Page 178 - parasitology for medical and clinical laboratoryprofessionals

158 CHAPTER 6

through translactational transmission to the infant of the sign is also limited. And, in addition, early in the parasitic
infection through breast-feeding by an infected mother. infection by roundworms, there may be few or no symp-
The roundworms of Ancylostoma duodenale, Neca- toms. When A. duodenale is suspected and eggs have
tor americanus (hookworms), and Ascaris lumbricoides been found, it is necessary to differentiate between the
are the most prevalent roundworms that cause nematode larvae of A. duodenale and Strongyloides stercoralis lar-
infections in humans. In addition, organisms similar to vae, because infection with the less frequently diagnosed
these that infect humans also infect cats and dogs. The S. stercoralis has a more serious impact on the health of
close attachment of animal to human has been present the victim and requires a different treatment.
since early civilization. This leads to the belief that these It is also difficult to differentiate between the eggs
organisms were shared by man and animal and reflects of Ancylostoma duodenale and Necator americanus. The
the close living arrangements. Over the years, slight evo- larvae of the two hookworm species, A. duodenale and
lutionary changes may have occurred where the organ- N. americanus, can be distinguished microscopically
isms became better suited to inhabit either the human or a but this differentiation is not typically done. The adult
lower animal. These organisms are chiefly spread by fecal worms of these two hookworm species, unlike those of
contamination of the environment, which would explain A. lumbricoides, can only be obtained through a surgical
the passing from humans to animal of these parasites. procedure, and if this is done a definitive identification
Diagnosis of nematode infection by hookworms of the species is possible. The best course of action is to
and Ascaris lumbricoides is achieved almost exclusively avoid contamination of the soil for any of these species
by the recovery of eggs or larvae. Eosinophilia does not just presented. Food sanitation and personal hygiene will
occur until tissue invasion has occurred, so this clinical go a long way toward diminishing these infections.

CASE STUDIES

1. A 12-year-old boy from a semi-rural area in the mountains of the southeastern United
States is out of school for the summer vacation. He plays in a small creek during the
summer. Upon using the restroom, the boy chanced to see a long and slender worm
in his stool. He had suffered from mild abdominal discomfort along with periodic
bouts of diarrhea. When he called his mother’s attention to an “earthworm” in his
stool, she took him to his pediatrician. What was the probable diagnosis, and how
would the diagnosis have been made?
2. A 70-year-old male farmer had experienced chronic weight loss, weakness, and dizzi-
ness as well as loose stools. The patient was previously diagnosed with hypertension
heart disease and chronic alcohol abuse. The anemia could be attributed to blood
loss from a recent mitral valve repair, but the patient denied any loss of appetite.
Laboratory results that included a complete blood count confirmed a low hemoglo-
bin of 9.1 g/dL (normal range should be 13 to 16 g/dL for a male). In addition to the
low hemoglobin, a moderately high eosinophil count of 9 percent, a possible indica-
tion of either an allergy to an environmental factor or to the immune reaction to a
parasitic infection. A stool specimen was sent to the microbiology laboratory for a
routine culture to rule out a bacterial infection of the intestinal tract along with an
ova and parasite (O&P) examination. The stool specimen visually resembled rice water
stool. An abundant number of thin larvae morphologically confirmed the diagnosis
of a parasitic infection. Distinguishing morphological characteristics of the larvae re-
vealed a rhabditiform larval stage of a parasite. What was the probable diagnosis, and
how would the diagnosis have been made?