Swine flu is a type of influenza virus which is endemic in pig populations. Like other members of the Orthomyxoviridae family of viruses, which cause influenza, this virus has a very high mutation rate, recombining with other subtypes of swine flu in addition to flu viruses which infect other animals, such as humans and birds. When swine flu acquires genetic material from avian and human influenzas, it can become zoonotic, which means that it may cross between species.
Two genera of influenza, Influenza A and Influenza B, are seen in pigs. In some regions, as many as 50% of pigs are infected, and different subtypes of flu evolve in different areas of the world. The versions of swine flu seen in European pigs, for example, are different from those observed in pigs in Asia. Common Influenza A subtypes seen in pigs include H1N1, H1N2, H3N1, and H3N2. Occasionally, humans who work closely with pigs will develop influenza infection as a result of close contact, but the virus will not spread further, because the virus can normally only be passed from pigs to people, not from person to person. Swine flu is not spread by eating pork, even in cases when the virus mutates and becomes dangerous to humans.
In very rare cases, swine flu can evolve so that it can spread from person to person, or from swine to birds to people, creating the risk of a flu epidemic or even a pandemic. This almost occurred in 1976, when a soldier at Fort Dix in the United States sickened and died as a result of swine flu infection, creating fears that a major outbreak of flu might occur. The United States rushed to create an appropriate vaccine and embarked on a mass vaccination program, but the flu failed to spread, and the hasty formulation of a vaccine was later blamed for numerous adverse reactions to vaccination.
When swine flu mutates so that it can be passed from person to person, it can be spread through droplets in the air such as those spread by coughing, and through contact with contaminated surfaces like doorknobs and counters. People are capable of spreading the virus before symptoms emerge, and for several days after they are treated and the flu is resolved. The symptoms of swine influenza are similar to those of other seasonal flus: fatigue, joint pain, nausea, runny nose, altered level of consciousness, and fever have all been documented in patients with strains of influenza which come from pigs.
Human flu vaccines are not effective against swine influenza, because the strains included in the human flu vaccine are not the same. In the event of a swine flu outbreak, health agencies would need to act quickly to type the virus and develop an effective vaccine. Fortunately, this flu is usually responsive to antiviral medications when treatment is offered shortly after signs of infection emerge. Public officials are on high alert for potential flu pandemics after the lessons of the devastating 1918 and 1968 flu outbreaks, which means that the public would quickly be alerted to a suspected swine flu outbreak in the early stages.
In April 2009, the Mexican government reported cases of swine influenza in Mexico City, and began to take measures to address a potential pandemic. Cases were also reported in the United States, and a health emergency was declared so that the Centers for Disease Control, World Health Organization, and other government agencies could initiate a response to the disease. When cases which can be spread from person to person, such as those seen in this outbreak, are documented, people can help protect themselves from the risk of catching the flu by washing their hands regularly, drinking lots of fluids, and avoiding large gatherings in and travel to areas with high numbers of documented cases. People should also seek medical treatment promptly if they develop flu symptoms, and they should comply with recommendations issued by public officials.
People should not stockpile medications against a flu outbreak, as they may be using the drugs incorrectly, which could contribute to the spread of drug resistance. Instead, patients who think that they are infected should visit a medical center for treatment and a prescription, and they should fully finish any course of antivirals prescribed.