There are many things that have changed over the years with this disease. The most important thing that has not changed is that after nearly 50 years of vaccination and management, the incidence of disease has not changed at all.

The virus can cause many syndromes, but the most important are pneumonia, abortion, hemorrhagic syndrome, and persistent infection. Of these, the syndrome that has received increasing attention in recent years is Persistent Infection (PI). PI occurs when a non-immune pregnant cow is exposed to the virus at less than 150 days gestation. The calf will likely be born infected with the virus and be a source of infection for others. These persistently infected calves do not usually live beyond two years of age, but occasionally will live a normal lifespan infecting others all the while. A persistently infected cow will always give birth to a PI calf. The PI herd bull is perhaps most devastating.

To prevent PI we need to provide adequate immunity to our materanal immunity. If this is done consistently, we should be able to eliminate PI\'s from the herd in a few years. Modified live vaccine administered pre-breeding has been the current plan. One vaccine now has approval for pregnant cows and should be given once per year .This product should be the best and easiest to apply to a given system.