Biomedical Engineering Reference
In-Depth Information
the living worm, onto a stick, which he or she then winds slowly, thus deliv-
ering the intact worm and relieving the patient of his parasitic burden.
The Rod of Asclepius, historically symbolizing the practice of medi-
cine, is inspired by the ancient ritual whereby the Dracunculus worm is
extracted.
Humans become infected when they drink water that has been contam-
inated with copepods (tiny organisms in Class Crustacea, Chapter 31)
containing a juvenile form of the organism. Readers will remember that
copepods are a favored secondary host for cestodes (Class Platyhelminthes,
Chapter 26). After ingestion by humans, the copepods die, and larvae are
released, to penetrate the stomach wall. The male worms die, but the
females migrate to subcutaneous tissue and continue to grow into adulthood
(about one year later). The infectious cycle is perpetuated when the mature
female adult (approaching a meter in length), pokes through the skin and
releases its larvae, predestined for
ingestion by secondary hosts (i.e.,
copepods).
As with several of the described nematodes (i.e., Ascaris lubricoides,
Enterobius vermicularis, and the common filarial species) humans are the
exclusive primary host of Dracunculus medinensis. Public health measures
have drastically reduced the occurrences of dracunculiasis in Africa and in
Pakistan.
Nematoda
Secernentea
Oxyurida
Oxyuridae
*Enterobius
Enterobius vermicularis, known as the pinworm in the USA, causes entero-
biasis, sometimes called oxyuriasis.
Humans are the primary and exclusive host of the pinworm. Eggs are
ingested, and the larvae emerge in the duodenum. The larvae migrate in the
direction of peristalsis, as they mature into adults. The adults mate in the
ileum and settle in the distal ileum, the proximal colon, or the appendix,
where the females become bloated with eggs. Afterwards, the adult females
(now about 1 cm in length) migrate to the anal skin where they lay their
eggs. The eggs infect other humans or re-infect the original host, through
fecal
oral contamination or through dispersal in the air (e.g., when bed
linens are shaken).
The most common symptom of pinworm is anal itching. Cases have been
reported of appendicitis caused by gravid pinworms obstructing the lumen of
the appendix.
Readers should avoid confusion by the lay-terms for Enterobius infection.
In the United States, Enterobius vermicularis is known as pinworm; in the
UK,
it
is known as threadworm. Adding to the confusion,
in the USA,
