Via CIDRAP, a must-read article by Robert Roos: Fears about mutant H5N1 hinge on ferrets as flu model. Excerpt:
Despite all of these parallels, there are some differences between flu in ferrets and humans, researchers say.
For example, Lowen commented, "Ferrets sneeze frequently when infected with seasonal influenza viruses, whereas humans tend to cough and not to sneeze." Also, she said, "Seasonal influenza in ferrets is perhaps milder than in humans, given that the ferrets in question are naive hosts (analogous to children infected for the first time)."
Another difference is that flu causes neurologic signs more often in ferrets, according to Peter Palese, PhD, professor and chair of the Department of Microbiology at Mount Sinai School of Medicine in New York City, who has been critical of the NSABB move to suppress details of the Fouchier and Kawaoka studies.
"Ferrets have a lot of neurologic symptoms with flu, and that certainly doesn't happen in humans," he said. "There's plenty of evidence that ferrets are a much too sensitive system."
He pointed to a 2007 study in the Journal of Virology, in which ferrets that were inoculated with high doses of H5N1 strains from Vietnam showed neurologic signs before dying. Also, in an earlier study, published in Avian Diseases in 2003, scientists found that ferrets infected with the 1997 strain of H5N1 from the first human cases ever confirmed, in Hong Kong, had neurologic manifestations of the infection.
Another researcher who has studied flu in animals, Daniel R. Perez, PhD, of the University of Maryland, agreed that neurologic manifestations are more common in ferrets than what the literature says about human cases. Perez is an associate professor of virology in the Department of Veterinary Medicine in the university's College of Agriculture and Natural Resources and program director for the Avian Influenza Cooperative Agricultural Project there.
Perez said there's a further difference: "In general, I'd say ferrets are more susceptible than humans to H5N1. The manifestations of the disease seem to be a lot more dramatic and noticeable in ferrets than humans. So the human immune system tends to handle the infection better than ferrets."
But he cautioned that not all strains of H5N1 have been tested in ferrets, and the animals are exposed to the virus in controlled laboratory conditions, unlike humans, making comparisons tricky.
He also observed that scientists face some technical limitations in studying the immune response of ferrets: "We are limited in making parallels between what happens in humans and ferrets in terms of the immune responses. We don't have reagents that are ferret-specific that allow us to study immune responses in ferrets the way we've studied them in mice."