- We will be looking at these slides:
- You need to know:
- how to identify the organism in a slide.
- what group the
organism belongs to (nematode, cestodes,
amoeboid protozoan, flagellate, etc).
superkingdom they belong to (most are eukaryotes).
- their common or scientific
name. (Most others require scientific name.)
- diagnostic criteria
of patients that have them.
- on most also know the mode of transmission.
Parasites belong to two kingdoms: protists and animals.
Although the parasitic protists are microbes, the parasitic animals
(worms) are not. Microbiologists still study them partially
because they are often diagnosed by their microscopic eggs.
These parasites often have complex life cycles that may involve two or
more species. The definitive host is the species where the
parasite can mature and reproduce sexually. The intermediate
host is a species where an immature (or juvenile) parasite can live
and reproduce asexually.
- Parasitic Protozoans
All of the parasitic protists are protozoans, a grouping of
animal-like protists. We will use a clinical approach to
classification because this is how diagnosis is often
determined. Parasitic protozoans usually have two or more life
stages. In protozoans that follow the fecal to oral route of
transmission, the trophozoite stage is the motile, reproductive form
of the parasite that may damage the host. When environmental
conditions become unfavorable, the trophozoite changes into the
immobile cyst stage. The cyst has a tough outer membrane that
allows the parasite to survive harsh environments, such as when the
parasite is outside of its host or in the acids of the stomach.
In the cyst stage, the parasite is in stasis (sort of like
spelling: Endamoeba) cyst and
trophozoite (slides none, Amoeboid protozoan)
causes severe and painful diarrhea, and amoebic dysentery (amebiasis).
Transmission is fecal to oral route. P.
Atlas p. 176. cyst1,
with ingested RBC's, trophozoite4
in human gut.
Entamoeba life cycle.
Balantidium coli: cyst & trophozoite life stages (slides A-1, Ciliate protozoan).
cause of balantidiasis (ulceration
of colon, bloody-mucoid stools,
diarrhea, constipation). Transmission is fecal to oral. P.
Atlas p. 179. cyst1,
in a wet mount
- Giardia lamblia: (or Giradia intestinalis) cyst and trophozoite
life stages (slide 10, Flagellate
causes diarrhea, dehydration, and abdominal
pain. Transmission is fecal to oral.
Atlas p. 180. cyst,
the flagella do not show up well if at all in a normal stain and a
- Trichomonas vaginalis: a trophozoite
life stage (slide a3, Flagellate
causes trichomoniasis, inflammation of the genitourinary mucosa. Symptoms
are more common in women than men. Transmission is through
Atlas p. 181. This parasite does not have a cyst
- Plasmodium vivax:
has a comples life cycle (a3-slide
is missing, Sporozoan
is one of four species that causes malaria.
Transmission is by the bite of the genus Anopheles (a-nawf'-a-lez). The life cycle of this parasite is much more complex than the two stages above.
This parasite is rather difficult to learn without slides, so just know
this information. Appearance
of Plasmodium in infected blood, how
heavy the parasite burden can be.
Atlas p. 183.
- Parasitic Helminthes
Helminthes are worms which is not a monophyletic group, it includes
three phyla: Annelids, Nematodes, and Platyhelminthes. Many are free-living organisms,
but we'll only study the parasitic helminthes. The life cycle of parasitic helminthes is often complex
involving two or more species. An immature parasite in an
intermediate species can encyst in a tissue and wait to be consumed by the definitive
or another intermediate host. This cyst is
very different from a protozoan cyst, but it has one similarity, it
can survive stomach acids. Once it passes the stomach, it
may develop into a mature parasite in the definitive species or
into another immature parasite in an intermediate species. Depending on the parasite, diagnosis is often made by checking
the patent's feces or anal region for characteristic eggs.
There are three types of parasitic helminthes in two phyla:
Platyhelminthes (flatworms) and Nematodes (roundworms). Parasitic
Platyhelminthes often lack or only have a partial digestive
system, absorbing food through their skin. They may also lack
other systems, such as a system for locomotion.
(flukes are parasitic flatworms, all flukes are parasites):
- Attaches to its host with suckers. Appearance is flat and
leaf-like and they contain only a partial digestive system.
(oriental liver fluke, slides a7)
causes liver disease (especially in the bile ducts).
P. Transmission is by consumption of undercooked or raw
Atlas p. 187. Oriental
(tapeworms are parasitic flatworms, all tapeworms are parasites)
- Attach to their host with a scolex that may have hooks or
suckers or both. Proglottids follow the scolex, each having
an ovary and a testis. When the proglotid matures, it is
full of eggs and may break off and be shed in the
cycle. All cestodes lack a digestive system
proglottid (beef tapeworm, slides
9a or a9).
Though we call this the beef tapeworm, cattle are
the intermediate host, humans are the definitive host.
Symptoms are usually mild stomach problems and weight loss.
Transmission is by consumption of a cyst in undercooked beef.
Note the absence of hooks.
Atlas p. 194. Beef
- Taenia solium (slides 9a)
Though we call this the pork tapeworm, swine are
the intermediate host, humans are usually the definitive host.
Symptoms are usually mild stomach problems and weight loss.
Yet, juvenile tapeworms sometimes migrate to other parts of the
body (when humans are an intermediate host), causing symptoms that
vary depending on the tissue infected, but they are usually mild.
Transmission is by consumption of a cyst in undercooked pork or by
consumption of eggs in contaminated food. Tapeworm1,
pisiformis (adult scolex,
slide 9a or a9)
Not in the Atlas
(has hooks and 4 suckers). This is the dog tapeworm.
adult, hydatid cysts and eggs (slides 6a)
Is the tapeworm of carnivores, humans can be an intermediate species.
P. Juvenile parasites migrate through human tissue
forming hydatid cysts which damages tissue, symptoms depend on
what tissue is damaged and its extent. Transmission is by
consumption of eggs usually in contaminated food or hands or by consumption
of a cyst in an undercooked intermediate species (such as sheep or
Atlas p. 192. Tapeworm,
cyst showing a scolex, life
- Parasitic Nematodes (parasitic round worms)
- Most nematodes are free-living, not parasitic, they are also the most abundant
- Parasitic Nematodes have separate male and female individuals and
they have a complete digestive system..
- Enterobius vermicularis,
female and adult male (pinworms
of humans, slides a7 or 7a)
causes mainly peri-anal itching
though other symptoms may occur. P.
Humans are the only host. Atlas p196. Transmission
is by (usually accidental) consumption of eggs. This is the
most common parasitic helminthes in the USA. Enterobious
infection on colon, ova.
Hyperlinks are to
give you additional pictures and pronunciation, do not spend a lot of time memorizing text on
these links. Also, some of the links require a fast internet connection. If there is a blue
P. by the parasite, it means that there
is an oral pronunciation of the parasite at my hyperlink (its the same web
page for all of them, so you have to find the parasite on the page and click
a link to hear it).