Hidden transmission of the H5N1 avian influenza virus found in Texas dairy cattle

Scientists from the National Center for Animal Diseases of the United States Department of Agriculture, with multiple university, state and federal collaborators, have identified the emergence and interstate propagation of highly pathogenic avian flu (H5N1) among dairy cattle.

Genetic analysis confirms that an event of restocking in wild birds preceded a single transmission to cattle, after which asymptomatic or presymptomatic cattle facilitated the propagation of the virus in the United States. The sequencing of the viral genome has revealed low -frequency mutations linked to the effectiveness of the transmission and the adaptation of mammals, which raises public health problems concerning future zoonotic spills.

Highly pathogenic avian influenza viruses cause critical damage to animal health and agricultural economy and may include a pandemic risk. Viruses linked to the goose / Guangdong 2.3.4.4 The H5NX clade of hemagglutinin has spread to nearly 100 countries, creating a recognized panzootic.

After a transatlantic introduction at the end of 2021, clade 2.3.4.4b H5N1 caused generalized epidemics across North America, leading to a mortality extended among wild birds, poultry and mammals. Transmission events between species have raised urgent concerns concerning the virus adaptation potential. The continuous circulation of HPAI clade 2.3.4.4.B in mammals requires careful monitoring to understand the risks for human infection and transmission.

In the study, “the emergence and interstate propagation of very pathogenic avian flu (H5N1) in dairy cattle in the United States” ScienceThe researchers conducted a genomic and epidemiological investigation to determine the source, the propagation and the implications of the epidemic in cattle.

Samples were obtained in 26 dairy farms in eight states and six poultry farms in three states during the initial epidemic.

The researchers carried out a sequencing of the whole genome on viral samples taken from cattle and poultry. Phylodynynamic analysis and Bayesian phylogenetic modeling have drawn the source and propagation of infection.

Epidemiological surveys have documented animal movement models associated with the dissemination of the virus. The evolving evaluations at the host characterized the genomic diversity among cattle isolates. The transmission channels were rebuilt using personalized genomic analysis software.

CLADE H5N1 2.3.4.4B Genotype B3.13 The influenza virus was confirmed in samples of milk with limited detection in nasal swabs.

Phylogenetic analysis has shown that the sequences of virus isolated from cattle have gathered in a single group, supporting a single wild event of bird overflowing to category at the end of 2023, with several months of silent transmission of cattle before a confirmation of March 2024. A restocking event in wild birds preceded the overflow.

After the introduction in cattle, the virus persisted in evidence of transmission of poultry cattle, raccoils, cats and wild birds, including common grackles, merles and pigeons.

A dairy worker was infected with a genotype slightly distinct from the sampled cattle but epidemiologically linked. Although the infection most likely came from cattle depending on the exposure history, the transmission of another non -sampled host cannot be fully excluded.

Epidemiological recordings and phylodyningomic modeling documented that the movement of dairy cattle in asymptomatic or presymptomatic Texas has led to the diffusion of the virus in eight states. Field data suggest that cows can lose virus for two or three weeks.

The sequence analysis of the whole genome has identified low -frequency genetic variants associated with virulence, the adaptation of mammals and the enlarged host range, indicating that the circulating virus in dairy cattle can have a latent scalable potential to become more transmissible or pathogenic in mammals. Although these variants are not dominant, surveillance is critical, because their expansion could increase zoonotic risk.

The continuous transmission of H5N1 HPAI in dairy cattle populations increases the risk of infection and propagation of the virus to humans and other animal hosts. Molecular markers associated with increased transmission efficiency and phenotypic changes have been detected at low frequency of cattle isolates.

Viruses circulating in cattle represent a potential pandemic threat, given the evidence of human livestock transmission events. Surveillance of cattle and other agricultural animals is essential for early alert and risk assessment. The results underline the need to test cattle before the interstate movement and a national milk test strategy.

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