Bird Flu Detected in Dairy Worker Who Had Contact with Infected Cattle in Texas

The Washington Post / Lena H. Sun, Rachel Roubein

13:12 JST, April 2, 2024

A dairy worker in Texas is being treated for bird flu, only 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, federal and state officials said Monday.

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 patient worked directly with sick cows at a dairy, so the virus was most likely transmitted through that close contact,” said Chris Van Deusen, a spokesman for the Texas Department of State Health Services.

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. And 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, Van Deusen said.

CDC spokesman Kevin Griffis said the investigation into how widely the virus has spread is ongoing. “At this time, we are not aware that any of the individual’s close contacts have experienced any symptoms,” he said. 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.

Still, any time the virus changes “that makes me sit up and take notice,” said Caitlin Rivers, an epidemiologist at the Johns Hopkins Center for Health Security. Its recent emergence in cattle and the likelihood of cow-to-cow transmission represents a worrisome change.

This marks the first time the highly pathogenic avian influenza has been identified in U.S. dairy cattle, the American Veterinary Medical Association said in a statement last week.

Matt Steele, chief executive of the Kansas Cattlemen’s Association, said beef and dairy producers constantly check the health of their animals. If an animal appears sick, they’ll pull it aside, take its temperature and call in a veterinarian, if needed.

The odds of infected meat or dairy products leaving the farm are “very, very low,” Steele said, citing a system of checks and balances between the producers and state and federal agencies. “This isn’t really a major disease outbreak” that would heavily impact the meat and dairy market, he said.

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.

Until now, only one human case had been identified in the United States. In 2022, a person in Colorado tested positive for the same strain of avian flu. The person was involved in culling poultry presumed to have been infected with H5N1 bird flu. The person reported fatigue for a few days as their only symptom and recovered, according to the CDC.

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. There are several scenarios: The virus could remain primarily a threat to animal health and then recede, as it has in the past. It may continue to circulate among animals, but not routinely infect humans. Or, in the worst case, it evolves to spread easily between people and becomes the next pandemic, Rivers said. Such a pandemic would have significant costs to human life, society and the global economy, she said.

Pandemic flu has long been the boogeyman of infectious-disease and public health experts because the influenza virus is known to be wily, constantly changing, with an ability to combine with other influenza viruses to form new subtypes. A pandemic flu occurs when a new strain of influenza emerges that can be transmitted easily from person to person, and for which there is little or no natural immunity.

The more the virus is able to circulate in mammalian species, the greater the opportunity for the pathogen to mutate to spread more efficiently between humans. Although the H5N1 bird flu has rarely infected humans, among the cases that have been diagnosed, the fatality rate is roughly 50 percent.

Rivers said it’s important for U.S. policymakers to be proactive. If this strain of bird flu becomes easily spread from human to human, “the opportunity we have to make a difference is very short,” she said, because there is no immunity in humans and transmission would be fast. “You can’t adopt a wait-and-see attitude.”

Bird flu is different from the influenza virus that affects humans. Seasonal flu vaccines for humans do not protect against avian viruses.

The CDC, the U.S. Agriculture Department, and the Food and Drug Administration, along with state health and veterinary officials, say they are closely monitoring developments. The CDC has a tool that gauges how likely bird flu will efficiently spread between humans. It was last updated in April 2023, after the virus had spread to a commercial mink farm in Spain.

H5 bird flu is widespread among wild birds and has been documented to infect dozens of other mammalian species, but it rarely spreads between them. These viruses have caused outbreaks in commercial and backyard poultry flocks, leading to the culling of millions of poultry. Epidemiologists have been worried about the growing number of mammals infected by the highly pathogenic avian influenza – commonly known as HPAI – around the world.

Last month, HPAI was 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. Unpasteurized milk from sick cattle collected from two dairy farms in Kansas and one in Texas, as well as a throat swab from a cow in another dairy in Texas, tested positive. 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 presumptive positive tests have also been reported from Idaho and New Mexico, federal officials said Friday.

Preliminary analysis has not found mutations that would make these viruses resistant to FDA-approved antiviral medications for flu, the CDC said Monday.

The United States has a small amount of bird flu vaccine that 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, according to an official at the U.S. Department of Health and Human Services who spoke on the condition of anonymity because of the ongoing investigation.