By Leah Douglas, Julie Steenhuysen and Tom Polansek
(Reuters) -A third U.S. dairy worker tested positive for bird flu after exposure to infected cows, becoming the first to develop respiratory problems, U.S. officials said on Thursday.
The infection was the second human case in Michigan, which has confirmed more cases of bird flu in dairy cattle than any other state. It also expands symptoms for human cases, after the two workers who previously tested positive only experienced conjunctivitis, or pink eye, and recovered.
The US Centers for Disease Control and Prevention (CDC) said the latest case does not change its assessment that bird flu poses a low risk to the general public and that no evidence of human-to-human transmission has been seen.
Nirav Shah, deputy director of the CDC, said on a call with reporters that the agency expected respiratory symptoms because previous new flu viruses also showed these symptoms.
“At the same time, respiratory symptoms increase the likelihood of exposing someone to the virus compared to (eye) symptoms,” Shah said.
Meanwhile, Michigan will soon begin testing dairy farm workers for signs of previous bird flu infection, a county health official told Reuters. State and local health officials have been monitoring exposed farmworkers for symptoms.
The ongoing bird flu outbreak in dairy cattle has affected 67 herds in nine states since March, according to CDC data.
The third employee who tested positive reported upper respiratory symptoms, including coughing without fever and eye discomfort with watery discharge, the CDC said.
The patient received antiviral treatment, isolated at home and symptoms resolved, the CDC said. Household contacts of the patient have not developed symptoms and are being monitored for illness, the agency added.
The worker worked on a different farm than the previous human case that Michigan reported on May 22, the state said.
CDC reported the first human case linked to dairy cattle in Texas on April 1. None of the three human cases are linked to the other, the agency said.
‘A MILD CASE’
“Although respiratory symptoms were present in this individual, it was still a mild case,” said Dr. Amesh Adalja, an infectious disease expert at the Johns Hopkins Center for Health Security. “This underlines the risk specific to dairy farm workers.”
CDC officials were eager to test blood samples from farm workers for signs of previous infection to help understand the extent of the bird flu outbreak.
County and Michigan state officials will work with the CDC on testing efforts, said Chad Shaw, health officer and director of environmental health at the Ionia County Health Department in Michigan. Details of the testing plan have not previously been reported.
Ionia County has reported bird flu infections in four dairy herds and four poultry flocks, according to state data.
The purpose of the testing is to distinguish how the virus spreads from farm to farm, including whether people have transmitted the virus asymptomatically, Shaw said, adding that he did not know when testing would begin or how many workers would be tested.
Shah said the CDC has been working with state health and agriculture departments on a series of studies to help understand the current risk to workers, whether workers have been infected before and what factors on a farm increase the risk of infection.
The CDC will design the surveys that any public health agency can use for those purposes, Shah said, adding that the Michigan Health Department was leading the testing effort.
Testing for previous infections is important to determine how widespread the virus is among people, said Michael Osterholm, an avian flu expert at the University of Minnesota. Widespread exposure could increase the chance that the virus will mutate and become more easily transmissible to humans.
“The real barrier to allowing us to sleep with one eye open is whether or not there is person-to-person transmission, and there is no evidence of that here,” Osterholm said.
Production of 4.8 million doses of bird flu vaccines will be completed this summer, David Boucher, director of infectious disease control at the U.S. Department of Health and Human Services, said on the press call.
The U.S. Department of Agriculture (USDA) is launching a pilot program that will allow enrolled farmers to test their dairy cows’ milk for bird flu in bulk instead of testing individual animals before shipping them across state lines, Eric Deeble, a senior adviser, told reporters . .
The details of that program were first reported by Reuters.
The USDA will also spend another $824 million to work with states on bird flu testing and surveillance, Deeble said.
