With reports of the first human death from bird flu in the US, some Americans are feeling an uncomfortable flashback to the early days of Covid-19. Although both viruses can cause breathing problems, they are very different. Covid was spreading easily from person to person when it arrived in the US in 2020, but bird flu has been lurking for years, mostly as a problem for animals.
Avian influenza, or bird flu, is a broad term that refers to several types of influenza that normally infect birds. The bird flu that’s been making news in the United States is a virus called H5N1. Some flu viruses carried by birds cause only mild infections and are classified as low-pathogenic viruses. In contrast, H5N1 often kills birds that catch it, so it is classified as a highly pathogenic avian influenza.
Although bird flu viruses primarily prey on birds, they can also spread to other animals, including humans. Human infections with bird flu viruses are rare, and they’re usually what scientists call dead-end infections because they don’t typically transmit from person to person. You may have heard of H5N1 only recently, but it’s not a new virus. Scientists have been tracking it for almost three decades.
It was first identified in geese in Southern China in 1996. Over the years, it has caused sporadic outbreaks in wild and farmed birds around the globe. The virus reappeared in North America in late 2021, and it quickly caught scientists’ attention because it seemed to have broadened its repertoire, spreading beyond birds and infecting a growing variety of mammals.
Since 2022, more than 130 million wild and farmed birds have been affected in America across all 50 states, 919 dairy herds have tested positive in 16 states, and 66 people have tested positive in 10 states, according to data from the US Centers for Disease Control and Prevention and the US Department of Agriculture. Scientists agree that the virus would need to evolve or retain key changes in its genetic sequence to start a pandemic.
Flu viruses can change in another way, too. Each virus has eight segments, and like kids in a lunch room, they are always looking to swap. When two viruses trade whole segments, it’s called a reassortment, and it results in quick and sometimes dramatic changes to a virus’ abilities. Scientists say either type of change could spell trouble for humans.
The two groups of people who are most at risk are dairy and poultry workers and people who have backyard bird flocks. The virus homes in on the udders of milking cows, and studies have found high concentrations of bird flu virus in raw milk. The milking parlors of dairies are wet environments, and workers can be infected if they get a splash of raw milk in their eyes or if they get milk on their hands and then rub their eyes.
For about a third of the total, the only symptom of infected farm workers has been red, irritated eyes. A recent study of the first 46 human cases in the current outbreak in the US found that 93% had conjunctivitis. The second most common symptom, experienced by about half of infected farm workers, was a fever. About a third of people with H5N1 had respiratory symptoms, but these were most common among poultry workers who were exposed during bird depopulation activities.
Two people in North America have had severe infections. The first was a 13-year-old girl in Canada, who became critically ill with lung and kidney failure and was put on life support for two weeks to give her organs time to recover. The second person, from Louisiana, was hospitalized with severe respiratory symptoms after exposure to a backyard flock and wild birds. That person, who was over age 65 and had underlying medical conditions, died this month, becoming the first death in the US from bird flu.
Milk and meat that have been heated to kill germs are safe. Even before H5N1 was a consideration, health officials cautioned against drinking raw milk or eating undercooked meat because both can harbor nasty germs like salmonella and E. coli.