Principles and Definitions (RJ&N Chs 1 & 2; Desowitz Chs 1& 2) Parasitology is a division of Symbiosis - two organisms living together. Categories of symbiosis are based on the effects of one organism on the other.

Phoresis-2 organisms traveling together

Mutualism- 2 organisms living together in which both benefit from the association; both are metabolically dependent on one another

Commensalism- Relationship in which the symbiont benefits from an association with a host which is passive to the relationship (not harmed or benefited)

Parasitism- definitions: Original meaning from the Greek is a relationship in which "one eats at another's table or lives at another's expense.“ RJ&N page 4 - "Parasitism is a relationship in which one of the participants, the parasite, either harms its host or in some sense lives at the expense of the host.“

Entamoeba invadens

Entamoeba invadens

Parasitism- definitions: Noble and Noble – Parasitology: The Biology of Animal Parasites  "Parasitism is an obligatory association between two distinct species in which the dependence of the parasite upon its host is a metabolic one involving mutual exchange of substances."

Our Definition Parasite-an organism which lives at least part of its life cycle on or within another organism (the host) upon which it is physiologically dependent and to which it causes harm in some way. In a parasitological or medical context, it is restricted to animal agents, i.e., protozoa, helminths, and arthropods.

Where are Parasites Found?

A brooding Glossiphonid leech with its young feeding on my wife’s leg!

Where are Parasites Found? Ectoparasite- a parasite which lives on the body surface of the host.

Where are Parasites Found? Endoparasite- a parasite which lives within the body of the host.

Definitions of Hosts Many parasites have more than one host in their life cycle. These hosts have different roles and are given specific names.

Definitions of Hosts

Definitions of Hosts Definitive host – a host in which the parasite reaches sexual maturity and undergoes reproduction.

Definitions of Hosts Definitive host – a host in which the parasite reaches sexual maturity and undergoes reproduction. Intermediate – a host in which the parasite undergoes larval development but does not reach sexual maturity.

Definitions of Hosts Definitive host – a host in which the parasite reaches sexual maturity and undergoes reproduction. Intermediate – a host in which the parasite undergoes larval development but does not reach sexual maturity. Paratenic host (Transport host) – a host in which a parasite survives without undergoing further development. A paratenic host accumulates and maintains stages of a parasite, and although beneficial, is not essential to the life cycle.

Definitions of Hosts Vector- any agent, either animate or inanimate (such as wind, water, or arthropod) that transmits an infectious organism.

Definitions of Hosts Vector- any agent, either animate or inanimate (such as wind, water, or arthropod) that transmits an infectious organism. Biological Vector- a vector in which a parasite lives or develops. The parasite undergoes morphologic change and/or multiplication, and the vector is usually essential for the life cycle.

Definitions of Hosts Vector- any agent, either animate or inanimate (such as wind, water, or arthropod) that transmits an infectious organism. Biological Vector- a vector in which a parasite lives or develops. The parasite undergoes morphologic change and/or multiplication, and the vector is usually essential for the life cycle. Mechanical Vector- a vector which transmits a parasite by mechanical means only. It may be living or non-living and is not essential for the parasite’s life cycle.

Host-Parasite Relationships Like other living organisms, parasites have basic need in order to survive and be successful.

Host-Parasite Relationships Habitat or substrate Energy source (food) Reproduction of own kind Dispersal

Host-Parasite Relationships Living animals present special problems as habitats or environments.

Host-Parasite Relationships They move around and disperse They have non-specific defense mechanisms They mount specific immune responses They age and change physiologically They die

Host-Parasite Relationships Some of the most important factors influencing parasite transmission and infection are related to host behavior.

Echinococcus Tapeworms

Echinococcus species

Echinococcus multilocularis

Echinococcus granulosus   Surgical removal of 3 unilocular hydatid cysts from a Kenyan woman.

Host-Parasite Relationships Innate behaviors Learned behaviors Ethnic and cultural practices Local customs or habits Religious practices