Parasitology Key Concepts: Hosts, Life Cycles, and Interactions

Phoresis

Involves two organisms traveling together without any biological or physiological interdependence.

Mutualism

Both organisms benefit, often with a necessary physiological reliance; typically obligatory.

Commensalism

One organism benefits while the other is unaffected, such as Entamoeba gingivalis in the human oral cavity.

Parasitism

One organism either harms or lives at the expense of its host.

Definitive Host

The host where the parasite achieves sexual maturity.

Intermediate Host

Necessary for the parasite's developmental stages but without sexual maturation.

Paratenic (Transport) Host

Doesn't support parasite development but can help bridge ecological gaps between hosts.

Reservoir (Amplifying) Host

Can carry a pathogen indefinitely without harm.

Dead-end or Incidental Hosts

Don't develop high parasite levels; unable to transmit the pathogen further.

Hyperparasitism

A parasite hosting another parasite.

Vector

An organism, often an arthropod, transmitting a pathogen from reservoir to host.

Aberrant Host

An atypical host for the parasite it carries.

Host Specificity

Some parasites are specific to one host, while others can develop in multiple hosts.

Ectoparasite

Lives on the host's surface. Ex. Tick- Ixodes scapularis.

Endoparasite

Resides inside the host. Ex. Trypanosoma brucei or Plasmodium falciparum.

Facultative Parasite

Doesn't rely on the host for survival; incidental.

Obligate Parasite

Needs a host for survival and life cycle completion.

Mechanical Damage

Causes physical harm or obstruction in tissues.

Physiologic Damage

Affects metabolism; consumes host's nutrients.

Direct Life Cycles

The parasite completes its life cycle within a single host species.

Indirect Life Cycles

Requires multiple host species for completion, typically involving 2-3 hosts: definitive, intermediate, and paratenic.

Prevalence

Proportion of a population infected at a specific time.

Incidence

Rate of new infections in a population.

Morbidity

Refers to illness or disease state.

Co-morbidities

Presence of simultaneous illnesses.

Mortality

Incidence of death due to a disease.

What is a Hypnozoite?

dormant; liver-stage parasites of P. Ovale and P. Vivax; can cause relapsing of Malaria months or years later

Schuffner’s dots

Fine; round; uniformly red or red-yellow staining dots in RBC infected with P. Vivax & P. Oavale

Hemozin

A disposal product formed from the digestion of blood by some blood-feeding parasites

Schizogony/Merogony

Production of Merzoite

Merozoite

Non-motile; egg-shaped/spherical cells specialized for entering RBCs

Gametogony

Production of Zygotes

Zygote

diploid cell formed when two haploid gametes in reproduction in protozoans

Sporogony

Productions of Sporozoites

Sporozoite

Infective; motile stage of certain parasitic protozoa

Oocysts (thick walled)

Thickwalled; resistant spore form that contains a zygote; produced after sexual reproduction; FECAL ORAL, in the environment

Oocysts (thin-walled)

Reinfection by a baby parasite without leaving the host; aims for compromised immune systems; you can reinfect yourself — autoinfection

Monoecious (Hermaphorditism)

Single individual; self-fertilization; asexual; mostly worms

Dioecious

Each individual is a separate gender; sexual reproduction