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.