Parasitology Flashcards
Define definitive host.
Host which supports sexually mature, reproducing adult parasite.
Define intermediate host.
Host which supports immature or non-reproductive forms of a parasite.
Describe protozoa.
Protozoa are unicellular eukaryotic organisms.
They undergo asexual reproduction, so parent and daughter cells have identical DNA.
Their size is 10 to 150 micrometres.
They have a heterotrophic mode of feeding as they derive food from the host.
Give an example of a medically important amoeba.
Amoebas are protozoa that have a pseudopod.
Entamoeba histolytica is a medically important amoeba which is transmitted by the feco-oral route.
The pathogen is acquired by either eating feces-contaminated food or drinking water that is contaminated by E. histolytica cysts.
The cysts pass through the stomach, but when they reach the intestines they undergo multiple fission.
E. histolytica then produces digestive enzymes that degrade gut epithelial cells, allowing the pathogen to enter the bloodstream and moving to other organs such as the skin, liver or lungs.
Disease produces gastrointestinal symptoms.
Give an example of a medically important flagellate.
Flagellates are protozoa that have flagella.
A medically important flagellate is Giardia intestinalis.
It is transmitted by the fecal-oral route, by contaminated food or water or by hands or fomites.
Disease produces gastrointestinal symptoms, such as: abdominal pain, bloating, diarrhoea, loss of appetite and weight loss.
Give an example of a medically important ciliate.
Ciliates are protozoa that have cilia.
An example of a medically important ciliate is Balantidium coli.
It is transmitted by the fecal-oral route and produces gastrointestinal symptoms, such as: abdominal pain, weight loss and intermittent diarrhoea containing blood and pus.
Give an example of a medically important apicomplexan.
Apicomplexans are protozoa that move by gliding over surfaces.
A medically important apicomplexan is Toxoplasma gondii.
Disease produces flu-like symptoms, but most people may be asymptomatic.
Describe the life cycle of parasites.
The cyst is the resistant, transmissible form of the protozoa.
It waits for the host to intake contaminated food or water.
When a host intakes the contaminated food or water, the cyst becomes active and forms trophozoite, which causes disease.
In adverse environment, cysts are formed, and the cycle is repeated.
Describe the general characteristics of helminths.
Helminths are eukaryotic, multicellular organisms that are dioecious, meaning they are male and female.
While in the infective stage, helminths form eggs, which are resistant and transmissible and can survive in the environment.
When it becomes active, it forms worms and larva, which cause disease.
They have a round, smooth appearance.
Describe the life cycle of nematodes and two examples of parasitic nematodes.
Nematodes undergo four moults and four larval stages to reach adult stage.
Enterobius vermicularis (pinworm) is a parasitic nematode which causes symptoms such as: irritability; pruritus ani; and insomnia.
Ascaris lumbricoides (giant roundworm) is another nematode which is taken in by consumption of eggs on contaminated food or water.
It causes symptoms such as: gastrointestinal symptoms; weight loss; and intestinal blockage.
Describe the general characteristics of cestodes and give an example of a parasitic cestode.
Cestodes are eukaryotic organisms which have a ribbon-like, segmented shape.
Cestodes have a scolex which has four suckers and two rings of hooks.
Taenia saginata are parasitic cestodes which cause symptoms such as: abdominal pain; weight loss; weakness; pruritus ani; and pain on excreting tapeworm segments.
Describe the general characteristics of trematodes and give an example of a parasitic trematode.
Trematodes are eukaryotic organisms which are flat and leaf-shaped.
Fasciola hepatica is a parasitic trematode.
It produces symptoms such as: fever; hepatomegaly; fatty food intolerance; jaundice; and gastrointestinal symptoms.
