contact with the natural host in the environment. In this respect, hantaviruses are of particular interest. The entire concern about emerging infections actually originated in a very small way about 10 years ago from a question about whether hantaviruses were a risk to laboratory workers. At that time, we knew of hantaviruses as an occupational hazard. In recent years, many more have been discovered, and now we know of literally dozens throughout the world, including a great number discovered only in the last few years throughout North and South America where they are harbored in very common wild rodents. Of course the possibility exists for these new infections to be introduced in facilities where other animals from the outside are brought into contact. Such knowledge of the great, not yet fully tapped biodiversity of microorganisms requires us to avoid complacency and to understand that detection and diagnosis remain essential tools for control.
Why might we be interested or concerned about emerging infections in laboratory animals? One compelling reason for all of us as laboratory animal disease specialists is of course the potential threat to the colonies as described by Dr. Smith and other speakers. The possibility exists that ectromelia could be reintroduced, and it is always a potential danger; many examples of rodent parvoviruses are a cause for concern, and perhaps the most dramatic parvovirus was canine parvovirus 2, which appeared in the late 1970s in dogs. There are still many discussions about how it was introduced, but it may have been an accident in vaccine production, a contaminant by another parvovirus during vaccine. We know from work by Colin Parish and others that once this virus appeared, it was able through essentially one mutation to expand its host range into dogs. It spread rapidly throughout the dog population causing very high mortality in puppies and other rapidly growing young dogs. It was replaced by another variant, and several waves of this process took place until several strains of this virus were distributed throughout the world.
Another emerging infection example is that of callitrichid hepatitis, which was really lymphocytic choriomeningitis (LCM), introduced into tamarins in the zoo. There it spread rapidly with rather fatal results throughout the captive tamarin population, possibly due to the feeding of contaminated material from newborn mice that had not been tested for LCM. The progression of this infection and others indicates the potential for surprise with a great biodiversity of microorganisms in existence.
Nevertheless, we should not despair over emerging infections. We know there are factors responsible for emerging infections introduced into a new popu