Ovine Progressive Pneumonia (OPP), also known as Maedi‑Visna (MV), is a chronic viral disease in sheep caused by a small ruminant lentivirus (SRLV). The virus mainly affects the lungs and mammary glands but can also cause neurological issues and joint problems. Infected sheep often appear healthy for 1–3 years, with signs most commonly emerging in older ewes. Typical symptoms include progressive weight loss despite good appetite (“thin ewe syndrome”), difficulty breathing, reduced milk production due to firm, non-painful udders (“hard bag”), and less frequently, lameness or neurological signs like circling or paralysis (Merck Veterinary Manual, Manitoba Co-operator).

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OPP spreads primarily through colostrum or milk from infected ewes and via prolonged nose-to-nose contact. Though rare, it can also be transmitted in utero or through semen (Government of British Columbia, APHIS). Studies suggest about 13% of Canadian cull ewes may be infected, though prevalence varies widely by region. Manitoba has seen confirmed outbreaks, including one near Boissevain where nearly half the flock tested positive (Delta Livestock Diagnostics).

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Because there is no vaccine or cure, prevention focuses on biosecurity and testing. Control strategies include serological testing (ELISA or AGID), quarantining new animals, removing infected ewes, and feeding lambs colostrum from virus-free sources. Manitoba producers often test through the Ontario Maedi‑Visna Flock Status Program (OMVFSP) or private labs, as no provincial surveillance program currently exists.

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OPP has serious economic and welfare impacts, including poor growth, high lamb mortality, lower milk production, and early culling. Due to its often hidden presence, it is known as an “iceberg disease,” where only a few affected animals show visible signs while many others carry the virus silently.

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To learn more about OPP/MV, visit sciensano.be, Merck Veterinary Manual, or easternalliancekatahdins.com.