Outbreaks of highly pathogenic avian influenza (HPAI) in poultry and dairy cattle have dropped off sharply in recent weeks, according to USDA databases. There was a similar but longer lull a year ago in bird flu, which has become the largest animal disease event in American agriculture, killing nearly 101 million birds in domestic flocks since it appeared in the United States in February 2022.
No cases of bird flu have been found in commercial poultry flocks since July 19, five weeks ago. The viral disease has been confirmed in three dairy herds since Aug. 5, three weeks ago.
Thirteen farmworkers have contracted mild cases of bird flu from exposure to infected dairy cattle and poultry since April. Ten of the cases were in Colorado. Public health officials say the risk to the general public is low and recommend that people wear protective equipment if they deal with infected or potentially infected animals. The jump by the virus to dairy cattle from birds gives the virus a possible route to threaten humans. Scientists say the H5N1 avian flu virus has not shown signs of becoming more communicable.
Last year, HPAI disappeared from commercial flocks for nearly six months, from April 19, when it was confirmed on two turkey farms in North Dakota and South Dakota, until Oct. 4, when it was found on a South Dakota turkey farm. In the interim, the disease was detected in six backyard flocks totaling 320 birds and at four live bird markets — three in Brooklyn and one in Union County in northern New Jersey — with 2,380 birds. Bird flu killed 20.9 million birds in domestic flocks during the final three months of 2023.
Since the last major HPAI discovery among large flocks this year, in Colorado, three outbreaks of bird flu have been reported in Florida, totaling 6,285 birds.
The most recent bird flu cases in dairy have been two herds in Colorado and one in Idaho. Colorado accounts for 64 of the 192 dairy herds in 13 states that have tested positive for the avian flu virus. It is the only state that requires weekly tests for bird flu in milk samples from every dairy farm.
Animal health officials say HPAI is spread by migratory waterfowl and their droppings. Outbreaks are more common during the colder months of the year. Among cattle, bird flu is spread from cow to cow with high viral loads found in the milk of infected cows. In poultry and dairy cattle, the disease can be spread from farm to farm by shared equipment and by contaminated clothing. The USDA stresses biosecurity on the farm to prevent the spread of the virus.
Nine of the 10 cases of avian flu in livestock workers in Colorado this year involved contract laborers who culled infected flocks on two egg farms. Bird flu has been reported in four dairy workers nationwide; two in Michigan and one each in Texas and Colorado.
HPAI has been reported among animals worldwide. “We’ve never seen anything like this,” said Maurice Pitesky, an expert in poultry disease modeling at the University of California-Davis. “It’s orders of magnitude larger and more complex than previous outbreaks,” he said in the UC-Davis magazine.