علم الطفيليات الطبية

Medical Parasitology Level 1

• Parasitology is the study of microorganisms living on or within other organisms (hosts).
• Medical parasitology is divided into three branches:
  • Medical Protozoology: Studying medically important protozoa that affect humans.
  • Medical Helminthology: Studying helminthes (worms) that affect humans.
  • Medical Entomology: Studying arthropods that cause or transmit diseases to humans.
• A parasite is a living organism that obtains nourishment and other needs from a host.
• The host is an organism that supports the parasite.

Host-Parasite Relationships

• Symbiosis: Two different organisms living together and interacting. Includes three types:
  • Mutualism: Beneficial to both organisms; they can't survive independently.
  • Commensalism: One organism benefits, the other isn't affected.
  • Parasitism: One organism benefits, the other is harmed.

Types of Parasites

• Based on location of infection:
  • Ectoparasites: Live on the skin surface of the host. (e.g., lice)
  • Endoparasites: Live within the host's body (e.g., blood parasites).
• Based on pathogenicity:
  • Pathogenic: Cause definite pathological lesions in the host (e.g., Entamoeba histolytica)
  • Non-pathogenic (Commensal): Obtain food and protection from the host without causing definite pathological lesions (e.g., Entamoeba coli)
  • Opportunistic: Don't cause disease in healthy individuals but can cause severe disease in immunocompromised hosts (e.g., Pneumocystis carinii)

Types of Hosts

• Host: An organism that harbors the parasite, bigger than the parasite.
  • Reservoir host: An organism that harbors the parasite and can pass it to other hosts.
  • Definitive (final) host: The host where the parasite reaches its adult stage and reproduces.
  • Intermediate host: A host that the parasite needs to complete a part of its life cycle.
  • Vector: An organism that transmits the parasite from one host to another.

Mechanisms of Infection

• Passive entry: Through feeding and drinking (water or insects), parasites (eggs or cysts) are transmitted (e.g., Giardia, Entamoeba, Ascaris)
• Active entry: By biting insects (e.g., mosquitoes transmit malaria; black flies transmit onchocerciasis; tsetse flies transmit sleeping sickness; sandflies transmit leishmaniasis).

Classification of Parasitology

• Protozoa: Unicellular organisms (e.g., Entamoeba, Plasmodium, Giardia)
• Helminths: Multicellular organisms (e.g., worms, flatworms, roundworms).
• Additional classification according to sites on the body: (e.g., intestinal, urogenital, blood, tissue protozoa)