Agriculture/Agriculture Avian flu is probably transmitted between cows through milking
The H5N1 avian flu virus is mainly transmitted between cows via milk. Probably primarily via the milking equipment. Infected animals probably do not pass on the pathogen via the air they breathe.
25.09.2024, 17:00
25.09.2024, 17:15
SDA
This was reported by a group led by Martin Beer from the Friedrich Loeffler Institute (FLI) in Greifswald and Jürgen Richt from Kansas State University in Manhattan following experiments in the journal "Nature".
In the experiments, the researchers infected calves and dairy cows with H5N1, in particular with the B3.13 variant, which was reported in dairy cows in the US state of Texas last March and affected 190 dairy farms in 13 US states at the beginning of August. Isolated cases have also been registered in humans on such farms.
The B3.13 variant is a mixture of an originally European and a North American bird flu virus, the authors write. Accordingly, this pathogen probably jumped to cattle at the end of 2023 or beginning of 2024 and then spread.
Cows infected via respiratory air remained healthy
Beer, Richt and colleagues have now specifically investigated how infections occur. To do this, they first infected Holstein cattle calves with the B3.13 variant via the nose and mouth and added three more calves to the group two days later. Although the team registered increased nasal mucus production and coughing in some of the originally infected animals, there was no fever or other symptoms of illness. Appetite and activity also remained normal.
The calves subsequently added to the group did not become infected. Seven days after infection, only half of the originally infected calves showed a small amount of viral genetic material in the tissue of the upper respiratory tract. Blood and other tissues contained no viral RNA.
Cows infected via the udder became ill
The situation was quite different in dairy cows that had been infected via the udder. They showed impaired general condition, postural disorders and lethargy just one day after infection. Milk production fell by over 90 percent in all of these cows.
On the second day after infection, the milk became slimy and viscous and quickly separated into liquid and solid components. This affected both the cows that had been infected with the B3.13 variant and three test animals that had been given a related European H5N1 variant.
Some cows euthanized
In both groups, one cow in each group became so ill that it had to be euthanized on the third day after infection. Milk samples from both groups showed high viral loads. Autopsies revealed that a considerable number of cells in the mammary glands had died. In genetic tests, the researchers found a mutation that probably enables the virus to multiply in certain cells of the udder.
However, there is a limitation to the significance of the study: an early variant of the bovine H5N1 virus from the USA was examined and only tested on a small number of animals, according to the FLI.
"Fortunately, no human-to-human transmission has been reported to date," write the study authors. "This supports the assumption that these strains have not yet overcome critical barriers to allow human-to-human transmission."
However, the team urges US dairy companies to be more vigilant if milk characteristics are noticed. They should then consider mammary gland inflammation as a result of avian influenza infection. An effective surveillance strategy is crucial for controlling the outbreak among cows.
