The US farmworker who caught bird flu from cows may be the first case of mammal-to-human transmission. His case also shows how difficult it is to track the infection.

CNN
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A US farm worker who caught bird flu after working with dairy cattle in Texas appears to be the first known case of transmission of the virus between mammals and humans, according to a new study.

The dairy worker sought treatment in late March after developing red, swollen and watery eyes with burst blood vessels. He did not, however, have a fever and his lungs were clear, according to a new letter on the case published Friday in the New England Journal of Medicine.

He has not reported any contact with sick or dead birds or other animals, but he has had repeated, direct and close contact with dairy cows in the same part of the state with other infected herds.

Although the man did not become seriously ill, his case is important because it confirms that humans can become infected with H5N1 after contact with cows. At the same time, it also leaves crucial questions unanswered and illustrates how difficult it will be to track infection in this vulnerable population of workers, where a positive test for an infectious disease could mean lost work days and salary.

“For farmworkers in particular, these are certainly people who are living in a state of economic desperation, and what they won’t do is they won’t get tested if they don’t have paid sick leave, because they can’t afford to be sent home and told to stay home and not work,” said Elizabeth Strater, director of strategic campaigns for United Farm Workers.

Strater said the UFW, like other groups, heard rumors of dairy workers being sick but didn’t want to be tested, but she said that’s nothing they can confirm.

Texas health officials said they had tested other sick dairy workers, some of whom had red eyes, but had illnesses other than bird flu.

“People who were tested volunteered to get tested,” said Lara Anton, senior press secretary for the Texas Department of State Health Services.

“It is likely that other people with symptoms did not want to be tested, so we cannot say with absolute certainty that no one else contracted H5N1. We can say with certainty that some people on dairy farms have tested positive for other respiratory viruses that commonly circulate in the human population,” Anton said.

In the case of the man who tested positive for bird flu, he and his immediate family members were given antiviral medications and they recovered without any lasting problems, the letter said.

Swabs from the patient’s eyes and lungs also revealed something interesting. While his eyes were teeming with the H5N1 virus, there was virtually no virus in his lungs. This could mean that the worker was infected through their eyes – either by rubbing them with contaminated hands or by splashing contaminated milk – rather than through their lungs, and that the virus never migrated there, or that the virus was unable to gain a foothold in his body. lungs, because it was adapted primarily to infect birds, but not human airway cells.

The letter on the case was written by researchers from the U.S. Centers for Disease Control and Prevention, doctors from the Texas Department of State Health Services and researchers from the Texas Tech Bioterrorism Response Laboratory.

Health officials said they could not further investigate how the man became infected because “epidemiological investigations could not be conducted at the farm” where he worked. They also could not test other workers on the same farm.

This type of testing is essential to answer questions about how the worker became infected, whether others were infected and, if so, how long they were infected, what types of symptoms they had, whether they presented some.

The CDC is currently looking for farms that will allow it to carry out such a detailed study.

“Understanding the current outbreak of avian influenza in dairy cattle is a vital priority to help protect human health,” the CDC said in a statement to CNN. “Discussions are underway with farms in several jurisdictions to participate in CDC-led epidemiological studies. In the meantime, states continue to test symptomatic farmworkers and monitor those who have been exposed to infected animals. The CDC also continues to closely monitor a robust nationwide influenza surveillance system. To date, no unusual influenza activity has been detected.