Parasitology Foundations - Helminths, Protozoa, and Arthropods

A comprehensive vocabulary review of core concepts, terminology, host/vector categories, life cycles, and key characteristics of nematodes, cestodes, and trematodes from VMED 5275.

Parasite

A smaller organism that lives on or in and at the expense of a larger organism called the host.

Endoparasite

A parasite living within the body of a host, resulting in an infection.

Ectoparasite

A parasite that lives on the external surface of a host or in the skin, resulting in an infestation.

Obligate Parasite

A parasite that always requires a host to complete its life cycle.

Facultative Parasite

An organism that acts as a parasite only if given the opportunity.

Host-Specific Parasite

A parasite that lives only on or in a single host species, such as lice.

Definitive Host

The host in which the adult or sexually reproductive processes of the parasite occur.

Intermediate Host

The host in which required development of intermediate or larval stages occurs.

Paratenic Host

A transport host infected with a parasite that undergoes no required development, remaining transferable until reaching the final host.

Reservoir Host

A host in which parasites may cycle other than the primary host species of interest.

Mechanical Vector

A vector that transmits parasites directly from host to host without any development of the parasite inside the vector.

Biological Vector

A vector that is required in the life cycle of a parasite for its development before transmission.

Direct Life Cycle

A parasite life cycle where the infective stage is reached in the environment without requiring an intermediate host.

Indirect Life Cycle

A parasite life cycle where the infective stage is reached inside an intermediate host.

Prepatent Period

The duration of time from initial infection until the production of parasite offspring.

Zoonosis

A disease of animals that can be transmitted to humans.

Cuticle

The non-living, outer protective layer of a nematode, secreted by the underlying living cellular tegument.

Parthenogenetic

A form of asexual reproduction where an embryo develops directly from an egg without fertilization, characteristic of parasitic female Strongyloides.

Strongylid Egg

An ellipsoidal, thin-shelled egg with a smooth surface containing an embryo in the morula stage, measuring $55\,\mu\text{m}$ to $90\,\mu\text{m}$ in length.

Strongyloides Egg

An ellipsoidal, thin-shelled, smooth-surfaced egg containing a fully formed larva when passed in feces, measuring $40\,\mu\text{m}$ to $60\,\mu\text{m}$ in diameter.

Ascarid Egg

A round to slightly oval, thick-walled egg containing a single cell with a pitted surface, measuring $60\,\mu\text{m}$ to $90\,\mu\text{m}$ in diameter.

Trichuris Egg

A thick-walled, football-shaped egg with a smooth shell and symmetrical bipolar plugs, measuring $70\,\mu\text{m}$ to $90\,\mu\text{m}$ in length.

Capillariid Egg

An egg similar in appearance to Trichuris but featuring asymmetrical bipolar plugs, measuring $55\,\mu\text{m}$ to $70\,\mu\text{m}$ in length.

Oxyuris equi

The large pinworm of horses, inhabiting the large intestine and producing eggs flattened on one side with an operculum at one end.

Hexacanth Embryo

The first-stage larva found within cyclophyllidean cestode eggs, characterized by possessing six hooklets.

Metacestode

General term for the intermediate developmental stages of cyclophyllidean cestodes, including cysticerci, coenuri, strobilocerci, hydatid cysts, multilocular cysts, and cysticercoids.

Plerocercoid

Also known as a sparganum, this is the second intermediate larval stage of diphyllobothriidean cestodes found in vertebrate hosts.

Miracidium

The ciliated larval stage of a trematode that hatches from an egg in aquatic conditions and infects a snail, the first intermediate host.

Paragonimus kellicotti

A lung fluke that uses freshwater snails as first intermediate hosts and crayfish or crabs as second intermediate hosts.