When it resurfaces in man, the human immune system is caught completely unprepared and a sudden, widespread epidemic occurs. The Spanish Flu pandemic of 1918 was the worst pestilence to afflict the human race. Over half a million died in the U.S., and thirty million more elsewhere on this planet. Another 50,000 died in 1957 when Asian Flu hit the U.S. and infected 45 million Americans. Scientists have identified three types of influenza virus.
•TYPE A is the most frequent and severe. Its subtypes are also the most subject to variation. Type A variants have been responsible for almost every major pandemic, including the Spanish Flu of 1918, the Asian Flu of 1957 and the Hong Kong Flu of 1968. Type A variants continue to cause flu epidemics every two to three years and it is the most common flu type encountered in the U.S. during winter.
•TYPE B causes local flu outbreaks, especially in spring or summer. Because it is less subject to variations, there are no important subtypes. However, Type B viruses do experience mutational drifts that can cause devastating new strains to appear every few years.
•TYPE C is rarely encountered nowadays.
Variants of each type are named for the major surface protein and for the proteins that induce immune response against the virus. The two major proteins are hemagglutinin (“H”) and neuraminidase (“N”). Thus H1N1 is a recent subtype that was identified in Chile in 1981, while H3N2 surfaced in the Philippines in 1983.
Although by itself flu is a self-limiting ailment and is rarely fatal, complications present a potentially serious risk to the elderly, the chronically ill and to some pregnant women; to those with chronic lung diseases such as tuberculosis, asthma, bronchitis and emphysema; or to patients with diabetes, heart disease, kidney disorders, cystic fibrosis or obesity.
As with the common cold, the severity and duration of influenza appears related to the victim’s immunocompetence. A person with a strong immune system may recover from flu in only four or five days while the infection can persist for ten days or more in a person with a compromised immune system.
In, say, a forty-year-old adult with an average immune system, fever typically lasts three days, after which symptoms gradually ameliorate. However, even though you may suddenly feel well, it’s advisable to schedule an extra day of rest at home in case of a relapse.
Although influenza is responsible for a whole catalog of miseries, one thing it does not cause is so-called “intestinal flu.” This term is commonly used to describe a variety of gastrointestinal ailments, such as persistent indigestion, nausea, and diarrhea, which people believe are caused by a flu-like virus. However, the comparison is inaccurate. Neither flu nor cold viruses produce any kind of gastrointestinal dysfunction nor are these problems related to the aftermath of a cold or flu.