Since the United States Department of Agriculture (USDA) announced on March 25 the contamination of a first herd of dairy cows in Texas with the H5N1 avian influenza virus, the infection has spread across the country. To date, around thirty dairy farms spread across nearly ten states, three of which border Canada, have been affected by this pathogen. An individual working on the Texas farm is currently the only confirmed human case. This contamination of mammals by a virus of avian origin has, however, alerted the World Health Organization (WHO), which fears the worst. Could this virus acquire mutations allowing it to attack humans and cause a pandemic? Overview of what we currently know about this virus, first detected in 1996.
How long has this virus been raging?
The H5N1 influenza virus was first detected in 1996 in birds in China. The 2.3.4.4b lineage of this virus which is currently raging in the United States first appeared in Asia and Europe in 2020-2021, where it caused die-offs among wild and domestic birds. It then reached North America in December 2021. We will remember the gannets on Bonaventure Island who fell victim to it during the summer of 2022. In addition to being very contagious among birds, this lineage has acquired the ability to infect mammals, including seals, leopards, lynx, foxes, bears, mink, domestic cats, and now dairy cows.
How did the virus spread among dairy cows across the country?
Presumably, the first cows contracted the virus through contact with infected birds or their droppings, or even through waste from infected chickens that had been used to feed them, says the Dr Donald Vinh, microbiologist-infectious disease specialist at the McGill University Health Center (MUHC). The infection would then have spread through the equipment used for milking cows, as well as during the transport of livestock from one farm to another, we suggest in an article published in Science. After testing the infected cows, USDA researchers discovered that the viruses were lodged not in the cows’ nostrils and blood, but in their milk, and were actively reproducing in the cows’ udders. . Droplets of contaminated milk on the gloves and clothing of workers carrying out milking, as well as on the milking suction cups, would therefore have contributed to transmitting the virus from one cow to another. In addition, scientists believe that the transfer of animals from the south of the country to the northern and Midwestern regions during the spring also contributed to the spread of the infection.
Is there any danger in consuming milk from these infected cows?
“Milk – and its derivatives – found in stores in the United States and Canada are necessarily pasteurized,” recalls Dr.r Vinh. Pasteurization is known to kill all living microbes, including viruses like H5N1 avian flu. However, we may find genomic fragments of viruses and viruses that died after pasteurization, but no live viruses. On the other hand, when milk is not pasteurized, it can contain infectious particles, not only influenza, but multiple types of bacteria. » If you only consume pasteurized milk, there is no risk of being infected. The Dr Vinh therefore recommends avoiding unpasteurized milk and products (cheese) made from raw milk.
What is the risk of transmission to humans?
So far, the H5N1 outbreak in dairy cows has only infected one person, who only developed conjunctivitis (reddened eyes). But the fact that the H5N1 flu virus — whose primary host was originally birds — is now successfully infecting mammals, such as dairy cows and farm cats, has increased scientists’ concern .
“Transmission from a mammal to humans seems uncommon and results in an infection that is not very dangerous, as in the case of the American worker, or a little more dangerous elsewhere in the world with a mortality rate of 30 to 50%,” sums up the Dr Vinh.
“Human cases are currently sporadic cases resulting from close and repeated contact with animals, which is unlikely to lead to an outbreak between humans. What would be really worrying would be if the virus infected pigs, as this animal can be infected with swine, avian and human flu viruses simultaneously. The pig is considered a melting pot for viruses to mix, making there a statistically higher risk of rearrangements in the virus genome occurring. [des échanges de segments d’ARN entre les souches aviaire, humaine et porcine]which could lead to the emergence of a completely new strain much more capable of infecting humans,” explains the infectious disease specialist.
The H1N1 viral strain, which caused a flu pandemic in 2009, resulted from such a rearrangement between viruses of swine, avian and human origin in pigs.
How can we protect ourselves against this pathogen?
Contact with infected birds and mammals should be minimized. Vaccination of duck farms and mammals may be considered. “But we cannot vaccinate all wild animals, which can also be infected,” points out Dr.r Vinh. First of all, we must test all farm animals that could be at risk or that are exposed to detect those who are infected, then quarantine those who are infected, or sometimes slaughter them. »
“We need to carry out proactive, constant and global surveillance in farms and populations of wild and captive animals, in order to detect affected pigs as early as possible, because in this case it will be much more worrying” , he said.
And for humans, there are two vaccine candidates likely to provide protection against the viral strain plaguing the United States. They could be produced en masse or in the quantities needed to vaccinate at-risk populations, such as farm workers. For the moment, “workers should wear masks, gloves and visors to protect themselves,” advises the Dr Vinh.