There are more questions than answers as researchers work to understand a rash of canine illnesses and a number of tests that suggest some dogs were infected with circovirus. Veterinarian Steven Krakowka, who along with two other researchers discovered the porcine circovirus 2 in 1997, said his work on the porcine virus showed circovirus does not act alone in swine. "There were a number of manipulations we had to do to get the virus to work. ... We eventually figured out that what was required [was] co-infections with other agents. The virus all by itself does not cause the disease," Dr. Krakowka said, noting that if that's the case in dogs, healthy animals could be carrying and shedding the virus.