Parasitology HC1 – Introduction
What is a parasite:
Eukaryotic organisms that have to live in or on other organisms (hosts) to complete its natural life
cycle → doesn’t always have to harm host
Medical parasitology: Eukaryotic organisms that infect human hosts
Symbiosis: organisms living together → close association between two organisms; (micro)organism
and hosts
1. Commensalism
• ‘’eating at the same table’’’
• Benefit is uni-directional
→ (micro)organism benefits, host is neither harmed nor helped
2. Mutualism
• A form of commensalism
• Benefit is bi-directional
→ Both host and (micro)organism benefit
3. Parasitism
• Benefit is uni-directional
→ (micro)organism benefits, host is harmed
Ecto parasites: Live ON the host → infestation
- Arthropoda
• Insecta (lice, fleas)
- Pediculosis humanus capitas (head louse)
- Pediculosis pubis (crab louse)
• Arachnida (mites, ticks)
- Sarcoptes scabiei (mite)
- Ixodes ricinus (tick)
Endo parasites: Live IN the host → infection
- Protozoa: unicellular
• Giardia, P.falciparum, etc.
- Metazoa: multicellular
• Tapeworm & other helminths
Facultative: the parasite may exist in a free living state
Obligate: the parasite cannot survive without its host
Different types of hosts:
- Definitive host: in which sexual replication takes place
- Intermediate host: only asexual replication takes place, so no sexual replication
- Accidental host: parasite is seldom found in this host, was infected by accident
Example with plasmodium (malaria):
- Mosquito is definitive host, since sexual replication takes place there
- Humans are intermediate host
,Protozoa
Unicellular eukaryotes
- Reproduction:
• Binary fission
• Schizogony
- Organelles of locomotion
• Rhizopods
• Flagellates
• Cilliates
• Sporozoans
- Leishmania tropica (Leishmaniasis)
- Plasmodium falciparum (Malaria)
- Toxoplasma gondii (Toxoplasmosis)
- Trypanosoma brucei (extracellular) (Sleeping sickness)
,Metazoa
Multicellular eukaryotes
- Helminths
- Morphology
• Trematodes (fluke)
• Cestodes (tapeworm)
• Nematodes (roundworm)
- Sex
• Male, female or hermaphroditic
- Schistosoma mansoni
• Trematode
- Taenia solium
• Cestode
- Enterobius vermicularis (aarsmade)
• Nematode
Definitive host in helminths is where you find the adult worm
, Protozoa can multiply within the host → so increase parasitic load
Helminths cannot multiply within the host, can lay eggs but they will leave the body via stool → so
stable population
Direct lifecycle: Parasite needs one host to complete its lifecycle
Bijv. Enterobius vermicularis:
Eggs are very sticky → itchy around anus → scratch → if hands are not washed can infect self again
(and others)
What is a parasite:
Eukaryotic organisms that have to live in or on other organisms (hosts) to complete its natural life
cycle → doesn’t always have to harm host
Medical parasitology: Eukaryotic organisms that infect human hosts
Symbiosis: organisms living together → close association between two organisms; (micro)organism
and hosts
1. Commensalism
• ‘’eating at the same table’’’
• Benefit is uni-directional
→ (micro)organism benefits, host is neither harmed nor helped
2. Mutualism
• A form of commensalism
• Benefit is bi-directional
→ Both host and (micro)organism benefit
3. Parasitism
• Benefit is uni-directional
→ (micro)organism benefits, host is harmed
Ecto parasites: Live ON the host → infestation
- Arthropoda
• Insecta (lice, fleas)
- Pediculosis humanus capitas (head louse)
- Pediculosis pubis (crab louse)
• Arachnida (mites, ticks)
- Sarcoptes scabiei (mite)
- Ixodes ricinus (tick)
Endo parasites: Live IN the host → infection
- Protozoa: unicellular
• Giardia, P.falciparum, etc.
- Metazoa: multicellular
• Tapeworm & other helminths
Facultative: the parasite may exist in a free living state
Obligate: the parasite cannot survive without its host
Different types of hosts:
- Definitive host: in which sexual replication takes place
- Intermediate host: only asexual replication takes place, so no sexual replication
- Accidental host: parasite is seldom found in this host, was infected by accident
Example with plasmodium (malaria):
- Mosquito is definitive host, since sexual replication takes place there
- Humans are intermediate host
,Protozoa
Unicellular eukaryotes
- Reproduction:
• Binary fission
• Schizogony
- Organelles of locomotion
• Rhizopods
• Flagellates
• Cilliates
• Sporozoans
- Leishmania tropica (Leishmaniasis)
- Plasmodium falciparum (Malaria)
- Toxoplasma gondii (Toxoplasmosis)
- Trypanosoma brucei (extracellular) (Sleeping sickness)
,Metazoa
Multicellular eukaryotes
- Helminths
- Morphology
• Trematodes (fluke)
• Cestodes (tapeworm)
• Nematodes (roundworm)
- Sex
• Male, female or hermaphroditic
- Schistosoma mansoni
• Trematode
- Taenia solium
• Cestode
- Enterobius vermicularis (aarsmade)
• Nematode
Definitive host in helminths is where you find the adult worm
, Protozoa can multiply within the host → so increase parasitic load
Helminths cannot multiply within the host, can lay eggs but they will leave the body via stool → so
stable population
Direct lifecycle: Parasite needs one host to complete its lifecycle
Bijv. Enterobius vermicularis:
Eggs are very sticky → itchy around anus → scratch → if hands are not washed can infect self again
(and others)
