JT

Eukaryotes: Fungi, Algae, Protozoa, and Helminths

Clinical Case Overview

  • As a Peace Corps nurse in West Africa, encounter with a 4-year-old girl with a swollen stomach.

    • Mother presents a large (10 cm) white worm coughed up by the girl.

    • Description of the worm: Cylindrical with tapered ends.

    • Question: What type of worm is it and how did she contract it?

  • Hint: Referring to data on helminths (pages 347-355).

Parasitic Diseases Statistics

  • Parasitic diseases affect approximately 1/3 of the world’s population, equating to more than 2 billion people.

    • Malaria: Causes about 1 million deaths annually, primarily in children.

    • Intestinal Protozoa and Helminths: Approximately 500 million infected individuals globally.

    • While more common in underdeveloped nations, the U.S. also sees millions affected.

    • Over 1 million new cases of trichomoniasis annually in the U.S.

    • About 60 million people infected with Trypanosoma cruzi.

Public Health Priorities

  • The Centers for Disease Control and Prevention (CDC) identifies five parasitic diseases as priority targets for public health action.

    • Criteria include:

    • The number of infections.

    • Severity of the illnesses.

    • Potential for prevention and treatment.

  • Discussion on emerging fungal pathogens, specifically Cryptococcus gattii in North America.

Eukaryotic Microorganisms Affecting Humans

  • Examination includes: fungi, algae, protozoa, parasitic helminths, and arthropods that transmit diseases.

  • Figure 12.1: Comparison of major characteristics of these eukaryotes is referenced.

Introduction to Fungi

Learning Objectives

  • 12-1: Defining characteristics of fungi.

  • 12-2: Differences between asexual and sexual reproduction in fungi.

  • 12-3: Key characteristics of the four fungal phyla.

  • 12-4: Consequences of fungi—beneficial and harmful effects.

Fungal Characteristics

  • Fungi Kingdom: Chemoheterotrophs that acquire food through absorption.

  • Predominantly multicellular (with the exception of yeasts).

  • Reproduction occurs through both sexual and asexual spores.

  • **Comparison of Fungi and Algae:

    • Algae:**

    • Belong to multiple super clades, can reproduce both sexually and asexually, and are photoautotrophic (produce various photosynthetic pigments).

    • Obtain nutrients mainly via diffusion.

    • Can be unicellular or multicellular, sometimes forming colonies, filaments, or aggregates.

    • Protozoa:

    • Diverse super clades, primarily chemoheterotrophic, with some exhibiting photoautotrophy.

    • Characterized as unicellular and capable of motility; often form resistant cysts.

    • Helminths:

    • Multicellular animals that are chemoheterotrophic; primarily obtain nutrients through ingestion.

    • Exhibit complex life cycles including stages such as egg, larva, and adult.

  • Arthropods:

    • Key vectors for disease transmission, including ticks and certain insects, particularly mosquitoes.

Key Concepts

  • Eukaryotic microorganisms cause human diseases, often diagnosed via microscopic examination.

  • Culturing fungi can be done on laboratory media, similar to bacteria.

  • Algal illnesses in humans arise from toxin ingestion, termed intoxicating instead of infectious.

  • Vectors are defined as arthropods transmitting infectious diseases.

  • Best control of arthropod-borne diseases achieved through limiting exposure to the vectors.

  • Treatment of eukaryotic infections poses challenges due to human cell similarity.

Regarding Fungi's Impact

  • Of the 100,000+ species of fungi, ~200 are pathogenic to humans.

  • Incidence of severe fungal infections is on the rise, particularly in healthcare settings and among immunocompromised individuals.

  • Fungal diseases also significantly impact economically important plants, incurring over $1 billion in annual losses.

Fungal Life Cycle and Structure Discussion

  • Fungal structures include hyphae, which can be:

    • Septate Hyphae: Contain cross-walls (septa).

    • Coenocytic Hyphae: No septa, appear as long cells with multiple nuclei.

  • Growth occurs by elongation at hyphal tips, and fragmentation of hyphae can yield new fungi.

  • Fungal colonies are classified as vegetative structures as they involve cellular metabolic activity and growth.

Fungi's Beneficial Roles

  • Fungi play a key ecological role as decomposers, recycling nutrients from dead matter.

  • This process sees fungi utilizing extracellular enzymes (e.g., cellulases) to break down plant compounds.

  • They also associate symbiotically with plants (mycorrhizae), enhancing mineral and water absorption in roots, and contribute to animal diets (e.g., fungi-farming ants).

  • Humans utilize fungi for various purposes including food production (mushrooms, breads) and pharmaceuticals (penicillin).

Clinical Case: Cryptococcus gattii as Pathogen

  • Cryptococcus gattii: Emerging fungal pathogen evidenced through raised fungi in a lung mass of Ethan and Waldo after extensive exposure in a forest ecosystem.

    • This case stresses the importance of diagnosis and treatment via antifungal agents in clinical settings.

    • Followed by implications for public health understanding the environmental interactions of these fungi.

Recommendations for Control and Research

  • Investigate fungal interactions in microbiomes.

  • Advancements in fungal disease therapeutics acknowledging their eukaryotic cellular structures.

  • The necessity of ongoing environmental assessments regarding fungal organisms affects public health and ecosystem health.