Excavates

Map of Africa Showing the Epidemiological Status of Countries Considered Endemic for Human African Trypanosomiasis

Trypanosoma forms in blood smear from patient with African trypanosomiasis

Life cycle of Trichomonas vaginalis, the cause of trichomoniasis in humansTrichomonas vaginalis resides in the female lower genital tract and the male urethra and prostate (1), where it replicates by binary fission (2). The parasite does not appear to have a cyst form, and does not survive well in the external environment. Trichomonas vaginalis is transmitted among humans, its only known host, primarily by sexual intercourse (3).From Centers for Disease Control Parasites and Health website

Life cycle of Chilomastix mesnili The resistant cyst stage in the life cycle of Chilomastix is responsible for transmission. Both cysts and trophozoites can be found in the feces (diagnostic stages) (1). Infection occurs by the ingestion of cysts in contaminated water or food or by the fecal-oral route (via hands or fomites, i.e., inanimate objects such as towels that transmit infectious organisms to a host) (2). In the large (and possibly small) intestine, excystation releases trophozoites.From Centers for Disease Control Parasites and Health website.

Life cycle of Enteromonas hominisBoth cysts (dormant stage) and trophozoites (active stage) of Enteromonas hominis are shed in feces. Infection occurs after the ingestion of cysts in fecal-contaminated food or water, or on fomites (inanimate objects or substances capable of transferring pathogens). In the large (and possibly small) intestine, excystation releases trophozoites. Enteromonas hominis resides in the large intestine, where it is regarded as a commensal (benefiting from its host but doing no harm) and is not known to cause disease.From Centers for Disease Control Parasites and Health website.

Life cycle of the flagellate Pentatrichomonas hominisPentatrichomonas hominis is a trichomonad flagellate with a worldwide distribution. Only trophozoites are shed in feces (1) as there is no known cyst stage for this species. Infection occurs after the ingestion of trophozoites in fecally-contaminated food or water or on fomites (i.e., other non-living objects or substances that can transmit them) (2). These organisms reside in the large intestine, where they are regarded as commensals (i.e., benefiting from but not harming their host) and are not known to cause disease in humans.From Centers for Disease Control Parasites and Health website

Life cycle of Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense, cause of African Sleeping SicknessDuring a blood meal on the mammalian host, an infected tsetse fly (genus Glossina) injects metacyclic trypomastigotes into skin tissue (trypomastigotes are the characteristic developmental stage that infects humans. The parasites enter the lymphatic system and pass into the bloodstream (1). Inside the host, they transform into bloodstream trypomastigotes (2), are carried to other sites throughout the body, reach other blood fluids (e.g., lymph, spinal fluid), and continue to replicate by binary fission (3). The entire life cycle of this parasite is represented by extracellular stages. The tsetse fly becomes infected with bloodstream trypomastigotes when taking a blood meal on an infected mammalian host (4,5). In the fly’s midgut, the parasites transform into procyclic trypomastigotes, multiply by binary fission (6), leave the midgut, and transform into epimastigotes (7). The epimastigotes reach the fly’s salivary glands and continue multiplication by binary fission (8). The cycle in the fly takes approximately 3 weeks. Humans are the main reservoir for Trypanosoma brucei gambiense, but this species can also be found in animals. Wild game animals are the main reservoir of T. b. rhodesiense. The subspecies Trypanosoma brucei brucei infects domestic and wild animals but usually not humans (but see the phylogeographic analysis by Balmer et al. 2011, which concludes that the three "subspecies"of T. brucei are not actually genetically or historically distinct lineages).From Centers for Disease Control Parasites and Health website.

Life cycle of Leishmania protozoans, the cause of leishmaniasis in humansProtozoans in the family Leishmania are well known as the cause of leishmaniasis in humans. Leishmaniasis is transmitted by the bite of infected female phlebotomine sandflies (Psychodidae:Phlebotominae). The sandflies inject the infective stage (i.e., promastigotes) from their proboscis during blood meals (1). Promastigotes that reach the puncture wound are phagocytized by macrophages (2) and other types of mononuclear phagocytic cells. Progmastigotes transform in these cells into the tissue stage of the parasite (i.e., amastigotes) (3), which multiply by simple division and proceed to infect other mononuclear phagocytic cells (4). Parasite, host, and other factors affect whether the infection becomes symptomatic and whether cutaneous or visceral leishmaniasis results. Sandflies become infected by ingesting infected cells during blood meals (5,6). In sandflies, amastigotes transform into promastigotes, develop in the gut (7) (in the hindgut for leishmanial organisms in the Viannia subgenus; in the midgut for organisms in the Leishmania subgenus), and migrate to the proboscis (8).From Centers for Disease Control Parasites and Health website.

This scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. In this particular image, a protective biofilm had been inhabited by numbers of what appeared to be unidentified bacterial microorganisms.Created: 2009

This scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. Visible in this particular image were a number of different microorganisms including elongated diatoms, and an amorphic gelatinous biofilm mass, which had enveloped amoeboid and bacterial organisms. For a colorized version of this image, see PHIL 11712.Created: 2009

This scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. Clearly visible in the center of this image, was a exquisitely-formed unidentified round vescicle-shaped microorganism, which may have been algal, or diatomic. Shaped like an ancient Grecian urn, the almost perfectly rounded smooth, flawless surface was made even more beautiful given its delicate structure. For a colorized version of this image, see PHIL 11709.Created: 2009

This scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. Clearly visible in the center of this image, was a exquisitely-formed unidentified round vescicle-shaped microorganism, which may have been algal, or diatomic. Shaped like an ancient Grecian urn, the almost perfectly rounded smooth, flawless surface was made even more beautiful given its delicate structure. For a colorized version of this image, see PHIL 11708.Created: 2009

Magnified 1200X, this scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. In this particular image, an unidentified amorphous strand of mucoidal biofilm was featured, which appeared to have enmeshed numbers of amoeboid organisms.Created: 2009

This scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. Occupying most of the field of view, an unidentified amorphous mucoidal biofilm was featured, which appeared to have enmeshed numbers of amoeboid organisms, while on the left was a strangely-beautiful microorganism displaying an outer surface studded with numerous projections, making it appear like a microscopic sea urchin. See PHIL 11715 for a colorized version of this image.Created: 2009

This scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. In this particular image, an unidentified amorphous mucoidal biofilm was featured, which appeared to have enmeshed numbers of amoeboid organisms.Created: 2009

This scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. In this particular image, unidentified species of diatoms are seen to be caught up in an amorphous gelatinous biofilm, which had entrapped stream particulates as well.Created: 2009

This scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. In this particular image, unidentified species of diatoms are seen to be caught up in an amorphous gelatinous biofilm, which had entrapped stream particulates as well. In the center, you’ll note what may have been an amoeboid organism.Created: 2009

This scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. In this particular image, unidentified sheets of algae were wrapped in a mass of what appeared to be a mucoid amorphous biofilm. See PHIL 11713 for a colorized version of this image.Created: 2009

This scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. In this particular image, a number of unidentified oblong elliptical-shaped diatoms were featured, along side amorphically-shaped masses of organically-composed biofilm.Created: 2009

At a magnification of 2000X, this scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream, which is mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. In this particular image, an expanding amorphous organic biofilm was featured within which numbers of amoeboid protozoa seemed to be embedded. For a colorized version of this image see PHIL 11714.Created: 2009

This scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. In this particular image, a number of unidentified oblong elliptical-shaped diatoms were featured.Created: 2009

At a magnification of 2000X, this scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream, which is mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae.Created: 2009

This scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream, which is mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. For a digitally-colorized version of this image see PHIL 11695.Created: 2009

Under a moderate magnification of 2000X, this digitally-colorized scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. In this particular view, a single copepod-like microorganism was seen occupying the field of view. Also, if you look closely towards the upper right corner, you’ll also notice the small grouping of bacteria, which had become enmeshed in a patch of biofilm.Created: 2009