ParasitologyParasitology

BY DR S.HASAN ASKARI BDS RDS MS LECTUERER AT Muhammad bin qasim medical and dental college

IntroductionIntroductionProtozoans are unicellular, eukaryotic

Most protozoa have two stages◦Trophozoite – A mobile, feeding reproducing

form surrounded by flexible cell membrane◦Cysts Non mobile ,non metabolizing ,non

reproducing form surrounded by a thick wall.◦Cysts is a protective capsule.

ReproductionReproduction

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

undergoes multiple divisions before the cell divides

Protozoa reproduce sexually by: Conjugation Gamete formation

Fission/budding/schizogony in Ciliate Fission/budding/schizogony in Ciliate protozoaprotozoa

ReproductionReproductionDefinitive Host harbors the sexually

reproducing stage of parasite

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

Representative Parasitic ProtozoansRepresentative Parasitic Protozoans

FlagellatedHave one or more whip like flagella.eg

intestinal and genitourinary .Giardia lamblia – enteritis – fecal contamination of drinking water. Trichomonas vaginalis – urethritis vaginitis - sexually transmited or contact with vaginal urethral dischargesTrypanosoma and leishmania – blood tissue

flagellate.

Representative Parasitic Representative Parasitic ProtozoansProtozoansCertain protoza such as leishmania and

trypanosoma have flagella and nonflagella .

Flagellated Trypanosoma and leishmania – blood tissue flagellate are called promastigotes or trypomastigotes.

Non flagellated form called amastigotes

T. cruzi – American trypanosomiasis Chagas disease.

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

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

UM

Amoeboid FormsAmoeboid FormsEntamoeba histolytica - mobility is by pseudopod (false

foot). Life cycle simple divided into two stages: trophozoite, and

the cyst .The amoebic trophozoites remain actively motile, feeding

on red blood cells, as long as environmental conditions are favorable. Dysentery and anemia. The cyst develops when environmental temperature or moisture drops.

In diagnosis the cysts are the only forms recognized. Trophozoites only in fresh stool specimens. Ulcers in intestinal mucosa cause amoebic dysentary. May invade peritoneal cavity invasion of liver. Inflammation, hemorage, secondary bacterial infection. More than 5% americans asymptomatic carriers. Montezumas’ revenge. Drinking water and salads.

Naeglaria fowleri

Meningoencephalitis. Swimming in polluted water results in

asymptomatic colonization of nasal passages. Invade cribiform plate through olfactory

openings resulting in rapid fulminating fatal meningoencephalitis. Spinal fluid contains many erythrocytes and trophozoites.

Post mortum diagnosis of trophozoites in the brain.

CiliatesCiliatesComplex protoza having row patches .2 kind of nuclei in each individual.Example:Balantidium coli is the only member of the

ciliate group that is pathogenic for humans. The organism is similar to amoebiasis cause tissue invasion and intestinal ulceration.

Large trophozoite with large macronulcleus Swine and monkeys important reservoirs.

Fecal oral route, swine feces contaminating local water supplies.

Food handlers substandard hygienic conditions.

FIGURE 13-15  Balantidium coli 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 is prominent; the adjacent micronucleus is not. An anterior cytostome (Cy) is usually visible.

Cy

C

Sporozoa:Sporozoa:Complex life cycle.Alternate sexual and asexual reproductive

phase .Sporozoan parasites that require two hosts for

completion of their life cycle. ExamplesPlasmodium species The mosquito for the

sexual reproductive stages. And the human or other animal (monkey) for the asexual stages.

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

Plasmodium Plasmodium

The hepatocytes rupture releasing merozoites

bind to red blood cells initiating the erythrocyte cycle of malaria (ring, trophozoite, and schizont stages).

In the human (intermediate host) asexual reproduction occurs and results in the rupture of the erythrocyte and release of merozoites the infect more erythrocytes.

FIGURE 13-27  Plasmodium life cycle.

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

ToxoplasmosisToxoplasmosis Toxoplasma gondii is an intracellular parasite found in a wide variety of animals including birds, mice, cats

and humans. The essential reservoir is the common house cat That has

eaten an infected rodent. The infective cysts are passed in cat feces where they can be

ingested by mice and/or humans. If infection occurs during the first trimester of pregnancy

spontaneous abortion, still birth or severe neurological disease.

Disease is usually mild to asymptomatic in immunologically competent adults. Immunocomprimised patient AIDS result with severe neurological disease.

Demostration of the banna shaped trophozoites in spinal fluid is one method of diagnosis. Newer monoclonal antibody serological methods will also diagnose the presence of the parasite.