The Oklahoma Department of Agriculture, Food, and Forestry recently confirmed the state's first highly pathogenic avian flu outbreak in a dairy herd, bringing the number of affected states to 13.
In research developments, a team from the US Department of Agriculture (USDA) reported results from H5N1 challenge studies in heifers and lactating cows, which showed that the virus can spread between cattle by both respiratory and mammary routes.
Oklahoma samples collected in April
In a July 12 statement, Oklahoma officials said the sample was collected by the dairy farm in April and was recently submitted to the USDA Animal and Plant Health Inspection Service (APHIS) for testing. It added that the herd has recovered and the farm has not reported any other cases.
Oklahoma State Veterinarian Rod Hall, DVM, said, "Our team has been in constant communication with Oklahoma dairies asking them to heighten their biosecurity practices. PPE [personal protective equipment] has also been made available to Oklahoma dairy farmers."
The statement did not provide information on the long delay between sample collection and publication of the test results.
In an update today, the USDA APHIS said 157 H5N1 outbreaks have now been confirmed in 13 states, which includes the Oklahoma herd plus additional new detections in Colorado and Idaho.
Infection routes in dairy herds
For the challenge study, USDA researchers in a biosafety-level 3 agriculture facility used a B3.13 genotype H5N1 virus to inoculate two nonpregnant but lactating Holstein cows by the intramammary route and five 1-year-old Holstein heifer calves by the aerosol route. Four of the calves received the virus, and one received buffered saline.
The scientists reported their findings on the preprint server bioRxiv. They have not been peer-reviewed.
The lactating cows infected by the intramammary route had significant milk disease that mirrored what farmers and scientists have previously reported. High viral RNA levels were detected in milk, and researchers isolated the virus, found lesions in mammary tissue, and saw evidence of seroconversion.
Virus persistence was still seen in mammary glands and milk for up to 24 days after inoculation.
Meanwhile, heifers who were infected through the airborne route had mild disease. Scientists found replicating virus in the airways and lungs, suggesting that asymptomatic cows are able to spread the virus to herd mates. The team also found evidence of seroconversion.
"Although respiratory infection was limited in the 4 heifers, the detection of viable virus in 2 out of 4 represents a mode of infection and transmission that, when applied to an animal facility that commonly holds hundreds of animals, implies there is a role for the respiratory route," they wrote.
