Lesson 2 Protozoans

• Protozoa


  Eukaryotes that are mostly unicellular organisms with fully functional animal cells
• Protozoa


  • They are facultative parasites which means they can be free-living or they can be parasitic
  • They are chemo-heterotrophs which feed on organic matter such as other organisms or organic tissues and debris
  • They are motile so they have locomotive organelles such as flagella, cilia, and pseudopods for movement and collection of food
  • They have highly specialized organelles for feeding, reproduction, and movement
  • Their cytoplasm is divided into ectoplasm (outer layer) and endoplasm (inner layer)
  • Their size ranges from 3 to 300 micrometers, with a few ciliates and Amoeba visible to the naked eye (4 to 5 mm)
  • They have an eyespot that can detect changes in light, respond to light, and learn by trial and error
• Types of Protozoa


  • Amoebas (sarcodines)
  • Ciliates
  • Flagellates (mastigophorans)
  • Apicomplexans
• Amoebas (sarcodines)


  Move using pseudopodia, reproduce by binary fission
• Ciliates


  Move using beds of cilia, reproduce by syngamy (permanent sexual reproduction)
• Flagellates (mastigophorans)


  Move using one or more flagella, reproduce by binary fission
• Apicomplexans


  Are non-motile, intracellular parasites, reproduce by syngamy
• Sarcodina


  Also known as Sarcodines, largest phylum, movement by pseudopods, mostly harmless intestinal protozoa
• Life cycle of Entamoeba Histolytica

  1. Non-motile cyst stage (infective stage found in formed stools)

  2. Motile trophozoite stage (found within intestinal & extra intestinal lesions and diarrheal stools, pathogenic stage)
• Amebiasis


  Disease caused by Entamoeba Histolytica
• Transmission of Entamoeba Histolytica

  1. Ingestion of cyst in contaminated food & water by fecal oral route

  2. Trophozoites cause local necrosis "flask-shaped" ulcer

  3. Abscess of the liver due to portal circulation invasion

  4. Worldwide infection, more common in tropical countries with poor sanitation

  5. Water is the major source of infection

  6. Sexual transmission may also occur
• Laboratory diagnosis of Amebiasis

  • Diarrheal stool: trophozoites are seen
  • Formed Stools: cysts are seen
• Treatment of Amebiasis


  • Symptomatic intestinal amebiasis or hepatic abscess: Metronidazole or Tinidazole
  • Asymptomatic cyst carriers: iodoquinol or paromomycin
• Prevention of Amebiasis


  • Good personal hygiene
  • Purification of water source
  • Avoid use of night soil (human feces) for fertilization of crops
  • Observe adequate cooking of vegetables
• Acanthamoeba Castellani


  Minor protozoan pathogen, free-living amoeba that causes meningoencephalitis, found in soil & freshwater lakes, survives in cold water, penetrates nasal mucosa & cribriform plate to produce fatal meningitis, carried into the skin or eyes during trauma, affects immunocompromised individuals
• Laboratory diagnosis of Acanthamoeba

  Diagnosis is made by finding of both trophozoites and cysts in the cerebrospinal fluid as well as brain tissue and corneal scrapings. Histologic examination of corneal scrapings may also be done. Calcofluor white, a stain usually used to demonstrate fungi, may be used to demonstrate the parasite in corneal scraping specimens.
• Treatment of Acanthamoeba


  Pentamidine, Ketoconazole, or Flucytosine may be effective, however, prognosis is poor even with treatment. For eye and skin involvement, topical miconazole, chlorhexidine, itraconazole, ketoconazole, rifampicin, or propamidine may be used. Propamidine has been documented to have the best success record.
• Prevention of Acanthamoeba


  Adequate boiling of water, regular disinfection of contact lenses, contact lens wearers advised to avoid using homemade non-sterile saline solutions.
• Naegleria Fowleri


  Minor protozoan pathogen, free-living amoeba that shares many characteristics with Acanthamoeba Castellani, found worldwide in soil and freshwater lakes, survives in thermal spring water but not in salt water, affects healthy individuals especially children, has three identified morphologic forms: trophozoite, flagellate, and cyst
• Laboratory diagnosis of Naegleria Fowleri


  Presence of the amoeboid in the cerebrospinal fluid
• Treatment of Naegleria Fowleri

  Treatment is ineffective because of its rapidly fatal course. Amphotericin B in combination with miconazole and rifampicin may be used.
• Prevention of Naegleria Fowleri

  No known means of prevention and control, prevention of contamination of water sources, adequate chlorination of swimming pools and hot tubs
• Phylum Sarcomastigophora


  Characterized by the possession of a definite body shape and the possession of one or more flagella, most species are free-living and mobile
• Trichomonas Vaginalis


  Pear-shaped organism with a central nucleus, four anterior flagella, and an undulating membrane, it exists only in the trophozoite form (infective and pathogenic), causes urogenital infections, located in the vagina and the prostate, infection is highest among sexually-active women in their thirties and lowest in post-menopausal women, common worldwide
• Trichomoniasis


  Disease caused by Trichomonas Vaginalis
• Transmission of Trichomonas Vaginalis

  Sexual intercourse, isolated from the urethra and vagina of infected women as well as the urethra and prostate gland of infected men, occasionally transmitted through toilet articles and clothing of infected individuals, infants may be infected during vaginal delivery
• Laboratory diagnosis of Trichomoniasis

  Finding of the characteristic trophozoite in a wet mount of vaginal or prostatic secretions, urine, and urethral discharges
• Treatment of Trichomoniasis


  Metronidazole, all sexual partners of an individual with the infection must be simultaneously treated to prevent "ping pong" infections
• Prevention of Trichomoniasis


  Maintain low pH of the vagina, use of condoms limit the transmission, health and sex education
• Giardia Lamblia


  Also known as Giardia Intestinalis or Giardia duodenale, worldwide distribution through contaminated water sources, 50% of infected individuals are asymptomatic and carriers, other than humans, mammals act as reservoirs, common among individuals that engage in oral-anal contact, high incidence in daycare center & in patients in mental hospitals, has two forms: trophozoite (pear-shaped or tear drop-shaped with 4 pairs of flagella, motility likened to falling leaf, resembles old man with whiskers, possesses a sucking disc to attached itself to the villi of the infected human) and cyst (oval & thick-walled with four nuclei, divided through binary fission, each cyst gives rise to 2 trophozoites during excystation in the intestinal tract)
• Transmission of Giardia Lamblia

  The parasite is primarily transmitted through ingestion of the cyst from fecally contaminated water and food. The cyst enters the stomach and is stimulated by the gastric acid to undergo excystation in the duodenum. The trophozoites then attach themselves to the duodenal mucosa through the sucking disks. Damage to the intestines is not due to invasion of the parasite but because of inflammation of the duodenal mucosa, leading to diarrhea with malabsorption of fat and proteins. The trophozoites may also be passed out with the feces.
• Cyst


  Oval & thick-walled with four nuclei
• Cyst division


  Divided through binary fission
• Mature cyst


  • Contain 4 nuclei with 4 median bodies
  • Each cyst gives rise to 2 trophozoites during excystation in the intestinal tract
• Asymptomatic Carrier State


  The infected individual unknowingly passes out the parasite with the feces which can then contaminate water
• Trypanosoma Cruzi is found primarily in South and Central America, rare in US, but increasing in immigrants from Latin America
• The bug (Triatoma or "cone-nose" bug or "kissing bug") lives in the walls of rural huts and feeds at night
• Vector


  Tse-tse Fly (Glossina)
• Reservoir


  • Human
  • Domestic Animals: Cattle
• African Sleeping Sickness


  • Demyelinating Encephalitis