H5N1 Flu’s Mammal Spread Sparks Pandemic Fears

Scientists have unveiled new insights into the spread of H5N1 bird flu among mammals, highlighting potential pandemic risks as outbreaks grow. Research published in Nature reveals how the virus, primarily known for infecting birds, has been transmitted from cows to various animals, including wild birds, cats, and raccoons. This study raises concerns about future human transmission as the virus spreads through poultry and dairy farms. Using genomic data, computer models, and tracking virus transmission, Cornell University researchers have demonstrated that infected cows in Texas spread H5N1 to a farm in Ohio. The virus also reached local cats, a raccoon, and wild birds. This study marks one of the first instances where researchers have identified “efficient and sustained mammalian-to-mammalian transmission” of the H5N1 strain, according to Diego Diel, a Cornell virology professor and study co-author.

Though H5N1 mainly targets birds, it has shown the ability to infect mammals, including humans. Diel notes that repeated transmission between mammals or from birds to mammals could increase the virus’s risk of adapting to humans, potentially leading to more effective human-to-human spread in the future. The research highlights that H5N1 can infect mammary gland cells, which are found in mammals, including humans. Infected cows’ milk contained high levels of the virus. The study found that infected cows likely transmitted the virus to cats and a raccoon through raw milk, while wild birds might have been exposed through environmental contamination or aerosols from milking and cleaning activities.

Despite clear evidence of mammalian transmission, genetic analysis did not indicate that the virus is currently more transmissible to humans. However, ongoing monitoring is crucial to detect any potential adaptation of H5N1 to human hosts. Before COVID-19, many experts predicted that a flu virus would cause the next human pandemic. Influenza viruses have caused four pandemics since 1900, including the 1918 Spanish Flu. They constantly mutate, evading immune defenses and treatments, which is why seasonal vaccinations are necessary. H5N1 has been a significant concern for health officials, with the World Health Organization and the Centers for Disease Control and Prevention classifying it as a potential pandemic pathogen. Since 1996, over 800 human infections have been reported, mostly following close contact with infected animals.

The H5N1 virus has impacted wild and domestic bird populations for years, but recent spillovers into mammals are increasingly alarming. Outbreaks among seals, sea lions, and a range of mammals, including dolphins and polar bears, have raised concerns. The virus’s presence in U.S. cattle, a previously undocumented occurrence, has surprised many scientists and intensified worries. The outbreak’s scope remains uncertain, with criticisms directed at officials for inadequate information sharing and testing. The intensive nature of cattle farming could facilitate the virus’s spread among mammals and to humans through milk and beef. While the risk to humans is currently considered low, monitoring efforts have been increased.

The federal government has a stockpile of vaccines to combat potential bird flu pandemics and is encouraging industry efforts to develop targeted H5N1 vaccines. Moderna recently received $176 million in federal funding to create an mRNA vaccine for bird flu, while GSK is also working on an mRNA vaccine following its acquisition of a product from CureVac. As of now, 11 human cases of H5 bird flu have been reported in the U.S. during the ongoing outbreak that started in 2022. These cases, linked to the H5N1 strain, resulted from close contact with infected animals, including dairy cows and poultry. Over 100 million domestic birds, 9,555 wild birds, and 168 dairy herds have been affected. Hawaii is the only state without confirmed H5N1 infections in wild birds, poultry, or other animals.

In June, a man in Mexico died from a different avian influenza strain, H5N2. This was the first known human case of H5N2, unrelated to the H5N1 strain. The World Health Organization noted that the man had no known contact with poultry or animals, and the source of infection remains unclear. The risk from H5N2 is considered low, with no additional cases reported after an investigation.