Page 42 - parasitology for medical and clinical laboratoryprofessionals

22 CHAPTER 2

personnel conducting the testing. The best way to avoid Helminthes (worms) and protozoa comprise the basic
problems associated with parasite infections is by edu- groups of parasites that infect humans. Another group,
cating oneself and others to avoid infection and to seek ectoparasites that live on the skin and hair, is common
treatment when signs present themselves. but does not cause the extreme medical conditions that
the previous two categories do.
MEDICAL CONDITIONS CREATED Helminths
BY PARASITIC INFECTIONS
Helminths, or worms, inhabit most areas of the world
Large numbers of intestinal parasites may even block the
and produce a large proportion of the parasitic infec-
intestinal tract or cause hemorrhage if they perforate the tions suffered by humans. Two main groups, pinworms
intestinal wall. Other extreme medical conditions pro-
and whipworms, are thought to comprise the majority
duced by parasitic infestation are: liver abscesses; appen- of these infections. The most common “worm” infecting
dicitis; peritonitis; hemorrhagic pancreatitis; anorexia (loss
children is pinworms. The organism, Enterobius vermic-
of appetite); and anemia and vitamin insufficiency related ularis, infects a significant number of children annually
to poor absorption of digested foods. Hookworm larvae
around the world, including the United States. Symp-
penetrate the skin and are most often contracted through toms are itching and irritation of the anus or vagina,
contact with contaminated soil. When hookworms reach
digestive disorders, insomnia, irritability, or nervousness.
adulthood, they may also steal the victim’s strength and Female worms crawl out of the anus and lay up to 15,000
vitality. Young hookworms have tooth-like structures by
eggs per day. Once exposed to the air, the eggs can sur-
which they burrow through the intestinal walls and feed vive about two days anywhere in the individual’s living
on blood. Symptoms from hookworms are iron deficiency,
environment. On a global basis it is estimated that up
abdominal pain, loss of appetite, pica (abnormal craving to 500 million people may be infected at any given time
to eat soil), protein deficiency, dry skin and hair, skin ir-
with pinworms. These worms are white and can grow to
ritations, and edema. Advanced cases are characterized by about a half inch in length.
a distended abdomen, stunted growth, delayed puberty,
The most commonly encountered whipworm, called
mental dullness, cardiac failure, and death.
Trichuris trichiura, is also estimated to be the causative
agent for up to five hundred million cases throughout the
Common Organisms That Cause world. Although infections with T. trichiura are considered
Parasitic Infections a tropical disease, most cases are found in Asia and to a lesser
extent in Africa and South America. The infection rate is
As many or more species of parasites exist than do different low in the United States but may be responsible for several
mammals and other basic forms of life that can potentially million cases which are found mostly in the rural Southeast.
infect humans and other mammals, marine life, plants, and Poor hygiene is responsible for most if not all infections by
those organisms that dwell in the ground. In addition, many the whipworm, as food raised in shady and moist soil that
of these may serve as hosts or intermediate hosts, and are has become contaminated with human feces can lead to
capable of infecting humans throughout the world. There an increased rate of infection. Mostly children with a high
are several anatomic categories of parasites have the ability risk of exposure are infected by this parasite. Symptoms of
to produce parasitosis in humans, to varying degrees. whipworms are bloody stools, pain in the lower abdomen,
weight loss, rectal prolapse, nausea, and anemia. Hemor-
CATEGORIES OF PARASITES rhage can occur when worms penetrate the intestinal wall
and bacterial infections from the normal flora that is found
The varieties of parasites that inhabit hosts throughout in large numbers in the intestine will usually follow.
the world are almost endless. The organisms range from
single-celled to multicelled organisms that are capable of Protozoa
infecting every living organism in existence. Some cause
extensive symptoms, signs, and suffering, whereas others The levels of infection are significant and the varieties of
exist at the expense of the host but cause little harm. parasites that infect humans number into the hundreds.