Recent discovery of a new strain of avian influenza has shown to easily cross species barriers. The latest variant of the virus has been found in dairy cattle in Nevada and contains a genetic mutation that allows it to replicate more effectively in mammals, including humans. The US Department of Agriculture’s Animal and Plant Health Inspection Service released a technical brief highlighting this finding.
Although the extent of the threat these viruses pose to humans is still uncertain, the CDC notes that the risk of H5N1 infection to the general public remains low. Individuals working on farms or with backyard flocks are considered to be at higher risk.
In a significant development, a dairy farm worker in Nevada has tested positive for H5N1, marking the first human case in the state. Symptoms include red, inflamed eyes, known as conjunctivitis. The CDC is currently verifying this positive test result.
Scientists are closely monitoring the situation in Nevada as gene sequencing has revealed that the affected cattle are infected with a subtype of the H5N1 virus known as D1.1. This strain has been linked to severe human infections in North America, including fatalities.
The affected herds in Churchill County, Nevada are the first known cases of transmission of the D1.1 virus to cattle, previously only found in birds and humans. The source of transmission to the cows is believed to be from contact with infected wild birds or their droppings in the vicinity of the farms.
The genetic analysis of the D1.1 viruses has uncovered a mutation that enhances the virus’s ability to replicate more efficiently in mammalian cells, including humans. This specific mutation has not been observed in other D1.1 infections in wild birds or poultry, raising the possibility of another animal species introducing the virus to the farms.
The mutation in question poses a potential threat to humans exposed to the infected cows, as it enables the virus to replicate more effectively. Dr. Seema Lakdawala, a microbiologist and immunologist at Emory University, emphasized the importance of understanding how the virus is spreading in dairy herds.
Viruses can mutate through drift or shift. Drift involves small genetic changes during replication, while shift results in significant changes when two different viruses exchange whole genome segments. D1.1 is a hybrid virus created through a shift, combining segments from different flu viruses.
A new strain of the H5N1 virus, known as D1.1, emerged in North America after being brought by wild birds from Asia in April 2022. This strain comprises genetic material from both a highly pathogenic H5N1 virus and a low-pathogenic flu virus already present in birds in North America. D1.1 became the dominant H5N1 lineage in North American wild birds after being first detected in September 2024.
In October, workers at a Washington state farm depopulating infected poultry tested positive for the D1.1 subtype, experiencing mild respiratory symptoms. A 13-year-old girl in British Columbia tested positive for the D1.1 strain in November, suffering severe illness and organ failure but ultimately surviving after intensive care. The source of her infection remains unknown.
Genome sequencing revealed mutations in the virus that could enhance its ability to infect humans. In December, a person over 65 in Louisiana, exposed to sick birds, became the first bird flu fatality in the nation after falling seriously ill with D1.1.
Scientists are investigating why D1.1 led to severe human cases. The virus’s genetic components, particularly the hemagglutinin (H) protein for cell infection and neuraminidase (N) for cell spread, play key roles. While the severity of bird flu viruses in birds does not necessarily correlate with their impact on humans, changes in the N segment of D1.1 may contribute to its ability to evade immunity from seasonal flu viruses.
Researchers are exploring the unique characteristics of D1.1 and its potential to adapt more readily to humans. The interplay between the H and N proteins of the virus is crucial, with mutations possibly enabling enhanced transmissibility and severity in human infections. Ongoing investigations aim to unravel the mechanisms behind the severe cases associated with the D1.1 strain.
The enzyme is seeking ways to escape and release all its copies back into the body. Typically, alterations in the N protein can compromise the efficiency of the virus in infecting cells, often at the expense of the H portion. Nevertheless, D1.1, under the scrutiny of researcher Hensley, is a potential outlier. His laboratory is conducting experiments to explore whether the N segment of D1.1 variants could facilitate changes in the H protein, potentially enhancing its ability to infect humans more effectively. “It is entirely plausible that this specific virus genotype may exhibit a greater propensity for adapting to human cells,” remarked Hensley. “However, conclusive evidence is still lacking.” This report includes contributions from CNN’s Meg Tirrell. For additional CNN updates and newsletters, please register an account at CNN.com.
