Federal health authorities have called for increased testing of agricultural workers dealing with bird flu, following a recent study that revealed some dairy staff showed signs of infection without presenting symptoms.
Dr. Nirav Shah, principal director at the U.S. Centers for Disease Control and Prevention (CDC), emphasized the importance of testing farmworkers who have close interactions with infected animals and recommending treatment for them, irrespective of whether they demonstrate any illness.
This revised guidance comes after serological tests were conducted on 115 farmworkers in Colorado and Michigan, revealing antibodies present in eight of the individuals—representing around 7%—indicative of prior exposure to the H5N1 influenza strain.
“The goal of these actions is to ensure worker safety, limit the transmission of H5 to humans, and decrease the chance for the virus to mutate,” Shah explained during a press briefing.
This CDC study marks a significant survey offering insight into the potential spread of the bird virus, first reported in dairy cows in March, to humans. It hints that more farmworkers may have been infected than the 46 currently identified across the United States, as the majority had interactions with potentially infected dairy cattle or poultry.
Experts outside the CDC remarked on the importance of this study prompting the agency to adjust its approach. Prior guidelines suggested testing and medical care for workers showing symptoms.
“This is a crucial shift that indicates these H5N1 viruses pose a higher risk than the CDC had previously recognized,” noted Dr. Gregory Gray, an academic specializing in infectious diseases at the University of Texas Medical Branch in Galveston.
Each added case in humans or animals presents an opportunity for the virus to mutate in potentially hazardous ways, according to Angela Rasmussen, a viral specialist at the University of Saskatchewan in Canada.
“This highlights our ineffective response to the H5N1 outbreak affecting humans and animals—continued spread from one species to another could eventually catch up with us,” Rasmussen stated in an email.
The CDC’s investigation comprised tests conducted between June and August on 45 workers in Michigan and 70 in Colorado. Among the eight workers who tested positive for antibodies, half reported no symptoms. All of these individuals were involved in cleaning milking facilities and did not use protective respiratory equipment like masks, although three reported using eye protection.
Researchers pointed out that high levels of the virus have been detected in the milk of affected cows, which amplifies the risk of exposure and potential infection.
They also noted that monitoring efforts for signs of illness among dairy workers have faced several challenges, including hesitancy from both farm owners and employees to participate in testing.
Critics of the federal government’s response have labeled it as delayed and insufficient.
“These investigations should have been prioritized and conducted months ago,” Rasmussen added.
To date, the virus has been confirmed in at least 446 cattle herds across 15 states. Recently, the Agriculture Department reported the first instance of bird flu in U.S. pigs, confirming the virus in a pig from an Oregon farm.
