Study Notes on Eukaryotes and Parasitology

Characterizing and Classifying Eukaryotes: Study Notes

Objectives

  • Describe major groups of Eukaryotes.
  • Describe how they differ from Prokaryotes.
  • List characteristics of all protozoa.
  • Classify protozoa and human diseases caused by protozoa.
  • List characteristics of fungi that distinguish them from other groups of eukaryotes.
  • List ways in which fungi are beneficial.
  • Classify fungi and human diseases caused by them.
  • Describe distinguishing characteristics of algae.
  • List different groups of fungi and describe distinguishing characteristics.
  • List economic benefits and diseases caused by algae.
  • List diseases transmitted by fleas, lice, mosquitoes, and kissing bugs.
  • Describe different groups of helminths, the diseases caused by them, and their mode of transmission.

Parasitology

  • Definition: The study of parasites, which include bacteria, viruses, protozoa, helminths, and arthropods living at the expense of a host.
  • Impact on host: Varies from little or no injury to moderate to severe injury.
  • Pathogens: Parasites that cause disease.

Types of Parasites

Ectoparasites

  • Definition: Live on the surface of other organisms (e.g., Ticks, Lice, Mites).

Endoparasites

  • Definition: Live within the body of other organisms (e.g., Protozoa, Helminths).

Obligated Parasites

  • Definition: Must spend at least part of their life cycle in/on a host (e.g., Protozoa that cause malaria).

Facultative Parasites

  • Definition: Normally free-living but can obtain nutrients from a host (e.g., soil fungi infecting humans).

Parasite Duration with Host

  • Permanent parasites: Remain in host after invasion (e.g., Tapeworm).
  • Temporary parasites: Feed on and leave the host (e.g., Biting insects).
  • Accidental parasites: Infect other hosts than their normal ones (e.g., Ticks).

Types of Symbiotic Relationships

Symbiosis

  • Definition: Means to live together.
Mutualism
  • Definition: Both partners benefit (e.g., intestinal bacteria synthesize vitamin K and vitamin B).
Commensalism
  • Definition: One partner benefits while the other is unharmed.
Parasitism
  • Definition: One organism derives benefit at the host's expense.

Types of Vectors

  • Definition: Arthropods that carry disease-causing microbes from one host to another.

Biological Vectors

  • Definition: Parasites go through part of their life cycle here (e.g., Malaria mosquito).

Mechanical Vectors

  • Definition: Transport contaminated material (e.g., Houseflies, cockroaches).

Host Classification

  • Definitive Host: Harbors the sexually reproductive stage of the parasite (e.g., Malaria in Anopheles mosquito).
  • Intermediate Host: Host where asexual reproduction occurs (e.g., malaria in humans).
  • Reservoir Host: Source of disease-causing organisms (e.g., wild rats as reservoirs for Plague).

Parasites and Host Defense

  • Evading Host Defenses: Parasites can evade host defenses by changing antigens faster than the host can produce antibodies.
  • Encystment: Formation of outer covering to protect against unfavorable conditions.

Eukaryotic Cells

  • Characteristics: More complex structures with a true nucleus enclosed by a nuclear membrane.
  • Types: May be unicellular or multicellular.
  • Ribosomal RNA: 80S.
  • Reproductive Methods: Asexual reproduction by budding, fragmentation, spore formation, and schizogony. Some reproduce sexually.

Classification of Eukarya

Major Groups

  • Algae
  • Protozoa
  • Fungi
  • Molds
  • Arthropods
  • Helminths

Protozoa

Definition and Characteristics

  • Group: Defined by being eukaryotic, unicellular, and lacking a cell wall.
  • Motility: Motile by cilia, flagella, and/or pseudopodia (except apicomplexans).

Distribution

  • Habitats: Require moist environments, found in ponds, streams, lakes, oceans, moist soil, and organic matter.
  • Pathogenicity: Very few are pathogens; all produce trophozoites and some form cysts.

Nutrition

  • Most Protozoa: Chemoheterotrophic, obtaining nutrients by phagocytizing bacteria, organic matter, or tissues of the host.

Reproduction

  • Asexual Reproduction: Most through binary fission or schizogony. Some engage in sexual reproduction via gametocytes forming diploid zygotes or conjugation.

Classification of Protozoa

Major Groups

  • Apicomplexa: Non-motile.
  • Sarcomastigophora: Includes mastigophora (flagellated protozoa).
  • Ciliophora: Ciliate protozoa.

Examples

  • Trypanosoma (causes African sleeping sickness, vector: tsetse fly).
  • Leishmania (causes leishmaniasis, vector: sand fly).
  • Trichomonas vaginalis (causes trichomoniasis).
  • Giardia intestinalis (causes giardiasis).

Protozoa - Specific Diseases

Trypanosoma brucei

  • Disease: African sleeping sickness.
  • Vector: Tsetse fly.
  • Symptoms: Fever, lymph node swelling, headache, neurological issues.

Giardia intestinalis

  • Common Name: Beaver fever.
  • Transmission: Contaminated water.
  • Symptoms: Diarrhea, abdominal pain.

Trichomonas vaginalis

  • Disease: Trichomoniasis.
  • Transmission: Sexual contact.
  • Symptoms: Vaginal discharge, urethritis in men.

Amoebae

Naegleria fowleri
  • Disease: Primary amoebic meningoencephalitis.
  • Transmission: Inhalation of cysts from warm freshwater.

Apicomplexa

Plasmodium spp.
  • Disease: Malaria.
  • Species: P. falciparum (most severe), P. vivax, P. ovale, P. malariae.
  • Symptoms: Fever, chills, anemia.

Disease Development

  • Malaria Life Cycle: Involves an exoerythrocytic cycle and an erythrocytic cycle within humans, with gametocytes developed in the spleen and liver of the mosquito.
  • Epidemiology: Endemic in tropical areas; significant mortality, especially in children.

Fungi

Characteristics

  • Environmental Presence: Ubiquitous, chemoheterotrophic, cell walls typically made of chitin.
  • Growth Conditions: Thrive in high sugar, salt, and acidic environments, optimal temperature range 20-35°C, and pH < 5.0.

Significance

  • Role: Decomposers; used in food production; antibiotic production; cause diseases in plants, animals, and humans.

Morphological Forms

  • Yeasts: Unicellular, varying shapes.
  • Molds: Multicellular, filamentous structures (hyphae and mycelium).
  • Dimorphic fungi: Exhibit yeast and mold forms depending on environmental conditions.

Human Disease

  • Infections: Mycoses have increased especially in immunocompromised individuals (e.g., AIDS).
  • Common Infections: Coccidioidomycosis, Blastomycosis, Histoplasmosis, Pneumocystis pneumonia.

Economic Importance

  • Positive: Fermentative and antimicrobial properties; used in pharmaceutical production.
  • Negative: Spoilage of food; diseases in crops.

Specific Fungal Diseases

Coccidioidomycosis
  • Symptoms: Flulike, can become systemic.
  • Pathogen: Coccidioides immitis.
  • Diagnosis/Treatment: Identification of spherules; treated with amphotericin B.
Blastomycosis
  • Symptoms: Flulike and can cause skin lesions.
  • Diagnosis/Treatment: Identification in specimens; treated similarly to coccidioidomycosis.
Histoplasmosis
  • Symptoms: Asymptomatic to severe respiratory infection.
  • Diagnosis/Treatment: Identification of fungi finds; resolves often without treatment in healthy individuals.

Helminths (Worms)

Helminthology

  • Definition: The science of worms; involves multicellular organisms with complex life cycles and reproductive systems.

Classification of Helminths

Types

  • Nematodes: Roundworms.
  • Trematodes: Flukes.
  • Cestodes: Tapeworms.

Nematodes (Roundworms)

Characteristics

  • Cylindrical body, complete digestive system, and separate sexes.

Common Examples

  • Enterobius vermicularis (Pinworm): Infects children, causes itching.
  • Ascaris lumbricoides: The largest nematode; causes abdominal pain and malnutrition.
  • Wuchereria bancrofti: Filarial worm, causes elephantiasis and filariasis.

Trematodes (Flukes)

Characteristics

  • Flat, leaf-shaped, with suckers for attachment.

Examples

  • Schistosomiasis caused by Schistosoma spp., infects many worldwide.

Cestodes (Tapeworms)

Characteristics

  • Scolex: Head containing hooks; proglottids for reproduction.

Common Examples

  • Taenia saginata: Beef tapeworm.
  • Diphyllobothrium latum: Fish tapeworm causing vitamin deficiencies.

Summary of Helminth Diseases

  • Includes enterobiasis, trichuriasis, ascaris infection, strongyloidiasis, and more. Symptoms vary but often include gastrointestinal disturbances, anemia, and in severe cases, organ damage.

Conclusion

Understanding eukaryotes' classification, characteristics, and their role in human health through parasitism is vital for managing diseases and improving public health.