General Parasitology Overview

General Parasitology

• Parasites are living organisms that obtain nourishment and shelter from another organism where they live.
• Parasitology is the study of the phenomena of dependence of one living organism on another.
• Medical parasitology focuses on parasites that affect humans.

Host

• A host is an organism that harbors a parasite.
• Host types include:
  • Definitive host: The host in which the parasite reaches its adult stage and reproduces sexually.
  • Intermediate host: A host in which the parasite develops to an immature or larval stage.
  • Reservoir host: A host that harbors a parasite and can pass it onto a susceptible host.

Parasites

• Parasites can be classified as:

  • Ectoparasites: Parasites that live on the surface of the host.
  • Endoparasites: Parasites that live inside the host's body.

• Parasites can be further classified by their association with the host as:

  • Temporary parasite: Parasite that spends only a part of their life cycle on a host
  • Permanent parasite: Parasite that spends their entire life cycle on a host.
  • Facultative parasite: Parasite that can live as a parasite or free living, depending on conditions.
  • Obligatory parasite: Parasite that must live as a parasite.
  • Occasional/Accidental parasite: Parasite that lives in an unusual host.

Nomenclature of Parasites

• Example: Ascaris lumbricoides Linnaeus, 1758 describes a specific species of parasitic roundworm.

The Study of Parasitology

• Study components include:
  • Epidemiology and geographical distribution.
  • Habitat
  • Morphology.
  • Life cycle.
  • Pathogenic effect and symptoms.
  • Diagnosis methods.
  • Treatment methods and treatments.
  • Prophylaxis (prevention).

Geographical Distribution

• Factors influencing distribution include:
  • Infection resources.
  • Life cycle of the parasite.
  • Susceptible hosts.

Prevalence of Parasitic Infections

• Examples:
  • Amebiasis: 1% of the world's population
  • Giardiasis: 200 million
  • Lymphatic filariasis: 128 million
  • Ascariasis: 128 billion
  • Hookworm: 128 billion
  • Trichuriasis: 900 million

Life Cycle

• Key components include:
  • Definitive host
  • Intermediate host
  • Reservoir host
  • Vector (living intermediary)

Diagnosis

• Diagnostic methods include:
  • Clinical manifestation (symptoms).
  • Laboratory analysis.

Treatment

• Treatments depend on the type of parasite.
• Chemotherapy (drugs targeting parasites) is often used.
• Some infections resolve on their own.

Prevention

• Strategies include:
  • Therapeutic prophylaxis (treatment to prevent infection).
  • Eradication of infection.
  • Personal (individual) prophylaxis (preventative measures).

Important Groups of Parasites

• Categories:
  • Sarcomastigophora
  • Mastigophora (flagellates)
  • Sarcodina (amoeba)
  • Apicomplexa (e.g. plasmodium)
  • Microspora
  • Minute, intracellular parasites

Additional Important Groups of Parasites

• Ciliophora
• Platyhelminthes
• Aschelminthes
• Arthropoda
• Insects
• Pentastomida
• Tongue worm

Additional note

• Mycology (study of fungi) is also related to parasitic infections.