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Chapter 10

Ascariasis

The roundworm, Ascaris lumbricoides, has been one of man's most constant companions since ancient times. It may have been the first human parasite ever described, since references to this helminth have been discovered in ancient texts from Greece, Mesopotamia, Rome and China; it was known to the ancient Egyptians, having been recorded on papyrus dated about 1550 B.C. Despite its long relationship with man, it is remarkable that the important details of the life cycle of Ascaris were unknown until 1916. Ascariasis is a cosmopolitan parasitic infection, especially prevalent among poor children in tropical countries with overcrowded slums and inadequate sanitation. Ascaris lumbricoides is the largest and most prevalent of the human nematodes, rivaling pinworms, whipworms, and hookworms for first place among the helminthic infections afflicting mankind. A considerable percentage of the world's population (perhaps as high as 23%) harbor roundworms and, in certain areas of the rural tropics, the incidence approaches 95%. In 1997, the WHO estimated there were 1.38 billion people infected with Ascaris.

Synonyms

Ascariasis. Ascaridiasis. Ascaridiosis. Ascariosis. Roundworm infection. "Worms." Sp: Ascaridiosis. Lumbricosis. Fr: Ascaridiose. Lumbricose. Ger: Spulwurmbefall. Askaridiasis.

Definition

Ascariasis is an infection by the roundworm, Ascaris lumbricoides, which is particularly frequent in children. Ascaris suum, a natural parasite of pigs, rarely infects man; only the larval stage, and not the adult form, has been recovered in humans. Related ascarids, Toxocara canis and cati, the roundworms of the dog and cat, cause visceral larva migrans in man. Another distant relative in the order Ascaridata is Anisakis, responsible for the infection anisakiasis detailed in the next chapter.

Geographic Distribution

Ascariasis most often affects those living in the warm, moist tropics, but few countries of the world are exempt. In 1947, the world incidence of ascariasis was estimated to be 643 million infected persons (488 million in Asia, 59 million in Africa, 32 million in Europe, 19 million in Russia, 42 million in Central and South America, and 3 million in North America). By 1979 it was estimated that between 800 million and one billion people were infected with Ascaris, ranking it third among the ten most common human infections. It is particularly common throughout Asia, especially in China, India, Sri Lanka,Southeast Asia, the Philippines, Japan, Russia, Afghanistan, and Iran. It is also prevalent throughout Africa and Egypt. In countries of Central and South America, the incidence ranges between 12 and 93% depending on the geographic area and climate and thoroughness of the survey. Endemic regions exist in Canada and the United States, especially in the Gulf Coast states and rural parts of the southern Appalachian range, where up to 30% of the population may be infected in some areas.

The incidence of ascariasis is greatest where warm, even temperatures and high humidity allow the eggs to embryonate throughout the year. Overpopulation and poor sanitation and sewage disposal likewise play key roles in the propagation of ascariasis.

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Copyright: Palmer and Reeder

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