The avian influenza virus is spreading like wildfire, fueled by commercial farming. Could the virus spread from cattle to humans and could milk become a common threat?
The bird flu has been spreading across the globe for several years. Especially in its mutated form, the highly pathogenic avian influenza (HPAI) poses a threat to wild birds and can cause major financial losses in animal farming. Highly pathogenic variants have been revealed for subtypes of H5 and H7, which are highly infectious and come with a mortality rate of up to 100 %. Wild birds can carry the virus without displaying symptoms and infect farmed animals via several transmission ways, such as droppings or saliva. If cases of HPAI are confirmed in Germany, the entire flock, including healthy animals, must be euthanized to avoid the spread to wild or commercially farmed birds.
Avian influenza is not limited to birds, but known to sporadically infect mammals as well. In Europe, several outbreaks in mammals have occurred in the past, with the majority affecting mink, raccoons and foxes from fur farms in Finland, as reported by the European Food Safety Authority (EFSA). But an even more worrying new infection has occurred in the US. For the first time, a human has presumably been infected with HPAI from another host than birds: dairy cattle.
The US have been hit by a large-scale avian influenza outbreak in 2022, with just shy of 10.000 reported cases of infected wild birds since its beginning. The currently circulating strain is a form of the H5N1 subtype, known to be extremely deadly and highly infectious to wild birds. It is often transmitted by wild migrating birds or seagulls into backyard poultry stocks or commercially farmed bird species.
Now, for the first time, cases of HPAI in dairy cows in Texas have been reported in March 2024, according to the Centers for Disease Control and Prevention (CDC). A person in Texas who had been in contact with infected cattle has now also tested positive for HPAI H5N1. If this presumed infection way is confirmed, this would be the first known case of infection via dairy cows.
The patient, who reported eye redness as the only symptom, was treated with an antiviral drug (oseltamivir) and told to isolate during recovery. The virus isolated from the patient is quite similar to the one found in cattle with a mutation that can be linked to a more efficient spread in mammals, as described in Nature. However, the virus did not display any new mutations that could be linked to a more effective way of spreading to or amongst humans specifically. If the virus were to mutate further, it could hold the risk of becoming more infectious to humans. But for now, according to the CDC, the risk of an infection remains low for humans. Only workers at poultry, dairy, or fur farms might have an elevated risk of infection. Symptoms do not differ from the common cold or flu: fever, coughing, sore throat, or shortness of breath.
According to current investigations, airborne infection ways of this subtype can be ruled out. Comparisons between mucus, throat and milk swabs of animals that tested positive revealed the viral levels in milk are significantly higher compared to other bodily fluids of the animals. If mucus and other bodily fluids of affected animals were confirmed to be non- or only slightly infectious, it would make this outbreak easier to control. Until then, the CDC recommends not to consume raw milk and to wear protective garments when handling it. Infection ways need to be revealed and investigated further to avoid major outbreaks that could affect humans as well.
Even though treatment options for this specific virus are not yet available, the foundation for a possible vaccine might already be available. “CDC has developed an H5 candidate vaccine virus that is nearly identical or, in many samples, identical to the hemagglutinin protein of recently detected clade 2.3.4.4b A(H5N1) viruses in birds and mammals. This H5 CVV could be used to produce a vaccine for people, if needed, and preliminary analysis indicates that it is expected to provide good protection against the currently circulating H5N1 influenza viruses in birds and other animals”, as stated on the website of the CDC. So, if the outbreak continues to spread in cattle and more people get infected by dairy cows, a vaccine might not be far from reach.
To keep the current outbreak under control, the Animal and Plant Health Inspection Services of the US Department of Agriculture are currently investigating reported cases. So far, there are confirmed cases in Michigan, Texas, New Mexico, South Dakota, North Carolina, Ohio, Kansas and Idaho. It is possible that wild birds carrying the virus were the source of infection in most cases, however, infected animals from Texas have been transported to Kansas and caused an outbreak on a dairy farm. It is now crucial to stop the transportation of cattle to other farms and avoid further infections.
So far, no mandatory testing regime has been put in order, but recommendations for the handling of livestock have been published. Farmers, veterinarians and workers at cattle, fur, and poultry farms are recommended to avoid direct physical contact with sick or dead animals, feces and raw milk and to wear personal protective equipment, such as gloves and filtering facepiece respirators. The public is recommended to stay away from wild animals or cadavers and not to consume raw or undercooked animal products such as raw meats or unpasteurized milk. Even though the CDC classifies the risk of infections of humans as small, this virus still holds a pandemic potential and must be monitored closely.
Image Source: Ibrahim Rifath, Unsplash
