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140 CHAPTER 6

Intestinal obstructions are a serious consequence that
Source: Centers for Disease Control and Prevention (CDC) Life Cycle
may result from a heavy infection by this parasite.

For the species of Ascaris that lives in the human intestine,
the male is somewhat smaller than the 12-inch maximum
length for the female. After eggs are passed with the
feces, they require a period of 2 weeks’ incubation in the
soil before they are viable and are capable of causing an
infection. After eating the eggs that have contaminated
vegetables harvested from the soil, the eggs hatch in the
intestine of the host and then enter the circulatory system
FIGURE 6-3 Fertilized egg of the roundworm Ascaris (the veins) by means of the hepatic portal circulatory system.
lumbricoides
This circulatory route takes the blood containing the newly
defecating. These organisms are readily visible and quite hatched larvae directly through the heart and into the lungs.
startling. Extensive written records of probable ascariasis A. lumbricoides worms do not mature immediately
have been found in sources including the Egyptian medical upon hatching but are able to migrate around the body
papyri, the works of Hippocrates in fifth century BC, Chi- and eventually travel to the lungs. There they migrate up
nese writings from the second and third centuries BC, and the respiratory passageways called the bronchioles and
texts of Roman and Arabic physicians (Cox, 2002). bronchi, where they are coughed up in sputum from the
The fertilized egg is broad and oval, and measures respiratory system and then swallowed. By this means
45 to 75 μm in length and 35 to 45 μm in breadth. The the larvae enter the intestines (the portion called the
thick but transparent shell is surrounded by a mammil- jejunum) where they continue infecting the body as they
lated outer covering that is dark yellow to brown and is develop into adult worms in the intestine (Figure 6-4).
bile-stained with an appearance that is singularly char- After approximately 2 months of infection, the eggs are
acteristic for the species. If the mammillated covering is deposited and are passed in the feces where they become
missing, the egg is said to be decorticated. Infertile eggs infective in warm, moist soil within 2 weeks. Females lay
are longer than fertilized eggs, ranging from 80 to 90 μm infertile eggs when males are not available for mating.
long and the interior of the egg shows disorganization and
no visible structures. Disease Transmission

Symptoms Humans are infected when they ingest embryonated eggs
from contaminated soil where feces have been deposited.
Adult ascarids normally cause few or no symptoms, but The eggs in feces usually include first-stage larvae and
heavy infections may result in nutritional deficiencies, maturation takes place in the soil, particularly hard clay
especially in children. In some patients, considerable soil. The second stage is reached in 2 weeks and is capa-
flatulence (emission of intestinal gas) may be experi- ble of causing ascariasis during which the person becom-
enced with an infection by A. lumbricoides. Migration ing infected by swallowing the embryonated eggs.
into the lungs may lead to hemorrhages and inflamma-
tory infiltrations upon which hemoptysis (coughing up Laboratory Diagnosis
of blood) may be observed. Eosinophilia, an increase in
a type of white blood cell occurring in allergic reactions Diagnosis most often is made by the identification
and parasitic infections, is often concurrently observed of either or both fertilized and unfertilized eggs of
with a set of signs that may include coughing, dyspnea A. lumbricoides. Adult worms may also be identified, as
(shortness of breath), and a mild fever. The intestinal they may pass from any body orifice including the anus,
phase includes abdominal discomfort and bloating along nose, or mouth. The larvae may also be found in sputum
with nausea, vomiting, pains, and diarrhea may occur. or gastric washings from infected individuals.