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Microbiology => Immunization => Influenza
Influenza
Influenza, acute, infectious, contagious disease of the respiratory tract, especially the trachea, colloquially called flu or, less often, grippe. The symptoms of a simple attack include dry cough, sore throat, nasal obstruction and discharge, and burning of the eyes; more complex cases are characterized by chill, sudden onset of fever, headache, aching of muscles and joints, and occasional gastrointestinal symptoms. In uncomplicated cases, symptoms fade and temperature drops to normal in a few days; the risk of death increases if the disease is accompanied or followed by viral pneumonia or bacterial pneumonia.
Since the 16th century, at least 31 influenza pandemics, which are very widespread epidemics, have been described. The most destructive epidemic of modern times, that of 1918, is estimated to have caused 20 million deaths; in the U.S. about 500,000 persons died, generally following the complication of bacterial pneumonia.
The three types of causative virus, known as A, B, and C, were isolated in 1933, 1940, and 1950, respectively; the first two are responsible for disease epidemics. In 1941 it was shown that influenza could be controlled by a vaccine containing virus. The problem of immunization is complicated, because the different types are antigenically unrelated and so do not induce cross-immunity. It is also complicated because immunity to a specific virus persists for less than a year and because these viruses exhibit the unique quality of periodically mutating to negate any immunity the race may develop. The problem has been met by creating polyvalent vaccines: Vaccine against type B is combined with vaccines against the subtypes of type A as they evolve. This has required a worldwide surveillance system to detect altered virus forms as soon as they arise, so that adequate stocks of vaccine can be prepared in time. Because it would be prohibitively expensive to prepare vaccine for the entire population each time the virus mutated, vaccine was for a long time administered only to those most susceptible to developing pneumonia when they contract influenza. In 1984, however, the U.S. Centers for Disease Control revised this list to include medical personnel who dealt with high-risk influenza patients and recommended that vaccine be dispensed to any persons who desired it.
The different antigenic types of influenza virus appear in cycles; for instance, the variant appearing in the 1978-79 season was identical to the virus that was widespread during the early 1950s. Some evidence exists that pandemics occurring 60 to 70 years apart are caused by the same form of virus. Based on this theory, public health officials expected in 1976 that the same virus that caused the 1918 pandemic would reappear. When this form of the organism (known colloquially as swine flu) was isolated from army recruits in Fort Dix, New Jersey, vaccine against it was prepared and mass inoculation was carried out in the U.S. No outbreak, however, of that form of influenza occurred.
The drug amantadine hydrochloride, which is taken orally, is effective in preventing influenza caused by influenza A virus, and also moderately effective in treating influenza A after symptoms have appeared. Amantadine is used as an adjunct to immunization for high-risk patients, but immunization is still considered the most effective way to combat the disease.
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