interdigital cleft, at coronet and bulbs of heals
    • These feet lesions often take a long time to heal as secondary bacterial infections may ensue and produce true deep ulcerative dermatitis
  • Teats on animals that are suckling may also develop vesicles
  • 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
    • Pigs have vesicles on snout, which are quickly traumatised to leave an eroded lesion
    • 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
  • 1967 + 2001 major outbreaks in UK
  • Still widespread in many parts of world especially S. America, far East
  • Foot and Mouth disease is NOT a highly fatal disease: approximately 5% mortality (usually young animals); older animals recover

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
  • 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 and send for testing

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
Prevention in the UK
  • Imported stock must come from virus-free countries that DO NOT vaccinate
  • Meat imported from endemic countries must be de-boned
In an Outbreak
  • ANY sign of lesions in a susceptible animal is NOTIFIABLE to the Divisional Veterinary Officer and local police
  • Once diagnosis is confirmed, all animals on the premises must be slaughtered and incinerated
  • Further disinfection of the premises
  • Movement is controlled within a 10-mile radius
  • Follow-up serology must be performed to ensure no spread has taken place
  • Ring vaccination with relevant subtype to create a barrier of immune animals (although this was not done in the 2001 outbreak)
In Endemic Areas
  • Disease cannot be prevented by slaughter due to large numbers of carrier stock
  • Annual Inactivated whole virus vaccination using local subtypes
    • Inactivated by azuridines, using alhydrogel adjuvant for cows, and oil for pigs
    • Attenuated virus reverts to virulence
    • Subunit vaccines ineffective
    • Expensive
    • 2 initial injections at 4 months (if dams vaccinated), followed by boosters every 6-12 months
    • Induces virus-neutralizing antibodies
  • Vaccination DOES NOT render meat harmful to consumers, but does affect when it can be exported

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


For more information

DEFRA

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