Chapter 11 - Lecture

Chapter 11: Eukaryotic Microbes & Invertebrate Infectious Agents

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• Title: Eukaryotic Microbes & Invertebrate Infectious Agents

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• Exam Performance Statistics:

  • Exam 2 Average: 81%

  • High Score: 102

  • Case Study 2 Average: 12/20

  • High Score: 20/20

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Chapter Objectives

• Define: The major categories of eukaryotic microbes and invertebrate parasites.

• Describe: The role of fungi and protists in the environment and human diseases.

• Outline: The infectious cycles of eukaryotic parasites.

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Eukaryotes: An Overview

• Characteristics:

  • Possess a nucleus and multiple membranous organelles.

  • Contain linear chromosomes that divide through mitosis.

  • Stages of eukaryotic mitosis: prophase, metaphase, anaphase, telophase.

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Eukaryotic Reproduction

• Two types of reproduction:

  • Asexual reproduction (mitosis) allows indefinite proliferation.

  • Sexual reproduction involves reassortment of genetic material and alternates between diploid (2n) and haploid (n) stages.

• Benefits of sexual reproduction include increased genetic diversity.

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Classification of Eukaryotes

• Major Categories:

  • Fungi & microsporidians

  • Algae & dinoflagellates

  • Amebas

  • Ciliates

  • Trypanosomes & metamonads

• Multicellular parasites (e.g., helminths, arthropods) are typically excluded from true microbe classification.

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Eukaryotic Microbes and Infectious Agents

• Fungi:

  • Non-motile; cell walls made of polysaccharides; include decomposers and parasites.

• Amebas:

  • Heterotrophic protists; motile using pseudopods.

• Ciliates:

  • Covered with cilia; used for capturing prey and locomotion.

• Apicomplexans:

  • Intracellular parasites; complex life cycles involves attachment and penetration of host cells.

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• Trypanosomes and Metamonads:

  • Extracellular parasites with complex life cycles.

• Algae:

  • Photosynthetic protists involved in marine ecosystems and oxygen production.

• Helminths:

  • Multicellular worms that include various parasitic forms.

• Arthropods:

  • Invertebrate creatures that can act as parasites or free-living.

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Fungi & Microsporidians

• Yeasts: Rapidly growing single-celled fungi.

• Saccharomyces cerevisiae:

  • Example of baker's yeast.

• Opportunistic pathogens:

  • Include Candida albicans and Pneumocystis carinii.

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• Fungi Structure:

  • Comprise mycelia and tough cell walls of chitin.

  • Chitin provides strength, allowing fungal penetration into softer substances.

  • Expand via asexual mitosis; undergo meiosis for gamete formation as necessary.

• Spores:

  • Key for fungal dispersal.

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Protozoa: Amebas

• Definition: Unicellular organisms with variable shapes; form pseudopods.

• Feeding: Predatory, consuming other protists and bacteria.

• Size: Can reach several mm.

• Types of Amebas:

  • Lobed: bulky pseudopods.

  • Filamentous: thin, needle-like pseudopods.

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Amebic Dysentery

• Entamoeba histolytica:

  • Transmission through fecal-oral route.

  • Cysts ingested, develop into trophozoites, invading intestinal mucosa.

  • Symptoms include diarrhea, bloody stools, and potential for abscesses in organs.

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Infectious Cycle of E. histolytica

1. Human ingests cysts.

2. Cysts excyst into trophozoites.

3. Trophozoites invade the intestinal lining.

4. In severe cases, they can disseminate through the bloodstream.

5. Cysts are excreted in feces.

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• Associated Infections:

  • Naegleria fowleri: Primary amebic meningoencephalitis.

  • Balamuthia mandrillaris: Associated with serious infections.

  • Acanthamoeba: Causes keratitis and is a host for certain bacterial pathogens.

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Protozoa: Ciliates

• Structure: Possess alveoli and cilia for movement and feeding.

• Feeding mechanism: Paramecia trap bacteria in oral grooves for digestion.

• Function: Contractile vacuoles maintain osmotic balance.

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Protozoa: Apicomplexans

• Named for their apical complex that facilitates host cell entry.

• Lifecycle: Typically involves multiple hosts for sexual and asexual reproduction stages.

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Malaria and Plasmodium

• Types: P. falciparum and P. vivax.

• Transmission: Mosquito-borne disease, major health concern in tropical regions.

• Global impact: 1-3 million deaths annually with increased risk due to various factors.

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• Life Cycle of Plasmodium:

  • Asexual reproduction in humans, sexual in mosquitoes.

  • Symptoms induced by red blood cell lysis: fever, chills occurring every 48-72 hours.

  • Treatments include chloroquine and mefloquine.

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Cryptosporidium parvum

• Waterborne pathogen affecting immunocompromised patients.

• Causes severe watery diarrhea.

• Resistant to water chlorination, linked to outbreaks (e.g., Milwaukee, 1993).

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Protozoa: Trypanosomes

• Overview: Elongated cells with flagellum, cause various diseases (sleeping sickness, Chagas’ disease).

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African Sleeping Sickness

• Caused by Trypanosoma brucei gambiense.

• Symptoms: Initially fever and lymphadenopathy, progresses to severe neurological effects.

• Treatment available: Eflornithine.

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• Life Cycle Dynamics:

  • Trypanosome interconversion essential for human infection.

  • Slender form proliferates in bloodstream; stumpy form requires tsetse fly for further development.

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Life Cycle of Trypanosomes

• Differentiation initiated within the host; transitions between slender and stumpy forms necessary for transmission cycles involving the tsetse fly.

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Protozoa: Metamonads

• Characteristics: Flagellated parasites, anaerobic and lacking mitochondria.

• Giardia lamblia: Notable cause of intestinal giardiasis, prevalent in water supplies exposed to animal feces.

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Algae and Dinoflagellates

• Role: Major photosynthetic producers responsible for carbon fixation and oxygen production.

• Types: Green algae (Chlorophyta), red algae (Rhodophyta), and evolution through secondary endosymbiosis.

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Dinoflagellates

• Function: Critical in marine ecosystems; contribute to ‘red tides’ and produce harmful toxins.

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Invertebrate Parasites: Helminths

• Overview: Mostly non-parasitic but parasitic forms create significant health burdens.

• Caenorhabditis elegans: A model organism for developmental studies.

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Helminth Classification

• Nematodes (roundworms): Cylindrical shape.

• Trematodes (flukes): Oval flatworms.

• Cestodes (tapeworms): Absorb nutrients through skin via a sucker head.

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Example: Pinworms

• Enterobius vermicularis: Most common helminth infection in the U.S.

• Transmission requires treating the entire household.

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Example: Hookworms

• Nematodes such as Ancylostoma duodenale and Necator americanus.

• Lifecycle begins with larvae in soil, penetrate skin, travel through bloodstream, attach to intestines.

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Example: Roundworms

• Ascaris lumbricoides: Transmitted through contaminated food; potential for severe health issues.

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Example: Tapeworms

• Transmission via larvae in undercooked meat; may grow extensively in the host.

• Historical note on tapeworms used for weight loss in the past.

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Arthropods

• Definition: Invertebrate animals with exoskeletons and jointed appendages; can be ectoparasites or free-living.

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Ticks

• Characteristics: Similar to mites; associated with Lyme disease (Borrelia burgdorferi) transmission.

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Bedbugs

• Cimex lectularius: Blood-feeding nocturnal pests that have shown resistance to older pesticides; increasing prevalence in many areas.