This document provides an overview of parasitology and summarizes key information about parasitic protozoans. It describes the life cycles of various protozoans including their modes of reproduction (e.g. fission, budding), hosts, and transmission. Representative parasitic protozoans are grouped by their structures and include flagellates like Giardia lamblia and Trichomonas vaginalis, amoeboid forms like Entamoeba histolytica, ciliates like Balantidium coli, and sporozoans like Plasmodium species which cause malaria. Details are provided on the life cycles and pathogenesis of several important protozoan parasites.

1. ParasitologyParasitology
BY DR S.HASAN ASKARI BDS RDS MS
LECTUERER AT Muhammad bin qasim medical and dental college

2. IntroductionIntroduction
Protozoans are unicellular, eukaryotic
Most protozoa have two stages
◦ Trophozoite – A mobile, feeding reproducing
form surrounded by flexible cell membrane
◦ Cysts Non mobile ,non metabolizing ,non
reproducing form surrounded by a thick wall.
◦ Cysts is a protective capsule.

3. ReproductionReproduction
Protozoa reproduce asexually by:
Fission (mitosis)
Budding
Schizogony a multiple fission – nucleus
undergoes multiple divisions before the cell
divides
Protozoa reproduce sexually by:
Conjugation
Gamete formation

4. Fission/budding/schizogony in Ciliate protozoaFission/budding/schizogony in Ciliate protozoa

5. ReproductionReproduction
Definitive Host harbors the sexually
reproducing stage of parasite
Intermediate Host harbors asexually
reproducing portion of the parasite’s life
cycle.

7. Representative Parasitic ProtozoansRepresentative Parasitic Protozoans
Flagellated
Have one or more whip like flagella.eg
intestinal and genitourinary .
Giardia lamblia – enteritis – fecal
contamination of drinking water.
Trichomonas vaginalis – urethritis vaginitis -
sexually transmited or contact with vaginal
urethral discharges
Trypanosoma and leishmania – blood tissue
flagellate.

9. Representative ParasiticRepresentative Parasitic
ProtozoansProtozoans
Certain protoza such as leishmania and
trypanosoma have flagella and nonflagella
.
Flagellated Trypanosoma and leishmania
– blood tissue flagellate are called
promastigotes or trypomastigotes.
Non flagellated form called amastigotes

11. T. cruzi – American trypanosomiasis Chagas
disease.
Vector = reduvid bug (kissing bug) because they
frequently bite humans around mouth (lips)
feeding on tissue fluids and defecating in the
wound. Parasites then migrate to cardiac
muscle, liver, and brain. Many animals serve as
reserviors for this parasite.

12. FIGURE 13-25 Trypanosoma brucei trypomastigotes in a blood smear (X1000).
The nucleus and undulating membrane (UM) are visible.
UM

13. Amoeboid FormsAmoeboid Forms
Entamoeba histolytica - mobility is by pseudopod (false
foot).
 Life cycle simple divided into two stages: trophozoite, and
the cyst .
The amoebic trophozoites remain actively motile, feeding
on red blood cells, as long as environmental conditions are
favorable. Dysentery and anemia. The cyst develops when
environmental temperature or moisture drops.
In diagnosis the cysts are the only forms recognized.
Trophozoites only in fresh stool specimens. Ulcers in
intestinal mucosa cause amoebic dysentary. May invade
peritoneal cavity invasion of liver. Inflammation,
hemorage, secondary bacterial infection. More than 5%
americans asymptomatic carriers. Montezumas’ revenge.
Drinking water and salads.

16. Naeglaria fowleri
 Meningoencephalitis.
Swimming in polluted water results in
asymptomatic colonization of nasal passages.
 Invade cribiform plate through olfactory
openings resulting in rapid fulminating fatal
meningoencephalitis. Spinal fluid contains
many erythrocytes and trophozoites.
Post mortum diagnosis of trophozoites in the
brain.

19. CiliatesCiliates
Complex protoza having row patches .
2 kind of nuclei in each individual.
Example:
Balantidium coli is the only member of the
ciliate group that is pathogenic for humans.
The organism is similar to amoebiasis
cause tissue invasion and intestinal ulceration.
Large trophozoite with large macronulcleus
Swine and monkeys important reservoirs.
Fecal oral route, swine feces contaminating
local water supplies.
 Food handlers substandard hygienic
conditions.

20. FIGURE 13-15 Balantidium coli trophozoite (X800). Trophozoites are oval in shape and have dimensions
of 50 to 100 µm long by 40 to 70 µm wide. Cilia (C) cover the cell surface. Internally, the macronucleus
is prominent; the adjacent micronucleus is not. An anterior cytostome (Cy) is usually visible.
Cy
C

21. Sporozoa:Sporozoa:
Complex life cycle.
Alternate sexual and asexual reproductive
phase .
Sporozoan parasites that require two hosts for
completion of their life cycle.
Examples
Plasmodium species The mosquito for the
sexual reproductive stages. And the human or
other animal (monkey) for the asexual stages.
Human infection is initiated by the bite of an
Anopheles mosquito which introduces the
sporozoites into the blood stream via the
mosquito saliva that acts as an anticoagulant.
They go to the liver where schizogamy occurs
for 18 -25 days.

22. PlasmodiumPlasmodium
The hepatocytes rupture releasing merozoites
bind to red blood cells initiating the erythrocyte cycle
of malaria (ring, trophozoite, and schizont stages).
 In the human (intermediate host) asexual reproduction
occurs and results in the rupture of the erythrocyte and
release of merozoites the infect more erythrocytes.

24. FIGURE 13-27 Plasmodium life cycle.

25. FIGURE 13-34 Plasmodium malariae schizont with 8 merozoites in a distinctive rosette arrangement (X1200).

27. ToxoplasmosisToxoplasmosis
 Toxoplasma gondii is an intracellular parasite
 found in a wide variety of animals including birds, mice, cats
and humans.
 The essential reservoir is the common house cat That has
eaten an infected rodent.
 The infective cysts are passed in cat feces where they can be
ingested by mice and/or humans.
 If infection occurs during the first trimester of pregnancy
spontaneous abortion, still birth or severe neurological
disease.
 Disease is usually mild to asymptomatic in immunologically
competent adults. Immunocomprimised patient AIDS result
with severe neurological disease.
 Demostration of the banna shaped trophozoites in spinal
fluid is one method of diagnosis. Newer monoclonal
antibody serological methods will also diagnose the presence
of the parasite.