d. Ascaris lumbricoides (pronounced AS-kar-is lum-bri-KOY-deez). Ascaris
lumbricoides is usually referred to as the large intestinal roundworm (See Figure 2-3).
The adult female intestinal roundworm ranges in size from 22 to 35cm, while the male is
from 10 to 31cm. The adult worms typically live in the lumen of the small intestine. The
worms subsist on the food present in the intestines and the cells of the host's intestinal
mucosa. After the infective egg is ingested by the human, the egg hatches and the
larva penetrate the wall of the small intestine. This larva then migrates through various
parts of the body until it reaches the small intestine, where it remains until it dies. The
spread of this parasite is made easier by poor sanitary conditions and poor hygiene.
The eggs of Ascaris lumbricoides are frequently ingested by small children through
hand to mouth contamination. Moist, loose soil provides a very favorable climate for the
preservation of the eggs. Many infestations of this parasite go unnoticed by the host,
since only a dozen or so worms are present. It is only when a worm is passed out in the
stool or when a routine fecal examination is performed that the infection is diagnosed.
Symptoms and signs associated with Ascaris lumbricoides infestation include cough,
low-grade fever, pneumonia, intestinal obstruction (when many worms are present), and
vomiting and abdominal pain (because of the movement of the worms).
Figure 2-3. Giant roundworm.
e. Ancylostoma duodenale (pronounced AN-si-LOS-tuh-muh DEW-o-de-NAY-
lee). Ancylostoma duodenale is commonly referred to as the Old World hookworm.
This parasite is found primarily in Europe and South America. Adult hookworms are
relatively small; males range from 5 to 11mm, and females range from 9 to 13mm.
Humans are almost always hosts of this parasite. After the eggs are passed from the
host, they hatch and become rhabditiform larvae. These larvae mature and derive
some of their nutrition from organic matter in the soil. Later, they penetrate the skin of
humans and travel through various locations in the body until the small intestine is
reached. The presence of moist, warm soil is favorable for the spread of these
parasites. The spread is also hastened by humans not wearing shoes (since the larvae
penetrate through the skin of the feet). Signs and symptoms associated with
Ancylostoma duodenale include the following.