The Highly pathogenic H5N1 avian influenza virus can be transmitted from mammal to mammal, an ability that increases the risk to humans. The spread of the pathogen from birds to dairy cattle in several US states has led to direct mammal-to-mammal contagion: it happened between cows, and from cows to cats and a raccoon. A team from Cornell University in the US discovered this. “This is one of the first times we have seen evidence of efficient and sustained mammal-to-mammal transmission of highly pathogenic H5N1 avian influenza,” says Diego Diel, associate professor of virology and director of the Laboratory of Virology at the Animal Health Diagnostic Center, College of Veterinary Medicine at the US university, co-corresponding author of a study to be published in ‘Nature’.
Whole-genome sequencing has not revealed any mutations that would make H5N1 more transmissible to humans, although the data clearly show mammal-to-mammal transmission. This is worrying because the virus could adapt to mammals, Diel warns.
Human cases of avian influenza
In the United States, 11 human cases of avian influenza have been reported so far, the first from infected birds in April 2022, all with mild symptoms. Of these infections, 4 were linked to the H5N1 outbreak in dairy cattle and 7 to poultry farms, including 4 cases reported in recent weeks in Colorado. These patients were infected with the same viral strain identified in cows, leading researchers to suspect that the virus came from dairy farms in the same county. Although the pathogen is capable of infecting humans and replicating in their bodies, the effectiveness of these infections is currently low. “The concern,” Diel clarifies, “is that potential mutations could occur that could lead to the virus adapting to mammals, spreading to humans, and potentially efficient transmission between humans in the future.” It is therefore essential to continue monitoring the pathogen in animals and humans, the scientist warns.
Measures
The U.S. Department of Agriculture – the USDA, among the agencies that funded the new study – has supported testing programs on the H5N1 virus, at no cost to producers. According to Diel, To contain any further spread of the pathogen, tests for early diagnosis of the infection, measures for greater biosecurity and quarantines in case of positive results would be needed.
In the US, H5N1 infections were first identified in January 2022 and have killed more than 100 million domestic birds and thousands of wild birds. Scientists at Cornell University’s Animal Health Diagnostic Center and the Texas A&M Veterinary Medical Diagnostic Laboratory — where another corresponding author on the new paper, Kiril Dimitrov, works — were among the first to report the virus in dairy cattle. The cows were likely infected by wild birds, reporting symptoms such as reduced appetite, stool changes, difficulty breathing, and a marked reduction in milk production. In cattle, a high tropism of the virus (the ability to infect certain cells or tissues) for the mammary gland and a high infectious viral load in the milk of infected animals were observed.
Using whole genome sequencing of characterized virus strains, patterns, and epidemiological information, researchers determined cases of cow-to-cow transmission when infected Texas cattle were moved to an Ohio farm with healthy cows. Sequencing also showed that the virus was transmitted to cats, a raccoon, and wild birds found dead on the farms. The cats and raccoon most likely became ill from drinking raw milk from infected cattle. As for the wild birds, although it is not known how they became infected, scientists suspect environmental contamination or aerosols emitted during milking or cleaning of milking parlors.
#Avian #Flu #Alert #Study #Risks #Humans
