As global health authorities have long suspected, the H5N1 bird flu virus is now spreading between mammals, significantly increasing the risk of future outbreaks among humans. This development has prompted experts to warn of the potential for sustained human-to-human transmission.
EVIDENCE OF MAMMAL-TO-MAMMAL TRANSMISSION
Virologist Diego Diel of Cornell University emphasizes the significance of these findings. “This is one of the first times that we are seeing evidence of efficient and sustained mammalian-to-mammalian transmission,” Diel notes. The ability of the H5N1 virus to move from one mammal to another poses new challenges for controlling the virus and preventing a future pandemic.
VIRULENCE OF THE H5N1 VIRUS
The B3.13 form of the H5N1 virus, known for its high virulence, has already had devastating effects on bird populations. Since 2022, the United States has seen the culling of 90 million domestic birds to contain the spread. Despite the severity of the outbreak in birds, the Centers for Disease Control and Prevention (CDC) maintains that the risk to the general public remains low. So far, only 11 people in the U.S. have contracted the virus, all reporting mild symptoms.
HUMAN FATALITY SPARKS CONCERN
However, the recent death of a vulnerable individual in Mexico from the related H5N2 virus is a stark reminder of the potential human toll. The possibility of the virus evolving to efficiently infect humans is a major concern. Diel explains, “The concern is that potential mutations could arise that could lead to adaptation to mammals, spillover into humans, and potential efficient transmission in humans in the future.”
GENETIC ADAPTABILITY AND SPREAD
H5N1’s ability to “steal” genes from other influenza viruses is a key factor in its adaptability and ease of transmission across mammalian species. This adaptability has led to the virus being detected in mammals across the globe, from polar bears in the Arctic to dolphins and seals in the Antarctic.
WIDE RANGE OF MAMMAL HOSTS
The virus has infected a diverse range of mammals, including otters, squirrels, dolphins, elephant seals, and even goats. Molecular virologist Daniel Perez, speaking to the Smithsonian Magazine, expresses concern about the virus’s capabilities. “I don’t think we have a good understanding of the molecular reason why these viruses, with this combination of gene segments, with these mutations, now have this inherent ability of infecting many more species than in the past,” Perez states.
DAIRY COW OUTBREAK IN THE US
One of the most troubling recent developments is the spread of H5N1 among dairy cows in the United States. The strain responsible for this outbreak was first identified in a Canada goose in Wyoming on January 25, 2024. This bird was found along the Central North American migratory bird flyway, a key route for the virus’s spread.
TRANSMISSION ACROSS STATES
By March 25, 2024, the virus had spread to dairy farms across multiple states. Genetic testing confirmed that the virus was spreading from cow to cow, rather than being transmitted by birds alone. The virus’s spread was exacerbated when apparently healthy cattle were transported interstate, leading to further outbreaks far from the original flyway.
IMPACT ON DAIRY PRODUCTS
The spread of the virus to cows has had significant implications for dairy production. Infected cows have been found to produce contaminated milk, which is discoloured and has an unusual texture. The virus’s preference for mammary gland tissues makes milk a particularly effective medium for the virus’s spread.
GLOBAL RESPONSE AND PREVENTIVE MEASURES
Health authorities worldwide are urging the public to practice good hygiene when in environments with wild birds. This includes careful hand sanitation and avoiding direct contact with wild animals. In addition, authorities are asking the public to report sightings of sick or dead birds to help track the spread of the virus.
AUSTRALIA AND NEW ZEALAND
Australia and New Zealand have so far remained free from reported cases of H5N1, but both countries are preparing for the virus’s likely arrival. The impact on wildlife in these regions could be devastating, given the unique and vulnerable species found there. Australia is already dealing with a mass culling of poultry due to outbreaks of H7 bird flu, which has led to widespread egg shortages.
VACCINATION EFFORTS FOR ENDANGERED SPECIES
In the US, efforts are underway to protect critically endangered species from the virus. California condors, for example, are being vaccinated to minimize the impact on their population. However, many other species may require similar interventions to prevent their decline.
Meanwhile, researchers are working on developing a human vaccine to protect against H5N1. The urgency of this research has increased with the virus’s spread among mammals, as the risk of human infection becomes more pronounced.
USDA’S NEW REGULATIONS
In response to the spread of H5N1 in dairy cows, the United States Department of Agriculture (USDA) has introduced new regulations. Dairy cattle must now test negative for the virus before they can be transported between states. These measures aim to prevent further spread and reduce the risk of the virus adapting to new mammalian hosts, thereby decreasing the pandemic risk to humans.
GROWING NEED FOR VIGILANCE
The ongoing spread of H5N1 among mammals underscores the need for continued vigilance and robust preventive measures. As the virus continues to evolve, the risk of it becoming a serious threat to human health grows. Authorities and researchers worldwide are working to contain the virus and prevent a future pandemic.
