Lecture 24: Parasitology I Flashcards
Name 3 ways in which parasites are different from bacteria and viruses in terms of structure.
- Parasites are eukaryotes, not prokaryotes
- Parasites can be single celled or multicellular
- Parasites have a nucleus and more complicated cellular structure
How do parasites differ from bacteria and viruses in terms of vaccines?
Unlike viruses and bacterial infections, which we have developed vaccines for, there is not a single vaccine for parasitic infections.
Compare the prevalence of parasitic infections in different parts of the world.
In the developed world, 5% of deaths are from infectious diseases (incl. parasitic diseases). In the developing world, 50% of deaths are from these disease.
Why are infectious parasitic diseases so much more common in some parts of the world?
Since they mostly affect the poor, there is less funding for vaccines than there would be in the first world.
What are the 2 major categories of parasitic infections? What is the difference between them?
Protozoan infections,which are unicellular, and helminth infections, which are multicellular.
Name 4 examples of protozoan infections.
Malaria, leishmaniasis, African Trypanosomiasis, South American Trypanosomiasis
For each of the 4 protozoan infections, state how they are transmitted.
Malaria: mosquito
Leishmaniasis: sandfly
African Trypanomiasis: Tsetse fly
South American Trypanomiasis: assassin bug
Name 6 examples of Helminth infections.
Ascaris, hookworm, trichuris, Lymphatic filariasis, Onchocerciasis, Schistosomiasis
For each of the 6 Helminth infections, state how they are transmitted.
Ascaris: soil transmitted
Hookworm: soil transmitted
Trichuris: soil transmitted
Lymphatic filariasis: insect - mosquito
Onchocerciasis: insect - black fly
Schistosomiasis: snails
What part of the world is Hookworm found in?
Africa, Asia, Latin America
What part of the world is Trichuris found in?
Africa, Asia, Latin America
What parts of the world is Ascaris found in?
Africa, Asia, Latin America
What parts of the world is Schistosomiasis found in?
Sub-saharan Africa, Latin America
What parts of the world is Lymphatic filariasis found in?
India, Asia, Latin America
What parts of the world is Onchocerciasis found in?
Africa, Latin America
What is the most prevalent Helminth infection in the world?
Ascariasis
What are the major at-risk regions for Helminth infections?
Africa, Asia, Latin America
What are the major soil-transmitted helminths?
Acascaris, Trichuris, and Hookworm
Explain where/how soil transmitted helminths live and replicate.
They live in the human gastrointestinal tract, but they do not replicate in the human host. They instead produce eggs that are excreted with human feces.
How are the 3 major soil transmitted helminths transmitted to human hosts?
Ascaris and Trichuris are transmitted through ingesting eggs. Hookworm is transmitted through the penetration of larvae through skin penetration.
Who is primarily affected by soil transmitted helminths? How are they affected?
Children in developing nations. They often have Ascariasis, Hookworm, and Trichuriasis at once, which can result in growth stunting, cognitive defects, and malnutrition.
How does having a soil-transmitted helminth affect susceptibility to other diseases? Give 3 examples.
It increases susceptibility to other infections such as Malaria, Tuberculosis, and HIV, because it suppresses the immune response.
How does the size of the female Ascaris compare to the size of the male Ascaris?
The female is substantially larger than the male.
Describe the life cycle of Ascaris, including:
a) How and in what form it enters the body
b) Where it lives in the body
c) How, in what form, and to where it exits the body
a) Enters via contaminated food/water in the form of a larvae, which has developed from a fertilized egg.
b) Lives in the small intestine of the host. Once the larvae are in the intestine, they go into the lungs, back down the trachea, and back into the small intestine, where they live as adults.
c) Eggs go into the ground through the feces. The fertilized eggs develop into larvae in the soil and the cycle restarts.
What is the typical length and lifespan of ascaris?
20 cm, 1 year
What is the typical length and lifespan of hookworm?
15 mm, 5 years
What is the typical length and lifespan of trichuris?
5 cm, 2 years
For the 3 soil transmitted helminths, how many eggs do they lay per day?
Ascaris: 200,000
Trichuris: 5000
Hookworm: 10,000
For the 3 soil transmitted helminths, do the males or females release eggs, or both?
Ascaris: both
Trichuris: only females
Hookworm: both
Describe the life cycle of hookworm, including:
a) How and in what form it enters the host
b) Where it lives in the host
c) How and in what form it exits the host
a) Enters as a larvae through the skin of bare feet
b) Lives in the small intestine of the host
c) Eggs leave through the feces. They grow into larvae in the ground and the cycle restarts.
Explain how the diagnosis of infection by soil transmitted helminths is done.
A stool sample is taken and put under a microscope, where the eggs of the STH can be observed. The intensity of infection is measured as well.
What is the intensity of infection of STH?
It is the number of eggs per gram of feces.
Name 2 drugs commonly used to treat soil transmitted helminths.
Benzimidazoles and Ivermectin.
Explain how drugs used to treat STH work and their shortcomings.
They target the removal of adult worms from the intestine by paralyzing them. However, they do not kill eggs.
Lymphatic filariasis can cause the condition […]
Elephantiasis
Lymphatic filariasis is transmitted by the vector […]
Mosquitoes
Lymphatic filariasis is transmitted by the parasite […]
Wuchereria bancroft
Describe the life cycle of Wuchereria bancroft, including:
a) How and in what form it enters the host
b) Where and in what form they live in the host
c) How and in what form they leave the host
d) Where they go when they leave the host
a) Larvae are transmitted by an infected mosquito
b) The adults infect the lymphatic system. The adults produce microfilaria, which enter the blood of the host.
c) Microfilaria get taken up by a mosquito that bites the human
d) The microfilaria develop into larvae in the gut of the mosquito
Onchocerciasis is transmitted by the vector […]
Black flies
Onchocerciasis is transmitted the parasite […]
Orchocerca Volvulus
Describe how onchocerca volvulus accumulate in the individual.
It bites an individual, and the larvae develop into males and females at the site of the bite. They then stay around the site. It can also enter and accumulate in the eye.
Describe the life cycle of onchocerca volvulus:
a) How and in what form it enters the host
b) Where and in what form it lives in the host
c) How and in what form it leaves the host
d) Where they go when they leave the host
a) Black fly bites a human and larvae enters the host
b) The subcutaneous tissues as larvae and adults. The adults produce microfilaria that live in skin/lymph of connective tissue or in blood/urine/eye.
c) Blackfly takes up microfilaria when it bites.
d) Microfilaria grow into larvae in the gut of black fly
Onchocerciasis can lead to the disease […]
River blindness (accumulation in the eye necessary)
Describe the geographic relationship between helminth infections and autoimmune disease.
The areas that are heavily affected by autoimmune disease (the 1st world) are opposite from those that are heavily affected by helminth infections. It is thought that intestine helminth infections may help appease autoimmune issues.
Explain how helminth infections might be used for good. Give a specific example of a helminth that can be used.
They may be able to reduce the inflammation associated with autoimmune diseases such as Crohn’s disease. This can be done with Trichuris, as it doesn’t lay eggs and can just live in the gut.
For the 3 soil transmitted helminths, do the males or females release eggs, or both?
Ascaris: both
Trichuris: only females
Hookworm: both
