Protozoa

• Kingdom Protista


  A very diverse kingdom with species that can move, obtain food, and reproduce in as many different ways as are found in all the other kingdoms combined
• Types of organisms in Kingdom Protista

  • Protozoans
  • Algae
• Protozoans


  The more animal-like protists that can usually move themselves and capture prey
• Protozoans


  • Paramecium
  • Amoeba
• Protozoa


  Microscopic unicellular eukaryotes with complex internal structure and metabolic activities
• Protozoa


  • More than 50,000 species have been described, most of which are free-living organisms
  • Found in almost every possible habitat
  • Anton van Leeuwenhoek was the first person to see protozoa, using microscopes he constructed with simple lenses
  • Virtually all humans have protozoa living in or on their body at some time, and many persons are infected with one or more species throughout their life
• Protozoan species

  • Commensals (normally not harmful)
  • Pathogens (usually produce disease)
• Protozoan diseases

  Range from very mild to life-threatening
• Individuals whose defenses are able to control but not eliminate a parasitic infection become carriers and constitute a source of infection for others
• Protozoa size

  • Most parasitic protozoa in humans are <50 μm in size
  • The smallest (mainly intracellular forms) are 1 to 10 μm long, but Balantidium coli may measure 150 μm
• Protozoan nucleus

  • Nucleus is vesicular, with scattered chromatin giving a diffuse appearance
  • One type of vesicular nucleus contains a more or less central body, called an endosome or karyosome
  • The endosome lacks DNA in the parasitic amebas and trypanosomes
• Protozoan organelles

  • Have functions similar to the organs of higher animals
  • The plasma membrane enclosing the cytoplasm also covers the projecting locomotory structures such as pseudopodia, cilia, and flagella
  • Outer surface layer of some, termed a pellicle, is sufficiently rigid to maintain a distinctive shape, as in the trypanosomes and Giardia
  • Cytoplasm is differentiated into ectoplasm (the outer, transparent layer) and endoplasm (the inner layer containing organelles)
  • Some protozoa have a cytosome or cell "mouth" for ingesting fluids or solid particles
  • Contractile vacuoles for osmoregulation occur in some, such as Naegleria and Balantidium
  • Many protozoa have subpellicular microtubules; in the Apicomplexa, which have no external organelles for locomotion, these provide a means for slow movement
  • Trichomonads and trypanosomes have a distinctive undulating membrane between the body wall and a flagellum
  • Many other structures occur in parasitic protozoa, including the Golgi apparatus, mitochondria, lysosomes, food vacuoles, conoids in the Apicomplexa, and other specialized structures
• Resistance


  The ability of a host to defend itself against a pathogen
• Mechanisms of resistance to protozoan parasites

  • Nonspecific factors
  • Cellular immunity
  • Humoral immunity
• Tissue damage from protozoal infection

  In chronic infections the tissue damage is often due to an immune response to the parasite and/or to host antigens as well as to changes in cytokine profiles
• Escape mechanisms of parasites

  • Antigenic masking
  • Acquiring a coating of antigen-antibody complexes or noncytotoxic antibodies that sterically blocks the binding of specific antibody or lymphocytes to the parasite surface antigens
  • Intracellular habitat protecting from direct effects of host's immune response
  • Changing surface antigens during the course of an infection
• Parasitic protozoan infections generally produce some degree of host immunosuppression, which may delay detection of antigenic variants and reduce the ability of the immune system to inhibit the growth of and/or to kill the parasites
• Entamoeba histolytica


  Protozoan parasite that causes intestinal disease( Amoebiasis)
• Entamoeba histolytica


  • Patients have acute or chronic diarrhea, which may progress to dysentery
  • Extraintestinal disease may be present as a complication or as a primary problem (e.g., liver, lung or brain abscess, or skin or perianal infection)
  • The trophozoite is 10 to 60 µm in diameter, ameboid, actively motile, and often erythrophagocytic
  • In stained specimens, the nucleus has a central karyosome with finely beaded peripheral chromatin
  • The cyst form is rounded, 10 to 20 µm in diameter, with 1-4 nuclei showing the characteristic appearance
  • A chromatoidal bar with rounded or square ends may be seen
  • Pathogenic strains can be grown at 37° C but not at room temperature and fall into specific enzyme assay groups
  • Multiplication in the host occurs by binary fission
  • Nuclear replication produces 4 nuclei during cyst maturation
  • During excystation the cyst divides to form 4 cells which immediately divide again to yield eight tiny amoebae
  • Colon may be colonized without invasion of mucosa
  • The critical factor determining colonization is the ability of the ameba to adhere to colonic mucosal lining cells
  • Invasion of the mucosa produces ulcers that sometimes progress by direct extension or by metastasis
  • Metastatic infection first involves the liver
  • Extension or metastasis from the liver may involve the lung, brain, or other viscera
  • Gastric acid and rapid intestinal transit are nonspecific defenses
  • Humoral antibody and cell-mediated immunity play limited roles in preventing dissemination
  • Fecal-oral transmission of cysts involves contaminated food or water
  • Amebas can be transmitted directly by sexual contact involving the anus
• Entamoeba histolytica infection


  • Acute diarrhea is the usual presentation of symptomatic disease
  • Ulceration is associated with occult or gross blood in stool and/or with a visceral abscess
  • The condition may be confirmed by identification of E. histolytica in the stool or in abscess aspirates
  • The ameba in abscesses line the wall of the abscess cavity and thus will be found in the last material aspirated from the abscess
  • Ameba can be cultured
  • Positive serologic tests, particularly tests showing rising antibody levels, may provide indirect evidence of infection
• Prevention of Entamoeba histolytica infection

  • Largely a matter of personal and public hygiene
  • There are no effective immunizations or prophylaxis
• Treatment of Entamoeba histolytica infection

  1. Acute intestinal disease is best treated with metronidazole at a dose of 750 mg three times a day orally for 10 day

  2. In children the dose is 40 mg/kg/day divided into three doses and given orally for 10 days

  3. Patients unable to take metronidazole may be given a broad spectrum antibiotic for two weeks

  4. To clear amebas from the gut: iodoquinol at an adult dose of 650 mg orally 3 times daily for 20 days or diloxanide furoate at an adult dose of 500 mg orally 3 times daily for 10 days

  5. Amebic liver abscess is best treated with metronidazole at several possible dose regimens, but cases of drug failure have been reported

  6. Chloroquine or dehydroemetine are less desirable alternatives

  7. Aspiration of the abscess is not helpful except for diagnostic purposes unless rupture is imminent
• Giardia lamblia

  Flagellate protozoan parasite that causes intestinal disease
• Giardiasis


  • May be asymptomatic or may cause a variety of intestinal symptoms, including chronic diarrhea, steatorrhea (fatty diarrhea), cramps, bloating, fatigue, and weight loss
  • The parasite is a distinctive flagellate trophozoite with two nuclei and an adhesive disk
  • Cysts are egg-shaped (6 × 12 μm)
  • Multiplication is by binary fission of trophozoites in the small intestine
  • Trophozoites begin to encyst as they pass through the lower small intestine; cysts are excreted in formed stool
  • Ingestion of cysts results in infection
  • The presence of intestinal trophozoites results in an increased turnover of intestinal epithelium, with replacement of mature cells by immature intestinal cells
  • The result is a reduced ability to digest and absorb fats and fat-soluble vitamins
  • Cellular and humoral immunity are involved in host defense
  • Infection does not regularly elicit antibodies
  • Fecal-oral transmission can occur via drinking water and may be a problem wherever sanitation is poor
• Diagnosis of Giardiasis

  1. Traditionally, Giardia is identified by cysts or trophozoites in stool

  2. Some cases are difficult to diagnose

  3. Other methods are to examine duodenal specimens for Giardia
• Prevention and control of Giardiasis

  1. Attention to personal hygiene (e.g., handwashing) will reduce direct transmission

  2. Another method of control is to treat drinking water by disinfection and/or filtration
• Trichomonas Vaginalis

  Trichomoniasis is a common urogenital disease in women
• Treatment of Giardiasis

  1. In the U.S., infections are treated with quinacrine or furazolidone

  2. Metronidazole is also effective, but not officially approved
• Trichomoniasis


  • Vaginitis with foul-smelling discharge and small hemorrhagic lesions
  • Frequency and painful of urination
  • Usually asymptomatic in men
• Trophozoiteof Trichomonas Vaginalis


  • Pear-shaped (7 to 23 μm long)
  • 4 anterior flagella and a 5th forming the outer edge of a short undulating membrane
  • Slender rod (axostyle) extends the length of the body and protrudes posteriorly
• Trophozoite division in trichomonas vaginalis


  Divides by binary fission in the urogenital tract
• Transfer of trophozoitein trichomonas vaginalis


  Usually directly from person to person
• A protective antibody response, if present, is short-lived
• The trichomonas vaginalis typically are transferred during sexual intercourse
• Demonstration of trichomonas vaginalis

  Can be demonstrated in vaginal fluid, scrapings, or washings
• Male sex partners may be asymptomatic carriers; if they are, both sex partners should be treated simultaneously
• Malaria

  Mosquito-borne infectious disease - female Anopheles mosquito
• Malaria causative agents

  • P. falciparum
  • P. vivax
  • P. ovale
  • P. malaria
• Malaria signs and symptoms

  • Flu-like
  • Hemolytic
  • Anemia
  • Jaundice
  • Hemoglobinuria
  • Convulsion
• Malaria diagnosis

  1. History of travel in malaria endemic area

  2. Clinical signs and symptoms

  3. Confirmatory - microscopic blood films

  4. Rapid Dx Test Kits (RDT)