principles and definitions (r and j chs 1 & 2) parasitology is a division of symbiosis - two...

Principles and Definitions (R and J 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.“

• R&J 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

• 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."

Parasitism- definitions:

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!

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


• Ectoparasite- a parasite which lives on the body surface of the host.


• 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.


• Definitive host – a host in which the parasite reaches sexual maturity and undergoes reproduction.


• 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.


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


• 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.


• Habitat or substrate

• Energy source (food)

• Reproduction of own kind

• Dispersal

• Living animals present special problems as habitats or environments.



• They move around and disperse

• They have non-specific defense mechanisms

• They mount specific immune responses

• They age and change physiologically

• They die


• 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.


• Innate behaviors

• Learned behaviors

• Ethnic and cultural practices

• Local customs or habits

• Religious practices

Your Areas of Responsibility

• Lectures

• Any specific assignments given

• A set of facts/info about selected species of parasites (A-I)

9 topics

• A- Morphology (structure)-size

9 topics

• B- Taxonomy: Largely based on morphology. Know where to place organism in the scheme of things.

Phylum ????? (Sarcodina)

9 topics

• C – Life cycle, including the ontogenetic (developmental) stages and their size.

9 topics

• C – Life cycle, including where found environmentally.

Be more specific! Habitat

9 topics

• C – Life cycle, including prepatent period: The period of time from infection of a host with a parasite until one can demonstrate that the host is infected by finding a stage of the parasite (cyst, egg, larva, etc.) in or form the host.

9 topics

• D – Geographic distribution: Where in the world would you find it?

Trypanosoma gambiense

9 topics

• E – Symptoms: Aspects which you observe (headaches, fever, jaundice, etc.)

9 topics

• F – Pathology: Damage from infection. Physical damage/changes done to body which you can see. Otherwise know as the consequences of the infection.

9 topics

• G – Diagnosis: How to look for the parasite, where to look, and what do you expect to see. Do not base on symptoms.

9 topics

• H – Epidemiology: How does it spread thru a population?

9 topics

• I – Drug of Choice and Prognosis: Treatment and what you expect to happen/prospects.

principles and definitions (r and j chs 1 & 2) parasitology is a division of symbiosis - two...

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