Maedi and visna are two different diseases in sheep that are caused by the same virus of the retrovirus family and belong to the so-called “slow virus diseases”.
Maedi (meaning dyspnoea) disease is characterised by shortness of breath and cough, which are caused by chronic progressive interstitial pneumonia.
Visna (meaning decay) is a slightly contagious but progressive disease of the central nervous system. The animals show paralysis because of a demyelination of the CNS as well as increasing decay.
In Germany, the disease is notifiable upon diagnosis in sheep and goats.