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The first human death from bird flu in the U.S. has some Americans feeling uneasy about the new virus that has been sending respiratory infections to hospitals in the early days of Covid-19. . Although both viruses can cause respiratory problems, they are very different.
In the year When it entered the US in 2020, Covid was easily spread from person to person, but bird flu had been hidden for years, mostly because of the animal problem. Scientists know more about the H5N1 bird flu than the SARS-CoV-2 virus, and the US has long been preparing for the threat of a new flu pandemic.
Still, the virus is making moves that deserve attention. Here's what you need to know about H5N1.
Avian influenza, or bird flu, is a broad term that refers to several types of influenza that commonly infect birds. The bird flu that's making the news in the United States is a virus called H5N1.
Some influenza viruses carried by birds cause only mild infections and are classified as low-pathogenic viruses. In contrast, H5N1 kills most of the birds it infects, so it is classified as the most pathogenic type of avian influenza.
To complicate matters, although bird flu viruses primarily infect birds, they can also spread to other animals, including humans. Human infections with bird flu viruses are rare, and are usually what scientists call dead-end infections because they are not normally transmitted from person to person.
You may have heard of H5N1 recently, but it is not a new virus. Scientists have been tracking it for three decades.
has been. First identified In 1996 geese in southern China. In recent years, it has caused occasional epidemics in wild and farm birds around the world.
The virus reappeared in North America in late 2021, and quickly caught the attention of scientists as it spread beyond birds and infecting a variety of developing mammals. In the current wave of infections, more than 48 species have spread. At least 26 countries.
It caused mass death. Marine mammals Including the 24,000 sea lion deaths in South America by 2023. In February 2024, Dr. Jeremy Farrar, Chief Scientist of the World Health Organization; It is called the ongoing distribution The H5N1 “Animal Pandemic”
More than 130 million from 2022 Wild and breeding birds Across all 50 states, 919 were affected in the US. Dairy herds 16 states tested positive and 66 people tested positive in 10 states. According to the information From the US Centers for Disease Control and Prevention and the US Department of Agriculture.
Could H5N1 be a new pandemic?
Scientists agree that the virus must have evolved or retained key changes in its genetic sequence.
Every time a virus infects a cell and replicates itself, it makes a mistake. Usually these mistakes are benign or harmful to the virus, but occasionally, there is a genetic change that helps the virus become better at infecting cells. Given the right set of circumstances, that version of the virus can compete with others and survive, infecting new hosts or new types of hosts.
Flu viruses can also mutate in other ways.
Every virus has eight parts, and like kids in the lunchroom, they always want to swap. When two viruses trade entire segments, it is called recombination and can lead to rapid and sometimes dramatic changes in viral abilities.
Scientists say any type of change can cause problems for humans. Although the H5N1 virus is very good at infecting birds and a threat to many different mammals, including dairy cows, it is still too complex to infect humans.
For example, in cows, the H5N1 virus primarily infects the mammary glands. This causes a significant reduction in milk production but usually does not kill the cow. In humans, the main route of infection seems to be through the eyes; Conjunctivitis, or red, inflamed eyes, seems to be the main symptom of infection.
Scientists think H5N1 infects the eye because flu viruses enter cells through a surface sugar called silicic acid. Birds – and human eyes – primarily have alpha 2,3 silicic acid receptors on their cells. But a different type of sialic acid receptor, alpha 2,6, is more widespread in the human respiratory tract. Human flu viruses, including those that cause seasonal influenza, have evolved alpha 2,6 receptors to infect cells.
Given enough time in the human body, the bird flu virus has shown a better ability to mutate, infecting different types of cells and tissues, from the eyes to the respiratory tract.
Researchers in Canada discovered key changes in the genome of the virus in teenagers who became seriously ill with HIV in November. These changes helped infect the cells in her airways. The HIV virus that infected a critically ill patient in Louisiana. Infectious disease experts warn that as the virus continues to spread, it is more likely that the disease will become a full-blown human disease.
If people become infected, it is almost always through contact with infected animals. Almost all of these so-called spillover infections are mild. And no one in the U.S. who has contracted H5N1 is known to have passed the infection on to another person.
The CDC and state public health departments are tracking farm workers who test positive and following up with anyone they saw when they were sick, a process called contact tracing. State public health laboratories are processing all influenza A sequences. Viruses found in routine flu tests. So far, two cases of bird flu have been detected in humans in this way.
The CDC estimates that the current population risk is low.
If you become ill within 10 days of contact with sick or dead animals or their waste, be sure to notify a health care provider of your exposure.
Although most H1N1 samples are captured by government public health laboratory systems, the CDC is working to expand testing, and large commercial laboratories such as Quest and Labcorp now have tests that detect H5 viruses.
That said, if doctors suspect bird flu infection, it is easier to diagnose patients.
Dr. Michael Osterholm, who directs the Center for Infection Research and Policy at the University of Minnesota, said the two groups of people most at risk are dairy and poultry workers and people with backyard poultry flocks.
The virus entered the udder of dairy cows, and Studies have been found High levels of avian influenza virus in raw milk.
Dairy dairies are wet areas, and workers can become infected if they get raw milk in their eyes or if they get milk on their hands and rub their eyes. Virus-laden milk droplets can become airborne if they are sprayed from milking equipment.
Birds shed the virus in their saliva, mucus, and feces, and their droppings and feathers can become airborne when they are burned in barns, especially during moulting.
“It could be up in the air,” Osterholm said. “So it's not just touching the birds, it's just the dust and dust that happens when you're interacting with birds.”
One of the most prominent symptoms in infected farm workers is red, irritated eyes. A A recent study Of the first 46 people in the US outbreak, 93% had conjunctivitis.
For about a third of the total, this was their only symptom. The second most common symptom experienced by about half of the infected farm workers was fever. HIV
In North America, two people have had a serious infection. The first, a 13-year-old from Canada, was on life support for two weeks to give her organs time to recover, with severe lung and kidney disease. It is not clear how she was exposed to the virus.
A second person from Louisiana was hospitalized with severe respiratory symptoms after coming into contact with a herd and wild birds. A man who was over 65 and had underlying medical conditions died this month, the first death from bird flu in the US.
Both of these patients had the D1.1 strain of the virus circulating in wild birds. It is different from the B3.13 virus that has been infecting workers on dairy farms. Researchers are investigating whether the D1.1 strain may cause more severe disease.
Warm milk and meat are safe to kill germs.
Even before H5N1 was taken into consideration, health officials warned against drinking raw milk or eating undercooked meat because both carry pathogens such as salmonella and E. They contain harmful germs like coli. Cats died drinking raw milk on farms.
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US Food and Drug Administration studies show that conventional pasteurization methods kill the virus, but refrigeration does not. USDA studies show that cooking meat to safe temperatures inactivates the virus.
A A recent study By inoculating raw milk from Stanford University with the virus and testing it on cells in the lab, the virus can infect cells for up to five days if it is still refrigerated.
No human infections have been linked to raw milk consumption, although an infant in California recently tested positive for the flu after drinking too much raw milk. The CDC was unable to confirm the infection, so this child is listed as a suspected case.