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Swine influenza is a respiratory illness that generally affects the pig population. Caused by the Influenza type A virus, regular outbreaks among pigs are common, however, while humans do not normally contract swine flu, it can and does happen.

Swine influenza virus is most commonly referred to as “swine flu.”   Researches believe the Spanish influenza pandemic (infectious disease that can spread worldwide) of 1918-1919 can be linked to the swine flu, though its pathogenic origin is still unknown.  Prior to and after 1918, most pandemics of influenza developed in Asia and spread worldwide, with the first wave hitting the United States in the spring of 1918.

What made the 1918 influenza pandemic unique, was that it affected both humans and swine at the same time.  A second wave of the virus swept across the globe between September-November of 1918, and proved highly fatal.

In some other nations, a third wave spread in 1919.  The differences between the three waves seemed to be that the last two waves were more complicated, severe and had a higher fatality rate.  Three pandemic waves of influenza within one year, occurring in rapid succession with little break between waves, was never before experienced.

In February of 1976, the New Jersey State Health Department sent virus samples to the Center for Disease Control in Atlanta, Georgia.  The samples were taken from recruits at Fort Dix, New Jersey,  who had exhibited influenza-like symptoms.  Many of the virus samples had isolates that were identified as A/Victoria/75 (H3N2), the most common strain, while two of the isolates were unable to be identified.  On February 10th, additional isolates were identified as being A/New Jersey/76 (Hsw 1N1), resembling the virus that caused the 1918 pandemic, better known as “swine flu.”

In 1974 and 1975, only two cases of swine flu were diagnosed in the United States.  Both of the subjects involved had close contact with pigs, but there no evidence to suggest the virus had spread beyond family members.

As a result of the 1976 swine flu incident at Fort Dix, New Jersey, millions of Americans were vaccinated against the virus.  While the strain at Fort Dix differs from the one currently detected in Mexico, people who received the vaccine in 1976, should still have enough immunity in the body to either prevent the illness or make a contracted case much milder.

Between 2005 and January of 2009, there have been 12 reported cases of swine flu diagnosed  in America, none of which resulted in a fatality. 

What is Swine Flu?

Swine influenza virus refers to cases of influenza that are caused by Orthomyxoviruses, which are found in the pig population.  There are three types of influenza viruses; type A, which causes viral outbreaks, type B which can be traced to sporadic cases and type C which does not cause disease reactions.  The swine influenza strains that have been isolated and classified to date are either Influenza A or a subtype of the genus Influenza A.

In 2009, the Center for Disease Control (CDC) determined that swine influenza (H1N1) is highly contagious and spreads from person-to-person, however, it is unknown how it is transmitted. However, a virus can mutate and as a result be passed from person-to-person.  The form of influenza that originated in Mexico is a genetic mix of of viruses that have been witnessed in pigs, birds and humans.  The strain of swine flu responsible for the 2009 outbreak in the United States is believed to have undergone a mutation allowing it to be spread from pigs to humans.

Signs and Symptoms of Swine Flu

The signs and symptoms of swine flu in humans are very similar to those that accompany other types of influenza viruses.  Signs and symptoms include the following:

  • Influenza-like illness (fever, sore throat and/or cough)
  • Mild respiratory illness (nasal congestion, rhinorrhea or runny nose) with or without fever
  • Vomiting
  • Diarrhea
  • Myalgia (pain in the muscle or multiple muscles)
  • Chills
  • Fever
  • Fatigue
  • Headache
  • Dyspnea (shortness of breath, difficult or labored breathing)
  • Conjunctivitis (rare but has been reported)
  • Severe cases of swine flu have caused pneumonia and respiratory failure and can become fatal

How Can Swine Flu Be Transmitted?

The spread of swine flu is thought to occur much in the same way that seasonal flu is spread.  Viruses are spread from person-to-person through droplets in a sneeze or cough.  Another way a virus can be spread is through contact with an infected surface (door knob, telephone headrest, shaking hands, etc.) and touching the mucous membranes (eyes, nose and mouth).

People that are infected with a virus can infect another person starting from day one before the symptoms develop, and for a period of up to seven days following onset of an illness.  Children and people with a compromised immune system may be contagious for longer periods of time.

What to Do if a Person Exhibits Swine Flu Symptoms

Is a person lives in an area in which swine flu has been identified and comes down with flu-like symptoms, fever, chills, nausea, runny nose, sore throat, vomiting, or diarrhea, it is important to contact a physician immediately.  A health care provider can determine if a person should be tested for the influenza virus or if treatment is needed.

If a person becomes sick, the CDC recommends to stay at home and avoid contact with others as much as possible, this will limit the likelihood of the virus being spread any further.  If a person becomes ill and exhibits any of the following warning signs, it is extremely important to seek emergency medical treatment.

In small children, the following warning signs warrant emergency medical treatment:

  • Rapid breathing or difficulty breathing
  • Cyanosis (blue color of the skin)
  • Dehydration
  • Lethargy
  • Highly irritable behavior
  • Flu-like symptoms get better and then return with fever and a worsened cough
  • Fever accompanied by a rash

In adults, the following warning signs need immediate medical care

  • Difficult breathing or shortness of breath
  • Pain, pressure or tightening in chest
  • Dizziness
  • Confusion
  • Severe and unrelenting vomiting


The CDC has activated the Emergency Operations Center to coordinate response about the emerging threat of swine flu.  The goal is to raise public awareness, decrease the spread of the disease and provide information and education for health care providers and public health officials about the risks and dangers associated with this newly identified strain of the influenza virus.  The situation surrounding the most recent swine flu outbreak is quickly evolving, the CDC will provide updated and relevant information as it becomes available.