90. Maedi-visna.

Question 1

Maedi-Visna Occurence + Ethiology?

Answer 1

Maedi-visna

• Retroviridae, Orthoretrovirinae, Lentivirus, Maedi-visna
• virus Susceptible: Ov (Cap, wild small Ru)

Occurrence:

• worldwide (except: NZ, Australia), Hungary

Etiology: Lentivirus

• Close relationship with caprine arthritis encephalitis virus, can be cultured(syncytium)
• Slow spread in flock

Question 2

Epidemiology?

Answer 2

Epidemiology:

• maintained by persistant infected sheep
• shedding via tracheal discharge and milk
• overcrowding predisposition, no indirect spreading
• seropositivity is increasing with age
• clinical signs seen above 3-4 years old (only appear in adults)

Question 3

Pathogenesis?

Answer 3

Pathogenesis:

• Clinical forms:
• Maedi = more frequent - pneumonia disease
• Visna = less frequent - CNS disease
• Both forms are caused by the same virus
• PO/aerogenic
• lns, myeloid cells, BM
• viremia (monocytes, persistent, lifelong)
• parenchymal organs - lungs, spleen, kidney, udder, testicles
• chronic inflammation: interstitial pneumonia, mononuclear infiltration, cytokines help infl
• Maedi: lungs - interstitial pneumonia (mononuclear infiltration), enlarged lungs
• Visna: CNS - perivascular infiltration, demyelinisation
• Antibodies: do NOT eliminate the virus, do not inhibit the replication of virus (only help diagnosing!)
• Clinical signs: not direct effect of virus, signs/lesions are from reaction of cellular immunity
• (persistent infection)

Question 4

Clinical signs?

Answer 4

Clinical signs:

• incubation is months - years
• Maedi: 3-4 yrs old, weight loss, dyspnoe, DRY cough (differentiate from ovine adenomatosis), reluctant to
• move, secondary bacterial complications can be it more severe (nasal discharge, wet coughing)
• Visna: above 2 years old, weakness of HL, ataxia, position of head (inclined), head/lip trembling, collapse,
• paralysis, weightloss

Question 5

Pathology?

Answer 5

Pathology

• Maedi: lungs (interstitial pneumonia, heavier lungs, but not collapsed - enlarged instead from the infiltration, rib-impressions from enlargement, intralobular pneumonia, hypertrophy of smooth muscles -
• compensation of dyspnoe, complications), enlarged LN
• Visna: atrophy of skeletal muscles, leukoencephalitis, demyelinisation
• Arthritis, orchitis, lymphoid hyperplasia

Question 6

Diagnosis and differential diagnosis?

Answer 6

Diagnosis:

• clinical signs, PM lesions
• Detection of virus: virus isolation, PCR
• Detection of antibodies: ELISA, AGP (hi atb in milk)
• Differentiation:
• Maedi: ovine pulmonary adenomatosis (also in adults, but much higher nasal discharge),
• pasteurellosis, mycoplasmosis
• Visna:
• listeriosis, scrapie, louping ill, rabies, brain abscess, tumor

Question 7

Prevention?

Answer 7

Prevention:

• NO treatment, early culling, NO vaccine
• Eradication:
• 1) Selection: test and slaughter: cull seropositive ewe and her lamb together
• 2) Generation shift: isolation of newborn lambs right after birth, feeding with cow milk or heat treated sheep milk, serological check at 6 months