Ovine Progressive Pneumonia
(Maedi)
Valerie Millette and Neil Versavel
Western College of Veterinary Medicine
Class 2009


   

maedi(source 8).

 




Background and Viral characteristics:

Ovine Progressive Pneumonia Virus (OPPV)  and Maedi virus infect sheep and goats and cause progressive wasting and respiratory distress, eventually leading to death. In Europe the diease caused by these viruses is called Maedi, while in North America it is called Ovine Progressive Pneumonia (OPP) (source 2). OPP is an important respiratory disease because it predisposes infected animals to secondary infection with other respiratory diseases (source 3).

OPPV and Maedi virus are non-oncogenic, ovine retroviruses of the lentivirus genus. Lentiviruses are single stranded RNA viruses from the family Retroviridae (source 1,2).  Maedi virus is the same lentivirus species as OPPV, but is genetically heterogenous from OPPV due to genetic drift.

Other lentiviruses: Caprine Arthritis Encephalitis Virus

OPPV has been found in all major sheep producing countries, except Australia, NewZealand, Iceland and Finland. (source 1).
In Canada, the first suspected case of Maedi was reported in the province of Quebec in 1973, and the virus was first isolated in Ontario in 1978 (source 3).


Sheep and goats are the only species known to be susceptible to the virus. Rabbits have also been shown to become infected, but development of disease is limited to the acute stage prior to the production of anti-viral antibodies. All breeds of sheep are susceptible, however within family lines of a particular breed, susceptibility varies.
Differences in breed susceptibility may be related to flock exposure and management practices. Higher prevalences have been found for one half Finnsheep crosses; the Ile de France breed is comparatively resistant to infection compared to Finnish Landrace sheep; certain strains of Icelandic sheep have been found to be more resistant to disease expression than other strains; crosses between Icelandic and Border Leicester breeds are shown to be particularly resistant (source 4), and there is no evidence of disease in bighorn sheep in the USA (source 2). Experimentally infected sheep of the Border Leicester breed were found to be significantly more susceptible to the signs and lesions of disease than were sheep of the Columbia breed(source 4).

There is no reported evidence of a difference in susceptibility to infection between the sexes, although a statistical association between sex and OPPV infection has been observed (source 4).


 

Pathogenesis and clinical pathology

Clinical Signs


Diagnosis


Post mortem


Differential Diagnoses


Prevention and control


Epidemiology


Glossary


References