Page 492 - Review of Medical Microbiology and Immunology ( PDFDrive )

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CHAPTER 56 Nematodes
congestive heart failure or respiratory paralysis.

Epidemiology
Trichinosis occurs worldwide, especially in Eastern Europe
and west Africa. In the United States, it is related to eating
home-prepared sausage, usually on farms where the pigs
are fed uncooked garbage. Bear and seal meat also are
sources. In many countries, the disease occurs primarily in
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mebooksfree.com mebooksfree.com Trichinella spiralis—larvae in skeletal muscle. Muscle biopsy reveals larvae within striated muscle (see mebooksfree.com
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hunters who eat undercooked wild game.
Laboratory Diagnosis
Figures 56–2K and 56–15). Serologic tests, especially the
FIGURE 56–15
bentonite flocculation test, become positive 3 weeks after
Three arrows point to Trichinella larvae within “nurse cells” in skeletal
infection.
muscle. (Source: Public Health Image Library, Centers for Disease Control and
Treatment
Prevention.)
larvae have infected the muscle, but for patients with severe
Pathogenesis & Clinical Findings
symptoms, steroids plus albendazole can be useful. Meben-
dazole is effective against the adult intestinal worms early
A few days after eating undercooked meat, usually pork, There is no effective treatment for trichinosis when the
WUCHERERIA mebooksfree.com
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in infection.
the patient experiences diarrhea followed 1 to 2 weeks later
by fever, muscle pain, periorbital edema, and eosino-
Prevention
philia. Subconjunctival hemorrhages are an important
The disease can be prevented by properly cooking pork and
diagnostic criterion. Signs of cardiac and central nervous
by feeding pigs only cooked garbage.
system disease are frequent, because the larvae migrate to
TISSUE NEMATODES

Disease
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that eventually obstructs the lymphatic vessels, causing
1
Wuchereria bancrofti causes filariasis. Elephantiasis is a
edema. Massive edema of the legs is called elephantiasis
striking feature of this disease. Tropical pulmonary eosino-
(Figure 56–19). Note that microfilariae do not cause
philia is an immediate hypersensitivity reaction to W. ban-
symptoms.
crofti in the lung.
Early infections are asymptomatic. Later, fever, lym-
phangitis, and cellulitis develop. Gradually, the obstruction
Important Properties
leads to edema and fibrosis of the legs and genitalia, espe-
cially the scrotum. Elephantiasis occurs mainly in patients
The life cycle of W. bancrofti is shown in Figure 56–16.
who have been repeatedly infected over a long period.
Humans are infected when the female mosquito (espe-
cially Anopheles and Culex species) deposits infective larvae
elephantiasis.
on the skin while biting. The larvae penetrate the skin,
Wolbachia species are Rickettsia-like bacteria found
enter a lymph node, and, after 1 year, mature to adults that
intracellularly within filarial nematodes such as
produce microfilariae (Figure 56–17A and 56–18). These Tourists, who typically are infected only once, do not get
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Wuchereria and Onchocerca. Wolbachia release endo-
circulate in the blood, chiefly at night, and are ingested by
toxin-like molecules that are thought to play a role in the
biting mosquitoes. Within the mosquito, the microfilariae
pathogenesis of Wuchereria and Onchocerca infections.
produce infective larvae that are transferred with the next
bite. Humans are the only definitive hosts.
kills the Wolbachia, resulting in a reduction in the number
of microfilaria and in the inflammatory response to the
nematode infection.
1
Brugia malayi causes filariasis in Malaysia.
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