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Samuel Scarpino says it’s time to ramp up response to avian flu after possible first case of human to human transmission in Missouri
Until recently, every human case of avian flu this year involved people who came in contact with infected poultry or cows.
But since the Centers for Disease Control and Prevention announced this month that a person in Missouri who contracted bird flu had no known contact with infected animals, health researchers are concerned about the possibility of human-to-human transmission.
“If it is human transmission of H5N1, that automatically raises the threat level,” says Samuel Scarpino, director of AI + life sciences at Northeastern’s Institute for Experiential AI.
“Once you start to have ongoing human-to-human transmission, you now have a selective advantage for mutations that arise that increase the chance of infecting more people,” Scarpino says.
“So the concern is that you start to create the evolutionary environment for an epidemic,” he says.
A human outbreak of avian flu raises the specter of a high mortality rate, with 55% of 258 people infected over an 11-year period ending in July in the Western Pacific succumbing to the disease, according to the World Health Organization.
So far all of the 14 people confirmed to be infected with H5N1 in the U.S. this year have made a full recovery.
There could “be something genetically different about this particular strain that makes it less problematic,” Scarpino says.
Other protective factors could be the fact cases seem to be caught early and are occurring among farm workers who tend to be younger, he says.
But Scarpino says this year’s U.S. case numbers — four from exposure to dairy cows, nine from exposure to chickens and one possible case of human transmission — are still too low to establish a mortality rate.
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“We are still within the margin of error on the case fatality rate. So it’s not like we’re out of the woods yet,” he says.
“It could be that it has a 10% case fatality rate, which would be 100 times higher than COVID,” Scarpino says. “That’s bad. The case fatality rate could still be really high.”
“If it had the case fatality rate that we’ve seen for past H5N1 outbreaks, we would expect it to be something like 500 times worse than COVID.”
Scarpino says many questions remain about the Missouri case, which the CDC identified in a hospitalized individual via the state’s seasonal flu surveillance system — the first time in the U.S. the system has identified a case of H5.
Genomic sequencing and polymerase chain reaction tests can confirm scientists’ suspicion that the virus is H5N1 and not the less pathogenic avian influenza subtype known as H5N2, Scarpino says.
Sequencing the genome will help health researchers establish the source of the infection and whether mutations are occurring to make it more transmissible from person to person, he says.
It’s surprising that the CDC has not announced results from genomic sequencing after announcing the human case Sept. 6, but it’s possible the federal health agency was not able to isolate enough virus to run a sample, Scarpino says.
If it’s a confirmed case of human-to-human transmission, it’s important to find who infected the patient in the Missouri hospital and “trace out around them to look for other infections,” he says.
“You want to find this person and then figure out if they infected other people that you haven’t found yet.”
“We really need to get this genome sequenced,” says Scarpino, who says the genome and source of infection “will tell us everything we need to know about the threat profile.”
“If it is human to human transmission of H5N1, then that means we’ve missed at least one animal spillover into a human that then led to a transmission event to another person and then a hospitalization,” Scarpino says.
Millions of chickens and ducks have been culled after being exposed to H5N1, which also sickens and kills wild birds.
Dairy cows may have symptoms but most of the H5N1 restrictions around cattle involve inhibiting their movement from state to state to prevent the spread of the virus, which has not yet been found in dairy cows in Missouri.
The fact that cows are fellow mammals likely increases the possibility of cattle infections leading to human-to-human transmission.
“If we are in a world where H5N1 is going to circulate in our dairy cows forever, it’s really just a matter of time before there’s a big outbreak,” Scarpino says.
“Eventually you’re going to end up with enough of the wrong things happening in a row that it takes off.”
“We have to eliminate this from the dairy cow populations,” via continued movement restrictions, increased surveillance and vaccination of cattle, Scarpino says.
“While I agree with the CDC that the threat level to the population is still low, overall the threat profile of this current outbreak will go up if this is a confirmed human-to-human transmission event of H5N1.”
Even if there is no ongoing transmission from the recently discovered human case, “we might not get lucky the next time.”