Diseases - Avian flu in cattle - "Udder is a chicken for the virus"
In the USA, the number of cattle infected with Avian Flu (H5N1) is on the rise. According to the US Centers for Disease Control and Prevention (CDC), there are now over 130 confirmed H5N1 infections in a dozen US states. The data on transmissions is still thin, and countermeasures are proceeding slowly, laments Vice President of the Friedrich-Loeffler-Institute (FLI), Martin Beer. If the US cannot get a hold of the virus, "we could be dealing with a completely new livestock disease on a global scale."
The H5N1 virus has been circulating among birds for decades - initially in Asia, now nearly worldwide. Water buffalo or other cattle species have never been affected, says Beer. In 2021, the virus made its leap to North America - and for the first time, possibly in the fall of 2023, cows fell ill. Researchers are surprised and increasingly concerned.
What does the leap to cattle mean?
There are 1.5 billion cattle worldwide, as Beer notes. If H5N1 gave rise to a new, global cattle disease, the risk for other livestock - such as if contaminated raw milk is fed to pigs - would also increase. Additionally, a mammal is biologically closer to humans than a bird. The zoonosis risk - the risk for transmission from animal to human - can depend on the adaptations that have occurred, as Beer explains.
What kind of virus is it?
H5N1 is an Influenza A Virus, like the human influenza viruses that circulate. H and N denote two proteins on the viral envelope: Hemagglutinin and Neuraminidase. They come in various subtypes (H1 to H16 and N1 to N9). The name H5N1 signifies the combination of the H5 and N1 proteins on the surface of the variant.
Since 1997, there have been increasing reports of H5N1 outbreaks, as FLI expert Beer explains. Since 2016, a subvariant of the virus, known as Clade 2.3.4.4b, has been spreading. The result was devastating bird flu outbreaks in nearly all parts of the world among wild birds, as well as poultry and - less frequently - other mammals like seals, mink, foxes, and bears, were affected. Australia has been spared - so far.
How did the jump to cattle occur?
According to current analysis, the outbreak in the US may have originated from a single case, explains Beer. The mode of transmission from wild bird to cow - whether through contaminated feed, contaminated bedding, or direct contact - remains unclear. However, researchers now know this: "If the virus gets into the uterus, it reproduces very strongly there," says Beer.
This is due to the receptors in the uterus: Different from, for example, those in the bovine nasal cavity, they are perfect anchoring points for the H5N1 variant - similar to those in birds. "The uterus is, in a way, a chicken for the virus." The virus can spread to other dairy cows through contaminated milking equipment, transportation to new farms and regions.
How should the situation in the US be evaluated?
Still not clear if the slow-starting countermeasures in the USA will be able to intervene in time. "It might be that the hype has passed by now", says Beer. "If the virus hasn't learned to spread efficiently from cow to cow through the nose by now." In such a case, further spread can only be made difficult.
There is a patchwork of rules when it comes to testing and protective measures. A comprehensive, nationwide targeted search for infected cows and strict quarantine measures have not been implemented yet. "It would be more uniform in Europe", says Beer. In addition, there is what is almost like a "glass cow" here, meaning a comprehensive tracking of all cows with a unique identification and corresponding databases. This is lacking in the USA.
The US authorities seem far from stopping the spread of avian flu among cattle. While some monitoring programs for more tests have been initiated, most of them are on a voluntary basis, says Beer. "This only works if it is mandatory. Otherwise, there are gaps."
Are the real numbers even higher?
From milk sample analyses and other indications, it can be concluded that there are cases that have not been recorded, according to Beer. Many US cattle farms are huge, with thousands of animals being kept. In total, there are only about 26,000 dairy farms, as Beer explains. Compared to that: There are approximately 26,000 in Bavaria alone, and around 50,000 nationwide in Germany.
In a large-scale operation, infections do not necessarily show up immediately - and farmers are not particularly eager to have their entire operation shut down due to detection of infections. In the case of possible transmissions to humans, it should be noted that many illegals work in US farms - who may avoid doctor visits due to corresponding symptoms.
Can people catch the disease from cows?
Three cases in people have been recorded by the CDC in the context of the outbreak in US cattle farming. In each case, a conjunctivitis was one of the symptoms, explains Beer. "The human has avian flu receptors in the eye." If a worker, for example, comes into contact with his eye while milking, the virus can adhere.
Pasteurized milk is considered harmless, as a study in the "Journal of Virology" confirmed. In about 20% of the approximately 300 pasteurized milk products from 132 US processing plants that were examined, non-infectious traces of the viral genome were found, but no infectious virus in any case.
An infection through raw milk is considered possible. Farm cats have frequently become infected through contaminated raw milk in recent months. In many of the recorded cases, the virus infected their brains, as Beer explains. "This is not new knowledge: There have already been avian flu outbreaks in Poland and South Korea in cats - always through contaminated food, not from cat to cat."
However, the situation is different for certain marine mammals and for fur farm animals such as mink and polar foxes. Transmissions between conspecifics are considered likely for marine mammals, and for animals in fur farms, they are considered largely secure, according to Beer.
At their facility, neurological symptoms, or brain damage, are a major concern. The number of fatal cases among animals is high.
What is the risk for Germany?
So far, H5N1 infections have only been reported in cattle in the USA. Since neither cows nor raw milk are imported into Europe, the risk of introduction is low, according to Beer. However, investigations at the FLI have shown that the H5N1 strain circulating in Germany can infect cattle. The virus has multiplied in the uterus and cows have shown symptoms such as milk production decrease, milk consistency change, and fever, the institute recently reported. This assessment - very low - does not change. This assessment also takes into account that, unlike in North and South America, there is currently no larger H5N1 wave among wild birds in Europe. "It's as quiet as it hasn't been in years," Beer says. "The number of detections has been declining significantly for weeks."
It is likely that a herd immunity has built up for the time being. A summer gap in infections was typical for bird flu - until the clade 2.3.4.4b began its global spread. However, the population will eventually become susceptible to the next wave, according to Beer.
What does 2.3.4.4b mean in total for humans?
So much animal suffering is associated with 2.3.4.4b - for humans, the variant is initially less harmful than previously circulating H5N1 strains. The virus is strongly adapted to birds, explains Beer. Since 2016, there have been fewer than 20 reported cases and mostly mild infections in humans - compared to hundreds in the past.
The virus itself is harmless to humans - and yet not, because it often finds its way to livestock due to the sheer number of infections in bird populations. They can act as a "mixed battery," as Beer explains: For example, a mink or pig could be infected with various Influenza-A strains, which could lead to the emergence of a new, more dangerous strain for humans.
"It's very important to keep H5N1 under control," says Beer. However, on the risk lists for a bird flu zoonosis, the virus is "only" in the middle: From H7N9, which has already been transmitted from person to person, and H5N6, which has also appeared in humans, as well as some swine influenza viruses, there is currently a greater zoonotic risk, according to current estimates.
Where is particularly vigilant observation necessary?
"Fur farms are a factor that has long been neglected," emphasizes Beer. Analyses from China showed that all possible influenza viruses can circulate among the animals in such a farm - which could lead to a potentially dangerous mixture.
In Denmark and the Netherlands, pelts farms are still stopped due to numerous Corona infections among pelts animals in the context of the pandemic, in Germany there is none. In Finland, such farms are being monitored comprehensively in the wake of problems with Sars-CoV-2 and H5N1.
"But there are many fur-bearing animals in countries with very little supervision," Beer warns. For instance, China produces several million mink fur pelts annually. In addition, millions of mink dogs and foxes are also produced. Belarus is also a major producer without transparent supervision.
What would await us if we jumped to humans?
The exact properties of a potential trigger cannot be predicted. However, it is clear that it would not be the first major Influenza-A pandemic. Since 1900, a total of four such pandemics have occurred: the Spanish Flu (H1N1) in 1918/19, the Hong Kong Flu (H2N2) in 1968, the Russian Flu (H1N1) in 1977, and the Swine Flu (H1N1) in 2009/10.
Would it be like the Corona-Pandemic?
"The situation is completely different from Sars-CoV-2," explains Beer. Influenza strains have been monitored for a long time. Regularly, candidate vaccines for protective vaccinations against potential pandemic-causing variants are being set. Such a vaccine has recently been ordered by 15 EU countries. Finnish pelts farmers' employees are already being vaccinated preventively.
In general, it differs from the Corona Virus: "We have known for a long time what needs to be done for an influenza vaccine," says Beer. Classically, production takes place in hen eggs, but work is also being done on mRNA vaccines. In case of an outbreak, protective vaccines could be produced quickly.
- The H5N1 virus has affected cattle in the USA, according to Vice President of the Friedrich-Loeffler-Institute, Martin Beer.
- Beer mentions that over 130 confirmed H5N1 infections have been reported in a dozen US states.
- The current data on transmissions is still thin, and countermeasures are moving slowly, laments Beer.
- The H5N1 virus has not affected water buffalo or other cattle species, as Beer notes.
- In 2021, the virus made its leap to North America, marking the first time cows were affected.
- Researchers are surprised and increasingly concerned about the jump to cattle, says Beer.
- If H5N1 gives rise to a new, global cattle disease, the risk for other livestock increases, as Beer explains.
- The jumping point to cattle is still unclear, according to Beer.
- The mode of transmission from wild bird to cow remains unclear, says Beer.
- Beer notes that if the virus gets into the uterus, it reproduces very strongly there.
- The risk for Germany, in terms of H5N1 infection, is considered low, according to Beer.
- Beer warns that fur farms should be subject to more vigilant observation due to the potential emergence of dangerous strains.
- According to Beer, keeping H5N1 under control is crucial to prevent a potential trigger for a major Influenza-A pandemic.
