Parasitology

Question 1

What is a parasite?

Answer 1

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

Question 2

direct life cycle

Answer 2

simple
one host

Question 3

indirect life cycle

Answer 3

complex
2 or more hosts

Question 4

definitive host

Answer 4

Host in which sexual reproduction takes place. Also known as final host

Question 5

intermediate host

Answer 5

Host in which only immature stages grow and develop. Asexual reproduction may or may not occur
host is required to complete lifecycle

Question 6

paratenic host

Answer 6

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

Question 7

normal host

Answer 7

animal recognized as part of the normal life cycle

Question 8

abnormal or abherrant host

Answer 8

• 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

Question 9

reservoir

Answer 9

host serves as a source of infection for other animals
does not suffer harm

Question 10

vector

Answer 10

invertebrate, usually arthropod, that transmits infectious disease
* Biological vector - parasite develops in the vector
* Mechanical vector - like a contaminated instrument

Question 11

parasitic infection vs infestation

Answer 11

Infection = endoparasite vs Infestation = ectoparasite
does not mean disease, only means that parasite is present

Question 12

microparasite

Answer 12

multiply inside of host

Question 13

macroparasite

Answer 13

offspring released into environment

Question 14

infectious vs infective

Answer 14

• 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 *

Question 15

prepatent period

Answer 15

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

Question 16

generation time

Answer 16

egg to egg

Question 17

patency

Answer 17

adult reproductive infection

Question 18

Will an exposed animal become infected?

Answer 18

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

Question 19

Will an infected animal become ill?

Answer 19

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

Question 20

how do parasites cause disease?

Answer 20

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

Question 21

70-30 rule

Answer 21

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