Download The Protozoa

The Protozoa
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Classification
•  Protozoans
•  Eukaryotic (Domain Eukarya)
•  Unicellular exclusively
•  Chemoheterotrophic
•  Kingdom: Protista
•  Phylum: Archaezoa or Mastigophora (“flagellates”)
•  Phylum: Amoebozoa or Sarcodina (“amoebas”)
•  Phylum: Ciliophora (“ciliates”)
•  Phylum: Apicomplexa (“obligate parasites”)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
General terminology and life cycles
• Trophozoite - “the feeding and growing stage”; the
vegetative form
• Eats bacteria and free nutrients (like sugars)
• Reproduction - Asexual
• Schizogony - “multiple fission” - nucleus divides repeatedly,
allowing one cell to give rise to many daughter cells
• Binary Fission - one nuclear division gives rise to two daughter
cells (closest to mitosis)
• Budding - outgrowth of a mature cell grows and becomes a new
daughter cell
• Reproduction - Sexual
• Conjugation - cells that have undergone a reduction division fuse,
exchange haploid micronuclei, and separate - each gives rise to two
daughter cells
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
General terminology and life cycles
• Encystment - in certain circumstances, a protective
capsule forms called a cyst. This is a “dormant”
stage, but may be observed in/required for parasitic
infection. It can allow parasitic protozoa to survive
outside the host.
• Life Cycles
• Parasitic protozoa often have complex life cycles with
multiple hosts involved:
• The DEFINITIVE HOST harbors the SEXUALLY
REPRODUCING stage
• INTERMEDIATE HOSTS harbor the ASEXUALLY
REPRODUCING stage(s)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Kingdom Protista/Sub-kingdom Protozoa
•  Eukaryotic
•  Unicellular
•  Chemoheterotrophs
•  Vegetative form is a
trophozoite
•  Asexual reproduction
by fission, budding, or
schizogony
•  Sexual reproduction
by conjugation
•  Some produce cysts
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Phylum Archaezoa or Mastigophora (flagellates)
•  Move using multiple
flagella
•  Giardia lamblia
•  Trichomonas vaginalis
(no cyst stage)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Giardiasis
•  Transmitted by
contaminated water,
usually in rural areas
•  Inhabits small intestine
of various mammals
•  Causes severe
gastroenteritis, also
called “Beaver fever”
•  Diagnosed by
microscopic
examination of feces
for cysts
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Giardia lamblia
Trichomoniasis - a type of vaginitis
•  Found in semen or urine of
male carriers (no symptoms)
•  Usually sexually transmitted,
possible to acquire from public
facilities
•  May be carried and cause no
symptoms in women.
•  Vaginal infection causes
irritation and profuse
discharge
•  Diagnosis by microscopic
identification of protozoan
•  Since there is no cyst, cannot
survive outside of host
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Trichomonas vaginalis
Amoebozoa or Sarcodina (amoebas)
•  Move using
pseudopods
“false feet”
•  Entamoeba
(parasitic)
•  Amoeba
(generally nonparasitic)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Amoebic Dysentery
•  Entamoeba histolytica
•  Causes diarrhea containing blood and mucus
•  Amoeba feeds on RBCs and GI tract tissues
•  Diagnosis by observing cysts in feces
•  Transmitted through ingestion of cysts
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Amoebic Dysentery
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Ciliophora (ciliates)
•  Move by cilia, which
are shorter and more
numerous than flagella
•  Generally free-living
•  Balantidium coli is the
only human parasite,
which causes a severe
but rare dysentery
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Apicomplexa
•  Nonmotile
•  Intracellular parasites
•  Complex life cycles
•  Plasmodium - Malaria is the fourth leading cause of
death by infectious disease
•  Cryptosporidium - can cause respiratory and gall
bladder infections in immunosuppressed individuals,
and may be a major cause of death.
•  Cyclospora
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Plasmodium life cycle: example of a
complex protozoan parasite
•  Plasmodium grows by sexual reproduction in the
Anopheles mosquito; if the mosquito “bites” a human, the
infective particles, called sporozoites, enter the blood and
travel to the liver.
•  They multiply (by schizogeny) in the liver, and the new
cells are called merozoites; these enter the blood and
infect red blood cells (ring stage).
•  As they grow asexually, the red blood cells eventually
rupture, releasing more merozoites and toxins which
cause the fever and chills associated with the disease.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Plasmodium life cycle
•  Some sexual cells called gametocytes are also formed,
and can be picked up by another mosquito to repeat
the cycle.
•  The mosquito is called the DEFINITIVE HOST because
it harbors the sexual stage; humans are called the
INTERMEDIATE HOST, because asexual reproduction
occurs in us.
•  Fever and chills are caused by toxins associated with
the organisms, and occur cyclically.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Cryptosporidiosis
•  Cryptosporidium
parvum
•  Transmitted by oocysts
in contaminated water
•  Causes severe
diarrhea, as it resides
in the intestine
•  Treated with oral
rehydration
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Cyclospora Diarrheal Infection
•  Cyclospora cayetanensis
•  Transmitted by oocysts in contaminated water
•  Diagnosed by microscopic examination for oocysts
•  Mostly shows up in immunosuppressed individuals
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings