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Parasites Overview

Types of Parasites

Protozoa

Definition: Single-cell eukaryotes.Characteristics:

  • Free-living species capable of infecting humans.

  • Multiply within the host until the immune response controls them.

  • Exhibit diverse forms of reproduction, including sexual and asexual reproduction.

  • Often cause long-lasting chronic infections.Infection Types:

  • Intracellular Parasites: Infect red blood cells, macrophages, and the brain, extracting nutrients directly from host cells.

  • Extracellular Parasites: Found in blood, intestines, and gastrointestinal tracts; derive nutrients by ingesting host cells.Adaptations:

  • Evolved intricate mechanisms to evade immune system attacks.Methods of Movement:

  • Cilia: Tiny hair-like structures that beat in a pattern, allowing mobility.

  • Flagella: Long, whip-like structures that move in waves and propel the protozoa.

  • Amoeboid Movement: Creation of pseudopodia allows movement by flowing cytoplasm.Transmission: Can occur via ingestion, sexual contact, or insect vectors.Reproductive Potential: High potential due to short generational times and rapid development.

Helminths

Definition: Large, multicellular organisms typically detectable with the naked eye in adults.Characteristics:

  • Parasitic worms that primarily inhabit the intestines of hosts.

  • Undergo complex life cycles involving different developmental stages.

  • Do not multiply in humans; instead, they exist in larval and adult forms.Groups:

  • Tapeworms (Cestoda): Flat, segmented worms that absorb nutrients through their skin.

  • Flukes (Trematoda): Leaf-shaped worms that often require intermediate hosts to complete their life cycle.

  • Roundworms (Nematoda): Cylindrical worms with a complete digestive system, can cause various diseases in hosts.Size: Varies from 100 micrometers to several meters in length.Transmission Methods:

  • Ingestion of eggs or larvae.

  • Ingestion of larvae in tissues of another host.

  • Skin penetration by larvae.

  • Vector bites.

Arthropods

Definition: Invertebrate animals characterized by jointed legs, segmented bodies, and chitinous exoskeletons.Diversity: Over 1 million species, but only a few are medically significant.Relevant Groups:

  • Insects: (e.g., lice, fleas, mosquitoes) that can act as vectors for diseases.

  • Arachnids: (e.g., mites, ticks, spiders) that can transmit pathogens or act as parasites themselves.Health Impact:

  • Vector Role: Carry diseases such as bacteria, viruses, and parasites that can infect humans or other animals.

  • Allergic Reactions: Some arthropods can provoke allergic responses in humans.

Summary of Parasite Types

  • Protozoa: Single-cell eukaryotes, free-living, multiply in hosts, immune-controlled.

  • Helminths: Parasitic worms mainly inhabiting animal intestines, including tapeworms, flukes, and roundworms with complex lifecycles.

  • Arthropods: The largest phylum with exoskeletons, including insects and ticks, serving as blood feeders and disease vectors.