PROTOZOAPROTOZOA

Chapter 12Chapter 12

IntroductionIntroduction

►Protozoans are unicellular, eukaryotic Protozoans are unicellular, eukaryotic chemoheterotrophic organisms. chemoheterotrophic organisms.

►Most protozoa have two stagesMost protozoa have two stages Trophozoite – the feeding and growing Trophozoite – the feeding and growing

stagestage Some protozoa will produce a protective Some protozoa will produce a protective

capsule called a cyst. A cyst allows the capsule called a cyst. A cyst allows the parasite to exist outside of the host and be parasite to exist outside of the host and be the infective stage allowing the parasite to the infective stage allowing the parasite to get to another host.get to another host.

ReproductionReproduction

Protozoa reproduce asexually by:Protozoa reproduce asexually by:Fission (mitosis)Fission (mitosis)BuddingBuddingSchizogony a multiple fission – nucleus Schizogony a multiple fission – nucleus

undergoes multiple divisions before the undergoes multiple divisions before the cell dividescell divides

Protozoa reproduce sexually by:Protozoa reproduce sexually by: ConjugationConjugation Gamete formationGamete formation

Fission of a CiliateFission of a Ciliate

FIGURE 13-3FIGURE 13-3    ParameciumParamecium undergoing transverse fission (X264). undergoing transverse fission (X264).

ReproductionReproduction

►Definitive HostDefinitive Host harbors the sexually harbors the sexually reproducing stage of parasitereproducing stage of parasite

►Intermediate HostIntermediate Host harbors asexually harbors asexually reproducing portion of the parasite’s reproducing portion of the parasite’s life cycle.life cycle.

Representative Parasitic Representative Parasitic ProtozoansProtozoans

►Flagellated FormsFlagellated FormsGiardia lambliaGiardia lamblia – enteritis – fecal – enteritis – fecal

contamination of drinking water. contamination of drinking water. Common in campers and hikers. Common in campers and hikers. Resistant to 1-2ppm ClResistant to 1-2ppm Cl2 2 use chemicals use chemicals plus filtrationplus filtration

Trichomonas vaginalisTrichomonas vaginalis – urethritis – urethritis vaginitis - sexually transmited or vaginitis - sexually transmited or contact with vaginal urethral contact with vaginal urethral dischargesdischarges

►Trypanosoma species do include Trypanosoma species do include nonflagellated forms in lifecycle. nonflagellated forms in lifecycle. Hemoflagellates cause two distinctly Hemoflagellates cause two distinctly different forms of disease:different forms of disease:T. gambiense African sleeping sickness T. gambiense African sleeping sickness

vector = Tsetse fly. Some animal vector = Tsetse fly. Some animal reservoirs suspected specifically hoofed reservoirs suspected specifically hoofed game animals. Enter wound created by game animals. Enter wound created by fly bite enter blood and lymph, eventually fly bite enter blood and lymph, eventually invading central nervous system. Control invading central nervous system. Control breeding sites of Tsetse, insecticides, breeding sites of Tsetse, insecticides, screens or netting, insect repellant. screens or netting, insect repellant. Insecticides have not been successful Insecticides have not been successful Female Tsetse flies mate once. Maybe Female Tsetse flies mate once. Maybe irradiation of male flies to induce sterility.irradiation of male flies to induce sterility.

►T. cruzi – American trypanosomiasis T. cruzi – American trypanosomiasis Chagas disease. Vector = reduvid bug Chagas disease. Vector = reduvid bug (kissing bug) because they frequently (kissing bug) because they frequently bite humans around mouth (lips) bite humans around mouth (lips) feeding on tissue fluids and defecating feeding on tissue fluids and defecating in the wound. Parasites then migrate in the wound. Parasites then migrate to cardiac muscle, liver, and brain. to cardiac muscle, liver, and brain. Many animals serve as reserviors for Many animals serve as reserviors for this parasite. this parasite.

FIGURE 13-25FIGURE 13-25    Trypanosoma brucei Trypanosoma brucei trypomastigotes in a blood smear (X1000). trypomastigotes in a blood smear (X1000). The nucleus and undulating membrane (UM) are visible.The nucleus and undulating membrane (UM) are visible.

UM

Leopard changing their spotsAntigenic shift No good vaccine

Amoeboid FormsAmoeboid Forms► Entamoeba histolytica - mobility is by Entamoeba histolytica - mobility is by

pseudopod (false foot). Life cycle simple divided pseudopod (false foot). Life cycle simple divided into two stages: trophozoite active feeding into two stages: trophozoite active feeding stage, and the cyst the quiescent resistant stage, and the cyst the quiescent resistant infective stage. The amoebic trophozoites infective stage. The amoebic trophozoites remain actively motile, feeding on red blood remain actively motile, feeding on red blood cells, as long as environmental conditions are cells, as long as environmental conditions are favorable. Dysentery and anemia. The cyst favorable. Dysentery and anemia. The cyst develops when environmental temperature or develops when environmental temperature or moisture drops. In diagnosis the cysts are the moisture drops. In diagnosis the cysts are the only forms recognized. Trophozoites only in only forms recognized. Trophozoites only in fresh stool specimens. Ulcers in intestinal fresh stool specimens. Ulcers in intestinal mucosa cause amoebic dysentary. May invade mucosa cause amoebic dysentary. May invade peritoneal cavity invasion of liver. peritoneal cavity invasion of liver. Inflammation, hemorage, secondary bacterial Inflammation, hemorage, secondary bacterial infection. More than 5% americans infection. More than 5% americans asymptomatic carriers. Montezumas’ revenge. asymptomatic carriers. Montezumas’ revenge. Drinking water and salads.Drinking water and salads.

FIGURE 13-6FIGURE 13-6    Entamoeba histolytica Entamoeba histolytica trophozoite (X800, iron hematoxylin stain). trophozoite (X800, iron hematoxylin stain). Trophozoites range in size from 12 to 60 µm. Notice the small, central karyosome, the beaded chromatin Trophozoites range in size from 12 to 60 µm. Notice the small, central karyosome, the beaded chromatin

at the nucleus’ margin, the ingested red blood cells and the finely granular cytoplasm. at the nucleus’ margin, the ingested red blood cells and the finely granular cytoplasm. Compare with an Compare with an Entamoeba coli Entamoeba coli trophozoite in Figure 13-8.trophozoite in Figure 13-8.

FIGURE 13-7FIGURE 13-7    Entamoeba histolyticaEntamoeba histolytica cysts. cysts. (a)(a) Cysts are spherical with diameter of 10 to 20 µm. Cysts are spherical with diameter of 10 to 20 µm. Two of the four nuclei are visible; other nuclear characteristics are as in the trophozoite. Two of the four nuclei are visible; other nuclear characteristics are as in the trophozoite.

Compare with an Compare with an Entamoeba coliEntamoeba coli cyst in Figure 13-9 (X1320, iron hematoxylin stain). cyst in Figure 13-9 (X1320, iron hematoxylin stain). (b)(b) E. histolyticaE. histolytica cyst (X1200, trichrome cyst (X1200, trichrome stain) with cytoplasmic chromatoidal bars (CB). These are found in approximately stain) with cytoplasmic chromatoidal bars (CB). These are found in approximately

10% of the cysts, have blunt ends and are composed of ribonucleoprotein.10% of the cysts, have blunt ends and are composed of ribonucleoprotein.

a b

CB

►Naeglaria fowleri – Meningoencephalitis. Naeglaria fowleri – Meningoencephalitis. Swimming in polluted water results in Swimming in polluted water results in asymptomatic colonization of nasal asymptomatic colonization of nasal passages. Invade cribiform plate through passages. Invade cribiform plate through olfactory openings resulting in rapid olfactory openings resulting in rapid fulminating fatal meningoencephalitis. fulminating fatal meningoencephalitis. Spinal fluid contains many erythrocytes Spinal fluid contains many erythrocytes and trophozoites. Post mortum diagnosis and trophozoites. Post mortum diagnosis of trophozoites in the brain. of trophozoites in the brain.

FIGURE 13-14FIGURE 13-14    Naegleria fowleri Naegleria fowleri trophozoite from culture (X1000, iron hematoxylin stain). trophozoite from culture (X1000, iron hematoxylin stain). Trophozoites are between 10 and 35 µm in size. Notice the large karyosome within the nucleus Trophozoites are between 10 and 35 µm in size. Notice the large karyosome within the nucleus

and the lobed pseudopods. Vacuoles (V) are also visible in the cytoplasm.and the lobed pseudopods. Vacuoles (V) are also visible in the cytoplasm.

V

CiliatesCiliates►Balantidium coli is the only member of Balantidium coli is the only member of

the ciliate group that is pathogenic for the ciliate group that is pathogenic for humans. The organism is similar to humans. The organism is similar to amoebiasis in that the organisms cause amoebiasis in that the organisms cause tissue invasion and intestinal tissue invasion and intestinal ulceration. Large trophozoite with large ulceration. Large trophozoite with large macronulcleus Swine and monkeys macronulcleus Swine and monkeys important reservoirs. Fecal oral route, important reservoirs. Fecal oral route, swine feces contaminating local water swine feces contaminating local water supplies. Food handlers substandard supplies. Food handlers substandard hygienic conditions. Extraintestinal hygienic conditions. Extraintestinal invasion of other organis is extremely invasion of other organis is extremely rare in balantidiasisrare in balantidiasis

FIGURE 13-15FIGURE 13-15    Balantidium coli Balantidium coli trophozoite (X800). Trophozoites are oval in shape and have dimensions trophozoite (X800). Trophozoites are oval in shape and have dimensions of 50 to 100 µm long by 40 to 70 µm wide. Cilia (C) cover the cell surface. Internally, the macronucleus of 50 to 100 µm long by 40 to 70 µm wide. Cilia (C) cover the cell surface. Internally, the macronucleus

is prominent; the adjacent micronucleus is not. An anterior cytostome (Cy) is usually visible.is prominent; the adjacent micronucleus is not. An anterior cytostome (Cy) is usually visible.

Cy

C

FIGURE 13-16FIGURE 13-16    Balantidium coliBalantidium coli cyst (X1000). Cysts are usually spherical and have cyst (X1000). Cysts are usually spherical and have a diameter in the range of 50 to 75 µm. There is a cyst wall and the cilia are absent. a diameter in the range of 50 to 75 µm. There is a cyst wall and the cilia are absent.

As in the trophozoite, the macronucleus is prominent, but the micronucleus may not be.As in the trophozoite, the macronucleus is prominent, but the micronucleus may not be.

Plasmodium speciesPlasmodium species►Sporozoan parasites that require two Sporozoan parasites that require two

hosts for completion of their life cycle. hosts for completion of their life cycle. The mosquito for the sexual reproductive The mosquito for the sexual reproductive stages. And the human or other animal stages. And the human or other animal (monkey) for the asexual stages.(monkey) for the asexual stages.

►Human infection is initiated by the bite of Human infection is initiated by the bite of an an AnophelesAnopheles mosquito which introduces mosquito which introduces the sporozoites into the blood stream via the sporozoites into the blood stream via the mosquito saliva that acts as an the mosquito saliva that acts as an anticoagulant. They go to the liver where anticoagulant. They go to the liver where schizogamy occurs for 18 -25 days. schizogamy occurs for 18 -25 days.

Plasmodium continuedPlasmodium continued► The hepatocytes rupture releasing merozoites The hepatocytes rupture releasing merozoites

that bind to red blood cells initiating the that bind to red blood cells initiating the erythrocyte cycle of malaria (ring, trophozoite, erythrocyte cycle of malaria (ring, trophozoite, and schizont stages). In the human and schizont stages). In the human (intermediate host) asexual reproduction (intermediate host) asexual reproduction occurs and results in the rupture of the occurs and results in the rupture of the erythrocyte and release of merozoites the erythrocyte and release of merozoites the infect more erythrocytes. Some merozoites infect more erythrocytes. Some merozoites also develop into male and female also develop into male and female gametocytes. If a female mosquito ingests gametocytes. If a female mosquito ingests the gametocytes, the sexual reproduction of the gametocytes, the sexual reproduction of malaria can be initiated with the eventual malaria can be initiated with the eventual production of sporozoites in the gut of the production of sporozoites in the gut of the mosquitoand the sporozoites migrate to the mosquitoand the sporozoites migrate to the salivary glands of the mosquito to be injected salivary glands of the mosquito to be injected into the indefinate host. into the indefinate host.

One disease selects for One disease selects for anotheranother

In Africa there has been a population of In Africa there has been a population of individuals that have a genetic individuals that have a genetic hemaglobinopathy Sickle cell anemia. This hemaglobinopathy Sickle cell anemia. This disease is controlled by two codominant genes disease is controlled by two codominant genes H = normal hemoglobin and h= abnormal H = normal hemoglobin and h= abnormal hemoglobin or sickle anemia. A person that hemoglobin or sickle anemia. A person that carries the h gene has fragile erythrocytes that carries the h gene has fragile erythrocytes that will not support the will not support the PlasmodiumPlasmodium parasite. parasite. Therefore, only HH children will succumb to Therefore, only HH children will succumb to malaria and the rest of the population will carry malaria and the rest of the population will carry the sickle cell gene.the sickle cell gene.

FIGURE 13-20FIGURE 13-20    Giardia lambliaGiardia lamblia trophozoite (X1320, iron hematoxylin stain). Trophozoites have a long, trophozoite (X1320, iron hematoxylin stain). Trophozoites have a long, tapering posterior end and range in size from 9 to 21 µm by 5 to 15 µm. There are two nuclei with small karyosomes. tapering posterior end and range in size from 9 to 21 µm by 5 to 15 µm. There are two nuclei with small karyosomes.

The two median bodies and the four pairs of flagella are not visible in this specimen.The two median bodies and the four pairs of flagella are not visible in this specimen.

FIGURE 13-21FIGURE 13-21    Giardia lambliaGiardia lamblia cyst (X1000, trichrome stain). cyst (X1000, trichrome stain). GiardiaGiardia cysts are smaller than trophozoites (8 to 12 µm by 7 to 10 µm), cysts are smaller than trophozoites (8 to 12 µm by 7 to 10 µm),

but the four nuclei with eccentric karyosomes and the median bodies (M) are still visible.but the four nuclei with eccentric karyosomes and the median bodies (M) are still visible.

M

FIGURE 13-27FIGURE 13-27    PlasmodiumPlasmodium life cycle. life cycle.

FIGURE 13-28FIGURE 13-28    Plasmodium falciparumPlasmodium falciparum ring stage in a red blood cell (X2640). ring stage in a red blood cell (X2640). The ring is the trophozoite. Note the chromatin dots in the nucleus.The ring is the trophozoite. Note the chromatin dots in the nucleus.

FIGURE 13-30FIGURE 13-30  Erythrocyte infected with   Erythrocyte infected with Plasmodium vivaxPlasmodium vivax (X1000). The parasite is in the ring stage, (X1000). The parasite is in the ring stage, and the red cell exhibits characteristic Schüffner’s dots in the cytoplasm. and the red cell exhibits characteristic Schüffner’s dots in the cytoplasm.

Schüffner’s dots are also seen in red cells infected with Schüffner’s dots are also seen in red cells infected with P. ovale.P. ovale.

FIGURE 13-32FIGURE 13-32    Plasmodium falciparumPlasmodium falciparum developing schizont in a red blood cell (X2640). developing schizont in a red blood cell (X2640). These are usually not seen in peripheral blood smears since they reside in visceral capillaries.These are usually not seen in peripheral blood smears since they reside in visceral capillaries.

FIGURE 13-34 FIGURE 13-34   Plasmodium malariaePlasmodium malariae schizont with 8 merozoites in a distinctive rosette arrangement (X1200). schizont with 8 merozoites in a distinctive rosette arrangement (X1200).

FIGURE 13-33FIGURE 13-33  A mature   A mature Plasmodium vivax Plasmodium vivax schizont composed of approximately 16 merozoites (X1200). schizont composed of approximately 16 merozoites (X1200). More than 12 merozoites distinguishes More than 12 merozoites distinguishes P. vivaxP. vivax from from P. malariaeP. malariae and and P. ovaleP. ovale, ,

which both typically have eight, but up to 12. which both typically have eight, but up to 12. P. falciparumP. falciparum may have up to 24 merozoites, may have up to 24 merozoites, but they are not typically seen in peripheral blood smears and so are not confused with but they are not typically seen in peripheral blood smears and so are not confused with P. vivaxP. vivax..

FIGURE 13-35 FIGURE 13-35   Plasmodium falciparumPlasmodium falciparum gametocyte in an erythrocyte (X1200). gametocyte in an erythrocyte (X1200). Differentiation between microgametocytes and megagametocytes is difficult in this species.Differentiation between microgametocytes and megagametocytes is difficult in this species.

ToxoplasmosisToxoplasmosis► Toxoplasma gondii is an intracellular parasite that is Toxoplasma gondii is an intracellular parasite that is

found in a wide variety of animals including birds, found in a wide variety of animals including birds, mice, cats and humans. The essential reservoir is the mice, cats and humans. The essential reservoir is the common house cat That has eaten an infected common house cat That has eaten an infected rodent. The infective cysts are passed in cat feces rodent. The infective cysts are passed in cat feces where they can be ingested by mice and/or humans. where they can be ingested by mice and/or humans. If infection occurs during the first trimester of If infection occurs during the first trimester of pregnancy spontaneous abortion, still birth or severe pregnancy spontaneous abortion, still birth or severe neurological disease. Disease is usually mild to neurological disease. Disease is usually mild to asymptomatic in immunologically competent adults. asymptomatic in immunologically competent adults. Immunocomprimised patient AIDS result with severe Immunocomprimised patient AIDS result with severe neurological disease. Demostration of the banna neurological disease. Demostration of the banna shaped trophozoites in spinal fluid is one method of shaped trophozoites in spinal fluid is one method of diagnosis. Newer monoclonal antibody serological diagnosis. Newer monoclonal antibody serological methods will also diagnose the presence of the methods will also diagnose the presence of the parasite.parasite.

FIGURE 13-36FIGURE 13-36    Toxoplasma gondii Toxoplasma gondii trophozoites (X1000). trophozoites (X1000). Notice the bow shaped cells with prominent nuclei.Notice the bow shaped cells with prominent nuclei.

Cryptosporidium parvumCryptosporidium parvum►Newly recognized parasite in immune Newly recognized parasite in immune

compromised humans, children, aged, AIDScompromised humans, children, aged, AIDS► Respiratory and gall bladder infections = Respiratory and gall bladder infections =

major cause of death major cause of death ► Transmitted through fecal oral route from Transmitted through fecal oral route from

cows, rodents and dogs and cats mainly cows, rodents and dogs and cats mainly water borne, but veterinary personnel, water borne, but veterinary personnel, animal handlers, day care centers, and animal handlers, day care centers, and homosexuals are at high risk.homosexuals are at high risk.

► Resistant to usually water purification Resistant to usually water purification methods –chlorination and ozonemethods –chlorination and ozone

FIGURE 13-38FIGURE 13-38    Cryptosporidium parvumCryptosporidium parvum oocysts from a human fecal sample (X1000, oocysts from a human fecal sample (X1000, modified acid-fast stain). Oocysts contain sporozoites (not visible) and are the infective stage. modified acid-fast stain). Oocysts contain sporozoites (not visible) and are the infective stage.

They are typically about 5µm in size.They are typically about 5µm in size.