Difference between revisions of "Visna-Maedi Virus"

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Also know as: '''''Maedi-Visna — Lymphoid Interstitial Pneumonia'''''
 
  
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== Introduction ==
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Maedi-Visna
  
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This disease is caused by a [[:Category:Retroviridae|retrovirus]] and affects sheep worldwide. It was originally seen in Iceland, hence the name is Icelandic in origin. The disease is slow to progress and is therefore only seen in sheep greater than 2 years old.
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====Pathogenesis====
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*Primary replication in '''lung macrophages'''
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*These then carry infection to '''brain, lung, udder and/or joints'''
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*T cells react: '''Type IV immune complex disease'''
 +
*Target organs become chronically inflamed after 2-6 years
 +
*Visna:
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**Inflammation results in '''demyelination''' with '''subacute meningitis''' around ventricles and choroid plexus
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**'''Posterior paresis''' progresses for up to a year until sheep can no longer stand
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**For more on joint pathology, see [[Infectious Arthritis#In Sheep|here]]
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*Maedi:
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**Alveolar septa become infiltrated by lymphocytes and macrophages
 +
**Smooth muscle hypertrophy
 +
**PM: lungs are heavy, rubbery and do not collapse
 +
*All result in loss of condition
 +
*Infected animals remain antibody and virus positive
  
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There occurs a primary replication in '''lung macrophages '''and these then carry infection to '''brain, lung, udder and/or joints.''' T cells react causing a '''Type IV immune complex disease. '''Target organs become chronically inflamed after 2-6 years.
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====Epidemiology====
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*Transfer via '''aerosol, milk or colostrum'''
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*Increased risk in '''winter housing'''
  
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'''Visna''' is the '''demyelination''' with '''subacute meningitis''' around ventricles and choroid plexus caused by inflammation. '''Posterior paresis''' progresses for up to a year until sheep can no longer stand.
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====Diagnosis====
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*Clinical signs
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*Serology: '''AGDT'''/'''ELISA''' for '''antibody'''
  
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'''Maedi''' is the lung part of the complex, with alveolar septa becoming infiltrated by [[lymphocytes]] and [[macrophages]], there is also smooth muscle hypertrophy. All these result in a loss of condition.
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====Control====
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*Seropositive and progeny must be removed from flock
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*Farm can be re-accredited after 2 years of clear tests
  
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Transmission of the disease is via aerosol, milk or colostrum and therefore there is increased risk of spread of the disease during winter housing.
 
  
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== Clinical Signs ==
 
  
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Lack of condition/weight loss, lameness and paresis. Coughing, harsh lung sounds on auscultation, increased respiratory rate and nasal discharge also occur with the respiratory part of the disease complex.
 
  
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== Diagnosis ==
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*Caused by a [[Retroviridae|retrovirus]]
 +
*The respiratory from of the disease caused by maedi-visna virus (Maedi) is also called '''lymphoid interstitial pneumonia'''
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*Transmitted by close contact and via milk
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*The pulmonary lesions develop very slowly hence this disease is uncommon in sheep < 2 years old
 +
*Increased respiratory rate upon exertion, loss of weight
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*Remains in [[Monocytes]] and macrophages
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*Gross findings
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**Severe [[Interstitial Pneumonia|interstitial pneumonia]]
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**Lungs fail to collapse properly on opening the chest and can weigh more than twice the normal weight
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**Impressions of the ribs remain on the visceral pleura
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**Lungs are a mottled grey/ tan colour - the lesions can vary from irregular grey speckling to homogeneous grey consolidation
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**Rubbery in consistence
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**Diaphragmatic lobes most affected
 +
**Associated bronchial and mediastinal lymph nodes are often enlarged
 +
*Histologically
 +
**Major features are extensive lymphoid proliferation around perivascular, peribronchial and peribronchiolar sheaths associated with pulmonary lymphatics
 +
**Many of these areas contain germinal centres and smooth muscle hyperplasia (in walls of terminal bronchioles and alveoli)
  
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Clinical signs and history can lead to a presumptive diagnosis of the disease. Due to the clinical signs, sheep affected are usually humanely destroyed.
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[[Category:Lentiviruses]][[Category:Sheep Viruses]]
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[[Category:To_Do_-_Clinical/Viruses]]
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A post mortem examination can be performed which will show lungs that are heavy, rubbery and do not collapse. Grossly, they will show signs of severe [[Interstitial Pneumonia|interstitial pneumonia]] and the impressions of the ribs will remain on the surface fo the lungs after removal from the body. They will appear a mottled, grey colour and speckling may also be present. The diaphragmatic lobes are usually the most severely affected. Bronchial and mediastinal lymph nodes are often enlarged.
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[[Category:Respiratory_Viral_Infections]]
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[[Category:Respiratory Diseases - Sheep]][[Category:Neurological Diseases - Sheep]]
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Serology can be used on the live animal to detect antibody or antigen by [[ELISA testing|ELISA]].
 
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== References ==
 
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Bridger, J and Russell, P (2007) '''Virology Study Guide''', ''Royal Veterinary College''.
 
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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''
 
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{{review}}
 
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{{OpenPages}}
 
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[[Category:Lentiviruses]] [[Category:Sheep_Viruses]] [[Category:Expert_Review - Farm Animal]] [[Category:Respiratory_Viral_Infections]] [[Category:Respiratory_Diseases_-_Sheep]] [[Category:Neurological_Diseases_-_Sheep]]
 

Revision as of 16:30, 3 March 2011


 This article is still under construction.


Maedi-Visna

Pathogenesis

  • Primary replication in lung macrophages
  • These then carry infection to brain, lung, udder and/or joints
  • T cells react: Type IV immune complex disease
  • Target organs become chronically inflamed after 2-6 years
  • Visna:
    • Inflammation results in demyelination with subacute meningitis around ventricles and choroid plexus
    • Posterior paresis progresses for up to a year until sheep can no longer stand
    • For more on joint pathology, see here
  • Maedi:
    • Alveolar septa become infiltrated by lymphocytes and macrophages
    • Smooth muscle hypertrophy
    • PM: lungs are heavy, rubbery and do not collapse
  • All result in loss of condition
  • Infected animals remain antibody and virus positive

Epidemiology

  • Transfer via aerosol, milk or colostrum
  • Increased risk in winter housing

Diagnosis

  • Clinical signs
  • Serology: AGDT/ELISA for antibody

Control

  • Seropositive and progeny must be removed from flock
  • Farm can be re-accredited after 2 years of clear tests



  • Caused by a retrovirus
  • The respiratory from of the disease caused by maedi-visna virus (Maedi) is also called lymphoid interstitial pneumonia
  • Transmitted by close contact and via milk
  • The pulmonary lesions develop very slowly hence this disease is uncommon in sheep < 2 years old
  • Increased respiratory rate upon exertion, loss of weight
  • Remains in Monocytes and macrophages
  • Gross findings
    • Severe interstitial pneumonia
    • Lungs fail to collapse properly on opening the chest and can weigh more than twice the normal weight
    • Impressions of the ribs remain on the visceral pleura
    • Lungs are a mottled grey/ tan colour - the lesions can vary from irregular grey speckling to homogeneous grey consolidation
    • Rubbery in consistence
    • Diaphragmatic lobes most affected
    • Associated bronchial and mediastinal lymph nodes are often enlarged
  • Histologically
    • Major features are extensive lymphoid proliferation around perivascular, peribronchial and peribronchiolar sheaths associated with pulmonary lymphatics
    • Many of these areas contain germinal centres and smooth muscle hyperplasia (in walls of terminal bronchioles and alveoli)
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