Parasitology: Types of Parasites

Parasites and Hosts

• A parasite is an organism that lives in or on another organism (host) and causes harm.
• Accidental parasite: a parasite that attacks an unnatural host and survives (e.g., Hymenolepis diminuta, a rat tapeworm).
• Intermittent parasite: arthropodes, such as mosquitoes, which periodically feed on larger organisms.
• Monoxen parasite: a parasite that completes its life cycle in or on one host.
• Heteroxen parasite: a parasite that completes its life cycle in or on more than one host.

Host and Parasite Relationships

• Definitive host: the host in which the sexual or adult form of the parasite is found.
• Intermediate host: the host in which the asexual or immature, or larval form of the parasite is found.
• Patient: a person who has parasites in their body and shows clinical symptoms.
• Carrier: a person who has parasites in their body but does not show symptoms.
• Reservoir host: an animal that harbors the same species of parasites as humans.

Parasite Classification

• Non-pathogenic parasites: live in/on the body of the host and do not cause disease.
• Pathogenic parasites: are disease-causing parasites.
• Opportunistic parasites: do not generally produce disease in healthy individuals but cause illness in individuals with impaired immunity.

Infection and Transmission

• Infection: the presence of a parasite in or on the tissues of the host.
• Infestation: the presence of arthropods on the skin of the host.
• Transmission: human-to-human, animal-to-human, food-borne, water-borne, blood-borne, vector-borne, and sexual transmission.

Protozoology

• Protoplasm: the body of protozoa.
• Ectoplasm: the external hyaline portion of the cytoplasm.
• Endoplasm: the internal granular portion of the cytoplasm.
• Pseudopods: false feet.

Protozoa Reproduction

• A) Syngamy: sexually different cells unite to form a zygote.
• B) Conjugation: 2 cells attach to each other, and the exchange of nuclear material occurs.

Medical Parasitology

• Nematodes (Roundworms): multicellular, macroscopic adult forms, microscopic eggs, complex life cycle.
• Trematodes (Flukes): multicellular, macroscopic adult forms, microscopic eggs, complex life cycle.
• Cestodes (Tapeworms): multicellular, macroscopic adult forms, microscopic eggs, complex life cycle.

Medical Helminthology

• Unsegmented body tapered at each end, body covered by tough cuticle that resists drying and crushing.
• Possess developed digestive and excretory organs.

Medical Entomology

• Insecta and Arachnida are studied in medical entomology.

Sporozoa

• A type of protozoa that has an apical complex that helps the organism enter the host cell.
• No locomotion organelles.

Protozoa Characteristics

• Small, microscopic, eukaryotes, unicellular organisms, wide range of sizes and shapes.
• Contain nucleus and functional organelles.
• Reproduce quickly, may have asexual and/or sexual phase in the host and/or vector.