Get the Facts Straight on Highly Pathogenic Avian Influenza
Updated as of 4.10.24
Now that the mystery illness impacting dairy herds in multiple states has been revealed as the same strain of influenza virus [Influenza A (H5N1)] that has been impacting the U.S. poultry flock, pork producers are asking a lot of questions. Is this strain transmittable to pigs? Should livestock producers with cattle and pigs be concerned about cross-species transmission?
Those are all important questions, but understanding influenza is the best place to start, says National Pork Board chief veterinarian Dusty Oedekoven.
“Highly Pathogenic Avian Influenza (HPAI) is influenza. HPAI is an official term defined by the severity of the mortality rate in poultry,” he explains.
Within strains of influenza A, the naming convention goes by two proteins on the outer surface of the virus: hemagglutinin (H type) and neuraminidase (N type). Typically, HPAI is of the H5 or H7 types, but there are many other possibilities as there are 18 hemagglutinin types and 11 neuraminidase types, he explains.
“Not all of those occur in poultry, not all of those occur in pigs, and not all of those occur in humans,” Oedekoven clarifies. “But the term highly pathogenic applies to poultry.”
He believes the reason it’s making headlines as HPAI is because it’s the same strain, H5N1, or similar strain that has been found recently in poultry where they have designated it as HPAI.
“Maybe that’s a narrow thing to tease apart,” he points out. “But in my mind, I hope we can separate that a little bit. This is influenza A virus.”
Influenza A viruses affect many warm-blooded animals, including birds and mammals. That’s nothing new, Oedekoven says. Influenza A viruses have been identified in cattle in the past, as well as swine and birds.
“If we think about influenza in domesticated species and humans, we are typically looking at the cycle between humans and pigs,” he says. “Pigs become amplifying hosts of influenza A viruses and the mixing vessel for different types of viruses, as are birds. Birds can get multiple viruses and those viruses mutate within the bird, and new strains evolve. That’s how we have new strains of the virus that emerge and become different strains.”
And that’s why receiving the annual flu vaccine is so important, he adds.
“It’s likely the vaccines we got last year were designed for a different strain than what we’re looking at this year because the virus reassorted and it’s slightly different. Scientists predicting which strain we might be dealing with for the vaccine are right sometimes, and sometimes they miss the mark a little and you may see more influenza in a given year,” he says.
Fact #1: The threat of influenza virus infection in people and pigs is ever present.
Oedekoven says he has not heard of the H5N1 strain being identified in pigs at this time.
“We know pigs are susceptible to influenza A viruses, and swine influe-nza is not uncommon in the U.S. We see outbreaks of routine swine influe-nza fairly frequently,” he says. “We don’t know if there’s any special higher risk of disease or illness or mortality for pigs due to this virus strain than any other swine influenza strain we have.”
The key is diligent observation. If producers see signs of illness in their pigs, Oedekoven urges them to contact their veterinarians.
On the same hand, if they see signs of respiratory illness or flu-like symptoms in people, seek advice from healthcare providers.
Influenza A viruses are common in people, just like they are pigs. Influenza viruses are constantly changing and reassorting.
“The threat of influenza virus infection in people and pigs is ever present. It’s why healthcare providers recommend people get annual influenza vaccines to prevent against new strains of the virus that are emerging all the time,” he says.
This doesn’t represent an elevated threat, Oedekoven adds.
“It’s recognition of a threat we know is there,” he says. “Influenza viruses exist and circulate in people all the time.”
Good sanitation and hygiene are important. If employers have workers who are ill with influenza signs, don’t let them come to work because they could potentially spread that disease to the pigs, which could cause more spread to other humans.
Fact #2: There’s no evidence to support a higher risk of influenza infection from cattle to pigs than exists otherwise.
“We’re not even sure yet to what extent this strain of influenza may be transmitted from cattle,” he says.
USDA reports bovine influenza A virus (originally referred to as HPAI in many reports) in dairy cattle was first identified in samples that included unpasteurized milk from one dairy farm in Texas and two in Kansas, as well as an oropharyngeal swab from another dairy in Texas. The virus was first confirmed in one Texas herd on March 21 by Iowa State University’s diagnostic lab that was helping Texas labs process samples more quickly. Affected farms also reported finding deceased wild birds on their properties.
“Most waterfowl and wild bird species can carry influenza viruses, but usually they don’t die from it. They are good carriers of it and can become infected and produce high levels of the virus and spread it. It’s always a good biosecurity practice to keep birds away from your pigs,” he says.
Remain Vigilant
Megan Niederwerder, executive director of the Swine Health Information Center (SHIC), encourages producers to keep close tabs on biosecurity protocols to reduce risk of pathogen exposure from wildlife.
“As part of the Swine Health Information Center’s Standardized Outbreak Investigation Form, there are several hazards associated with wild birds that can be proactively considered to enhance biosecurity,” Niederwerder explains.
Examples include surface water, wild bird access to inside swine barns, equipment stored outside, compost piles, mortality disposal boxes, open feed bags, open feed bin covers and feed spillage fed to pigs, she says.
“It is important to clean and disinfect tools and equipment with potential exposure to wildlife prior to utilizing inside facilities housing pigs,” Niederwerder says.
Prompt investigation is key, Oedekoven says. This helps veterinarians and producers handle disease challenges better. USDA notes additional testing is underway, including genome sequencing, to characterize the strain(s) associated with the detections.
Spread the Word
Pork producers play an important role in disseminating truth, Oedekoven says. According to the Centers for Disease Control and Prevention, influenza has not been shown to spread through eating properly handled pork.
“You can’t get influenza from eating or handling pork,” Oedekoven emphasized. “There’s not a risk of acquiring influenza that way. The way that it is transmitted is through aerosolization and direct contact between infected animals, including humans.”
Read More:
Piecing the Puzzle Together: Diagnostic Monitoring and Flu Prevention
Veterinarians Answer Questions on Influenza
Meat Institute: Properly Prepared Beef is Safe to Eat; HPAI is not a Food Safety Threat
