|
|
An
ovum of Hymenolepis diminuta |
 |
|
H. diminuta-
Round or slightly oval, size 70-86 um x 60-80 um, with striated
outer membrane and a thin inner membrane. The space between the
membranes is smooth or faintly granular. The oncosphere has six hooks.
Distinguished mainly by being typically larger, lacks polar
filaments and has a yellow transparent cover. |
|
H. nana-
Eggs are oval or subspehrical and smaller, ranging 40-60 um x 30-50
um. On the inner membrane are two poles, from which 4 to 8 polar
filaments spread out between the two membranes. The oncosphere has six
hooks. Notice in picture the extra detail of the two polar thickenings
on the membrane of the oncosphere with filaments extending into the
space around the hexacanth embryo. |
|
H. nana
adults reside in the ileal
portion of the small intestine. From them, proglottids are produced,
which release eggs that are immediately infective. Passed in the stool,
these eggs cannot survive for more that 10 days outside the host.
After ingestion of eggs in contaminated food, water, or anything
contaminated by feces, the oncosphere is released from within the egg
This hatches in the small
intestine, and the hexacanth burrows into the tissues of the small
intestine and a cystercoid forms. When it matures upon rupture of the
villus, the cysticercoid returns to the intestinal lumen. Here, it
envaginates its scolex, which attaches to the intestinal mucosa to
develop into an adult. An alternate mode of infection consists of
internal autoinfection, where the eggs release their oncospheres
directly into the intestine without passage through tthe external
environment. The life span of an adult worm is 4-6 weeks, but internal
autoinfection allows it to perist for years with hight host population
density. In addition, when eggs are ingested by insects, they develop
into cystercoids, which can infect humans or rodents upon ingestion |
|
Humans and other animals
become infected when they intentionally or unintentionally eat
material contaminated by insects. H. nana is the only cestode
that parasitizes humans without requiring an intermediate host. It is
possible for the worm's entire life cycle to be completed in the bowel,
so infection can persist for years. H diminuta is a cestode of
rodents infrequently seen in humans. |
|
|
 |
Hymenolepiasis is caused by two cestodes
(tapeworm) species,
Hymenolepis nana (the
dwarf tapeworm, adults measuring 15 to 40 mm in length) and
Hymenolepis dimnuta
(rat tapeworm, adults measuring 20 to 60 cm in length).
Hymenolepis diminuta is a cestode of rodents infrequently seen in
humans and frequently found in rodents. |
Geographic Distribution:
Hymenolepis nana
is the most
common cause of all cestode infections, and is encountered worldwide. In
temperate areas its incidence is higher in children and institutionalized
groups.
Hymenolepis diminuta,
while less
frequent, has been reported from various areas of the world.
H. diminuta - The Rat Tapeworm
This tapeworm is much longer
than H. nana, growing up to 60cm or more in length. This is
primarily a parasite of the rat, humans only being infected by
accidental ingestion of the insect intermediate host (see
lifecycles
below). This species is of more importance as a research model for the
study of the biochemistry, physiology, chemotherapy and immunology of
tapeworm infections.
Hymenolepis
diminuta:
eggs of H.nana must be distinguished
from eggs of H.diminuta.
Eggs of H.diminuta are larger (70-85 by 60-80 µm) and lack the
polar filaments.
Typical egg, measuring between 70 by 80 µm; spherical form and
yellow-transparent cover.
The internal membrane (that surrounds the oncosphere)
has polar salients without filaments and six hooks on its interior.
 |
 |
 |
|
An ovum of Hymenolepis nana |
Hymenolepis nana egg. |
Hymenolepis nana egg. |
 |
 |
 |
|
Hymenolepis nana:
typical egg, measuring between 30 and 47 µm in diameter,
containing an oncosphere with an internal cover with polar thickenings
and 6 hooks. |
HYMENOLEPIS NANA |
H. nana-
Eggs are oval or subspehrical and smaller, ranging 40-60 um x 30-50 um.
On the inner membrane are two poles, from which 4 to 8 polar filaments
spread out between the two membranes. The oncosphere has six hooks.
Notice in picture the extra detail of the two polar thickenings on the
membrane of the oncosphere with filaments extending into the space
around the hexacanth embryo. |
H. nana - The Dwarf Tapeworm
This tapeworm is relatively
small, growing up to 4cm in length, the size of the parasite being
inversely proportional to the number of worms present in the infection.
Infections, which are more commonly seen in children in warmer climates,
are characterised by the presence of numerous parasites (both
cysticercoid larvae and adults) in the small intestine. Infection is by
ingestion of soil contaminated with faeces containing eggs (see
lifecycles
below), and may give rise to abdominal discomfort.
Egg of
Hymenolepis nana.
These eggs are oval or subspherical and smaller than those of H.
diminuta, their size being 40 to 60 µm X 30 to 50 µm. On the inner
membrane are two poles, from which 4 to 8 polar filaments spread out
between the two membranes. The oncosphere has six hooks (seen as dark
lines at 8 o'clock). Image contributed by Georgia Department of Public
Health
SOURCE
|
Português
USA
