Here's how it works: after a pathologist has performed an autopsy on a diseased animal -- in this case, a baby seal -- epidemiologists come up with a list
of likely suspects that may have contributed to the creature's death. Then comes a battery of genetic tests designed to eliminate the wrong culprits. With
a bit of synthetic DNA called a fluorescent probe, scientists can screen a sample of infected tissue for genes that serve as identifiers of specific
viruses or bacteria.
These probes work a bit like litmus tests: they change color when they come into contact with the right illness gene. But the probes
are programmed beforehand only to respond to a particular gene. This allows researchers to rule out diseases as they go.
Once the researchers have struck some options from the list, things get easier. "When we identify influenza," Anthony told me, "the next thing to do is sequence the
entire genome [of the virus] and identify where the virus likely originated. And what we do is, we compare the sequence of the virus we found with a large
database of influenza viruses, and we look to see what is the closest related to it."
As it happens, the virus Anthony and his team discovered in the baby seals shares a 96 percent genetic match with H3N8, an avian flu that affects North
American ducks. Because seals and ducks have been known to interact with one another on shorelines, the researchers think that's how the germ was passed
from one species to the other -- although they still aren't sure when the spillover happened, or how severe it was.
"For example, were the birds constantly shedding the virus and randomly, one day, for some reason, a seal became affected? Were there lots of spillover
events? We don't know any of that," said Anthony.
It's also unclear what's going on with the other four percent of the virus' genetic sequence. While Anthony is "very confident" that they've
identified the right strain of flu, it's possible, he said, that the discrepancy reflects mutations the bug has undergone in order to adapt to its new
"We've found many mutations within the genome that separate it from the avian close relative -- the avian strain," said Anthony. "It could be that any one
of those mutations, or all of those mutations, are necessary for increased virulence. If the virus persists over time, it may accumulate more
mutations and the virulence may increase or decrease. We really don't know."
The virus' constant evolution has scientists calling for further surveillance -- both of the bug itself as well as of seal and duck populations in New
England. There's a slight potential for a human spillover of the virus, Anthony admits. The gene sequence has one mutation that in previous viruses has been linked
to higher virulence. But for the moment, scientists don't know whether that mutation does the same thing in the seal virus as it's done in others.
What is for sure: when the lives of baby seals are at stake, the rest of us start paying attention.