2. A parasite is an organism that obtains food and
shelter from another organism and derives all
benefits from this association. The parasite is
termed obligate when it can live only in a host;
it is classified as facultative when it can live
both in a host as well as in free form. Parasites
that live inside the body are termed
endoparasites whereas those that exist on the
body surface are called ecto-parasites.
Parasites that cause harm to the host are
pathogenic parasites while those that benefit
from the host without causing it any harm are
known as commensals.
3. The organism that harbors the parasite and suffers
a loss caused by the parasite is a host. The host
in which the parasite lives its adult and sexual
stage is the definitive host whereas the host in
which a parasite lives as the larval and asexual
stage is the intermediate host. Other hosts
that harbor the parasite and thus ensure
continuity of the parasite's life cycle and act as
additional sources of human infection are known
as reservoir hosts. An organism (usually an
insect) that is responsible for transmitting the
parasitic infection is known as the vector.
4. Taxonomic classification of
protozoa
Sub kingdom
Phylum
Sub-phylum
Genus-
examples
Species-
examples
Protozoa
Sarcomastig-
ophora
further divided into
Sarcodina-- -
move by pseudopodia
Entamoeba
E.
histolytica
Mastigophora
move by flagella
Giardia
G. lamblia
Apicomplexa
no organelle of
locomotion
Plasmodium
P.
falciparum,
P. vivax,
P.
malariae,
P. ovale
Ciliophora
move by cillia
Balantidium
B. coli
5. V. PROTOZOA
Unicellular, chemoheterotrophic, eukaryotic organisms of
kingdom Protista (3-2000 mm).
Protozoan means “first animal”.
20,000 species, only a few are pathogens.
Most are free-living organisms that inhabit water and soil.
Some live in association with other organisms as parasites
or symbionts.
Reproduce asexually by fission, budding, or schizogony.
Some exhibit sexual reproduction (e.g.: Paramecium).
Trophozoite: Vegetative stage which feeds upon bacteria
and particulate nutrients.
Cyst: Some protozoa produce a protective capsule under
adverse conditions (toxins, scarce water, food, or oxygen).
6. V. PROTOZOA (Continued)
Nutrition
Most are heterotrophic aerobes. Intestinal protozoa can
grow anaerobically.
Some ingest whole algae, yeast, bacteria, or smaller
protozoans. Others live on dead and decaying matter.
Parasitic protozoa break down and absorb nutrients from
their hosts.
Some transport food across the membrane.
Others have a protective covering (pellicle) and required
specialized structures to take in food.
– Ciliates take in food through a cytostome.
Digestion takes place in vacuoles.
Waste may be eliminated through plasma membrane or an
anal pore.
7. Protozoan classification
Four major groups of protozoa are
recognised and often given the status of
phylum* . Note, however, that in the
animal kingdom proper (Metazoa* ), phyla
are distinguished on their different body
plans and that no comparable body plans
are found in Protozoa.
8. Protozoan classification
• The groups are:
• flagellates (or Mastigophora)
• amoebae (or Sarcodina)
• sporozoans (or Sporozoa, Apicomplexa)
and
• ciliates (or Ciliophora).
12. Protozoa
.“eukaryote”..has genetic material encased
in a nuclear membrane (unlike bacteria
and viruses)
• ..classified traditionally by morphology
(eg. organelles of locomotion), life cycle
and mechanisms of reproduction etc.
13. • Mastigophora: movement with flagella -
e.g. Trichomonas, Giardia
• Sarcodina: pseudopodia, e.g. Entamoeba
histolytica
• Apicomplexa: apical complex, no
locomotor apparatus;
• sexual reproduction, e.g. cryptosporidium,
malaria, toxoplasma
• Ciliophora: movement with cilia, e.g.
Balantidium.
18. Biology
• Two morphological stages occur;
• Trophozoite - metabolically active
invasive stage, moves with pseudopodia,
ingests RBC, lives in colon and is found in
fresh diarrheal stool;
• divides by binary fission.
• Trophozoite 10-60 µm
• cogwheel distribution of nuclear chromatin
• Hematophagous
• unidirectional movement with pseudopodia
19. • Cyst - "vegetative" inactive form resistant
to unfavourable environmental conditions
outside human host;
• 4 nuclei
• This is the infective form resistant to
stomach acid if swallowed
• survives up to 30 days;
• excyst to trophozoite on passing through
stomach
• cyst 10-20 µm
• chromotoidal body
20. Adaptations
• Cyst: a dormant form characterized by a
hardened external covering in which
metabolic activity has ceased.
– Form in response to nutrient deficiency,
drought, and decreased oxygen
concentration, or pH or temperature changes.
– Emerge when conditions improve
21. Contractile vacuole
• An organelle that expels fluid from the
cell.
• Freshwater organisms are usually
hypertonic relative to their environment so
water continually diffuses into them.
• To maintain homeostasis, it must use
contractile vacuole to rid cell of excess
water.
23. Diagnosis
:
• - stool examination - for trophozoites and
cysts
- amoebic serology
- abscess aspirate
- Entamoeba dispar a non-pathogen is
indistinguishable by microscopy and is a
much more common intestinal protozoan
than Entamoeba histolytica. Antigen
capture and PCR tests can distinguish E.
dispar from E. histolytica in heavier
infections.
