Introduction to parasitology

Question 1

Define parasite…

Answer 1

An organism of one species which survives by obtaining nutrients and shelter from an organism (host) of another species. (not always detrimental to host)

Question 2

Define paratenic host…

Answer 2

A host that is infected with immature parasite but is inactive. ie. does not grow, does not die. eg. remains as a cyst

Question 3

Define endoparasite…

Answer 3

a parasite that lives within the body of a host ie. within internal organs

Question 4

Define ectoparasite…

Answer 4

a parasite that lives on the surface of the host

Question 5

Define obligatory parasite…

Answer 5

A parasite that cannot live/reproduce without a suitable host

Question 6

Define facultative parasite…

Answer 6

Not originally a parasite (free-living) but once inside host can survive, often causing problems to the host

Question 7

Define intermediate host…

Answer 7

A host infected with larvae/eggs (immature parasite) that actively feed, grow & develop further within the host

Question 8

Define definitive host…

Answer 8

A host in which the parasite reaches maturity and, if possible, reproduces.

Question 9

Define prepatent period…

Answer 9

The period of time in which the parasite enters the host until the signs of infection become apparent eg. eggs in faeces

Question 10

When should diagnostic tests be done if parasite infection is suspected?

Answer 10

After the prepatent period for definite diagnosis

Question 11

Define infective stage…

Answer 11

Stage at which parasite enters the body of host and causes infection

Question 12

Define direct life cycle…

Answer 12

Parasite only requires 1 host (definitive OR intermediate host)

Question 13

Define indirect life cycle…

Answer 13

A parasite that completes it’s life cycle between 2 different host species

Question 14

Define migratory life cycle…

Answer 14

Life cycle that occurs thru different organs eg. mozzie bite -> blood -> liver… one host, one parasite

Question 15

Define non-migratory life cycle…

Answer 15

Life cycle that occurs in and affects only one body system eg. intestinal tract - mouth -> stomach -> SI -> LI…

Question 16

Name and briefly explain 5 common routes of infection with parasites. For each rout provide an example.

Answer 16

• oral via fecal matter ingested unintentionally eg. E. coli
• direct contact eg. Bovicola (lice)
• thru vector from infected animals blood into new hosts blood eg. Culicoides (mozzies/sandflies)
• venereal via vaginal penetration and introduction of parasite into reproductive tract eg. Trichomonas vaginalis (protozoa)
• vertical transmission during pregnancy of infected mother eg. Neospora
• inhalation when parasite enters upper/lower airway (nasal/tracheal) eg. Pneumonyssoides caninum

Question 17

How can the availability of an intermediate host affect parasitism?

Answer 17

When intermediate hosts are freely available, parasites relying on those intermediate host can obtain nutrients, grow and develop. If intermediate hosts are not ‘available’ then parasites cannot undergo these critical stages and ultimately develop into adults -> lower infection

Question 18

List and briefly explain 5 different ways parasites can harm their host. For each way, name a parasite.

Answer 18

• Cause mechanical blockages (bile duct, blood) eg. liver fluke
  Necrosis ??
• Can cause haemorrhage when juveniles attach to blood vessels eg. Ancylostoma duodenale (hookworm)
• Can cause irritation on the skin during attachment and feeding eg. Boophilus (ticks)
• Can cause thrombus formation in horse arteries due to larval stages eg. Strongylus vulgaris (blood worm)
• May prevent nutrient absorption from small intestines of animals eg. Giardia (anaerobic protozoa)