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interaction between two organisms of different species, living together in intimate association. Implies no mutual or unilateral benefit or metabolic dependency


a kind of sybiosis in which on symbiont (the commensal) is benefited, while the other (host) is neither helped nor harmed by the association. The host provides food and or shelter to the commensal, which lives without benefit or harm to the host


a kind of symbiosis in which both sybionts are metabolically dependant upon each other, and both are benefited by the association


a kind of sybiosis in which one symbiont (the parasite) is metabolically dependant on the other (host) and at the same time, may be harmful to it by deprivation or damage


a kind of symbiosis in which one symbiont (phoront) is mechanically carried about by its host. No metabolic interaction or dependancy occurs


an organism which lives at least part of its life cycle on or with in another organism (host) upon which it is metabolically dependant and to which it may cause harm. In parasitology or from medical point of veiw, it is restricted to animal agents, i.e, protozoa, helminths, and arthropods


a parasite which lives on the body surface of the host


a parasite which lives within the body of host

Obligate parasite

a parasite which is completely dependent on the host for its exsistance during part or all its life cycle

Facultative parasite

parasite which is not completely dependent on the host for its exsistence. It can and usually does complete its life cycle as a free-living organism, but, alternatively, can complete part or all its life cycle in or on the host

Monoxenous (homoxenous) parasite

a parasite which has one type of host (lives within single host) in its life cycle

Heteroxenous (euryxenous) parasite

a parasite with two or more types of hosts (lives in more than one host) in its life cycle

Temporary (intermittent) parasite

a parasite which contacts its host only to feed then leaves


a parasite which is parasitic on or ith in another parasite


a living plant or animal which harborsand or gives sustenance to a symbiont

Natural host (typical host)

a host which the parasite is commonly found and which the parasite can complete its development (or appropriate phase of its development neccessary for subsequent completion of its life cycle

Accidental host

a host in which the parasite is not commonly found. neverless, it is one suitable for the parasite's development. In some instances, the accidental host beomes the dead end host

Aberrant host

a host in which the parasite cannot complete its development or the appropriate phase of its development

Definitive host

a host in which the parasite undergoes sexual reproducion or reaches the adult stage. If there is no sexual reproduction in the life of the parasite, the host most important to humans is the definitive host

Intermediate host

a host which harbors the asexual or immature stages of a parasite and which in some stage of its development of the parasite takes place

Paratenic host (transport host)

a host in which a parasite survives, but in which no further development of the parasite takes place. It accumulates and maintains stages of the parasite butis not essential to the life cycle

Dead end host

a host in which the parasite reaches an end point and is unable to continue its life cycle

Reservoir host

any host in which the parasite lives and is available for transmission to another susceptible host. In parasitology, the term usually refers to a host which harbors a stage of the parasite similar to that found in the natural host. It is not the most important host


any agent, either animate or inanimate (such as wind,water,or arthropod) that transmits an infectious organism

Biological vector

a living vector which is essential for the development and life cycle of the parasite and in which the parasit undergoes morphologic change and/or multiplication

Mechanical vector

a vector which is not essential for the development or life cycle of the parasite: may be living or non living

Direct life cycle

a life cycle in which there is only a definitive host, with no intermediate hosts involved

Indirect life cycle

a life cycle which there is a definitive host and one or more intermediate hosts involved.

Heterogonic life style

a life cycle involving alternation of parasitic and free living generations

Homogonic life style

a life cyclein which all generations are parasitic or all are free living. there is no (or little) alteration of the two

Active transmission

transmission in which either an active, aggresive parasite itself seeks out the host and enters it or a biological vector actively seeks out the host and brings the parasite to it

Passive transmission

transmission in which the host/parasite contact is more or less accidental; usually accidental ingestion of the parasite or due y mechanical vectorsspread b


any particular form in the life cycle of a parasite which can be distinguished from all of its other forms

Infective stage

that stage in the life cycle of a parasite which is capable of producing infection of a host


any pre-adult stage in the life cycleof an organism, other than the egg, that is morphologically distant from the adult


reinfection by the progeny of a parasite while they are still with in the body of the host


reinfection by the progeny of a parasite which hatch on the skin and reenter the body of the host


a new, superimposed infection of an individual host that already bears infection by the same species of parasite

Prepatent period (biological incubation period)

the period of a time from infection of a host with a parasite until one can demonstrate that the host is infected by finding a stage of a parasite (eggs, larva, ect) in or from the host

Patent period

a period of time from first demonstration of a parasite in or from the host until one can no longer demonstrate that the host is infected (parasite dies from natural causes)

Clinical incubation period

a period of time from infection of a host with a parasite until clinical signs are apparent

Natural resistance

inherit resistance of a species against infection with a certian strain or species of parasite

Age resistance

resistance in which unexposed hosts are more susceptibe to infection by a parasite as young animals than they are when they are older

Reverse age resistene

resistance in which unexposed hosts are more susceptible to infection by a parasite as older animals than they are when they are younger


resistance of a host to superinfection which persists only as long as the parasites which provoke it survive and are present in the host. It is resistance conferred by a still exsisting infection, the organism of which are not destroyed by the resistance. It may be complete or partial resistance

Host specificity

the restriction of a parasite to one or more kinds of hosts; the degree to which a parasite is able to mature in more than one host species


a presence of parasite stages in the circulating blood


living in feces. Usually applied to non parasites or pseudo-parasites which may be ingested and passed through the intestinal tract without having infected the animal


the eating of feces


the parasite is resent on or with in the host and is potentually pathogenic; however the animal does not exhibit outward clinical signs of disease


the parasite is present on or within the host and does produce obvious injury or harm to the host. The host exhibits obvious outward clinical signs of clinical paratism


parasites wich live on the body of the host


parasites that live within the host

Erratic or aberrant parasites

parasites that wander away from their usual sites of infection

Incidental parasite

a parasite can occur in a host in which it usually does not live

Facultative parasite

organisms that are free-living in nature and become parasitic in certain hosts

Obligatory parasite

parasites that must lead a parasitic existence. Most of the parasites that affect domestic animals are obligatory parasites

Periodic parasite

parasites that mke short frequent visits to the host to feed.


short term relationshipin which one symbiont benefits at the expense of the other ( cat and mouse)


the smaller member of the relationship is mechanically carried about by the larger member (flea on a dog)


association in which both organism in relationship benefits


association in which one symbiont benefits and the other niether benefits nor is harmed


association that exists between two organisms of a different species in which one member (parasite) lives on or within the other member (host) and may cause harm. Parasite is metablically dependent on host

Homoxenous or monoxenous parasite

parasite that will infect only one type of host

Stenoxenous parasite

parasite with very narrow host ranges

Euryxenous parasite

parasites with very broad host ranges

Qualitative method

reveals whether parasites are present or not

types of qualitative method

fecal floatation, centrifuge, direct smear

Quantitive method

indicates the number of eggs or cysts present in each gram 0f feces. Indicates the number of adult parasites with in the host

types of quantitive methods

stolls-egg counting technique, modified Wisconsin sugar flotation method,McMaster technique

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