Opossums prove valuable in labs.

As medical researchers explore increasingly sophisticated questions about the human body, many are looking beyond rats and mice for animal models with systems that more closely resemble those of people. Moving away from non-human primates because of expense, risk of disease, and fear of vandalism by animal rights activists, a number of scientists around the world are turning to marsupials, some of whose anatomic features closely resemble those of primates. In addition to the North American, or Virginia, opossum, they are taking great interest in a smaller South American cousin called Monodelphis, the gray short-tailed opossum.

"A lot of good work has been done with rats and mice, but now we need new models to develop more sophisticated studies," explains William J. Krause II, professor of anatomy and neurobiology at the University of Missouri-Columbia School of Medicine. "In the next few years, we're going to see a lot more work done with marsupials, particularly Monodelphis."

The Virginia opossum is considered the world's most primitive marsupial and most closely resembles a common ancestor from which all marsupial species evolved upon migration to South America and perhaps across a land bridge to Australia millions of years ago. Using Virginia opossums, University of Missouri scientists Leonard Forte and Ronald Freeman have made several breakthroughs into the cause of secretory diarrhea...