CNN
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The first person to contract a severe case of H5N1 bird flu in the United States has died, according to the Louisiana Department of Health. This is the first human death from bird flu in the United States.

The person, who was over 65 and reportedly had underlying health conditions, was hospitalized with flu after being exposed to a flock of birds in the backyard and wild birds.

Louisiana health officials said their investigation revealed no additional human cases linked to this patient’s infection.

Flu experts warn that the H5N1 virus would show its teeth in spreading infections.

“We have been studying the family tree of this virus for about 25 years and this is probably the worst form of the virus we have ever seen. “So the fact that this ultimately resulted in a fatal infection is tragic but not surprising,” said Dr. Richard Webby, who directs the World Health Organization Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds at St. Jude’s Children’s Research Hospital.

According to the World Health Organization, about 900 bird flu infections in humans have been reported worldwide since 2003, and about half of those people have died. That would give the virus a 50% mortality rate, which would make it extraordinarily deadly — but experts don’t actually think it kills half of the people infected.

Because severe cases are reported more frequently than mild cases, mild illnesses are likely not included in this number.

But even if the actual mortality rate were ten times lower – about 5% – it would still be a serious virus to contend with. For example, the mortality rate for the ancestral strain of Covid-19 has been estimated at around 2.6%.

A recent study by scientists at the U.S. Centers for Disease Control and Prevention of the first 46 human cases of H5N1 in the U.S. last year found that almost all of them were mild and, except for one, occurred after contact with infected livestock .

The Louisiana patient was infected with the D1.1 clade of avian influenza virus, a strain that circulates in wild birds and poultry. It differs from the variant that circulates among dairy cows.

Scientists don’t know whether it causes more severe illness in people. D1.1 also infected a seriously ill teenager hospitalized in Canada. The teen, a 13-year-old girl, was treated in the intensive care unit and recovered, but investigators don’t know how she was exposed to the disease.

D1.1 infections have also been detected in poultry farm workers in Washington. These cases appear to have been milder.

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The CDC reported in late December that a genetic analysis of the virus that infected the Louisiana patient found changes that are expected to improve and contribute to its ability to infect people’s upper respiratory tract it spreads more easily from person to person. The same changes were not observed in the birds the person was exposed to, officials said, suggesting they developed in the person after they were infected.

CDC officials continue to investigate the case by examining the virus in “serial samples,” or blood tests, taken from the patient over time. This gives them more information about how the virus developed in the patient’s body.

“The evolution of the virus is worrying, but shows how we must prevent any potential spillover infection to reduce the risk of onward transmission to others,” said Dr. Seema Lakdawala, a microbiologist and immunologist who studies influenza transmission at the Emory University School of Medicine.

In a statement Monday, the CDC called the death tragic but said this single case did not increase the threat level of H5N1.

“CDC has carefully reviewed the available information regarding the individual who died in Louisiana and continues to believe that the risk to the general public remains low. “Importantly, no person-to-person transmission has been detected,” the statement said.

“In addition, there are no worrisome virological changes that are actively spreading in wild birds, poultry or cows that would increase the risk to human health,” the statement said.

While most people remain at low risk of bird flu, people who keep chickens and other birds in their backyards need to be careful, as do workers on dairy and poultry farms, health officials said.

People who work with animals or have come into contact with sick or dead animals or their feces should monitor for breathing problems and red eyes for 10 days after exposure. If they develop symptoms, they should tell their doctor about their recent exposure.

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