Influenza

Influenza, commonly shortened to “flu,” is an extremely contagious respiratory illness caused by influenza A or B viruses. Flu appears most frequently in winter and early spring. The flu virus attacks the body by spreading through the upper and/or lower respiratory tract.

Flu is spread when you inhale droplets in the air that contain the flu virus, make direct contact with respiratory secretions through sharing drinks or utensils, or handle items contaminated by an infected person. In the latter case, the flu virus on your skin infects you when you touch or rub your eyes, nose, or mouth. That’s why frequent and thorough hand washing is a key way to limit the spread of influenza. Flu symptoms start to develop from one to four days after infection with the virus.

While anyone can get flu, infants, the elderly, and people with chronic ailments such as diabetes, heart disease, lung disease, and HIV/AIDS are at highest risk for flu complications. Despite advances in flu prevention and treatment, influenza and its complications are still fatal to about 36,000 people in the United States each year.

Specific strains of flu can be prevented by a flu vaccine, either a flu shot or FluMist (a nasal spray). In addition, flu antiviral medications are available to prevent flu. Some of these medications may also reduce the severity and the duration of flu if started within the first 48 hours of flu symptoms.

Researchers divide flu viruses into three general categories: types A, B and C. All three types can mutate, or change into new strains, and type A influenza mutates often, yielding new strains of the virus every few years. This means that you can never develop a permanent immunity to influenza. Even if you develop antibodies against a flu virus one year, those antibodies are unlikely to protect you against a new strain of the flu virus the next year.

Type A mutations are responsible for major flu epidemics every few years. Type B is less common and generally results in milder cases of flu. However, major flu epidemics can occur with type B every three to five years.

Type C causes infection but does not cause typical flu symptoms. Both influenza A and B have been linked to the development of Reye’s syndrome, a potentially fatal complication that usually affects children and  teens under 18. Widespread outbreaks of Reye’s syndrome have occurred with influenza type B and also with chickenpox, but other viruses have been implicated. The risk of Reye’s syndrome is increased when taking aspirin, so children should not take aspirin during a viral illness such as cold or flu.

Most influenza viruses that infect humans seem to originate in parts of Asia, where close contact between livestock and people creates a hospitable environment for mutation and transmission of viruses. Swine, or pigs, can catch both avian (meaning from birds, such as poultry) and human forms of a virus and act as hosts for these different viral strains to meet and mutate into new forms. The swine then infect people with the new form of the virus in the same way in which people infect each other — by transmitting viruses through droplets in the air that people breathe in.

Swine flu is a respiratory disease that normally occurs in pigs, but a new strain of swine flu called the 2009 H1N1 virus has recently spread worldwide. This virus can spread from person to person in the same way as the seasonal flu spreads. You can’t catch swine flu from eating pork or pork products. Swine flu causes symptoms similar to those of the human flu, but some people who are infected develop vomiting and diarrhea and more severe symptoms, such as pneumonia or respiratory failure.

The seasonal flu vaccine is not effective against swine flu, but antiviral drugs such as oseltamivir (Tamiflu) or zanamivir (Relenza) can help prevent disease and treat it so symptoms clear up more quickly. You can avoid getting sick by washing your hands regularly with soap and water or an alcohol-based hand sanitizer, staying away from people who appear to be sick, and not touching your nose or mouth.