Hymenolepis nana

Lots of photos for this one....probably too many, but didn't know what else to do with them!

Hymenolepis nana  (Cestode) –Parasite

Also known as the “dwarf tapeworm”

Geographic Distribution:

Hymenolepis nana is a cosmopolitan parasite as it has worldwide distribution.

Associated Disease:

Hymenolepiasis, or Dwarf Tapeworm Infection.   H.nana is often carried by the common house mouse.  While it is more frequently isolated from children, adults are also quite susceptible.  The location of the worm in the infected host is the small intestine.  Light infections may be asymptomatic however a large worm burden may cause abdominal pain, diarrhoea, headaches, dizziness and anorexia.

Life Cycle:

Infection usually occurs following the ingestion of H.nana eggs (ova) which make their way to the small intestine where they subsequently hatch.  The released sixed-hooked oncospheres, bury into the intestinal villi where, after a few days, they develop into cysticercoid larvae.  The cysticercoid larvae are quite small, containing a single scolex.  When mature, the larvae break out of the intestinal villi to enter the lumen of the small intestine.  From the ingestion of eggs to the emergence of mature worms may take between two to three weeks.

Eggs of H.nana may also develop into infective cysticercoids in various intermediate hosts, particularly grain beetles.  Accidental ingestion with contaminated grain products allows the larva to grow into adult worms in mice and most probably, in humans as well.

Autoinfection is also possible.  In this case, eggs passed by the adult tapeworm hatch within the intestine, develop through the cysticercoid stage and mature within the intestine as adult tapeworms.

Egg (Ova) Morphology:

H.nana eggs are spherical to sub-spherical in shape and have a thin hyaline (clear) shell.  They measure between 30 – 47 µm in diameter.  The six-hooklet oncosphere is surrounded by a membrane with two polar thickenings, from which arise four to eight filaments that extend into the space between the embryo and the outer shell.  The related Hymenolepis diminuta has no polar filaments and this is one feature that aids in their differentiation.

Hymenolepis nana egg (ova): a first look at the fairly low power of 250 times magnification.  Here an egg is seen amongst other fecal debris in a concentrated fecal specimen.  Care must be taken so as not to over look the parasite as there may be other structures that may mimic or obscure the egg in the concentrate.

(Fecal concentrate, 250X, DMD-108)

 Hymenolepis nana egg:  A closer view of the H.nana ova in a fecal concentrate.

(400X, Nikon)

 Hymenolepis nana egg:  Typical appearance of H.nana egg.

(400X, Nikon)

 Hymenolepis nana egg:  More detail revealed.

(400+10X, DMD-108)

H.nana eggs are spherical to sub-spherical in shape.  They may be described as 'broadly oval'.

Hymenolepis nana egg:  Another view - inset showing details.

(400X, Nikon)

Hymenolepis nana egg:  Four hooklets are visible in the lower left of the inner oncosphere surrounded by a membrane.

(400X, Nikon)

Hymenolepis nana egg: Another view with the magnified inset showing the position of one of two polar thickenings from which 4 to 8 polar filaments (PF) arise.

(400X, Nikon)

Hymenolepis nana egg:  Yet another view.

(500X, Nikon)

Hymenolepis nana egg:  Ditto

Hymenolepis nana egg:  Now were getting to higher magnifications. Eggs (Ova) measure between 30 – 47 µm in diameter.

(1000X, Nikon)

Hymenolepis nana egg: Learn to recognize the ova regarless of the orientation and the shape it may be in.  (500X, Nikon)

Hymenolepis nana egg:  Cell wall appears to be damaged on the left side of this photo.  Cell may not be viable,  (500X, Nikon)

Hymenolepis nana egg:  Oncosphere with a few of the six hooklets are visible in this photo.

(1000X, Nikon)

Hymenolepis nana egg:  The pointed structures within the oncosphere (upper part of the inner cellular structure) are the hooklets.  Thin, hyaline cellular wall is evident as well.

(1000X, Nikon)

Hymenolepis nana egg:  Ditto

(1000X, Nikon)

Hymenolepis nana egg:  At least four of the six hooklets are seen within the oncosphere which is surrounded by a membrane.  This is contained withing the cell surrounded by the hyaline cell wall.

(1000X, Nikon)

You should be able to recognize the Hymenolipis ova in a fecal concentrate after having viewed all the preceding photos.  While the characteristic structures are most clearly viewed in a freshly passed or concentrated fecal specimen, you should be able to recognize the egg in a stained smear as well.  A number of photos of  iron-hematoxylin stained permanent smears follow.

 Hymenolepis nana egg:  Here in the same field, one can see that the uptake of the stain and the appearance of the egg can differ significantly.

(500X, Nikon)

Hymenolepis nana egg:  At first glance, the egg may even resemble a large amoeba cyst such as Entamoeba coli.  Focusing through the cell will not reveal the 8 nuclei expected in E.coli.  The size difference also should eliminate the cyst.  (1000X, Nikon)

Hymenolepis nana egg: Ditto

(500X, Nikon)

Hymenolepis nana egg:  Oncosphere visible, surrounded by a clearing with the outer cell wall barely visible.

(1000X, Nikon)

 Hymenolepis nana egg: Oncosphere is visible but cell wall is not.

(1000X, Nikon)

Hymenolepis nana egg: Iron-Hematoxylin stained showing little detail in the oncosphere but cell wall is visible.  (1000X, DMD-108)

Hymenolepis nana egg:  Another variation of the egg's appearance in an Iron-hematoxylin stained smear.

(1000X, DMD-108)

Hymenolepis nana egg:  Dehydration process during staining has distorted the cell wall

(1000+10X, DMD-108)

Hymenolepis nana egg:  Egg with outer cell wall and inner ocosphere.  Shadows of several hooklets can be seen within,  (1000+10X, DMD-108)

Hymenolepis nana egg:  Last one.

(1000+10X, DMD-108)

Adult Worm Morphology:
 H.nana adult tapeworms are quite small, measuring 2.5 – 4.0 cm in length.  The tiny, knob-like scolex has four suckers and a rostellum bearing a ring of 20 - 30 hooklets.  Proglottids (segments) are wider than they are long.

Sorry, I have no worm to take a photo of, however they can be found elsewhere on the web.

Diagnosis:

Diagnosis is made by demonstrating the characteristic eggs in the fecal sample.  Unstained, concentrated specimens are preferable as the details are more evident.  Also, thin-shelled eggs may collapse on permanent stained smears, making them difficult to identify.  Specimens preserved in PVA (polyvinyl alcohol) do not exhibit morphological characteristic nearly as well as those preserved in formalin fixed specimens.  The adult worm or proglottid segments are rarely seen in the stool.

Confusion may occur with the related Hymenolepis diminuta, however H.dimunata eggs of the ‘Rat Tapeworm’ are much larger (70 – 85 by 60 - 80 µm in diameter) than those of H.nana.  They also do not possess the polar filaments as previously mentioned.

Return to Top (Most Recent Posts)

*  *  *

Ascaris lumbricoides

Ascaris lumbricoides (Intestinal Nematode)  “Roundworm”

Geographic Distribution:

Ascaris lumbricoides can be found throughout the world but is more commonly found in moist temperate and tropical regions.  Ascaris is increasingly prevalent where poor sanitation exists.  In cultures where human excrement (night soil) is used as fertilizer, infection may again be greater.

Pathogenicity:

Infection occurs with the ingestion of fully embryonated eggs (ova).  Infection with Ascaris lumbricoides is termed Ascariasis and it affects more of the world’s population than any other parasitic disease.   Ingestion of small numbers of eggs may be asymptomatic for the host however larger numbers may cause Ascaris pneumonitis[i] or Loeffler’s[ii] syndrome.  Those infected with Ascaris lumbricoides may develop asthmatic attacks, shortness of breath, wheezing or a persistent cough.  A heavy infection in the small intestine may result in a bowel obstruction, especially in children.  Symptoms may include fever and generalized malaise possibly with abdominal distension, associated tenderness and possible vomiting.

Life Cycle:

Ingested embryonated eggs travel to the duodenum (small intestine) where they hatch and begin an obligatory migration throughout the body before they return to the duodenum to mature into adulthood.  Hatched larvae start the migration by penetrating the duodenum wall to enter the blood or lymphatic system which eventually carries the larvae to the liver and the heart to eventually enter pulmonary circulation.  In the lungs, the larvae break free of the capillaries to enter the aveoli where they continue to grow.  After about 3 weeks, they begin to migrate through respiratory passages to reach the esophagus where they are swallowed and once again reach the small intestine.

At about two to three months post ingestion of the eggs, the now mature worms begin to lay their own eggs.  It has been estimated that mature female worms may produce an average of 200,000 eggs daily.  Ascaris lumbricoides females are oviparous[iii].  When passed, the eggs require about 2 to 3 weeks outside of the host to develop into the infective embryonated stage.  While the eggs are susceptible to excessive heat and drying, they can remain viable in moist soils for long periods of time.

Ascaris Worm:

The adult Ascaris lumbricoides worms area creamy-white in colour, occasionally with a pinkish cast.  Female worms range from 20 to 35 cm in length.  Males are generally shorter and usually do not exceed 30 cm.  Female worms are also generally thicker (3-6 mm) than the more slender males (2-4 mm).  Males can be distinguished from females by their incurved tail.  Females have a straight tail.  Adult worms are believed to live up to a year.  Ascaris worms do not attach themselves to the intestinal wall but rather maintain their position through constant movement.

 Ascaris lumbricoides: Adult male worm show with its distinctive curved tail.  This particular worm was about 24 cm or 10 in in length, (Nikon-Macroscopic)

Ascaris Eggs (Ova):

Diagnosis of ascariasis is by the demonstration of the characteristic eggs in the feces.

Fertile eggs are broadly oval in shape and typically yellow-brown in colour, stained by the bile in freshly passed stools.  They measure 45 to 75 µm in length by 35 to 50 µm in breadth.  The outer albuminoid coat is coarsely mammillated covers a smooth shell which is difficult to distinguish in laboratory preparations.  Some confusion in diagnosis may occur if the Ascaris egg has lost its mammillated coat (decorticated) as it may somewhat resemble Hookworm or Trichostrongylus species ova.   Ascaris eggs contain only one cell when passed in the feces.

Infertile eggs are elongate, about 85 – 95 µm by 43 – 47 µm in size.  Their mammillated layer may vary from being coarsely irregular to a relatively smooth layer, almost devoid of mammillations. The internal contents of infertile eggs appear as a mass of disorganized, refractile granules.

Note:  All the following photos are take from the re-suspended sediment after fecal concentration.

 Ascaris lumbricoides egg seen in the center of the photograph.

(Nikon, 250X)

  Ascaris lumbricoides egg  has a distinctive appearance.  This egg shows the rough looking surface due to the mammillated albuminoid coat.

(DMD-108, 400X)

 Ascaris lumbricoides: another photo of the egg with its rough mammillated coat.

(Nikon, 400X)

 Ascaris lumbricoides: a photo of the egg with an alternate focus inserted for comparison.  As the egg is three-dimensional, adjusting the focus can aid in visualizing the egg's structure.

(Nikon, 400X)

 Ascaris lumbricoides: as above.

(DMD-108, 400X)

 Ascaris lumbricoides: Two A.lumbricoides eggs seen in the same field.

(Nikon, 400X)

 Ascaris lumbricoides: Typical appearance of the Ascaris egg.  The presence of these eggs in a fecal specimen is diagnostic for an Ascaris infection.

(DMD-108, 400+10X)

 Ascaris lumbricoides: The thick albuminoid mammillated layer is quite evident on this fertile Ascaris egg.  (DMD-108, 400+10X)

 Ascaris lumbricoides: As above with a slightly altered focus.

(DMD-108, 400+10X)

  Ascaris lumbricoides:  Another photo of the Ascaris egg in a fecal concentrate.

(DMD-108, 400+10X)

 Ascaris lumbricoides: As above but with an alternate focus of this fertile Ascaris egg.  I post these alternate focus photos in an attempt to demonstrate the three-dimensional nature of the egg and their complexity.  (DMD-108, 400+10X)

 Ascaris lumbricoides:  Yet another example, 'cause more is better!.

(DMD-108, 400+10X)

 Ascaris lumbricoides: At a higher magnification.  The large single cell interior is clearly visible.

(Nikon, 1000X)

 Ascaris lumbricoides ova:  Okay, more is better, right?  Another photo showing the thick outer albuminoid mammillated layer.  The inner wall often cannot be visualized unless the egg loses this outer layer (decorticated).  The single celled contents are clearly visible.

(Nikon, 1000X)

 Ascaris lumbricoides:   Too many photos?  I have to do something with them!  Another photo of the Ascaris egg however it appears as if the interior cell has divided into four or more individual cells.

(Nikon, 1000X)

 Ascaris lumbricoides: An Ascaris egg with the inset enlargement of the Ascaris egg.  There appears to have been a number of divisions of the original cell contained within the egg.

(Nikon, 250X)

Too many photos?  Just a few more to go..

While the Ascaris lumbricoides ova can be found in iron-hematoxylin stained preparations, the eggs usually stain so intensely that they appear as silhouettes and very little structural information can be discerned.  They may be missed by an inexperienced eye.  A thinner part of the stained slide may offer the best chance of recognizing and finding these eggs.  The sedimentation concentration wet preparation technique is preferable in visualizing these eggs when present.

Note: The following photos are taken from Iron-Hematoxylin stained fecal preparations.

  Ascaris lumbricoides:Two Ascaris eggs are seen in this photo which appear as two large dark masses on either side of the picture.  The dark blob in the lower center is just an artifact present in the stool and clearly does not have the outline of the Ascaris egg.

(Nikon, 250X)

 Ascaris lumbricoides: As with the concentrates, if a good microscopic field is found in the stained preparation, the Ascaris egg exhibits different textures as one focuses through it.

(Nikon, 1000X)

 Ascaris lumbricoides: Same photo as above but with altered focusing.  The mammillated layer appears as a scalloped edge surrounding the single celled contents of the egg.

(Nikon, 1000X)

 Ascaris lumbricoides: In most iron-hematoxylin stained preparations the Ascaris ova will be heavily stained and often appear in silhouette with very little structure revealed.

(Nikon, 1000X)

 Ascaris lumbricoides: As above.  If a thin field can be found, the stained ova may show some detail.

(Nikon, 1000X)

 Ascaris lumbricoides: Okay, last one.  This egg doesn`t look particularly healthy.  The `scalloped`edge of the mammillated coat is somewhat visible along the upper edge.

(Nikon, 1000X)

Diagnostic Problems:

Both fertile and infertile Ascaris eggs concentrate well however well using sedimentation techniques, however, if the laboratory only uses a flotation method for concentrating, infertile eggs may be missed by this technique.

---

[i] Pneumonitis refers to an inflammation of the lungs which can be cause by a variety of agents, from allergic, chemical or an infection.  Ascaris pneumonitis is an inflammation caused by the presence of Ascaris lumbricoides migration through the lungs.

[ii] Löffler's syndrome or Loeffler's syndrome is a disease in which eosinophils accumulate in the lung in response to a parasitic infection.

[iii] Oviparous –egg development and maturation occurs outside of the female worm.

(Return to Top; Most Recent Posts)

*  *  *