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Emerging Infections: Microbial Threats to Health in the United States
restrictions on the use of most pesticides in recreational and wildlife areas limit our ability to control plauge in the event of an epizootic.
Influenza, like plaugue, has caused illness and death among humans for hundreds of years. Given this history, it is somewhat disconcerting that today many people consider this viral disease an unpleasant but basically harmless illness. A diagnosis of influenza nowadays often generates little more than sympathy from one's friends and family, yet one need look no further than the early 1900s to realize the seriousness of the threat that can be posed by this pathogen.
Although influenza pandemics have varied in the severity of their impact, all have caused widespread disease and death. This was especially true of the 1918 influenza A pandemic, which claimed more than 20 million lives worldwide in less than a year and ranks among the worst disasters in human history. In the United States alone, it is estimated that one in four people became ill during the pandemic and that 500,000 died. Mortality from influenza and pneumonia was estimated as 4.8 per 1,000 cases in 1918, three times that of immediately preceding years.
The symptoms of infection with influenza virus are familiar to nearly everyone: fever, chills, headache, muscular aches, and cough. Although most people recover fully within a week, even during pandemics, the elderly, the very young, and those with chronic diseases are at risk of death from the viral infection itself or from complications resulting from secondary bacterial pneumonia. (This kind of pneumonia is responsible for most influenza deaths in persons over the age of 60.)
The origin of the 1918 influenza pandemic remains in doubt, but it may have begun with a mild but sizable outbreak of illness in the United States early in that year, concurrent with the final stages of World War I. The outbreak was confined primarily to military camps and crowded workplaces and was distinctive, in retrospect, because of the large number of young adults who died of the disease. Overall, however, the initial mortality rate was low, and in many places the outbreak passed without comment. Indeed, what turned out to be the first wave of the pandemic was recognized only after the second wave had passed.
The first wave swept across North America in March and April and then subsided almost as rapidly as it had appeared; the infection moved on to Europe, where it first reached epidemic levels in France in April 1918. Over the following several months, influenza spread throughout the whole of Europe. European-based fighting forces found themselves losing the service of significant numbers of troops to what became popularly known (except in Spain) as the Spanish flu, owing to its high incidence in Spain.