A new report on the first human bird flu case tied to the outbreak in cows in the United States suggests that the Texas man may be the first detected case of the H5N1 virus transmitting from a mammal to a person.

Nearly 900 people in 23 countries have been infected with the H5N1 bird flu virus since it started spreading from Southeast Asia in late 2003. But previous human cases were all linked to transmission from infected birds, typically domestic poultry.

The report, published Friday by the New England Journal of Medicine, details the unidentified man’s symptoms and his possible route of infection. It was written by scientists from the Centers for Disease Control and Prevention, the Texas Department of State Health Services, and the Texas Tech University Bioterrorism Response Laboratory in Lubbock.

How the man became infected cannot be proven; while the cattle on the farm where he worked reportedly suffered from a decline in milk and other symptoms seen in herds that have tested positive for H5N1, no animal testing at that farm was undertaken. The authors noted, though, that nearby farms where dairy cows experienced the same symptoms tested positive for the virus.