Scientists at the University of Texas Medical Branch (UTMB) have detected the highly pathogenic H5N1 avian influenza virus (HPAIV) in cow and milk samples from two dairy farms in Texas.
This research is currently The medRxiv preprint* server highlights the need for development Effective interventions against H5N1 HPAIV to prevent pathogen spillover.
Image credit: McKenzie Kizer / Shutterstock
background
*Important Notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and should not be considered definitive, treated as a guide for clinical practice/health-related actions, or treated as established information.
H5N1 highly pathogenic avian influenza A viruses (HPAIVs) have caused millions of deaths in wild and domestic birds worldwide. Recently, these viruses have been identified in many animal species, with HPAIV H5N1 HA lineage 2.3.3.4b being the most predominant type in these shedding events.
The USDA has recently detected H5N1 HPAIV infections on 172 livestock farms in 13 states, and four dairy and nine poultry workers have recently been suspected to be infected.
Given the seriousness of the situation, the current study was designed to investigate the presence of a novel respiratory virus on two dairy farms in Texas.
Study design
The study was conducted on two Texas dairy farms where H5N1 HPAIV infections had recently been detected in cows. The farm owners invited the scientists to investigate a research proposal to study emerging respiratory viruses on livestock farms in the United States and Mexico.
A total of 17 farmworkers were recruited in the study and provided nasopharyngeal and serum samples for analysis. Five of the 17 reported experiencing respiratory illness and using various medications for their symptoms.
A total of 39 cow nasal swab samples and 14 milk samples were collected from both farms for molecular analysis, cell and egg culture, Sanger sequencing and next generation sequencing for isolation and characterization of respiratory viruses.
Three-hour bioaerosol samples were also collected from different farm areas to investigate the presence of the new virus in the environment.
Important Observations
The study detected H5N1 HPAIV in 9 of 14 milk samples and 1 of 39 nasal swab samples from cows, but no nasopharyngeal swabs from farm workers tested positive for influenza A viruses or coronaviruses.
One of the nasal swabs taken from the sick cow confirmed the presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
Two of 14 serum samples collected from farmworkers showed elevated levels of neutralizing antibodies against recombinant influenza A H5N1 viruses.
None of the 24 bioaerosol samples collected from both farms showed molecular evidence of influenza A or coronavirus.
The H5N1-positive milk samples were further analyzed using Sanger and next-generation sequencing to characterize the virus, which revealed that the virus was closely related to other H5N1 virus strains of lineage 2.3.4.4b that have recently circulated in Texas.
Mutational analysis revealed the presence of multiple common mutations across the isolated viral genomes, which are associated with viral virulence and growth, altered host specificity, and drug resistance.
Significance of the study
The study revealed the presence of H5N1 HPAIV infection in cows on two dairy farms in Texas: the virus was only detected in a nasal swab sample from one cow, but approximately 64% of milk samples tested positive for H5N1 HPAIV.
These findings indicate that although the virus is rapidly cleared from nasal tissues, infected cows may shed H5N1 HPAIV into milk for extended periods of time.
Most importantly, the detection of anti-HPAIV neutralizing antibodies in farmworkers highlights the possibility of prior infection that was not detected during the acute infection phase.
This highlights the possible underreporting of HPAIV infections among agricultural workers, which may result in large-scale outbreaks outside agricultural worker communities.
“We’re confident that more people are infected than we know,” Gregory Gray, MD, a UTMB infectious disease researcher and lead author of the paper, told NPR, “and that’s mainly because we’ve been so poor at monitoring.”
The Centers for Disease Control and Prevention (CDC) will decide whether to vaccinate farmworkers with HPAIV vaccines based on surveillance data showing a low prevalence of HPAIV infection.
This low incidence rate is due to low rates of testing among farmworkers, and many infections may remain undiagnosed among people who have been in contact with sick dairy cows.
“What we’re seeing may not be the tip of the iceberg, but it’s certainly not the whole story,” said Richard Webby, director of the World Health Organization Collaborating Center for Influenza at St. Jude Children’s Research Hospital in Memphis, Tennessee.
Little research has been done on dairy farms to identify new respiratory viruses due to fears of losing business, and as Gregory Gray noted, without a concerted effort between the government and the livestock industry, the risk to the U.S. from this virus will remain unknown.
This highlights the need to collect more comprehensive epidemiological data necessary to plan future interventions against H5N1 HPAIV on cattle farms.
*Important Notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and should not be considered definitive, treated as a guide for clinical practice/health-related actions, or treated as established information.
