Distribution and Incidence
This nematode was known to ancient writers in China, India, Mesopotamia, and Europe, and was present in pre-Columbian America. The World Health Organization estimated in the early 1980s that between 800 and 1,300 million people harbored an average of six worms each.
The true figure may be even higher. Surveys have demonstrated infection in more than 50 percent of sampled populations in such countries as Bangladesh, Brazil, China, Colombia, India, Iran, Kenya, Mexico, Tanzania, and Vietnam, and the rate approaches 100 percent in many rural areas. In China, it was estimated that the 1947 Ascaris population produced 18,000 tons of eggs a year; they may be even more productive today. The worm is also common in developed countries, although improved sanitation has greatly reduced prevalence in recent decades. During the 1960s, surveys conducted in school children and other groups showed infection rates of 2.5 to 75 percent in Italy, 21 percent in Spain, 40 to 80 percent in Portugal, 18 percent in Romania, 2 to 5 percent in urban Japan, and up to 20 percent in the Japanese countryside. Foci still exist in some rural areas in the southern United States.
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