Protozoa means "first animal" and refers to simple eukaryotic organisms composed of a single cell (e.g. amoebae). Reproduction may be through simple cell division (e.g. the ameboflagellates) or sexual involving the fusion of gametes in part of the life cycle (e.g. the apicomplexa) as described below. Some protozoa can form a protective cyst stage capable of withstanding harsh environmental conditions.
Ameboflagellates
These use pseudopodia or flagella for locomotion.
Amoebae. These are characterized by a feeding and dividing trophozoite stage that can form a temporary resistant cyst stage.
Entamoeba histolytica is the cause of amoebic dysentery producing severe infection of the intestines that can spread to the liver. The organism is characterized by a trophozoite and cyst stage. E. histolytica is an example of a true parasite in that the organism cannot multiply outside of the host. Other amoebae occur naturally in soil and water environments which is their preferred habitat for feeding and replication. These amoebae are termed "free-living" as they have no natural host in which parasitism occurs. They can infect man opportunistically producing severe and often fatal disease. Such free-living amoebae are the Acanthameba, Naegleria fowleri and Balamuthia mandrillaris, all of which can infect the central nervous system. In addition, Acanthameba species can also invade the eye.
Flagellates
These organisms have flagella in the trophozoite stage. Trichomonas vaginalis is a common sexually transmitted organism causing trichomoniasis infection of the vagina and urethra. Giardia lamblia causes giardiasis producing symptoms of diarrhea and other intestinal disturbances. Infection arises from the ingestion of cysts, usually through contaminated water.
Trypanosoma brucei gambiense and T. brucei rhodesiense cause trypanosomiasis, more commonly known as African sleeping sickness. The disease is an arthropod (insect)-borne infections and is spread by the bite of the tsetse fly in which part of the trypanosome life cycle is completed. The eventual invasion of the central nervous system by the trypanosomes gives rise a comatosed state from which the common name for the disease is derived.
Trypanosoma cruzi causes Chagas' disease (American trypanosomiasis). The intermediate host in this case are triatomid bugs that feed off the blood of man. Infection results from the inoculation of the bug's feces that contains the organism into the bite wound. Individuals who survive the acute stage of the disease are frequently left with chronic and progressive neuronal and smooth muscle lesions in the heart and gastrointestinal tract. T. cruzi has an extensive reservoir in wild and domestic mammals and therefore Chagas' disease is a zoonosis.
Ameboflagellates
These use pseudopodia or flagella for locomotion.
Amoebae. These are characterized by a feeding and dividing trophozoite stage that can form a temporary resistant cyst stage.
Entamoeba histolytica is the cause of amoebic dysentery producing severe infection of the intestines that can spread to the liver. The organism is characterized by a trophozoite and cyst stage. E. histolytica is an example of a true parasite in that the organism cannot multiply outside of the host. Other amoebae occur naturally in soil and water environments which is their preferred habitat for feeding and replication. These amoebae are termed "free-living" as they have no natural host in which parasitism occurs. They can infect man opportunistically producing severe and often fatal disease. Such free-living amoebae are the Acanthameba, Naegleria fowleri and Balamuthia mandrillaris, all of which can infect the central nervous system. In addition, Acanthameba species can also invade the eye.
Flagellates
These organisms have flagella in the trophozoite stage. Trichomonas vaginalis is a common sexually transmitted organism causing trichomoniasis infection of the vagina and urethra. Giardia lamblia causes giardiasis producing symptoms of diarrhea and other intestinal disturbances. Infection arises from the ingestion of cysts, usually through contaminated water.
Trypanosoma brucei gambiense and T. brucei rhodesiense cause trypanosomiasis, more commonly known as African sleeping sickness. The disease is an arthropod (insect)-borne infections and is spread by the bite of the tsetse fly in which part of the trypanosome life cycle is completed. The eventual invasion of the central nervous system by the trypanosomes gives rise a comatosed state from which the common name for the disease is derived.
Trypanosoma cruzi causes Chagas' disease (American trypanosomiasis). The intermediate host in this case are triatomid bugs that feed off the blood of man. Infection results from the inoculation of the bug's feces that contains the organism into the bite wound. Individuals who survive the acute stage of the disease are frequently left with chronic and progressive neuronal and smooth muscle lesions in the heart and gastrointestinal tract. T. cruzi has an extensive reservoir in wild and domestic mammals and therefore Chagas' disease is a zoonosis.
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