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PARASITIC
HELMINTHS
1. The Nematodes
(Roundworms)
Organ Systems of
Nematodes
Morphology of
Nematodes
a. Ascaris
lumbricoides
| Phylum Nematoda: Ascaris lumbricoides, adults (male &
female) |
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| Ova of Ascaris
lumbricoides |
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Ascaris
lumbricoides
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b. Enterobius
vermicularis (pinworms)
Enterobius vermicularis
(pinworm)
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Ova of
Enterobius vermicularis
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Phylum Nematodda: Enterobius vermicularis, adult, female
Parasite
|
Disease
|
Diagnostic
Stage
|
Source of Infection
|
Clinical Symptoms
|
| Enterobius vermicularis |
Pinworm infestation |
Ova from perianal region, collected
using tape |
Ingestion of ova on hands and fomites or
linens |
Pruritis ani, diarrhea, or none |
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c.
Trichinella spiralis
|
Trichinella
spiralis Encysted in Muscle Tissue
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Phylum Nematoda: Trichinella spiralis,
adult (male)
The adult is 2 to 4 mm long, barely visible in fecal material. Adults can
be observed microscopically in the stools of patients, but only during the
first few weeks of infestation.
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Trichinella spiralis, adult (female)
The female trichina worm releases fully developed, viable larvae instead
of ova. This is different than other roundworms which release eggs.
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Trichinella spiralis,
encysted in muscle tissue
This is a "tissue" parasite--the larvae are found encysted in muscle
tissue; most frequently, the diaphragm, thoracic and abdominal walls,
tongue, biceps and deltoid muscles
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Trichinella spiralis,
encysted (closer view)
Human are infected by eating the trichinella larvae in infected,
undercooked pork or bear meat. The larvae mature within four to five days.
Male and female worms mate in the intestine, and the female burrows into the
intestinal wall, enters the lymph nodes and deposits the larvae. They
lymphatic system carries the larvae throughout the system via the blood
stream, where they eventually encyst in striated muscle tissue
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2. The Cestodes
(Tapeworms)
Tapeworm (Cestode)
Morphology
|
Gravid Proglottis of
theTapeworm Taenia pisiformis (Cestode)
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Scolex of Taenia
solium
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The Tapeworm Taenia pisiformis
(Cestode)
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Parasite
|
Disease
|
Diagnostic Stage
|
Infective Stage
|
Clinical Symptoms
|
| Taenia solium (beef tapeworm) |
Beef tapeworm infestation |
Ova (eggs) or proglottids (segments) in feces |
Cysticercus (larvae) or ova ingested with undercooked
meat of infested cattle |
Diarrhea, increased appetite, intestinal obstruction |
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3. The
Trematodes (Flukes)
|
Morphology of a
Liver Fluke (Trematode)
|
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| The Liver Fluke Fasciola
hepatica (trematode) |
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Morphology of a
Blood Fluke (Trematode)
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The Blood Fluke Schistosoma
(Trematode)
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