Parasitology 1 - Introduction to Parasitology (Michael)

Question 1

Define the term parasite

Answer 1

An organism that lives in (endoparasite) or on (ectoparasite) another (host) to its own advantage and to the disadvantage of the host.

Question 2

Into what groups are parasites classified based of their habitat

Answer 2

Ectoparasites

• Parasites living on or affecting the skin surface of the host.
• Tick and lice

Endoparasites

• Parasites living within the body of the host.
• Intestinal worms, Plasmodium spp., and Schistosoma spp.

Question 3

Into what groups are parasites classified depending on their dependence on the host

Answer 3

Obligate parasites

• Cannot complete their life cycle without spending some time in a parasitic relationship.
• Many obligate parasites have free living stages but it does not last very long.
• Vespula acadica

Facultative parasites

• Not normally parasitic.
• Rarely infect humans but can be fatal.
• Free-living nematodes

Incidental (accidental) parasites

• When a parasite attaches or enters the body of a species different from its normal one.
• Raccoon worm: Baylisascaris

Question 4

Into what groups are parasites classified depending on their pathogenicity

Answer 4

Pathogenic parasites

• Cause severe disease in the host.
• Plasmodium spp.

Opportunistic parasites

• Cause mild disease in immunologically healthy individuals but cause severe disease in immunodeficient hosts.
• Toxoplasma gondii

Question 5

Define the four different types of host

Answer 5

Definitive host - host in which the parasite reaches sexual maturity.

Intermediate host - host required for completion of the life cycle but one in which the parasite does not reach sexual maturity.

Paratenic host - host in which the parasite does not undergo any development but in which it remains alive and infective to another host.

Reservoir host

• An animal that harbours an infection that can be transmitted to humans.
• Leishmania spp. in dogs

Question 6

Distinguish between indirect and direct life cycles

Answer 6

Indirect life cycle

• Multiple hosts or involvement of a vector.
• Involves a definitive host and an intermediate host.
• Schistosoma spp.

Direct life cycle

• Parasite completes life cycle in a single host.
• The infective stage such as an ovum, cyst, larva, is passed out of the body which infects other hosts.
• Entamoeba

Question 7

Describe the three parasite stages

Answer 7

Diagnostic stage - A developmental stage of a pathogenic organism that can be detected in stool, blood, urine, sputum, CSF or other bodily secretions.

Infective stage - The stage at which a parasite is capable of entering the host and continuing development within the host.

Pre-patent period - The interval between exposure to infection and the onset of illness.

Question 8

What is zoonoses and give an example organism

Answer 8

• Disease spread between animals and people.

- Cryptosporidium