First case of H5N1 avian influenza in pigs confirmed in the United States

The United States Department of Agriculture (USDA) has confirmed the first infection of pigs with H5N1 avian influenza. The case was reported on a private farm in Oregon. Authorities say the discovery does not jeopardize the security of the pork product supply. They stress that the risk to the general population remains low.

The case was identified on a farm in Crook County where there had previously been an outbreak in poultry. USDA’s National Veterinary Services Laboratories (NVSL) tested five pigs as a preventative measure, although they showed no symptoms of the disease. Test results were negative for two animals, one tested positive, and two are still awaiting diagnosis. All were euthanized for further evaluation.

“The livestock and poultry on this farm shared water sources, housing and equipment. In other states, this combination has allowed transmission of the virus between species,” explains the USDA. The hatchery is quarantined to prevent further spread. Other animals such as sheep and goats remain under surveillance.

No signs of mutation

NVSL analyzed the genomic sequence of a virus strain found in pigs and poultry. So far, they have found no evidence of pathogen mutation to suggest that H5N1 avian influenza can be transmitted from person to person. They reiterate that the current risk to the population is low. “Genetic sequencing of these samples is ongoing, although sequencing results may be inconclusive due to the low levels of virus detected,” they add. There have been 36 human cases of H5N1 avian influenza reported in the United States this year. With the exception of one, all cases involved farm workers who came into contact with infected animals.

A study led by Richard Webby, director of the World Health Organization’s (WHO) Avian Pathology Research Centre, found that since 2021, the H5N1 virus has become more infectious and its transmission rate has increased in North America, Europe, Asia and Africa. This more virulent strain has infected cows, sea lions, foxes, mice, dogs, cats and ferrets.

“Our worst suspicions are confirmed: the virus is increasingly adapting to different regions of the world. At any moment, this could become one of the most serious health crises,” Rafel Ojeda, an animal veterinarian at the National Autonomous University of Mexico, said last year.

WHO reports that from 2003 to April 1, 2024, 889 cases of H5N1 avian influenza virus infection were reported worldwide in 23 countries. He asked health workers to monitor the evolution of the virus for new cases in animals or humans. He asks the public to be attentive to the symptoms of the disease. These include fever above 37.8°C, chills, cough, sore throat, runny or stuffy nose, headaches, fatigue, difficulty breathing, diarrhea, nausea, vomiting and seizures in severe cases.

Health organizations around the world are taking measures to contain the spread of the virus among various mammal species. The USDA has approved two field trials of vaccine candidates designed to protect dairy cows against H5N1.