Swine Influenza

Last Modified: June 04, 2024
Adult pig looking through a fence.

Swine influenza is an upper respiratory disease of pigs caused by type A influenza viruses (IAV). Symptoms of infection may include difficulty breathing, loss of appetite, and weight loss, resulting in economic losses to producers. Although most swine IAVs don't affect humans, sporadic cases have been found in people who have contact with sick pigs.

Swine influenza is widespread in North and South America, Asia, and Europe. The most common strains found in the United States are H1N1, H1N2, and H3N2. The World Organisation for Animal Health does not require reporting for cases of IAV-S, nor is it a regulated disease in the United States.

Swine influenza usually causes high morbidity but low mortality. In many cases, swine show no signs of illness. Animals are typically symptomatic 1–3 days after infection. If you see any of these signs in your swine, contact your veterinarian and isolate the sick animal(s) from the rest of the herd, if possible.

Here's what to look for:

  • Coughing (sounds like barking)
  • Sneezing
  • High fever
  • Difficulty breathing
  • Runny nose
  • Not eating
  • Lethargy
  • Red or inflamed eyes

IAV-S is spread mainly through close contact, coughing, and sneezing. Contaminated objects (such as farm equipment) can indirectly spread the disease. Swine influenza viruses are not transmitted through food and present no food safety concerns.

Vaccinate your pigs. Vaccinating your herd for influenza A with a commercially available or autogenous influenza vaccine can reduce clinical signs and virus shedding (though viruses can change rapidly, and vaccination may not provide full protection against a modified strain).

Practice good biosecurity and hygiene. Good practices include:

  • Permit only essential workers and vehicles onto your farm.
  • Avoid visiting other livestock farms.
  • Do not share equipment or vehicles with other farms or between healthy and sick animals.
  • Clean and disinfect items that may carry the virus from one location to another (such as shoes, clothes, and vehicles).
  • Shower in and out.
  • Purchase animals from reputable sources and document their origin.
  • Isolate and monitor new animals or animals returning from exhibitions.
  • Use appropriate cleaning and disinfection products and protocols.
  • Consider getting a seasonal flu vaccine.

Prevent the spread of IAV-S at fairs and other events. Follow guidelines from the National Assembly of State Animal Health Officials, the National Association of State Public Health Veterinarians, and the Centers for Disease Control and Prevention (CDC) to minimize influenza transmission at swine exhibitions.

Some actions you can take include:

  • Don't eat or drink or put anything in your mouth in the swine barn or show area.
  • Don't take toys, pacifiers, cups, bottles, strollers, or similar items into the pig barn or show area.
  • Wash your hands often.

Isolate sick animals from the rest of the herd and contact your veterinarian to provide supportive care.

Report Signs of Animal Disease

Producers or owners who suspect an animal disease should contact their veterinarian to evaluate the animal or herd. Find an accredited veterinarian.

Animal health professionals (veterinarians; diagnostic laboratories; public health, zoo, or wildlife personnel; and others) report diagnosed or suspected cases of nationally listed reportable animal diseases to APHIS Area Veterinarians in Charge and to the State animal health official as applicable under State reporting regulations. 

Controlling Swine Flu

APHIS works with animal health and public health officials and the swine industry to carry out a robust and coordinated Influenza A Swine Surveillance Program. Swine are susceptible to infection by human, avian, and swine influenza viruses, which can lead to novel reassortments. The surveillance program aims to identify influenza viruses circulating in swine, proactively identify reassortment viruses that could impact public health, and gain knowledge to contribute to improved animal health diagnostics and vaccines. The USDA provides genetics sequencing from surveillance samples to GenBank, a publicly available database managed by the U.S. Department of Health and Human Services' National Institutes of Health. Virus isolates collected through the program are available to the National Veterinary Services Laboratories upon request.

APHIS works closely with USDA Agricultural Research Service (ARS) researchers to better understand the virus and develop methods to prevent or control it. ARS developed an interactive web tool, ocoFLUshow, to visualize and explore trends in the genetic and geographic diversity of IAV derived from the APHIS surveillance system. The tool provides information useful in identifying relevant viruses circulating in swine herds for further characterization and vaccine strain selection.

Quarterly Reports

FY 2024:

FY 2023:

FY 2022:

FY 2021

FY 2020: 

FY 2019: 

FY 2018: 

Previous years' reports are available upon request.