H5N1 dairy first mammal-to-human case

Texas health officials said on April 1, 2024 that a dairy worker had tested positive for H5N1 after exposure to cattle presumed to be infected, creating the first known human case linked to dairy cows in the United States. CDC said the infection was thought to be the first likely instance of mammal-to-human spread of H5N1. WHO said the worker, an adult in Texas, developed conjunctivitis on March 27 while working at a commercial dairy farm. (cdc.gov) The case became a key marker in the 2024 dairy outbreak because it tied the virus in cattle to a human infection under field conditions. ### When did officials first connect H5N1 in a person to dairy cattle? April 1, 2024 is the date U.S. officials publicly confirmed the human case. Texas Department of State Health Services said the patient had direct exposure to dairy cattle presumed to be infected with avian influenza, and CDC described it as the first U.S. human H5N1 case linked to cattle exposure. Texas also said the case did not change the risk assessment for the general public, which remained low. WHO said the United States notified it of the laboratory-confirmed Texas case on April 1. (cdc.gov) The agency said the person was older than 18 and had a history of exposure to dairy cattle on a commercial farm before developing conjunctivitis. ### Why was this case described as mammal-to-human transmission? CDC said the Texas infection was thought to be the first likely mammal-to-human spread of H5N1 because the person had exposure to dairy cows, not poultry, during the outbreak under investigation. That distinction mattered because H5N1 had long been associated mainly with birds and poultry outbreaks, while the 2024 U.S. event involved the virus moving through dairy herds. (dshs.texas.gov) WHO’s May 2024 questions-and-answers page said H5N1 infections in mammals, including humans, had been documented before, but the U.S. dairy episode added a new exposure setting involving cattle. (who.int) A joint FAO-WHO-WOAH assessment issued in April 2024 also addressed the recent H5N1 detections in dairy cattle in the United States. ### When was H5N1 in dairy cattle itself confirmed? USDA said on March 25, 2024 that unpasteurized milk samples from sick cattle on dairies in Kansas and Texas, along with a swab from another Texas dairy, tested positive for highly pathogenic avian influenza. (cdc.gov) USDA’s National Veterinary Services Laboratories confirmed those detections as H5N1 clade 2.3.4.4b, according to the agency’s epidemiologic brief. USDA later said the disease was first detected in dairy cattle in March 2024 and that the federal government responded with testing, sequencing and movement controls. (who.int) On April 24, USDA issued a federal order, effective April 29, requiring testing for lactating dairy cattle before interstate movement and reporting of positive tests. ### What did officials say about broader risk and additional cases? CDC said in a report covering the early outbreak that about 350 farm workers with exposure to dairy cattle or raw milk had been monitored as of May 22, 2024. (aphis.usda.gov) That surveillance identified a second human case in Michigan, also involving conjunctivitis, and CDC said no unusual influenza activity trends had been detected in the United States at that time. Texas health officials and CDC both said the risk to the general public remained low, while people exposed to infected animals or contaminated materials faced higher risk and were advised to take precautions. (usda.gov) CDC also said candidate vaccine viruses were available and laboratory analyses indicated the viruses circulating in cows and other animals were susceptible to FDA-approved antivirals. ### Where can readers track the next official updates? CDC’s current H5N1 situation summary continues to post human case updates tied to infected dairy cows, and USDA’s livestock H5N1 pages continue to track dairy-herd detections and response measures. (cdc.gov) Those federal pages remain the main public sources for new human case counts, herd reports and control actions. (cdc.gov) (dshs.texas.gov)