Page 495 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com localized, nonerythematous, subcutaneous edema (Calabar mebooksfree.com
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PART VI Parasitology
484
tissue, ultimately concentrating in the eyes. There they
cause lesions that can lead to blindness. Loss of subcutane-
swellings). The most dramatic finding is an adult worm
ous elastic fibers leads to wrinkled skin, which is called
crawling across the conjunctiva of the eye, a harmless but
disconcerting event.
“hanging groin” when it occurs in the inguinal region.
Thickening, scaling, and dryness of the skin accompanied
by severe itching are the manifestations of a dermatitis
often called “lizard skin.”
The disease is found only in tropical central and west
The role of Wolbachia in the pathogenesis of onchocer-
Africa, the habitat of the vector Chrysops.
ciasis has been discussed earlier in “Wuchereria.” Epidemiology
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mebooksfree.com mebooksfree.com mebooksfree.com blood smear (see Figure 56–17C). There are no useful sero- mebooksfree.com
Laboratory Diagnosis
Epidemiology
Diagnosis is made by visualization of the microfilariae in a
Millions of people are affected in Africa and Central America.
The disease is a major cause of blindness. It is called river
logic tests.
blindness, because the blackflies develop in rivers and peo-
ple who live along those rivers are affected. Infection rates
Treatment
are often greater than 80% in areas of endemic infection.
Diethylcarbamazine eliminates the microfilariae and may
Laboratory Diagnosis
kill the adults. Worms in the eyes may require surgical
Biopsy of the affected skin reveals microfilariae (see
Figure 56–17B). Examination of the blood for microfilariae
Prevention
is not useful because they do not circulate in the blood. excision.
Eosinophilia is common. Serologic tests are not helpful.
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Control of the fly by insecticides can prevent the disease.
Treatment
Ivermectin is effective against microfilariae but not adults.
Disease
Suramin kills adult worms but is quite toxic and is used
particularly in those with eye disease. Skin nodules can be
Dracunculus medinensis (guinea fire worm) causes
removed surgically, but new nodules can develop; therefore,
dracunculiasis.
a surgical cure is unlikely in areas of endemic infection.
Important Properties
Prevention
Humans are infected when tiny crustaceans (copepods)
Prevention involves control of the blackfly with insecti-
containing infective larvae are swallowed in drinking
cides. Ivermectin prevents the disease.
water. The larvae are released in the small intestine and
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migrate into the body, where they develop into adults.
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Meter-long adult females cause the skin to ulcerate and
LOA
then release motile larvae into fresh water. Copepods eat
Disease
completed when these are ingested in the water.
Loa loa causes loiasis.
Pathogenesis & Clinical Findings
Important Properties
The adult female produces a substance that causes inflam-
Humans are infected by the bite of the deer fly (mango fly),
mation, blistering, and ulceration of the skin, usually of
Chrysops, which deposits infective larvae on the skin. The
larvae enter the bite wound, wander in the body, and
itches, and the ulcer can become secondarily infected.
develop into adults. The females release microfilariae
Diagnosis is usually made clinically by finding the worm
(see Figure 56–17C) that enter the blood, particularly during
in the skin ulcer.
the day. The microfilariae are taken up by the fly during a the lower extremities. The inflamed papule burns and
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blood meal and differentiate into infective larvae, which
continue the cycle when the fly bites the next person.
Epidemiology
Pathogenesis & Clinical Findings
Health Organization (WHO) has greatly reduced the num-
ber of cases. During the year 2015, only 22 new cases were
There is no inflammatory response to the microfilariae or
adults, but a hypersensitivity reaction causes transient,
detected worldwide. The cases occurred in four African

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