Parasitic Protozoa Chapter 6
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Questions and Answers

What is the size range of Precyst in Entamoeba histolytica?

10–20 μm

Which stage of Entamoeba histolytica is the infective form found in the feces of carriers?

  • Trophozoite
  • Precyst
  • Quadrinucleated cyst
  • Cyst (correct)
  • Mature quadrinucleated cyst is the infective form of Entamoeba histolytica.

    True

    Giardia lamblia infects humans and other __________.

    <p>mammals</p> Signup and view all the answers

    What is the most common parasitic cause of STDs?

    <p>Trichomoniasis</p> Signup and view all the answers

    Trichomoniasis is caused by a protozoan parasite that particularly infects columnar epithelium.

    <p>False</p> Signup and view all the answers

    What is the incubation period for trichomoniasis?

    <p>10 days</p> Signup and view all the answers

    Trichomoniasis can be prevented by treatment of ________.

    <p>both the partners</p> Signup and view all the answers

    What does the name 'proto-zoa' literally mean?

    <p>First animals</p> Signup and view all the answers

    Protozoa have the ability to move using locomotor organelles or a gliding mechanism throughout their entire life cycle.

    <p>True</p> Signup and view all the answers

    What is the organelle in protozoa responsible for locomotion and engulfment of food?

    <p>pseudopodia</p> Signup and view all the answers

    In some protozoa like Toxoplasma, they multiply by internal budding, resulting in the formation of two daughter cells, a process known as ________.

    <p>endodyogeny</p> Signup and view all the answers

    Match the classification of protozoans with their phyla:

    <p>Sarcomastigophora = Flagellae or pseudopodia for locomotion Apicomplexa = Includes Plasmodium for malaria Microspora = Affects immunocompromised individuals Ciliophora = Has cilia for movement</p> Signup and view all the answers

    Which form of Giardia is small and oval, surrounded by a hyaline cyst wall?

    <p>Cyst</p> Signup and view all the answers

    Giardia completes its life cycle in multiple hosts.

    <p>False</p> Signup and view all the answers

    What is the primary mode of transmission of Giardia infection?

    <p>Ingestion of food and water contaminated with mature cysts</p> Signup and view all the answers

    Giardia trophozoites adhere to the duodenal mucosa by the bilobed adhesive __________ disc.

    <p>ventral</p> Signup and view all the answers

    Match the following clinical features with their descriptions:

    <p>Malabsorption of fat = Leads to foul smelling profuse frothy diarrhea Disaccharidase deficiencies = Lead to lactose intolerance Malabsorption of vitamin B12 and folic acid = Result in specific nutrient deficiencies Protein loosing enteropathy = Characterized by protein loss through the gastrointestinal tract</p> Signup and view all the answers

    What are the two types of trypomastigotes liberated to the blood upon rupture of the pseudocyst?

    <p>Slender highly motile forms and broader less motile forms</p> Signup and view all the answers

    What are the two forms of trypomastigotes that persist in the blood to be taken up by the insect vector during a blood meal?

    <p>Slender highly motile and broader less motile forms</p> Signup and view all the answers

    Chagas Disease can be transmitted transovarianly in bugs.

    <p>False</p> Signup and view all the answers

    Chagas Disease is characterized by the formation of an erythematous subcutaneous nodule called _______ at the site of deposition of bug's feces.

    <p>Chagoma</p> Signup and view all the answers

    Match the Trypanosoma brucei subspecies with their corresponding disease:

    <p>T.brucei gambiense = West African sleeping sickness T.brucei rhodesiense = East African sleeping sickness T.brucei brucei = Infects cattle only</p> Signup and view all the answers

    What are the cutaneous lesions of L.V.guyanensis and L.V.peruviana known as?

    <p>forest yaws (pain bois) and uta</p> Signup and view all the answers

    Which species is the new world variant of L.L.infantum?

    <p>Leishmania Leishmania chagasi</p> Signup and view all the answers

    Is pentavalent antimonial the drug of choice for New World CL?

    <p>True</p> Signup and view all the answers

    In humans, the sporozoites of Plasmodium are directly introduced into the blood circulation by a female Anopheles mosquito's _____.

    <p>salivary gland</p> Signup and view all the answers

    What are the two subgenera of Leishmania?

    <p>L.Leishmania and L.Viannia</p> Signup and view all the answers

    Promastigotes of subgenus Viannia develop in the midgut and hindgut of sandflies.

    <p>False</p> Signup and view all the answers

    In Old World Leishmaniasis, the parasite Leishmania donovani causes __________ leishmaniasis.

    <p>visceral</p> Signup and view all the answers

    What is the incubation period range for visceral leishmaniasis (VL)?

    <p>2-6 months</p> Signup and view all the answers

    What is the shape of gametocytes in P. falciparum?

    <p>Banana</p> Signup and view all the answers

    Gametocytes cause clinical illness.

    <p>False</p> Signup and view all the answers

    What role do individuals harboring gametocytes play in the transmission of the disease?

    <p>Carriers or reservoirs of infection</p> Signup and view all the answers

    Gametocytes are effective in transmission of the infection if they are mature, viable, and present in sufficient density, usually 12 per cubic mm of ______.

    <p>blood</p> Signup and view all the answers

    Match the following Plasmodium species with their time of appearance of gametocytes in the circulation:

    <p>P. vivax = 4–5 days P. falciparum = 10–12 days P. malariae = 11–14 days P. ovale = 5–6 days</p> Signup and view all the answers

    What is the extrinsic incubation period for P. falciparum at 25°C?

    <p>9–10 days</p> Signup and view all the answers

    Sequestration of parasites occurs in Plasmodium falciparum.

    <p>True</p> Signup and view all the answers

    What are the two forms in which the organism exists?

    <p>trophozoite and cyst</p> Signup and view all the answers

    What is the size range of the oval-shaped trophozoite?

    <p>30-300 μm in length, 30-100 μm in breadth</p> Signup and view all the answers

    The trophozoite is considered the dormant form of the organism.

    <p>False</p> Signup and view all the answers

    The trophozoite has a row of tiny delicate __ (organ of locomotion) covering its body.

    <p>cilia</p> Signup and view all the answers

    What does the anteriorend of the trophozoite bear that leads to a mouth?

    <p>groove (peristome)</p> Signup and view all the answers

    What does the endoplasm of trophozoite contain?

    <p>Two nuclei and numerous food vacuoles</p> Signup and view all the answers

    Study Notes

    Introduction to Parasitic Protozoa

    • Protozoa are single-celled organisms that exist as structurally and functionally independent individual cells.
    • They come in many different shapes and sizes, ranging from amoeba to paramecium with complex structures.
    • Protozoans have developed complex subcellular features (membranes & organelles) to survive in their environments.

    Characteristics of Protozoa

    • A single cell performs all functions: reproduction, digestion, respiration, and excretion.
    • They do not have a cell wall, but some possess a flexible layer or a rigid shell of inorganic materials outside the cell membrane.
    • They have the ability to move from one place to another during their entire life cycle using their locomotor organelles or by a gliding mechanism.
    • They are heterotrophic, deriving nutrients from the body fluids of their hosts or ingesting particulates like bacteria, yeast, and algae.
    • They reproduce by asexual means, although some groups also have sexual modes of reproduction.

    Structure of a Protozoan Cell

    • A typical protozoan cell is bounded by a trilaminar unit membrane supported by a sheet of contractile fibrils.
    • The cytoplasm consists of two portions: ectoplasm (outer homogeneous part) and endoplasm (inner granular part containing the nucleus).
    • Ectoplasm serves as the organ for locomotion, engulfment of food, and respiration, while endoplasm contains structures like Golgi bodies, endoplasmic reticulum, food vacuoles, and contractile vacuoles.

    Reproduction in Protozoa

    • Asexual reproduction occurs by binary fission, multiple fission, or endodyogeny.
    • Sexual reproduction occurs by conjugation (in ciliates) or gametogony (in Sporozoa).

    Life Cycle of a Parasitic Protozoan

    • The life cycle can involve a single host (e.g., intestinal flagellates and ciliates) or two hosts (e.g., Plasmodium).
    • Asexual reproduction occurs in one host, and sexual reproduction occurs in another host.

    Classification of Protozoa

    • Medical important parasitic protozoa are classified into the kingdom Protista, subkingdom Protozoa, and further divided into four phyla: Sarcomastigophora, Apicomplexa, Microspora, and Ciliophora.

    Phylum Sarcomastigophora

    • Includes many unicellular or colonial, autotrophic, or heterotrophic organisms that use flagellae, pseudopodia, or both for locomotion.
    • Subdivided into two subphyla: Sarcodina (amibe) and Mastigophora (flagellates).

    Entamoeba histolytica

    • A single-celled protozoan that constantly changes its shape.
    • Classification based on habitat: intestinal amoebae and free-living amoebae.
    • Entamoeba histolytica is a parasitic amoeba that can cause amoebic dysentery and amoebic liver abscess.
    • Life cycle involves three stages: trophozoite, precyst, and cyst.
    • Trophozoite is the invasive form, precyst is the intermediate stage, and cyst is the infective form.
    • Transmission occurs through the feco-oral route, sexual contact, or vectors like flies and cockroaches.

    Clinical Manifestation of Amoebiasis

    • Asymptomatic amoebiasis: About 90% of infected persons are asymptomatic carriers.
    • Intestinal amoebiasis: Characterized by four clinical forms - amoebic dysentery, amoebic appendicitis, ameboma, and fulminant colitis.
    • Amoebic liver abscess: Presents with tender hepatomegaly, fever, weight loss, sweating, and weakness.### Diagnosis of Intestinal Amoebiasis
    • Stool microscopy detects cysts and trophozoites
    • Stool culture and polyxenic and axenic culture are also used
    • Stool antigen detection methods include:
      • Counter Current Immune Electrophoresis (CIEP)
      • Enzyme Linked Immunosorbent Assay (ELISA)
      • Immunochromatographic Test (ICT)
    • Serology tests for amoebic antigen and amoebic antibody
    • Isoenzyme (zymodene) analysis and molecular diagnosis using PCR

    Diagnosis of Amoebic Liver Abscess

    • Microscopy detects trophozoites
    • Stool culture and antigen detection using ELISA
    • Antibody detection using:
      • Indirect hemagglutination Test (IHA)
      • ELISA
      • Indirect fluorescent antibody Test (IFA)
    • Histopathology using PAS stain
    • Molecular diagnosis using PCR
    • Ultrasonography

    Treatment of Intestinal Amoebiasis and Amoebic Liver Abscess

    • Metronidazole or tinidazole is the drug of choice
    • Other measures include:
      • Fluid and electrolyte replacement
      • Symptomatic treatment

    Prevention of Intestinal Amoebiasis

    • Avoid ingestion of food and water contaminated with human feces
    • Treatment of asymptomatic persons who pass E.histolytica cysts in the stool

    Subphylum Mastigophora: Class Zoomastigophora (Flagellates)

    • Flagellates are protozoans that use flagella for locomotion
    • Flagella are slender, long, and thread-like extensions of cytoplasm
    • Flagella arise from kinetoplast (made up of copies of mitochondrial DNA)

    Classification of Flagellates based on Habitat

    • Lumen-dwelling flagellates: found in the alimentary tract and urogenital tract
    • Hemoflagellates: found in blood and tissues

    Lumen-dwelling Flagellates

    • Examples:
      • Giardia lamblia
      • Enteromonas hominis
      • Retortamonas intestinalis
      • Chilomastix mesnili
      • Dientamoeba fragilis
      • Trichomonas tenax
      • Pentatrichomonas hominis

    Hemoflagellates

    • Examples:
      • Leishmania
      • Trypanosoma

    Giardia lambia

    • First observed by A.V.Leeuwenhoek in 1681
    • Different species of Giardia can be differentiated based on the origin of the host
    • Giardia lamblia is the most common protozoan pathogen and is worldwide distributed
    • Infection is endemic in places with poor sanitation

    Morphology of Giardia lamblia

    • Trophozoite has a falling leaf-like motility
    • Shape:
      • Pear shaped (or tear drop or tennis racket shaped) in front view
      • Sickle shaped in lateral view
    • Bilaterally symmetrical with:
      • One pair of nuclei
      • Pair of median bodies
      • Four pairs of basal bodies or blepharoplasty
      • Four pairs of flagella
      • Pair of parabasal bodies
      • Pair of axoneme or axostyle

    Life Cycle of Giardia lamblia

    • Host: completes its life cycle in one host
    • Infective form: mature cyst
    • Mode of transmission: ingestion of food and water contaminated with mature cysts
    • Excystation: two trophozoites are released from each cyst in the duodenum
    • Multiplication: trophozoites multiply by longitudinal binary fission
    • Adhesion: trophozoites adhere to the duodenal mucosa by the bilobed adhesive ventral disc
    • Encystation: begins in the large intestine

    Pathogenicity of Giardia lamblia

    • Infective dose: as few as 10-25 cysts can initiate the infection
    • Risk factors: children, elderly, debilitated persons, and patients with cystic fibrosis
    • Pathogenic mechanisms:
      • Adhesion to duodenal mucosa
      • Disruption of the intestinal epithelial brush border
      • Malabsorption
      • Elaboration of enterotoxin
    • Malabsorption: types include:
      • Malabsorption of fat
      • Disaccharidase deficiencies
      • Malabsorption of vitamin B12 and folic acid
      • Protein losing enteropathy

    Clinical Features of Giardiasis

    • Asymptomatic carriers
    • Acute giardiasis:
      • Incubation period: 1-3 weeks
      • Symptoms: diarrhea, abdominal pain, bloating, belching, and vomiting
      • Foul smelling diarrhea with fat and mucus
    • Chronic giardiasis:
      • Intermittent and recurring symptoms
      • Foul smelling diarrhea, foul flatus, and weight loss
      • Uncommon symptoms: fever, presence of blood and/or mucus in the stools

    Diagnosis of Giardiasis

    • Stool examination: detects cysts and trophozoites
    • Entero-test: antigen detection in stool
    • ELISA, ICT, and other serological tests
    • Culture
    • Molecular method: PCR
    • Radiological findings: barium meal, X-ray

    Treatment of Giardiasis

    • Metronidazole or tinidazole
    • Nitazoxanide
    • Furazolidone
    • Paromomycin

    Prevention of Giardiasis

    • Improved food and personal hygiene
    • Boiling or filtering of potentially contaminated water
    • Treatment of asymptomatic carriers
    • No vaccine is currently available### Trichomoniasis
    • Caused by the parasite Trichomonas vaginalis
    • Can cause low birth weight, neonatal pneumonia, and conjunctivitis in infants born to infected mothers
    • Diagnosis methods:
      • Direct microscopy (wet saline mounting, permanent stain, acridine orange fluorescent stain, direct fluorescent antibody test)
      • Culture (gold standard method)
      • Antigen detection in vaginal secretion (ELISA, ICT, etc.)
      • Antibody detection (ELISA)
      • Molecular method (PCR)
      • Other supportive tests (raised vaginal pH, positive whiff test)
    • Treatment:
      • Metronidazole or tinidazole (2g, single dose is usually effective)
      • Both sexual partners must be treated simultaneously to prevent reinfection
      • Resistance to metronidazole is rare but has been reported (2.5-10% to metronidazole, <1% to tinidazole)
      • Mechanism of resistance development: controlled by hydrogenosome
    • Prevention:
      • Treatment of both partners
      • Safe sex practices (use of condoms)
      • Avoidance of sex with infected person
      • Vaccine (no effective vaccine licensed so far, but trials are ongoing)

    Hemoflagellates

    • Flagellated protozoa that complete their life cycle in two hosts (vertebrate host and insect vector)
    • Morphology:
      • Oval to elongated body
      • Nucleus
      • Single flagellum arising from kinetoplast (consists of blepharoplasty and parabasal body connected by a delicate fibril, represents multiple copies of mitochondrial DNA)
      • Axoneme (or axostyle) extending from blepharoplast to the cell wall (represents the intracellular portion of flagellum)
    • Based on arrangement of flagellum, they exist in four morphological stages:
      • Amastigote form (round to oval, lacks flagellum, found in reticuloendothelial cells of infected humans)
      • Promastigote form (lanceolate shaped, kinetoplast is anterior to nucleus, found in the mid-gut of insect vector)
      • Epimastigote form (elongated, kinetoplast is placed close to the nucleus, found in the insect vector)
      • Trypomastigote form (elongated and spindle shaped, kinetoplast lies near the posterior end, found in the insect vector and peripheral blood of humans)

    Trypanosoma

    • Classification:
      • Human Trypanosomes (T. cruzi, T. brucei)
      • Animal Trypanosomes (T. brucei brucei, T. congolense, T. vivax, T. rangeli, T. evansi, T. lewisi, T. equiperdum)
    • T. cruzi:
      • Causes South American trypanosomiasis (Chagas' disease)
      • Transmitted by reduviid bug (triatomine bug)
      • Found in peripheral blood and tissues of humans
      • Morphology:
        • Amastigote form (intracellular parasite)
        • Trypomastigote form (extracellular, found in peripheral blood)
      • Life cycle:
        • In vertebrate host (human): trypomastigote form transforms into amastigote form
        • In insect vector (reduviid bug): trypomastigote form transforms into epimastigote form, and finally into metacyclic trypomastigote form
      • Pathogenicity and clinical features:
        • Acute Chagas' disease: characterized by chagoma, Romana's sign, generalized lymphadenopathy, hepatosplenomegaly, severe myocarditis, and neurologic signs
        • Chronic Chagas' disease: manifests years or decades after initial infection, characterized by cardiac form, gastrointestinal form, and mixed forms

    T. brucei

    • Causes African trypanosomiasis (sleeping sickness)
    • Transmitted by tsetse fly
    • Found in peripheral blood and tissues of humans
    • Morphology:
      • Long slender trypomastigote form (found in peripheral blood)
      • Short stumpy trypomastigote form (found in tissues)
    • Life cycle:
      • In vertebrate host (human): trypomastigote form transforms into amastigote form
      • In insect vector (tsetse fly): trypomastigote form transforms into epimastigote form, and finally into metacyclic trypomastigote form
    • Pathogenicity and clinical features:
      • Trypanosomal chancre (self-limited inflammatory lesion)
      • Stage I disease: characterized by systemic febrile illness, lymphadenopathy, pruritus, maculopapular rashes, and transient edema
      • Stage II disease: characterized by invasion of the CNS, progressive daytime somnolence, restlessness, and insomnia at night, and abnormal speech with few extrapyramidal signs

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