It’s the season to get your flu shot, and pork producers are encouraged to make sure and get their vaccinations to protect people and their pigs.
“Everyone associated with the farm should be vaccinated, whether they work directly with pigs or not,” said Dr. Heather Fowler, veterinarian and director of producer and public health for the Pork Checkoff, in a news release.
Human flu viruses can infect pigs and introduce new flu viruses into the swine population, according to the Centers for Disease Control and Prevention website.
“Human flu viruses infect pigs fairly frequently,” said Dr. Andrew S. Bowman, of the Animal Influenza Ecology and Epidemiology Research Program, Department of Veterinary Preventive Medicine of Ohio State University. “The flu viruses in humans are different from the ones in pigs.”
Pigs are exceptional in that they can be infected by flu viruses from other pigs, from humans and from birds.
“It is quite common for pigs to get influenza,” said Dr. Vijaykrishna Dhanasekaran, head of the Disease Ecology and Evolutionary Genetics, Biomedicine Discovery Institute of Monash University in Melbourne, Australia.
Dhanasekaran is one the world’s leading experts on swine viruses and works with the World Health Organization’s Collaborating Center for Reference and Research on Influenza.
“There are many stable lineages of swine viruses that circulate in U.S. pigs and cause increased rates of infection in the winter months,” he said. “In large enough swine populations these introduced viruses have become endemic and circulate among pigs for the long-term – sometimes for decades.”
The continued circulation of these viruses in pigs is a major problem, he said.
Fortunately, while the morbidity of flu in pigs is high, mortality is generally low, Bowman said. Swine have about a 3% death-rate from influenza. The biggest risk is from secondary viral or bacterial infections, which may increase severity, he said.
“The disease is exacerbated by secondary bacterial infection, and we do not want to use terrible antibiotics,” Dhanasekaran said.
There are three main flu viruses that circulate in U.S. pigs: H1N1, H1N2 and H3N2.
“Within each of these subtypes, there are many different strains of viruses,” said Dr. Marie Culhane, associate professor at the University Of Minnesota College of Veterinary Medicine. “The flu viruses that normally circulate in pigs can infect people, but this is not common.”
Unfortunately, the influenza virus is crafty and can change, Bowman said.
“Pigs have been termed the mixing vessel of flu,” Dhanasekaran said. “These virus lineages mostly originate from humans that pass on the seasonal flu viruses to pigs on contact, and sometimes they also get infected from bird flu (avian influenza) especially in low biosecurity settings.”
In such cases, two different flu strains can exchange genes and create a new strain, Bowman said. Researchers call this “reassortment.”
Influenza viruses that normally circulate in pigs are called variant viruses when they are found in people, Culhane said. When a pig gets infected with a virus that is normally found in a human – that is called reverse zoonosis or spillover.
The CDC reports that cases of human infection with variant viruses have mainly occurred in people who have been near infected pigs in public settings such as fairs or petting zoos, or who work directly with infected pigs.
In 2012, there were 313 variant cases reported to the CDC – the largest number of cases reported in a single year.
Dr. Lisa Becton, a veterinarian for the National Pork Board, said that between 2012 and 2013 there was an abnormally high number of variant cases, including a significant outbreak at the 2013 Indiana State Fair.
To avoid infection, producers can look for signs of influenza, these include: coughing (“barking”), sneezing, high fevers, breathing difficulties, discharge from the nose and going off feed.
“Pigs show many of the same symptoms as humans when they get various strains of the flu,” said Benny Mote, swine specialist with the University of Nebraska-Lincoln Extension.
Once a pig has the flu, it is all about treating the symptoms, Becton said.
“Some people give their pigs aspirin and raise the heat in the holding area,” she said. “Of course, prevention is preferable to treatment.”
Treating a pig with flu is comparable to how to treat a human. Usually the infection will run its course in a week or so, Bowman said.
It is possible to lessen the risk of infections in pigs or the severity of the illness by using proper ventilation systems and practicing good hygiene.
“A person can protect themselves from getting influenza from a pig by washing their hands and not eating or sleeping near the pigs. The kids at the fairs actually used to do this,” Culhane said. “It is also a good idea to restrict contact with pigs if you are immunocompromised – very elderly, very young, undergoing medical treatments that suppress the immune system or pregnant.”
Producers can vaccinate their herds and pig caretakers with seasonal influenza vaccines. The CDC states that flu vaccines for pigs can help, but are not 100% effective.
“It is common for swine to be vaccinated for multiple strains of flu as a precaution and to best protect the health of our swine herds.” said Mote.
Still, people who get vaccinated annually against human influenza can still get sick from swine influenza viruses, and pigs that have been vaccinated for swine influenza can still get sick from some human influenza viruses.
“Flu viruses change all the time,” Becton said. “The best thing producers can do is work with their vets to find the best solution for their situation.”
Jon Burleson can be reached at email@example.com.