MA

Protozoan Phyla Notes

Phylum Sarcomastagophora

  • Kingdom: Protozoa
  • Includes subphyla Mastigaphora (flagella organisms) and Sarcodyna (pseudopods)

Subphylum Mastigaphora

  • Includes: Giardiasis, Leishmaniasis, Trichomoniasis, and Trypanosomiasis

Subphylum Sarcodyna

  • Includes: Amoeba proteus (non-disease causing) and Entamoeba histolytica

Giardiasis

  • Causative agent: Giardia lamblia
  • Most common waterborne illness in the United States.
  • Contracted from non-purified water sources (e.g., streams).
  • Backpackers should use iodine purification tablets or boil water.
  • Two-thirds of individuals exposed develop symptoms.
  • Infection requires as few as 10 cysts due to low infectious dose.
  • Reservoirs: beaver, raccoon, muskrat, dogs, and cats (typically asymptomatic).
  • Hosts: Organisms that show symptoms.
  • Incubation period: 6-20 days.
  • Symptoms: Range from mild indigestion to severe diarrhea lasting for days.
  • Duration: Usually lasts 1-4 weeks and is often self-limiting.
  • Prevention: Boiling water for at least 1 minute (5 minutes recommended), using bleach, iodine, or water purification tablets.
  • Treatment: Metronidazole (Flagyl), which is also an antifungal agent and treats Clostridium difficile infection.
  • Trophozoite form looks like an alien head, guitar pick, or pear cut in half lengthwise.
  • Has multiple flagella.
  • Two nuclei present.
  • Attaches to the intestinal lining using sucker-like structures.
  • Giardia stool has a very distinctive odor.

Leishmaniasis (Kala Azar)

  • Causative agent: Various Leishmania species (e.g., Leishmania domini).
  • Insect vector: Female sand fly (not sand flea).
  • Only female sandflies collect a blood meal since they require protein to produce eggs.
  • Reservoirs: Rodents, possums, anteaters, sloths, and dogs.
  • Incubation period: 2 weeks to several months.
  • Three forms: cutaneous, mucocutaneous, and visceral.

Cutaneous Leishmaniasis

  • A papule (blister-like) appears at the site of the bite (about 1 inch in diameter).
  • Self-limiting, heals, and goes away.
  • Leaves cratered scar tissue.

Mucocutaneous Leishmaniasis

  • Occurs in 80% of individuals with cutaneous leishmaniasis.
  • Organism spreads to mucous membranes (oral and nasal passages).
  • Forms open wounds or lesions that do not heal well.
  • Wounds can become infected with secondary organisms, especially bacteria, leading to potentially fatal infections.

Visceral Leishmaniasis

  • Can be asymptomatic or self-limiting, or frank visceral leishmaniasis.
  • Frank visceral leishmaniasis occurs 2-4 months after the bite.
  • Symptoms: Fever (intermittent), anorexia, malaise, weight loss, and diarrhea.
  • If untreated, can lead to anemia, enlargement of the spleen, and enlargement of the liver.
  • Without treatment, death typically occurs 2-3 years after the onset of symptoms.
  • The organism looks like a green bean cut in half lengthwise, with flagella on either end.
  • Not common in the United States due to the absence of sandflies but is found in the Middle East and parts of Africa.

Trichomoniasis

  • Causative agent: Trichomonas vaginalis
  • Sexually transmitted infection (STI).
  • No known animal reservoirs; only found in humans.
  • Third most common cause of vaginal symptoms in women (after bacterial vaginosis and candidiasis).
  • 2.5 to 3 million new cases diagnosed annually in the United States.
  • Requires large amounts of water to survive; easily destroyed if cells dry out.
  • Can survive on moist objects (towels, bathing suits, bathtubs, toilet seats).
  • Most often spread through sexual contact.
  • Infected children raise concerns about sexual abuse, leading to investigations by child and family services.
  • Prevention: Condoms.
  • Treatment: Metronidazole.

Symptoms

  • Men:
    • Mostly asymptomatic.
    • If symptoms occur: Painful or burning urination, painful testes, and a tender prostate gland.
  • Women:
    • Itching of the vulva and inner thighs.
    • Vaginal itching and burning.
    • Burning or painful urination.
    • Key symptom: Frothy, yellowish-green vaginal discharge with a rotten egg odor (malodorous).
  • Characterized by an undulating membrane that spins the cell for attachment to host cells.
  • Also has flagella for movement.

Trypanosomiasis

  • Causative agent: Trypanosoma species.
  • Two diseases: Chagas disease and African sleeping sickness.

Chagas Disease

  • Causative agent: Trypanosoma cruzii.
  • Found primarily in Central and South America.
  • Transmitted by the kissing bug.
  • Kissing bugs regurgitate food on the host, causing irritation and potential entry point for the parasite when the host scratches.
  • Causes systemic disease, damaging the heart and intestine.

African Sleeping Sickness

  • Causative agent: Trypanosoma brucei.
  • Found only on the African continent.
  • Transmitted by female tsetse flies.
  • Symptoms arise a week after the bite, with a tender bump near the bite site, which may open, and regionally enlarged lymph nodes.
  • The organism is injected directly into the host's bloodstream via fly saliva.
  • Eventually affects the central nervous system.
  • Progressive symptoms: gradual loss of interest in enjoyable activities, increased episodes of sleeping, poor coordination, confusion, slurred speech.
  • Terminal stage: coma, leading to death.
  • Trypanosomes visible in the bloodstream (snake-like organisms among red blood cells).

Varieties of Trypanosoma brucei

  • Trypanosoma brucei rhodesiense
    • Found in East and Southern Africa (grassy, cattle-raising areas).
    • Most dangerous form, progresses rapidly.
    • Death within six months.
  • Trypanosoma brucei gambiense
    • Found in Central and West Africa (forested regions).
    • Slower progression.
    • Death usually due to secondary infection.
    • 95% of infections are chronic with recurring symptoms.

Prevention & Treatment

  • Prevention: Insect repellent, protective clothing, clearing brush to eliminate breeding grounds.
  • Treatment: Toxic drugs with severe side effects; slim chance of successful treatment once the central nervous system is affected.