Protozoan Diseases

Life cycle

Protozoa have often complex life cycles that feature 2 or more stages and one or more hosts. Important protozoan stages:

• Cysts: Highly resistant stage
• Trophozoite: Feeding stage; often the pathogenic stage
• Other stages: Sporozoites, Merozoites, oocysts

Pathogenesis

1. Adhesion: Giardia
2. Intracellular replication: Plasmodium
3. Hydrolytic enzymes: Trypanosomes
4. Hypersensitivity reactions: Trypanosomes
5. Evasion of host defenses

Protozoan pathogens

Entamoeba histolytica

• Disease: Amebiasis
• Microscopy: Amoeba; cysts
• Transmission: oral - fecal route
• Symptoms: abdominal pain, cramps, bloody stools
• Complications: abscesses (liver, lung, brain), fever

Giardia lamblia

• Disease: Giardiasis (Beaver fever)
• Microscopy: Flagellated protozoan with 2 'eyes'; cysts
• Transmission: Contaminated water (wilderness); animal reservoir (zoonotic)
• Symptoms: foul-smelling diarrhea, cramps, flatulence, fatty stools
• Complications: Severe malabsorption disease

Trichomonas vaginalis

• Disease: Vaginitis / Trichomoniasis
• Microscopy: Flagellated protozoan (trophozoites)
• Transmission: STD
• Symptoms: Burning, itching, vaginal discharge, painful urination

Balantidium coli

• Disease: Balantidiasis
• Microscopy: Ciliated protozoan; cysts
• Transmission: Contaminated water via animal reservoir (pigs, monkeys)
• Symptoms: Abdominal pain, bloody stools, nausea, anorexia
• Complications: Ulceration due to invasion of colon wall

Cryptosporidium parvum

• Disease: Cryptosporidiasis
• Microscopy: Coccidian protozoan; oocysts in stool
• Transmission: Contaminated water supply; zoonotic
• Symptoms: Watery diarrhea
• Complications: AIDS - up to 50 stools per day, dehydration, long-term infection

Cyclospora cayetanensis

• Disease: Cyclosporiasis
• Microscopy: Coccidian protozoan; oocyst
• Transmission: Contaminated water (animal reservoir)
• Symptoms: diarrhea, nausea, cramps, anorexia
• Complications: AIDS: Prolonged and severe disease
• Pathogenesis: Inflammation of intestinal epithelium; intracellular invasion
• Treatment: Trimeth - sulfa

Microsporidia

• Disease: Microsporidiosis
• Microscopy: Infective spores; intracellular merozoites without organelles
• Transmission: oral-fecal (contaminated water)
• Symptoms: persistent diarrhea (AIDS)
• Pathogenesis: Intracellular life cycle
• Treatment: none proven

Plasmodium spp.

• Disease: Malaria
• Microscopy: Trophozoites, merozoites, and gametocytes in plasma and RBCs
• Transmission: Anopheles mosquito (vector)
• Symptoms: Fever and chills in 24 - 72 hour patterns
• Complications: Liver, kidney and brain damage

Babesia microti

• Disease: Babesiosis
• Microscopy: Sporozoan protozoa
• Transmission: Ticks (vector)
• Symptoms: malaise, fever, headache, chills, sweating, fatigue
• Complications: Anemia, renal failure

Toxoplasma gondii

• Disease: Toxoplasmosis
• Microscopy: Protozoa: Oocysts, sporozoites, bradyzoites, tachyzoites
• Transmission: Ingestion of contaminated food or oocysts from cat feces
• Symptoms: chills, fever, headaches, myalgia, fatigue
• Complications: Mostly in AIDS; blindness, encephalitis, myocarditis

Acanthamoeba, Naegleria & Balamuthia

• Disease:
  • Acanthamoeba keratitis (Acanthamoeba spp.)
  • Amebic meningoencephalitis: Naegleria fowleri
• Microscopy: Amoebae, cysts may be seen
• Transmission: Swimming water, contact lens solution
• Complications: Granulomatous encephalitis, disseminated infections (AIDS) - Acanthamoeba, Balamuthia

Leishmania spp.

• Disease: Leishmaniasis
• Microscopy: Flagellated protozoa
• Transmission: Sandfly bite (vector)
• Symptoms: ulceration at bite site, mucous membranes, internal organs 
• Complications: disfiguring ulcers; internal organ damage & death

Trypanosoma brucei

• Disease: African Sleeping Sickness
• Microscopy: Flagellated protozoa with undulating membrane
• Transmission: Tsetse fly (vector)
• Symptoms: Ulcer at bite site, fever, myalgia, arthralgia
• Complications: lethargy, retardation, convulsions, death

Trypanosoma cruzi

• Disease: Chagas' Disease
• Microscopy: Flagellated protozoa; intracellular amastigote
• Transmission: Kissing bugs (vector)
• Symptoms: reddening around bite; facial rash; fever, malaise, myalgia, fatigue
• Complications: chronic infection enlarging heart, liver, spleen; brain granulomas