Parasitology Terminology

Parasitology

the study of parasites and their relationship to their host

Symbiosis

“Living together”— close interrelationship between two different organisms for long periods of time

Phoresis

two symbionts traveling together; no physiologic or biologic dependence

Mutualism

both organisms benefit from this relationship

Commensalism

one benefits, the other is unaffected

Parasitism

one organism (parasite) benefits, one organism (host) is harmed

Ectoparasites

found on (not in) host; example: tick, mite, flea, fly

Endoparasites

found internally in host; example: hookworms in intestine

Facultative parasite

“opportunist”— not normally a parasite (does not require host to survive) but will become parasitic if opportunity arises

Obligate Parasite

all or part of the life cycle must be a parasitic relationship with host

Incidental (exotic) parasite

normal host is a different species

• may not survive very long in wrong host

• may survive and be highly pathogenic in wrong host

Definitive Host

harbors sexual (mature) stages of parasite; if parasite undergoes sexual reproduction, it will occur in this host

Intermediate Host

required in life cycle of parasite; parasite undergoes some development in this host

Paratenic or Transport Host

no parasite development in this host, but parasite remains alive ineffective for a normal host

sort of a parasite “fail-safe” plan to continue its existence)

Reservoir Host

a host that serves as a source for the parasite to be transmitted to the usual host

example: wild animals such as antelopes in Africa can serve as reservoir hosts for the protozoan parasite Trypanosoma brucei rhodesiense that can cause fatal cases of “sleeping sickness” in humans

Vectors

organisms that transmit parasites to a vertebrate host

Biological Vector

• essential to the life cycle completion of the parasite

• parasite must undergo some of its life cycle development in this vector

Mechanical Vector

• vector is not required in the life cycle of parasite

• vector physically transfers infective stage of parasite to new host

Zoonosis

infectious agent (parasite) that can be transmitted from animals to man

Sylvan cycle

a parasite cycles through its life cycle among wild animals normally (man gets into the cycle accidentally, usually)

Urban Cycle

a parasite cycles among domestic animals (and rats). Easy for man to get included in this cycle

Niche

• tissue site in host to which a parasite will locate

• some parasites are very specific— will locate to only one tissue in host

Host specificity

• will depend upon the particular parasite

• varies from non-specific to very host specific

Host susceptibility

parasite can establish infection before host can eliminate it

Host resistance

host eliminates before parasite can establish infection

Etiology

the cause of a disease (can involve infectious agents, genetic factors and/or environment

Pathogenesis

the process involved in the development of the disease

Infection

multiplication of organisms inhabiting the body

Disease

characterized by presence of clinical signs/symptoms

Non-pathogenic

does not cause disease in host

• a commensal organism is this

Pathogen

can cause disease in host

Amastigote

kinetoplast and kinetosome above the nucleus, flagellum short and confine in pocket. cell is globular.

Promastigote

kinetoplast and kinetosome at anterior end of cell, flagellum free and lone; cell is elongated

Epimastigote

kinetoplast and kinetosome close and anterior to the nucleus; there is a short undulating membrane before the flagellum emerges at the anterior of the cell; cell is elongated

Trypomastigote

kinetoplast and kinetosome at posterior end of cell; flagellum forms an undulating membrane that runs the length of the cell and may continue free when it reaches the anterior end; cell is elongated