pandemic influenza




Swine influenza is a respiratory disease of pigs caused by type A influenza viruses. In affected pigs, it causes cough, fever, nasal discharge, lethargy and difficulty breathing. Influenza A viruses are classified by two components of the viral surface, hemagglutinin (H) and neuraminidase (N). Different types of influenza A viruses are infectious to avian and mammalian species. Pigs and people are susceptible to influenza A viruses from both avian and mammalian sources. Infection with multiple viruses can lead to the creation of new “reassorted” viruses with components of pig, bird and human flu origin. Classical swine flu (H1N1) was first isolated in 1930, and many other subtypes have since been identified (e.g. H3N2, H1N2). In the United States, swine influenza outbreaks are most common in fall and winter. In Minnesota, we see peaks of swine flu activity in April through May and September through November.

Is the newly identified North American H1N1 human influenza due to “swine influenza” virus?

The new H1N1 outbreak strain, first identified in California in April of 2009, is a combination of influenza virus segments from a number of hosts (swine, avian and human). As yet there is no substantiated link between human cases and swine exposure (investigations are ongoing). Given the mixed origin of the virus, and lack of clear association with pigs, the World Organization for Animal Health suggests the disease be called ‘North American Influenza’.

How can a pig virus affect humans?

Just like other influenza viruses (including human flu), swine influenza viruses are constantly changing. The capacity of flu viruses for interspecies transmission can be altered by gradual changes over many years or by abrupt exchanges of genetic material with other influenza virus types. This means that occasionally these viruses may become capable of infecting people as well as pigs. Recent studies have documented that 10 to 20% of workers in swine facilities and veterinarians have evidence of prior exposure to swine influenza virus. Nearly all these individuals do not recall becoming ill or have mild symptoms that resemble human seasonal influenza infection.

Can the newly identified H1N1 virus infect pigs?

The new H1N1 strain causing human cases in April of 2009 has not been found in pigs. National and international public health authorities (including World Health Organization, U.S. Centers for Disease Control and Prevention, and the United States Department of Agriculture) are investigating links between the outbreak strain, sources of human infection, and circulation in domestic and wild animals.

How do humans become infected with influenza viruses from pigs?

Transmission of influenza from pigs to people usually results from direct contact with infected pigs. In a limited number of cases, the virus has then been transmitted from one person to another. Transmission occurs via the same route as human flu, where a person’s coughing or sneezing releases the virus into the air or onto environmental surfaces. Others then become infected by breathing the virus in directly or by touching their nose, mouth, and eyes after touching a contaminated surface. While swine influenza is very common in pigs, human clinical cases seem to be uncommon and rarely severe.

It is apparent that the new North American H1N1 virus is capable of transmission from person to person. There is no evidence of pig to human transmission of this new virus.

Can influenza viruses be transmitted by eating pork?

There is no record of influenza transmission via meat, and any theoretical risk from handling pork is negligible. Cooking meat to the recommended internal temperature of 160-170° F inactivates the virus.

What are the symptom of North American (H1N1) influenza infections in humans?

The symptoms seen in this outbreak are no different from human seasonal influenza infections. These include fever, cough, sore throat, lethargy, and decreased appetite. Occasionally people report nausea, vomiting and diarrhea.

How is influenza infections diagnosed in people?

Influenza A infections are diagnosed from respiratory specimens (usually a swab from the nose or throat) collected within 4-5 days of illness onset. Children may shed virus in their nasal secretions for up to 10 days. In general, the sooner samples are taken after onset of symptoms, the better. If a virus is not a typical seasonal influenza strain, the Minnesota Department of Health will forward samples to the Centers for Disease Control and Prevention (CDC) for further characterization.

What should swine workers do to protect themselves against swine influenza?

All people working with pigs should be aware of the recommendations made by the CDC and the National Pork Board. These include good hygiene practices such as washing hands (before and after handling pigs, before and after eating, and before and after smoking or any other activity that involves contact of an employee’s hands with his nose, mouth or eyes). In addition, the use of personal protective equipment, such as gloves, face masks, coveralls and boots, may play a role in preventing transmission. Because the North American Influenza (2009) influenza virus has never been isolated from pigs in the USA, there is concern that it could be introduced to swine by people.

People working with swine are encouraged to consult resources available on the National Pork Board website, .

Where can I get more information?
Much of this information was obtained from the Centers for Disease Control and Prevention (CDC) website. There is more information from the CDC available at From here, you can access more detailed facts on swine flu, as well as updates on current swine flu investigations.
Recursos en Español están accesible aquí: .
Information is also available from the Minnesota Department of Health,

Source :
University of Minnesota College of Veterinary Medicine
1365 Gortner Avenue St. Paul, MN 55108 612-624-9227

What is swine influenza?
Influenza Defined
Influenza Viruses - Types, Subtypes, and Strains
What is pandemic influenza A(H1N1) 2009 virus?
Definitions for identification of pandemic influenza A(H1N1) 2009
Case Management & Infection Control
Who should be tested?
Step-by-step guide for specimen collection, storage and transportation
Doctors/Nurses directions to Patients/Parents
How Influenza Viruses Change: Drift and Shift
The 2009 Influenza Pandemic
International Health Regulations
Vaccine Development and Use
Naming the Virus Strain
Information for Families and Visitors
New Pandemic Influenza A (H1N1) 2009
Pandemic (H1N1) 2009 Influenza Guidance
Recent Results from Studies with the new 2009 A/H1N1 Influenza A Virus
Continued pandemic influenza virus detections across Europe with increased activity in the UK (Northern Ireland)
Highly Pathogenic Avian Influenza Virus H5N1 and Wild Birds