Protozoa are unicellular eukaryotes that inhabit water and soil and feed on organic matter. They display various modes of motility including pseudopods, cilia, and flagella. Many protozoa have complex life cycles with trophozoite and cyst stages and require multiple hosts to complete their life cycles. Some pathogenic protozoa cause diseases in humans through fecal-oral or insect transmission, infecting the gut or blood and potentially spreading to other organs. Common diseases include malaria, African sleeping sickness, leishmaniasis, and amoebic dysentery.

1. Pathogenic eukaryotes: protozoa
Protozoa = unicellular eukaryotes
• Inhabit water and soil
• Members of kingdom protista
• Have nuclei and complex organelles
• Can’t be classified as fungi, animalia, or plantae

2. Protozoa: types of motility
Three main types of protozoa:
Amoeboid protozoa
• move by a gliding motion produced by
lobe-like pseudopods extending from
the cell
Ciliates
• Hair-like cilia whose vibrating motion
moves the ciliate through water
Flagellates
• one or more whip-like flagella that they
use to propel themselves through the
water

3. Protozoa: Nutrition
Chemoheterotrophic = need organic compounds (carbs,
fats, proteins) from environment
• instead of producing it themselves from sunlight or
inorganic compounds
• Some transport food across the plasma membrane
Pellicle = protective coating on some protozoa
• Requires special structures to take in food
Cytostome = mouth-like opening used
by ciliates; wave their cilia to move
food toward it

4. • Amoebas engulf food by
surrounding it with
pseudopods and
phagocytizing it
Protozoa: Nutrition
Pictured: Amoeba protozoan
feeding on a paramecium

5. Protozoa: Nutrition
Vacuoles = membrane-enclosed
compartments where digestion
takes place
• Waste is eliminated through
plasma membrane or an anal
pore
Pictured: paramecium (a ciliate
protozoa)
• Contain remnants of meal:
some euglenoid
(chlorophyll-containing)
protozoa

6. Two-stage life cycle:
Trophozite = feeding and growing stage; eats bacteria
and small particulate nutrients
Cyst = a protective capsule that permits the protozoa to
survive under unfavorable conditions
• Can live outside a host
• Must be excreted from a host to get into a new
host
Protozoa: life cycle

7. Beneficial Protozoa
• Nearly 20,000 protozoan species
• Very few causing human diseases
Ex) Nosema locustae
• Phylum Microspora
• Used as insecticide to kill grasshoppers,
crickets
• Will not affect humans or animals; only
pathogenic to certain insects

8. Phylum Archaezoa
• Many live as parasites in the digestive tract of animals
• Lack mitochondria
• Mitosome = remnant of an ancestral mitochondria
• Most have two or more flagella
Ex) Giardia lamblia
• Small intestine  Giardiasis
• Trophozite: eight flagella
• Excreted in feces as cysts
• Cysts ingested by new host
Giardia cyst

9. Ex) Trichomonas vaginalis
• Human parasite causing trichomoniasis
• Undulating membrane bordered by flagellum
• No cyst stage – must be transmitted from host to host
quickly before dessication occurs
Phylum Archaezoa
Transmission =
sexually transmitted
Symptoms =
inflammation,
burning, itching

10. Phylum Amoebozoa
Entamoeba histolytica
• Amoebic dysentery (amoebiasis)
• Only pathogenic amoeba in human intestine
• Transmission = ingestion of fecal cysts
• Lectins = proteins used to attach to plasma membranes
• Can cause lesions in intestinal wall  enter blood stream and
end up in liver  abscesses
• Move by extending pseudopods
• Food vacuoles = created when
pseudopods surround food, bring
it into the cell
E. Histolytica
trophozoite with
pseudopod

11. Phylum Apicomplexa
• Obligate intracellular parasites
• Have complexes at the apex (tip) of their cells
• contain enzymes to penetrate host tissues
• Motile structures (flagella, pseudopods) only present in
the gamete stages
• Complex life cycle
• Transmission between several hosts:
Definitive host = harbors the sexually reproducing
stage of the protozoa
Intermediate host = harbors the asexual
reproduction stage

12. Phylum Apicomplexa
Plasmodium: malaria
• Reproduce sexually in the Anopheles mosquito
Sporozoites = infective stage plasmodium transferred to
human through Anopheles bite
• Undergo schizogony in liver  merozoites
• Infect RBCs  rupture; release more merozoites
• asexual reproductive cycle continues
• Some develop into sexual forms
(gametocytes)
• Can be picked up by another
mosquito  infect new host

13. Phylum Apicomplexa
Malaria continued
Symptoms
• Fever, chills in 36-48 hour cycles caused by waste
released upon rupture of red blood cells
• Hemorraging caused by blockage of blood vessels
• Infected RBCs display adhesive proteins to avoid
destruction by spleen
Prevention
• Vaccine development is difficult due to complex life
cycle of Plasmodium
• Prevention of Anopheles bite
• Mefloquine, chloroquine, atovacuone/proguanil:
preventive when visiting malaria prone regions

14. Cryptosporidium parvum (Cyptosporidosis)
• Transmitted by ingestion of oocysts
• Animal feces, contaminated lakes & rivers
• Lives within cells of small intestine
Phylum Apicomplexa
Symptoms =
Cholera-like
diarrhea for 10-
14 days
Left: Crytpo SEM

15. Phylum Ciliophora
The ciliates: cilia are similar in structure to flagella
• Arranged in precise rows, move in unison
Ex) Balantidium coli
• Only ciliate human parasite
• Severe dysentery
Transmission = ingestion of fecal cysts
• cysts release trophozoites into large intestine  destroy
host cells by secreting proteases
• Feed on cell and tissue fragments
• Propel through environment
• Push food to the cytostome

16. Phylum Euglenozoa
Euglenoids = not parasitic; one of two Euglenozoa classes
• Photoautotrophs: use chloroplasts for photosynthesis
• Red anterior eyespot
• organelle containing pigmented carotenoids
• senses light to direct the cell towards it
• Anterior flagellum
• Facultative
chemoheterotrophs = ingest
organic matter through their
cytostome in the absence of
light

17. Phylum Euglenozoa
Hemoflagellates = blood parasites
• Transmitted by blood-feeding insect bites
• Long-slender shapes and undulating membranes
Trypanosoma: Trypanosomiasis
• aka African sleeping sickness
• Tsetse fly vector
• Parasite enters blood and
lymphatic system  transported to
other sites
• Eventually crosses blood-brain
barrier
Trypanosoma brucei SEM

18. Phylum Euglenozoa
Symptoms
• Fever, headaches, joint pain, lymph swelling
• Tryptophol = chemical produced by trypanosoma
that induces sleep
• Deterioration of CNS
Prevention = elimination of tsetse fly
• release of radiation-sterilized males
• vaccination difficult (antigenic variation)
Treatment = eflornithine; blocks enzyme
required for proliferation

19. Phylum Euglenozoa
Visceral (Leishmania donovani)
• invasion of internal organs like liver, spleen, kidneys
- Fatal without treatment
Cutaneous (Leishmania tropica)
• skin lesions
Mucocutaneous (Leishmania braziliensis)
• disfiguring destruction of nasal and oral mucosa
Leishmania: Leishmaniasis
• Tropical and mediterranean
climates
• Sandfly vector
Macrophage infected with
Leishmania donovani