Westchester Community College 8

Overview of Protozoan Diversity

  • Protozoans exhibit significant genetic diversity.

  • Focus on animal-like protozoans, categorized by their movement mechanisms.

Phylum Mastigophora (Flagellates)

  • Definition: Protozoans that use flagella for motility.

  • Behavior: Generally free-living organisms. They do not desire to inhabit hosts and cause disease accidentally.

  • Example Disease: Giardiasis (caused by Giardia lamblia):

    • Commonly associated with traveler's diarrhea.

    • Transmission through contaminated water (e.g., drinking water in foreign countries) and undercooked food.

    • Symptoms: foul-smelling, oily diarrhea due to inability to digest fats (absence of mitochondria leading to anaerobic metabolism).

  • Pathophysiology:

    • Giardia's lack of mitochondria leads to reliance on carbohydrates and proteins for energy, refusing to digest fats.

    • Diarrhea is self-limiting but can lead to intestinal malabsorption if prolonged, leading to nutrient deficiency.

    • Parasite Classification: Defined as a parasite only when it causes significant disease beyond self-limiting symptoms.

Trichomonas vaginalis

  • Definition: The only protozoan known to cause sexually transmitted infections.

  • Prevalence: 1.6 million cases per year in the US; often asymptomatic in males and only symptomatic in about 10% of females.

  • Symptoms:

    • Painful urination and discharge with a specific odor.

    • Generally treatable with antiprotozoal drugs but has potential for leading to complications, much like chlamydia and gonorrhea.

Amoebas

  • Definition: Protists that move via cytoplasmic streaming; characterized as blobs.

  • Key Pathogens:

    1. Entamoeba histolytica:

      • Causes amoebiasis, sometimes referred to as amoebic dysentery.

      • Transmission through contaminated food/water leading to severe intestinal damage.

      • If untreated, can invade the liver and lungs, causing severe complications.

    2. Acanthamoeba:

      • Primarily contracted through contaminated water (e.g., recreational swimming).

      • Can lead to keratitis and potentially blindness.

    3. Naegleria fowleri:

      • Transmits via the olfactory nerve from contaminated water (e.g., lakes, ponds).

      • Causes primary amoebic encephalitis with a very high mortality rate (around 95%).

Ciliophora

  • Characteristics: Use cilia for movement; abundant in freshwaters.

  • Valentinian coli:

    • A zoonotic pathogen leading to diarrhea but usually not life-threatening.

    • Infection occurs mainly through fecal contamination.

Apicomplexa

  • Characteristics: Obligate parasites with no means of motility; require a host for survival and reproduction.

  • Transmission: Typically involves complex life cycles with both definitive (sexual reproduction) and intermediate hosts (asexual reproduction).

  • Example Pathogen:

    • Babesia: Rare disease associated with Lyme disease; requires understanding of host species for its life cycle dynamics.

    • Generally less pathogenic to definitive hosts than to intermediate hosts.

Summary Points

  • Many protozoans are free-living, but significant health threats arise when they inadvertently infect human hosts.

  • Proper sanitation and awareness of contaminated water sources are crucial for prevention of protozoan infections.

  • Regular health screenings for sexually transmitted infections and water-safety awareness are essential in managing risks associated with protozoan pathogens.