Difference between revisions of "Visna-Maedi Virus"
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**Inflammation results in '''demyelination''' with '''subacute meningitis''' around ventricles and choroid plexus | **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 | **'''Posterior paresis''' progresses for up to a year until sheep can no longer stand | ||
| − | **For more on joint pathology, see [[ | + | **For more on joint pathology, see [[Infectious Arthritis#In Sheep|here]] |
*Maedi: | *Maedi: | ||
**Alveolar septa become infiltrated by lymphocytes and macrophages | **Alveolar septa become infiltrated by lymphocytes and macrophages | ||
Revision as of 16:30, 3 March 2011
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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)