The details, reported online in the New England Journal of Medicine, underscore the risk to farm workers in the ongoing outbreak among U.S. dairy cattle and the need to wear protective gear to avoid infection.
The outbreak the first in cattle is so far known to have infected 36 dairy herds in nine states.
Infection by the bird virus is rare in humans, and the dairy worker’s case, first reported in March, represents only the second known human infection in the United States.
It follows a worrisome spread of the virus in a variety of mammal species, raising concerns that widespread exposure to people could cause the virus to spread more easily among the population and spark a global pandemic.
The U.S. Centers for Disease Control and Prevention (CDC) in the report said the farm worker developed a serious infection in his right eye known as conjunctivitis, or pink eye, but had no signs of respiratory infection or fever.
The worker had not reported any contact with sick or dead birds or other animals but did have close exposure to sick dairy cows, with symptoms such as decreased milk production, reduced appetite, and lethargy.
The worker had been wearing gloves but no respiratory or eye protection.
The CDC is urging farmers, workers, and emergency responders to wear appropriate protective gear when in direct or close physical contact with sick birds, livestock, feces, raw milk, or contaminated surfaces.
An analysis of the outbreak released on Thursday by the U.S. Department of Agriculture suggests the virus has been circulating in U.S. dairy cows for about four months before being reported on March 25.