Maedi Visna
Maedi Visna (MV) is a progressive wasting disease of sheep caused by a lentivirus. This chronic disease affects the lungs, udder, and overall body condition, leading to significant production losses within the flock. The disease is prevalent in many sheep-producing countries and is known by various names, such as ovine progressive pneumonia in North America.
Symptoms and Diagnosis 🩺
Early Signs
The early signs of MV can be difficult to spot due to the slow progression of the disease. Clinical signs are often seen in older sheep and include chronic pneumonia with breathing difficulties or exercise intolerance. Neurological signs such as a ‘dragging’ hindlimb gait or circling can also be observed. Chronic mastitis cases are associated with hungry or poor-growing lambs.
Advanced Symptoms
As the disease progresses, affected animals may exhibit gradual loss of condition, tachypnoea, and respiratory distress. In more advanced cases, flared nostrils, neck extension, and open-mouth breathing can occur. The disease can be confirmed on a post-mortem of cull ewes, where the lungs are firm and heavy when removed.
Diagnosis
MV can be diagnosed via blood samples once the ewe has formed an antibody response. Testing should be routinely carried out annually or even more frequently in affected flocks. Positive animals should be culled, and lambs from infected ewes should not be retained for breeding as they may have become infected via the colostrum or milk.
Treatment 💊
Unfortunately, there is no cure for Maedi Visna. The disease is ultimately fatal, and treatment focuses on managing symptoms and preventing the spread of the virus within the flock. Infected animals should be culled to prevent further transmission.
Prevention 🛡️
Preventing Infection
There is no vaccine available for MV, and due to the long incubation period of the disease, detection in live animals can be problematic. Preventing infection involves routine testing and culling of positive animals. Lambs from infected ewes should not be retained for breeding. It is also sensible to source replacement ewes from flocks that routinely screen for MV to reduce the chance of buying in infected animals.
Biosecurity Measures
Implementing strict biosecurity measures can help prevent the spread of MV. This includes maintaining good hygiene practices, avoiding the sharing of equipment between infected and non-infected animals, and ensuring that new animals introduced to the flock are tested and free of the virus.