the protozoa - semantic scholar

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

The Protozoa


•  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”)

Classification


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


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)


•  Eukaryotic •  Unicellular •  Chemoheterotrophs •  Vegetative form is a

trophozoite •  Asexual reproduction

by fission, budding, or schizogony

•  Sexual reproduction by conjugation

•  Some produce cysts

Kingdom Protista/Sub-kingdom Protozoa


•  Move using multiple flagella

•  Giardia lamblia •  Trichomonas vaginalis

(no cyst stage)

Phylum Archaezoa or Mastigophora (flagellates)


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

Giardia lamblia


•  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

Trichomoniasis - a type of vaginitis

Trichomonas vaginalis


•  Move using pseudopods “false feet”

•  Entamoeba (parasitic)

•  Amoeba (generally non-parasitic)

Amoebozoa or Sarcodina (amoebas)


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


Amoebic Dysentery


•  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

Ciliophora (ciliates)


•  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

Apicomplexa


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.


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.


Cryptosporidiosis

•  Cryptosporidium parvum

•  Transmitted by oocysts in contaminated water

•  Causes severe diarrhea, as it resides in the intestine

•  Treated with oral rehydration


•  Cyclospora cayetanensis •  Transmitted by oocysts in contaminated water •  Diagnosed by microscopic examination for oocysts •  Mostly shows up in immunosuppressed individuals

Cyclospora Diarrheal Infection

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