The H5N1 bird flu virus appears to behave unusually in livestock in several ways. Now a person has been infected by a dairy cow. What consequences arise from this?

H5N1 bird flu, which is circulating around the world, is believed to have been transmitted from dairy cows to humans for the first time. However, according to the US Centers for Disease Control (CDC), the affected person only had symptoms of conjunctivitis; She is being treated with antiviral medication and is recovering, the authority wrote in a statement. Avian flu viruses occasionally trigger conjunctivitis in humans because certain cell receptors in our eyes are similar to those in the respiratory tract of birds.

In the United States, H5N1 is currently circulating among dairy cows in at least five states. The infected person probably had contact with infected animals. The virus belongs to line 2.3.4.4b, a variant that has been causing devastating epidemics among wild birds around the world since the beginning of 2021 and has also repeatedly infected mammals. The virus has already been discovered in many different species of mammals, including dogs, cats, bears and seals.

Surprisingly, the infection spreads between cows.

However, the fact that the infection is spreading among cows is a surprise. Livestock occasionally become infected with influenza viruses, but also with influenza D, a pathogen of its own. Cattle are generally not very susceptible to influenza A, which also includes H5N1. Furthermore, the vast majority of mammals infected with 2.3.4.4b so far have been carnivores, which likely became infected by eating sick birds. This is unlikely to happen with livestock; The animals probably became infected through contaminated water or food. It is currently unknown whether the infection is also transmitted directly between livestock, but it is considered possible.

It is extremely rare for people to become infected with this specific line of virus, especially considering its spread. So far there have been at least 13 human infections with 2.3.4.4b and three people have died. The risk of major outbreaks or even a pandemic is considered very low, also because there is currently no known human-to-human transmission. However, results from a study of poultry markets in Egypt suggest there may be many more human infections than previously known. Twice as many people had antibodies against 2.3.4.4b as against previous H5N1 variants, suggesting the virus is more contagious to mammals.

The risk from the H5N1 virus is still considered low

The fact that the virus is now appearing in domestic animals could also indicate a greater danger to humans. On farms, potentially more people have contact with infected animals than with sick wild birds. And although in the event of outbreaks of bird flu in poultry farms the entire population must be killed and destroyed, this is not mandatory for livestock. Infectious aerosols can also appear during cleaning of systems, as well as during the slaughter and processing of infected animals.

There is also the possibility of the virus entering the human food chain. This is very unlikely with contaminated milk because pasteurization destroys the virus. However, it is not yet known whether and to what extent cattle are also infected with H5N1. While in dairy cows the infection is evident in the quality of the milk, in feedlots the symptoms may be too subtle to be detected.

H5N1 behaves differently than before

However, it is still completely uncertain how dangerous the situation overall is. The U.S. Centers for Disease Control still considers the risk to the general population to be low. The biggest problem so far is that people who have animals could become infected with the virus themselves, as in the current case. People have much closer contact with dairy cows than with poultry. The need to reassess the risk to the general population also depends on how animals become infected.

Normally, H5N1 rarely spreads permanently among mammals. The wide distribution among dairy cows and the fact that the animals become ill from an influenza A virus that is normally harmless to livestock at least suggests that H5N1 behaves differently here than before. If this is because a line of viruses with different properties has emerged, that would also change the risk assessment for humans.

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