Just one person has been confirmed to have contracted highly pathogenic avian influenza amid the current outbreak of the illness among cattle in the United States, but some scientists think the number of infected people is likely higher.
“We know that some of the workers sought medical care for influenza-like illness and conjunctivitis at the same time the H5N1 was ravaging the dairy farms,” Gregory Gray, an infectious disease epidemiologist at the University of Texas Medical Branch in Galveston, said in an interview with KERA News.
The man confirmed to have contracted the virus worked with dairy cattle in Texas. Highly pathogenic avian influenza, also known as H5N1, has infected at least 33 herds in nine states but is typically not fatal to cattle. However, it has also impacted poultry ranches, where it is lethal to the livestock. Nearly 2 million egg-laying hens were euthanized at one Texas facility in April, as previously reported by The Dallas Express.
Several obstacles make identifying spillover cases difficult for researchers, including workers’ reluctance to seek medical care due to a lack of insurance or residency and ranchers’ wariness of negative publicity.
“If the idea was to try to identify where there was spillover from these facilities to human populations, you’d want to try to test as many workers as possible,” environmental epidemiologist at Boston University School of Public Health Jessica Leibler told KERA.
The CDC reported on May 3 that more than 30 people exposed to infected cattle have been tested during the current outbreak, and more than 220 people are being monitored. Since this particular strain of bird flu first arrived in the United States in 2022, the CDC said it tested 200 people and monitored some 9,000 others. That year, a poultry worker in Colorado became the first person in the United States to contract the virus.
So far, there has been no evidence of human-to-human transmission, according to the CDC. It is thought the risk is low based on what is known about the virus at this time, according to Nirav Shah, principal deputy director at the CDC, who spoke at a roundtable discussion at the Council on Foreign Relations on May 1.
“As with any major outbreak, this is moving at the speed of a bullet train,” Shah said. “What we’ll be talking about is a snapshot of that fast-moving train.”
Researchers believe the virus jumped from birds to dairy cattle about four months ago, but it is not known how or why. The virus has also infected dozens of other mammals, including seals, dolphins, dogs, and cats, as reported by NBC News.
As the virus mutates, it may become infectious to other animals. In the United States, no cases of infection have been detected in hogs, but researchers in Indonesia have found the virus in local swine herds.
Officials with the U.S. Department of Agriculture (USDA) and the Food and Drug Administration are closely monitoring the commercial milk supply. Recently, fragments of the virus were found in commercial milk, but it is not believed to pose a danger, as previously reported by DX. Nearly all commercial milk in the United States undergoes pasteurization, which raises the temperature of the milk to a level that the virus cannot survive. USDA recommends that people avoid consuming unpasteurized milk products.
