Page 496 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com Treatment CHAPTER 56 Nematodes 485 mebooksfree.com
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countries (Chad, Ethiopia, Mali, and South Sudan). Prior to
the campaign, the disease occurred over large areas of
The time-honored treatment consists of gradually extract-
tropical Africa, the Middle East, and India, where tens of
ing the worm by winding it up on a stick over a period of
millions of people were infected.
days.
Laboratory Diagnosis
Prevention
The laboratory usually does not play a role in diagnosis.
Prevention consists of filtering or boiling drinking water.
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NEMATODES WHOSE LARVAE CAUSE DISEASE

TOXOCARA
Dogs should be dewormed, and children should be pre-
Disease
vented from eating soil.
Toxocara canis is the major cause of visceral larva migrans.
Toxocara cati and several other related nematodes also
cause this disease.
Cutaneous larva migrans is caused by the filariform larvae of
Important Properties ANCYLOSTOMA
A. caninum (dog hookworm) and Ancylostoma braziliense
(cat hookworm), as well as other nematodes. The organism
mebooksfree.com mebooksfree.com mebooksfree.com causing an inflammatory response. The lesions (“creeping mebooksfree.com
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The definitive host for T. canis is the dog. The adult T. canis
cannot complete its life cycle in humans. The larvae pene-
female in the dog intestine produces eggs that are passed in
trate the skin and migrate through subcutaneous tissue,
the feces into the soil. Humans ingest soil containing the
eggs, which hatch into larvae in the small intestine. The
eruption”) are extremely pruritic (Figure 56–20). The disease
larvae migrate to many organs, especially the liver, brain,
occurs primarily in the southern United States, in children
and eyes. The larvae eventually are encapsulated and die.
and construction workers who are exposed to infected soil.
The life cycle is not completed in humans; humans are
The diagnosis is made clinically; the laboratory is of little
therefore accidental, dead-end hosts.
value. Albendazole or ivermectin is usually effective.
Pathogenesis & Clinical Findings
Pathology is related to the granulomas that form around
the dead larvae as a result of a delayed hypersensitivity
The larvae of the rat lung nematode Angiostrongylus canto-
response to larval proteins. The most serious clinical find- ANGIOSTRONGYLUS
nensis cause eosinophilic meningitis (i.e., a meningitis
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ing is blindness associated with retinal involvement. Fever,
hepatomegaly, and eosinophilia are common.
Epidemiology
Young children are primarily affected, because they are
likely to ingest soil containing the eggs. Toxocara canis is a
common parasite of dogs in the United States.

Laboratory Diagnosis
Serologic tests are commonly used, but the definitive diag-
nosis depends on visualizing the larvae in tissue. The pres-
ence of hypergammaglobulinemia and eosinophilia
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mebooksfree.com mebooksfree.com mebooksfree.com FIGURE 56–20 Ancylostoma caninum—cutaneous larva mebooksfree.com
supports the diagnosis.
Treatment
The treatment of choice is either albendazole or mebenda-
migrans. Note serpiginous rash on foot. (Reproduced with permission from
zole, but there is no proven effective treatment. Many
Dr. Richard P. Usatine. From Usatine RP: A rash on the feet and buttocks. West J Med.
patients recover without treatment.
170:334, 1999.)

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