Since early 2022, a highly pathogenic strain of avian flu, H5N1, has been infecting wild aquatic birds and domestic poultry in the United States. More than 85 million birds in 48 states have died as a result of the virus or have been culled after exposure to infected birds.
This same strain has now spread to cows. Health officials have detected H5N1 in cattle across 16 herds in six states. And earlier this month, the Centers for Disease Control and Prevention reported a case of bird flu in a dairy worker in Texas who likely contracted the virus from cattle.
This is an alarming situation that must be monitored closely. Livestock workers and owners of backyard flocks need to take extra precautions, and clinicians should be on the lookout for new human cases. Most Americans, though, should not be concerned about the risk of avian flu to them at this time. Avian influenza is not new. The first description of it dates from the late 1800s. Like human flu viruses, there are multiple strains of bird flu. Some strains cause mild or no symptoms. Others are associated with mortality rates as high as 90 to 100 percent in domesticated bird species.
Many bird flu viruses originate in wild aquatic fowl and are then passed on to chickens, turkeys and other domestic birds. While most transmission occurs among birds, some viral strains can cross over to infect mammals. The H5N1 strain has already been detected in more than 200 mammals in the United States.
That includes humans. In addition to the Texas dairy worker, an individual in Colorado working with poultry was diagnosed with H5N1 in 2022. The dairy worker’s only symptom was eye inflammation, and the poultry worker experienced fatigue. But prior cases from elsewhere in the world have resulted in pneumonia, multiple organ failure and death.