Parasitic Protozoa - Flagellated Protozoa

Flagellated Protozoa

Overview

  • Flagellates are generally spindle-shaped and possess flagella.
  • Several flagellates are significant human pathogens.
  • The Archeazoa are a group within the flagellates.

Main Pathogens

  • Trypanosoma brucei (gambiense and rhodesiense)
  • Trypanosoma cruzi
  • Leishmania
  • Giardia
  • Trichomonas

Trypanosomiasis in Africa: African Sleeping Sickness

  • Also known as African Sleeping Sickness.
  • Transmitted by the bite of the tsetse fly (Glossina species).
  • Characterized by:
    • Fever
    • Severe headache
    • Rash
    • Late-stage CNS signs: lethargy, insensitivity to pain, difficulty waking up.
  • Has rendered millions of square miles in Africa uninhabitable.

Trypanosoma brucei

  • Observed on blood smear.
  • Two types of African Sleeping Sickness:
    • T.b. gambiense: chronic
    • T.b. rhodesiense: rapid

Trypanosomiasis in America: Chagas’ Disease

  • Trypanosoma cruzi causes Chagas’ disease.
  • Occurs in Central and South America & Mexico.
  • Transmitted by the Reduviid bug (kissing bug), which typically bites near the mouth or eye.
  • The bug's feces enter the sore created by the bite, leading to infection.
  • The sore created by the bite is called chagomas.
  • Causes acute disease in children, including:
    • Fever
    • Malaise
    • Lymphadenopathy
  • Can result in irreversible sequelae:
    • Cardiac damage
    • Megaesophagus
    • Megacolon

Leishmaniasis

  • Vector: Sand fly
  • Types:
    • Cutaneous (Baghdad Boil):
      • Crater-like skin lesions that heal spontaneously, leaving permanent scars.
      • Affected U.S. troops stationed in Iraq and Afghanistan.
    • Mucocutaneous:
      • Affects mucous membranes and skin.
      • Destroys tissue of the nose, mouth, and throat, leading to disfigurement.
      • Most common in the Yucatan Peninsula of Mexico & Central and South America
    • Visceral (Kala-Azar):
      • Parasite migrates to internal organs such as the liver, spleen, and bone marrow.
      • Fatal if untreated.
      • Second-largest parasitic killer in the world (after malaria), with an estimated 500,000 cases each year worldwide.
      • Opportunistic in AIDS patients.
      • Symptoms: Fever, chills, diarrhea, progressive hepatosplenomegaly, skin hyperpigmentation. Appears 4 months after infection.

Archaezoa

  • Lack mitochondria, possibly due to evolving before eukaryotes acquired them or due to subsequent loss.
  • Typically spindle-shaped with flagella.
  • Two important human pathogens:
    1. Trichomonas vaginalis
    2. Giardia intestinalis (lamblia)

Trichomonas vaginalis

  • Found in the vagina and male urinary tract.
  • Causes trichomoniasis, an STD in females; males are primarily asymptomatic.
  • Possesses an undulating membrane and lacks a cyst stage.
  • Requires rapid transmission before it dries out.
  • Usually transmitted by sex, rarely via toilets or towels.
  • Common STD in the U.S.
  • Diagnosis: observation of motility in wet prep of vaginal discharge.
  • Treated with Flagyl.

Giardia intestinalis (lamblia)

  • Found in the small intestine of mammals, which shed cysts in feces.
  • The diagnostic form of the disease, Giardiasis, is usually the cyst.
  • In the duodenum, it exists as a trophozoite (bearded man), attaching to the intestinal mucosa using sucking disks (rarely found in stools).
  • Causes diarrhea, malaise, nausea, weakness, weight loss, abdominal cramps (or can be an asymptomatic carrier - 7% of the population).
  • In daycare settings, 5-15% of children in diapers are infected; easily spread from one child to another.
  • Diagnosis: stool exam or string test.

Giardia intestinalis Life Cycle

  • Excystation occurs in the duodenum.
  • Multiplication occurs by longitudinal binary fission.
  • Cyst (infective stage).
  • Trophozoite and cyst are found in feces.
  • Cyst has a 'vase of flowers' appearance while a trophozoite appears as a 'bearded man'.

Giardia & Water

  • Most common cause of epidemic waterborne diarrheal disease.
  • Can be a danger to water supply since cysts can be shed by animals in feces, and are resistant to potable water levels of chlorination.
  • Can infect pools if fecal material enters the pool and chlorine levels are not adequate to kill cysts.
  • Can be a danger to campers and hikers who drink unfiltered water or swim and swallow water, especially common in areas inhabited by beavers (“Beaver’s Fever”).