Experiment confirms that bird flu in the US is spread by milking procedures

An experiment with cows in a high-security laboratory in the United States offers alarming data on the possibility of stopping the global bird flu epidemic, the worst recorded in history.

American and German scientists experimentally infected calves and dairy cows in a level 3 security laboratory to determine the transmission route of the highly pathogenic avian influenza, which is affecting animals on 231 farms in 14 U.S. states. The results confirm that the H5N1 virus accumulates in the udders and milk of cows, and is probably being transmitted by industrial milking systems.

The authors of the paper warn that the H5N1 virus variant spreading in Europe is also capable of infecting dairy cows and making them sick. With a single jump of the virus from a wild bird to a farm animal, Europe could be in the same position as the U.S.

The study comes just days after the U.S. Center for Disease Control reported that a second health worker had developed respiratory symptoms after caring for a patient who tested positive for H5N1 in the state of Missouri, but wasn’t tested for influenza. This is worrying since the Missouri patient is the only case who did not have contact with poultry or dairy cows. It is not known how they were infected.

Fatality rate: 52%

In 1996, an H5N1 virus from wild birds jumped to domestic geese in Asia. The spread of the pathogen led to the culling of 400 million chickens and other poultry, more than in the 36 previous epidemics recorded. According to the World Health Organization, 887 cases of infection in humans and 462 deaths have been detected since then, a fatality rate of 52%.

In 2021, a new H5N1 subvariant known as 2.3.4.4b developed the ability to infect mammals, both wild and domestic, causing episodes of mass mortality. Since then, it has spread throughout Asia, Europe, America and Antarctica. The epicenter of the crisis is now in the United States, where this new avian flu in cows continues to spread on dairy farms.

The new study, published in Nature, a leading source of world science, compared the infectivity of the H5N1 variant circulating in cattle in the United States by injecting viruses into the udders of dairy cows and the snouts of calves. The results show that animals infected via the respiratory route barely suffer symptoms and did not transmit the disease to other animals. Meanwhile, dairy cows infected via the udder did suffer severe illness, with high fever and lack of appetite, and their milk production plummeted.

The study also infected dairy cows with a variant of H5N1 isolated from wild birds in Europe. The animals also became ill, showing that the American variant is not the only one capable of causing a large epidemic in cattle. The symptoms were so severe that some animals had to be euthanized early. Although the experiment cannot exactly reproduce the conditions found on farms, its results are consistent with the fatality rate of up to 5% of animals observed on livestock farms, the authors explain.

The origin of this epidemic is probably a single jump of H5N1 from a wild bird to a cow late last year or early this year, the study says. The movement of cattle between states is believed to have been responsible for the spread of the virus, which circulated for weeks without being detected.

Juergen Richt, a researcher at Kansas State University, where the study was conducted, told EL PAÍS: “Our experiments show that the virus spreads mainly through milking and probably through milking equipment.” “It seems that the replication of the virus in cows is limited to the mammary glands. It is worrying that H5N1 continues to be transmitted between dairy cows, because it may allow it to adapt even more,” he added.

Mandatory tests and quarantines

The big question is whether the spread of H5N1 can be stopped. Martin Beer from the Friedrich-Loeffler Institute in Germany, co-author of the study, believes: “Mandatory testing should be introduced to identify all affected farms, followed by individual testing, quarantine and isolation of infected animals.” “It would also help if all cows were tested before they were transported and hygiene measures were reinforced on farms,” he adds. At present, each state is following its own control protocols without any binding federal guidelines.

Natalia Majó, a veterinary pathologist and director of the Animal Health Research Centre (IRTA-CRESA) in Barcelona, believes that “the situation is very worrying.” “In Europe, it seems that we are getting used to ignoring this news, partly because this year there has been very little expansion of avian flu. But this work shows us that the same thing can happen here as in the United States with a single introduction of the virus from a single infected bird. Surveillance is essential,” she says.

For Elisa Pérez, a veterinary virologist at Spain’s CSIC Animal Health Research Center, she admits: “Just a few months ago I would have said that it was impossible for an avian virus to spread so quickly among mammals.”

H5N1 has mutated to take advantage of the molecular receptors of the mammary glands and has already infected 59 species of mammals, including humans. The number of viral particles in cows’ milk is “about 100 million per milliliter, a very high amount,” warns the researcher. The expert assumes that calves are becoming infected by feeding. “Most infected people had conjunctivitis, probably due to splashes during milking,” she adds.

For the scientist, the big question is why this crisis in livestock is only affecting the United States, especially now that it is known that this country’s variant is not the only one capable of making cows sick. “In Canada, for example, there has not been a single case. Nor in Europe. Perhaps it is due to some characteristic of the farms there that we have not yet identified, or to closer contact with infected birds, possibly through watering troughs,” she ventures.

In any case, the researcher believes that “once such an epidemic has started, it is very difficult to stop.” “There needs to be a willingness to carry out mass surveillance,” she argues. When H5N1 infects a cow, its milk production drops by up to 90%, explains Pérez. This may be the best warning sign to detect an outbreak and stop it before it is too late.

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