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Intestinal Nematodes 139

the itching of the anus can be effective with the use of food contaminated with infective eggs is eaten and the
various types of soothing anti-itch creams or similar prep- larvae emerge from the ingested eggs in the intestine.
arations. Recurrence of the infection is likely if bed linens The history of ascariasis is long and has been
and bed clothes are not thoroughly washed to kill both determined to have been an infection plaguing humans
eggs and worms, and if personal hygiene is not practiced, since before recorded history. The eggs of A. lumbricoides
including thorough hand washing following trips to the have been found in human coprolites (stony casts of feces,
bathroom and when playing with other children. also known as coproliths) from several regions in South
America that, by various dating procedures, are believed to
ASCARIS LUMBRICOIDES have been excreted several thousand years ago. In particu-
lar, the regions now known as Peru and Brazil have both
Ascaris lumbricoides, sometimes considered the “large yielded evidence of A. lumbricoides in ancient specimens
roundworm,” is one of six worms classified by Linnaeus, (Cox, 2002). Throughout the countries of southwest Asia
who performed most of his observations and studies be- and China, there also is evidence of A. lumbricoides as well
tween the 1730s and 1750s. His work took him to countries as in a Middle Kingdom Egyptian mummy dating from
throughout several areas of the world, which confirmed the 1938 to 1600 BC and from China in the Ming Dynasty
widespread range of the parasite. Linnaeus is credited with between AD 1368 and 1644 (Cox, 2002).
giving the scientific name to Ascaris lumbricoides, along with The evidence from Europe would most likely be
other plants and animals. The names of some of the organ- scanty at best because human specimens are less well pre-
isms he classified more than 270 years ago have remained served than those in drier climates, accounting for little ar-
unchanged. It has been stated in a number of publications chaeological evidence of the organisms in human remains
by health departments and other health care agencies that from the continent. In the late 1600s Edward Tyson, an
up to one billion people or perhaps one-seventh of the English physician, wrote of and detailed a description of
world population are now infected with A. lumbricoides, the worm itself, although ascariasis had been described
because it is a parasite found around the globe. and treatment documented from several centuries before
The chief source of most of the infections by this Tyson’s contribution. Tyson had learned from Veslius’
parasite is the practice of using human feces to fertilize book that described Lumbricus teres (teres means earth)
soil where food is grown. The adult worm lives in the as perhaps the cause of A. lumbricoides infections con-
intestine (Figure 6-2) and the female produces eggs that tracted from contaminated soil. Anatomical studies require
pass with fecal materials, where the larvae within the good illustrations as well as verbal descriptions, and Tyson’s
eggs develop and reach an infective stage in soil. Foods work was spread broadly over a number of disciplines.
grown and gathered from agricultural areas where the Tyson’s work contained the first illustration of dis-
soil is contaminated by feces containing eggs from this sected internal parasites that depicted both males and
species may directly transmit the eggs to humans when females as well as the eggs of the female. But he greatly un-
derestimated the number of eggs that may be produced,
with the belief that only around 1000 eggs were laid by
each parasite. But later investigations revealed that a sin-
Source: Centers for Disease Control and Prevention (CDC) Therefore it is easy to see that an epidemic could easily
gle female worm is capable of producing up to 200,000
eggs per day during a 1- to 2-year life span (Figure 6-3).

start with only a few of the organisms. Tyson believed the
worms reproduced sexually in the intestine, but he did
not make the connection of how they arrived there.

Morphology

up to 35 cm (more than 12 inches) in length and that is often
excreted in the feces, and is sometimes seen protruding
FIGURE 6-2 Ascaris lumbricoides nematodes; larger A. lumbricoides is a considerably large worm that may reach
female can reach over 12 inches from or emerging from the anus even when the victim is not