Parasitology Flashcards
What is a parasite?
An organism that lives in or on another living organism (host), obtaining from it part or all of its nutrients
* Wide definition
* Cause harm to the host
* Some degree of adaptive structural modification
* Parasites only include those organisms that are eukaryotes
direct life cycle
simple
one host
indirect life cycle
complex
2 or more hosts
definitive host
Host in which sexual reproduction takes place. Also known as final host
intermediate host
Host in which only immature stages grow and develop. Asexual reproduction may or may not occur
host is required to complete lifecycle
paratenic host
Host not required to complete the life cycle but help parasite to get the host. No parasitic development of any kind take place.
Also known as transport host
normal host
animal recognized as part of the normal life cycle
abnormal or abherrant host
- dead end
- Animal not normally used as a host
- Often (not always) associated with disease
- Animal could be an abnormal definitive, intermediate or transport host, depending on which stage of the parasite life cycle is present
reservoir
host serves as a source of infection for other animals
does not suffer harm
vector
invertebrate, usually arthropod, that transmits infectious disease
* Biological vector - parasite develops in the vector
* Mechanical vector - like a contaminated instrument
parasitic infection vs infestation
Infection = endoparasite vs Infestation = ectoparasite
does not mean disease, only means that parasite is present
microparasite
multiply inside of host
macroparasite
offspring released into environment
infectious vs infective
- Infectious: caused or capable of being communicated by infection
- Infective: Parasite stage capable of infect the host. Many parasites are not able to cause infection until after some period of development in the environment *
prepatent period
Term used with internal parasites - mainly macroparasites
* It’s the time required following infection of the definitive host to reach reproductive maturity (sexual reproduction): period before production of eggs/cysts, etc.
* Not the same as the generation time: egg to egg
* Patency: adult reproductive infection
generation time
egg to egg
patency
adult reproductive infection
Will an exposed animal become infected?
not always
* Parasites usually require appropriate stimulus/i to recognize potential host
* Intracellular parasites need specific receptors on cells of appropriate hosts
* GI helminths often need specific cues like pH, bile
Will an infected animal become ill?
not always
Infection/Infestation vs Disease
Parasite usually requires appropriate stimulus/i to recognize potential host
Host response
* Innate immunity
* Adaptive immunity
Normal immunity typically limits, but does not eliminate parasite infection
* Limits reinfection, reduces growth and reproduction of parasites
* Often full expression of immunity requires presence of active infection
how do parasites cause disease?
Parasite-induced trauma to cells, tissues, and organs
Changes in cellular growth patterns
Interference with host nutrient acquisition
Toxins released by the parasites
The host immune response to infection
70-30 rule
on average
Top 30% has 70% of the worms
Bottom 70% has 30% of the worms
overall: few animals with high # of parasites, many animals with few parasites
sometimes called 80/20 rule
