a A third case of H5 avian influenza linked to an ongoing cattle outbreak in the United States has been detected in a Michigan farmworker, state health officials confirmed Thursday.
The state health department said in a statement that the person, whose name was not released, worked on a dairy farm and had close contact with infected cows — a different farm from the one where human cases were identified last week.
“In this case, the respiratory symptoms developed after direct contact with an infected cow,” Natasha Bagdasarian, chief medical officer for the Michigan Department of Health and Human Services, said in a statement. The infected person was not wearing protective gear, she said.
The CDC said in a separate statement that the person had complained of “eye discomfort” with a non-feverish cough and watery eye discharge.
The employee was given an antiviral drug for influenza and is recovering, according to both statements. The CDC said the employee has been instructed to isolate and that household contacts will also be offered the antiviral medication. The statements did not say whether they agreed to take the medication.
“No other employees at the farm have reported symptoms, and all staff are being monitored. There is currently no indication of person-to-person transmission of the A(H5N1) virus,” the CDC said.
There have been four known cases of H5 virus infection reported in the United States (three since the start of the cattle epidemic), but this is the first time that infected individuals have reported respiratory symptoms. Two human cases reported earlier this year involved only conjunctivitis, also known as pink eye. Those cases occurred in Texas and Michigan, and both involved farm workers who had contact with infected cattle.
The first case of H5N1 virus in the United States occurred in April 2022 in a Colorado man who had been involved in culling chickens at a poultry farm where the virus had spread. The man tested positive for the virus but reported only feeling fatigue.
The importance of respiratory symptoms relates to the potential for spread of the infection. In humans, influenza is transmitted through the respiratory tract. People with influenza virus in their respiratory tract are more likely to spread the virus, if it is transmissible from person to person, than people with eye infections. So far, the H5 virus has not been found to spread easily from person to person, and Michigan officials say the risk to the general public is low.
The Michigan state statement described the virus simply as an H5 virus. The CDC, which is conducting confirmatory testing for H5N1 cases, said it is attempting to generate a complete genetic sequence of the virus and will release more information within the next day or two if that effort is successful.
Before this outbreak, it wasn’t thought that cows could be infected by the virus, and this assumption likely contributed to the slow realization that the mystery illness that had been affecting milk production on several dairy farms in the Texas Panhandle since February was in fact avian influenza.
Since H5N1 was announced as the cause of the decline in milk production in late March, the USDA has confirmed that 67 herds in nine states are infected. One of the infected herds is made up of alpacas, and the rest are dairy cows.
Infectious disease experts suspect the outbreak is more widespread than the number of affected states would suggest, a suggestion supported by a Food and Drug Administration study of commercial milk: Of nearly 300 pasteurized milk products purchased in 38 states, one in five tested positive for the H5N1 virus using polymerase chain reaction tests. Attempts to culture live virus from the positive milk were unsuccessful, supporting the FDA’s view that pasteurization kills the virus.
However, there are concerns that if the cows that produced the unpasteurized milk (commonly known as raw milk) were infected with H5N1, consumers could be exposed to dangerous levels of the virus.
A study published last week in the New England Journal of Medicine found that mice fed raw milk purportedly from infected cows became sick enough to have to be euthanized. There have been reports of cats dying on farms with infected herds, and one infected alpaca showed neurological symptoms before dying, Idaho Department of Agriculture spokesperson Sydney Kennedy told STAT in an email.
The virus is deadly to poultry and has been confirmed to have killed several mammal species, from polar bears to foxes, zoo tigers to sea lions, but it does not generally make cattle seriously ill. As a result, there is little incentive for farmers to agree to have their cattle tested. Cases continue to rise in most states with confirmed cases of infected cattle, but no new states have acknowledged having infected cattle since Colorado joined the list on April 25.
A federal order that went into effect April 29 requires farmers to test some of the dairy cows they plan to transport across state lines, but the mandate is for a maximum of 30 cows per shipment, and farmers can choose which cows to test.
The USDA said Wednesday that about 2,500 pre-movement tests had been conducted. It did not say how many of those had returned positive results, and the agency has not accepted or responded to STAT’s request for that figure.
Sarah Owermohle and Rachel Cohrs Zhang contributed reporting.
