Diseases due to Eukaryotic Pathogens

Overview

Eukaryotic pathogens include protozoa and fungi, both of which are significant causes of human disease. These organisms possess complex cellular structures and diverse life cycles, contributing to their pathogenicity and clinical manifestations.

• Protozoa: Unicellular, eukaryotic organisms, often classified by their mode of locomotion.

• Fungi: Multicellular or unicellular eukaryotes, including molds, yeasts, and dermatophytes.

Protozoa

Main Characteristics

• Eukaryotic

• Unicellular

• No cell wall

• Locomotion: Characterized by flagella, pseudopods, cilia, or non-motile forms.

Classification by Locomotion

• Flagella: Long, whip-like structures for movement (e.g., Giardia lamblia, Trichomonas vaginalis).

• Pseudopods: Temporary projections of cytoplasm (e.g., Amoeba proteus, Entamoeba histolytica).

• Cilia: Short, hair-like structures (e.g., Paramecium).

• None motile: Some apicomplexans (e.g., Plasmodium).

Mastigophorans (Flagellates)

• Trichomonas vaginalis: Parabasalid protozoan, causes trichomoniasis (a sexually transmitted infection).

• Giardia intestinalis: Causes giardiasis, a diarrheal disease from contaminated water.

Trichomonas vaginalis

• Lacks mitochondria, has a single nucleus, and a parabolic body.

• Resides in the human vagina; numbers controlled by vaginal pH.

• Symptoms: Vaginal discharge, genital itching, painful urination, and occasionally genital redness and burning.

• Transmission: Sexual contact; most common curable STI.

• Treatment: Metronidazole, tinidazole, secnidazole.

Giardia intestinalis

• Feeds off intestinal lining, causes malabsorption and diarrhea.

• Transmission: Ingestion of cysts from contaminated water or food.

Amebozoa or Sarcodina

• Move and feed using pseudopods.

• Entamoeba histolytica: Causes amoebic dysentery; invades the gut lining.

• Transmission: Ingestion of cysts from contaminated food or water.

Amebo-flagellates

• Naegleria fowleri: "Brain-eating amoeba" found in warm freshwater and soil.

• Life cycle forms: cyst, trophozoite (feeding/reproductive), flagellate (motile).

• Pathogenesis: Trophozoites enter via the nose, migrate to the brain, causing Primary Amebic Meningoencephalitis (PAM).

• Symptoms: Rapid onset of fever, headache, confusion, seizures, and death.

• Occurrence: Rare, but almost always fatal.

Apicomplexa

• Nonmotile, obligate intracellular parasites with complex life cycles.

• Examples: Toxoplasma gondii (fetal infections), Cryptosporidium (waterborne illness), Plasmodium spp. (malaria).

Plasmodium spp. and Malaria

• Transmitted by Anopheles mosquitoes.

• Life cycle includes sexual reproduction in mosquitoes and asexual reproduction in humans.

• Infects red blood cells, causing periodic fevers and anemia.

• Four main species infect humans: P. falciparum (malignant tertian malaria), P. vivax, P. ovale, P. malariae; P. knowlesi is emerging.

Plasmodium Life Cycle

• Asexual phase: Sporozoites enter human via mosquito bite.

• Exoerythrocytic phase: Sporozoites infect liver cells, develop into merozoites.

• Erythrocytic phase: Merozoites infect red blood cells, undergo schizogony.

• Fever phase: Rupture of red blood cells releases parasites, causing fever.

• Gametocyte phase: Gametocytes ingested by mosquito, sexual reproduction occurs.

Table: Human Malaria Species and Blood Stages

Fungi

General Characteristics

• Mycology: Study of fungi.

• Eukaryotic chemoheterotrophs; digest food externally and absorb nutrients.

• Aerobic or facultative anaerobic.

• Most are multicellular; yeasts are unicellular and can be dimorphic.

• Cell walls made of chitin, not cellulose.

Fungal Structures

• Thallus: Fungal body, composed of hyphae.

• Hyphae: Filamentous structures; septate (with cross-walls) or coenocytic (without septa).

• Mycelium: Mass of hyphae.

• Vegetative hyphae: Nutrient absorption.

• Aerial hyphae: Reproduction.

• Spores: Produced sexually or asexually.

Yeasts and Dimorphic Fungi

• Budding yeasts: Divide unevenly.

• Fission yeasts: Divide evenly.

• Dimorphic fungi: Yeast-like at 37°C, mold-like at 25°C.

Common Skin Diseases Due to Fungi

Cutaneous Mycoses (Ringworm)

• Caused by dermatophytes; infect keratinized tissues (skin, hair, nails).

• Named by location:

  • Tinea capitis: Scalp

  • Tinea barbae: Beard

  • Tinea corporis: Body

  • Tinea cruris: Groin

  • Tinea pedis: Foot

  • Tinea manuum: Hand

• Transmission: Direct contact.

• Symptoms: Scaly, itchy, inflamed skin.

• Treatment: Topical antifungals.

Superficial Mycoses: Tinea Versicolor

• Etiology: Malassezia furfur.

• Feeds on skin oil; causes mild scaling and pigment changes ("sun spots").

• Treatment: Topical antifungals.

Systemic Mycoses: Candidiasis

• Opportunistic infections caused by Candida albicans.

• Common microbiota of skin and mucous membranes.

• Transmission: Person-to-person.

• Symptoms: Range from superficial (oral thrush, vaginal yeast infection) to systemic (in immunocompromised).

Largest Organism on Earth

Armillaria (Honey Fungus)

• The largest living organism is a fungus (Armillaria genus), spanning over 2.4 miles in Oregon.

• Demonstrates the ecological significance and adaptability of fungi.

Key Terms and Concepts

• Chemoheterotroph: Organism that obtains energy and carbon from organic compounds.

• Dimorphic: Ability to exist in two forms (yeast and mold).

• Schizogony: Asexual reproduction by multiple fission, seen in Plasmodium.

• Chitin: Nitrogen-containing polysaccharide in fungal cell walls.

Summary Table: Major Eukaryotic Pathogens

Additional info: These notes expand on the original slides by providing definitions, life cycle details, and clinical relevance for each pathogen, as well as summary tables for comparison and study.