An experiment on cows in a high-security laboratory in the United States offers alarming data on the possibility of stopping the global epidemic of bird flu, the worst ever recorded in history.
American and German scientists have experimentally infected calves and dairy cows in a level 3 security laboratory to clarify the transmission route of the highly pathogenic avian influenza, which is already affecting animals on 231 farms in 14 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 circulating in Europe is also capable of infecting dairy cows and making them sick. The same thing that happens in the US can happen in Europe with a single jump of the virus from a wild bird to a farm animal.
The paper is published days after the US Centers for Disease Control acknowledged that a second health worker had symptoms after treating a patient infected with H5N1 in Missouri, and who was not tested for the flu. The lack of confirmation is worrying, since this patient is the only case of infection that did not have contact with animals or raw cow’s milk. The form of contagion is still a mystery..
A lethality of 52%
In 1996, an H5N1 virus from wild birds jumped to domestic geese in Asia. The spread of the pathogen forced the culling of 400 million chickens and other poultry, more than in the 36 previous outbreaks recorded. According to the World Health Organization, 887 cases of human infection and 462 deaths have since been detected, a total of 1.8 million people. lethality 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 epicentre of the crisis is now in the United States, where this new avian flu in cows continues its unstoppable expansion on dairy farms.
The new study, published in Naturea leading global body of science, has compared the infectivity of the H5N1 variant circulating in US cattle by injecting viruses into the udders of dairy cows and the snouts of calves. The results show that animals infected via the respiratory tract barely suffer symptoms and do not transmit the disease to other animals. Meanwhile, dairy cows infected via the udder do suffer severe illness, with high fever and lack of appetite, and their milk production plummets.
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 mortality rate of up to 5% of animals observed on some 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 Richta researcher at Kansas State University, where the study was carried out, explains to EL PAÍS: “Our experiments show that the virus has its main route of spread through milk and probably the 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 adds.
Mandatory tests and quarantines
The big question is whether the spread of H5N1 can be stopped. Martin Beerfrom the Friedrich-Loeffler Institute in Germany and 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 mandatory federal guidelines.
Natalia Majóveterinary pathologist and director of the Animal Health Research Centre (IRTA-CRESA) in Barcelona, believes that “the situation is very worrying”. “In Europe we seem to be 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 points out.
For Elisa Pereza veterinary virologist at the CSIC Animal Health Research Centre, admits: “Just a few months ago I would have said that it was impossible for an avian virus to spread among mammals so quickly.”
H5N1 has mutated to take advantage of molecular receptors in the mammary glands and has already infected 59 species 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 affects only the United States, especially now that it is known that the variant of this country 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.” “A willingness to carry out mass surveillance is necessary,” she points out. When H5N1 infects a cow, its milk production drops by up to 90%, explains Pérez. This may be the best warning sign for detecting an outbreak and stopping it before it is too late.
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