A dairy worker in Texas is being treated for bird flu, the second human case in the United States of an illness caused by a highly virulent virus that has recently rampaged through dairy cows in five states. The patient, who experienced eye inflammation as the only symptom, was tested for flu late last week, with confirmatory testing performed by the Centers for Disease Control and Prevention over the weekend. The patient was told to isolate and is being treated with oseltamivir, an antiviral drug sold under the brand name Tamiflu. The newly emerged case does not change the risk for the general public, which remains low, federal officials said.
The case has alarmed disease trackers monitoring for the worst-case scenario: human-to-human transmission of the pathogen, which has happened infrequently worldwide, typically among family members engaged in work with animals. It raises questions about whether this pathogen is now more easily transmitted among mammals. Texas health officials are working with other state and federal agencies to provide guidance to dairies about precautions workers should take to minimize the risk of transmission from animals and encourage those who become ill to get tested.
The investigation into how widely the virus has spread is ongoing, and officials do not yet know the specific route of transmission. While the CDC considers the risk of infection for the general public to be low, people with close or prolonged, unprotected exposures to infected birds or other animals (including livestock) or to environments contaminated by infected birds or other animals are at greater risk of infection.
Human infections with avian influenza viruses are uncommon but have occurred sporadically worldwide. The CDC has been monitoring for illness among people exposed to H5 virus-infected birds since outbreaks were first detected in U.S. wild birds and poultry in 2021.
Human illnesses with H5N1 bird flu have ranged from mild, such as eye infections and upper respiratory symptoms, to severe illness, such as pneumonia, that have resulted in death in other countries. Experts worry about the potential for viral evolution, which could remain primarily a threat to animal health and then recede, continue to circulate among animals but not routinely infect humans, or evolve to spread easily between people and become the next pandemic, with significant costs to human life, society, and the global economy.
Pandemic flu is a rapidly changing virus that can easily spread between humans and other mammalian species, with little or no natural immunity. The H5N1 bird flu, which has rarely infected humans, has a fatality rate of around 50% among cases diagnosed. U.S. policymakers must be proactive to prevent this strain from spreading quickly, as there is no immunity in humans and transmission would be fast.
Bird flu is different from the influenza virus that affects humans, and seasonal flu vaccines do not protect against avian viruses. The CDC, the U.S. Agriculture Department, and the Food and Drug Administration are closely monitoring developments, with a tool that gauges how likely bird flu will efficiently spread between humans. HPAI, or highly pathogenic avian influenza, has been found in a baby goat in Minnesota, the first case in U.S. livestock.
The virus was detected in dairy herds in Texas and Kansas on March 25, and testing showed the genetic clade to be the same that is widespread among birds globally. Since then, bird flu has spread to additional herds in at least five states, adding evidence that the virus may be spreading cow-to-cow. The strain was confirmed in a Michigan dairy on March 29 and in a New Mexico dairy on April 1, and presumptive positive tests have also been reported from Idaho.
Preliminary analysis has not found mutations that would make these viruses resistant to FDA-approved antiviral medications for flu. The United States has a small amount of bird flu vaccine targeted an earlier bird flu strain, part of a program to prepare for strains of influenza virus with pandemic potential. With the latest spread of bird flu, vaccine candidates are being developed and tested that are expected to match the current strain.
