By: Robert W. Frenck Jr, MD, FAAP
What do COVID-19, Lyme disease and influenza have in common? All are zoonotic infections typically found in animals—but they can spread to humans.
Pigs and
birds are the two main animal hosts for influenza. Influenza virus infects the animal and reproduces in its cells. Swine flu in pigs causes symptoms that are similar to flu in humans: a respiratory infection that may include fever, cough, runny nose and red eyes. Swine flu viruses spread year-round in pigs. But just like influenza in people, cases of swine flu usually occur more commonly in late fall and winter.
Infections with flu viruses that spread from pigs to people happen every year, often at agricultural fairs. In July 2024, swine flu was reported in a child in Colorado and an adult in Michigan. The child developed an infection after attending an agricultural event. They did not require hospital caer for the infection. Public health experts are still investigating the cause of infection in the person in Ingham County, Michigan.
Some people are at higher risk of serious illness from
zoonotic diseases like swine flu:
children younger than age 5 years;
people with certain long-term health conditions like asthma and other lung diseases, diabetes, heart disease, weakened immune systems, neurological or neurodevelopmental conditions;
pregnant women and
people age 65 years and older.
How does swine flu spread to people?
Rarely, swine flu spreads from pigs to people and on occasion, people can spread flu to pigs! Most commonly, infected pigs spread the virus to people who have direct or indirect contact with:
pig saliva, urine, feces, blood other fluids,
scratches and bites from a pig, or by eating or drinking contaminated food or water (for example, eating or drinking with unclean hands after touching a pig at a fair). However, if meat from pigs is
handled and prepared properly, there is no evidence that you will catch swine flu by
eating pork.
Infections that spread to people often occur through close contact with infected pigs. For example, the virus has spread in pig barns and at livestock exhibits at fairs. The virus can spread through the air when infected pigs cough or sneeze. People also can get infected from droplets of infected pigs that land in their nose or mouth and if they breathe infected droplets in the air. The infection also can spread to a person if they touch a surface with virus on it and then touch their mouth or nose.
Most of the time, even if the varieties of flu found in birds and swine do infect a person, it is not common for those people to spread the virus to others. But if you are at high risk for zoonotic diseases such as swine flu and you plan to attend a fair where pigs are present, you should avoid direct contact with pigs or their barns.
What precautions can families take if they have contact with pigs?
People who have contact with pigs should follow precautions to avoid the spread of germs:
Do not eat or drink or put anything in your mouth in pig barns or show arenas.
Do not take toys, pacifiers, cups, bottles, strollers or similar items into pig barns and show arenas.
Make sure children wash their hands with soap and water or use alcohol-based hand sanitizer gel after touching pigs, corrals or fences, food and water dishes and other surfaces.
2009 swine flu pandemic: lessons learned
Swine flu from the influenza A virus has caused a pandemic in humans in the past. For example,
in 2009, a new flu virus that was originally in swine was identified in California. It quickly spread throughout the country and the rest of the world.
All ages of people were infected. Children and young adults were at higher risk—possibly because they were less likely to have immunity from a past infection. To control the pandemic, the United States used
effective strategies, including:
Short-term school closure: 600,000 children from 980 schools were affected.
Vaccination and antivirals: An H1N1 influenza vaccine and antiviral drugs (oseltamivir, peramivir, zanamivir, and baloxavir) were made available.
In total, 60 million people were infected, 274,000 were hospitalized and 12,469 died from the virus in the United States. It took a combination of public health measures to ease the pandemic. H1N1 viruses continue to circulate to this day.
More information
About Dr. Frenck:
 Robert W. Frenck Jr, MD, FAAP, is board-certified in pediatrics and pediatric infectious diseases and a member of the AAP Section on Infectious Diseases. He practices at Cincinnati Children's Hospital Medical Center and is a professor of pediatrics at the University of Cincinnati.
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