Lecture 24: Parasitology I

Question 1

Name 3 ways in which parasites are different from bacteria and viruses in terms of structure.

Answer 1

1. Parasites are eukaryotes, not prokaryotes
2. Parasites can be single celled or multicellular
3. Parasites have a nucleus and more complicated cellular structure

Question 2

How do parasites differ from bacteria and viruses in terms of vaccines?

Answer 2

Unlike viruses and bacterial infections, which we have developed vaccines for, there is not a single vaccine for parasitic infections.

Question 3

Compare the prevalence of parasitic infections in different parts of the world.

Answer 3

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.

Question 4

Why are infectious parasitic diseases so much more common in some parts of the world?

Answer 4

Since they mostly affect the poor, there is less funding for vaccines than there would be in the first world.

Question 5

What are the 2 major categories of parasitic infections? What is the difference between them?

Answer 5

Protozoan infections,which are unicellular, and helminth infections, which are multicellular.

Question 6

Name 4 examples of protozoan infections.

Answer 6

Malaria, leishmaniasis, African Trypanosomiasis, South American Trypanosomiasis

Question 7

For each of the 4 protozoan infections, state how they are transmitted.

Answer 7

Malaria: mosquito
Leishmaniasis: sandfly
African Trypanomiasis: Tsetse fly
South American Trypanomiasis: assassin bug

Question 8

Name 6 examples of Helminth infections.

Answer 8

Ascaris, hookworm, trichuris, Lymphatic filariasis, Onchocerciasis, Schistosomiasis

Question 9

For each of the 6 Helminth infections, state how they are transmitted.

Answer 9

Ascaris: soil transmitted
Hookworm: soil transmitted
Trichuris: soil transmitted
Lymphatic filariasis: insect - mosquito
Onchocerciasis: insect - black fly
Schistosomiasis: snails

Question 10

What part of the world is Hookworm found in?

Answer 10

Africa, Asia, Latin America

Question 11

What part of the world is Trichuris found in?

Answer 11

Africa, Asia, Latin America

Question 12

What parts of the world is Ascaris found in?

Answer 12

Africa, Asia, Latin America

Question 13

What parts of the world is Schistosomiasis found in?

Answer 13

Sub-saharan Africa, Latin America

Question 14

What parts of the world is Lymphatic filariasis found in?

Answer 14

India, Asia, Latin America

Question 15

What parts of the world is Onchocerciasis found in?

Answer 15

Africa, Latin America

Question 16

What is the most prevalent Helminth infection in the world?

Answer 16

Ascariasis

Question 17

What are the major at-risk regions for Helminth infections?

Answer 17

Africa, Asia, Latin America

Question 18

What are the major soil-transmitted helminths?

Answer 18

Acascaris, Trichuris, and Hookworm

Question 19

Explain where/how soil transmitted helminths live and replicate.

Answer 19

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.

Question 20

How are the 3 major soil transmitted helminths transmitted to human hosts?

Answer 20

Ascaris and Trichuris are transmitted through ingesting eggs. Hookworm is transmitted through the penetration of larvae through skin penetration.

Question 21

Who is primarily affected by soil transmitted helminths? How are they affected?

Answer 21

Children in developing nations. They often have Ascariasis, Hookworm, and Trichuriasis at once, which can result in growth stunting, cognitive defects, and malnutrition.

Question 22

How does having a soil-transmitted helminth affect susceptibility to other diseases? Give 3 examples.

Answer 22

It increases susceptibility to other infections such as Malaria, Tuberculosis, and HIV, because it suppresses the immune response.

Question 23

How does the size of the female Ascaris compare to the size of the male Ascaris?

Answer 23

The female is substantially larger than the male.

Question 24

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

Answer 24

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.

Question 25

What is the typical length and lifespan of ascaris?

Answer 25

20 cm, 1 year

Question 26

What is the typical length and lifespan of hookworm?

Answer 26

15 mm, 5 years

Question 27

What is the typical length and lifespan of trichuris?

Answer 27

5 cm, 2 years

Question 28

For the 3 soil transmitted helminths, how many eggs do they lay per day?

Answer 28

Ascaris: 200,000
Trichuris: 5000
Hookworm: 10,000

Question 29

For the 3 soil transmitted helminths, do the males or females release eggs, or both?

Answer 29

Ascaris: both
Trichuris: only females
Hookworm: both

Question 30

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

Answer 30

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.

Question 31

Explain how the diagnosis of infection by soil transmitted helminths is done.

Answer 31

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.

Question 32

What is the intensity of infection of STH?

Answer 32

It is the number of eggs per gram of feces.

Question 33

Name 2 drugs commonly used to treat soil transmitted helminths.

Answer 33

Benzimidazoles and Ivermectin.

Question 34

Explain how drugs used to treat STH work and their shortcomings.

Answer 34

They target the removal of adult worms from the intestine by paralyzing them. However, they do not kill eggs.

Question 35

Lymphatic filariasis can cause the condition […]

Answer 35

Elephantiasis

Question 36

Lymphatic filariasis is transmitted by the vector […]

Answer 36

Mosquitoes

Question 37

Lymphatic filariasis is transmitted by the parasite […]

Answer 37

Wuchereria bancroft

Question 38

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

Answer 38

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

Question 39

Onchocerciasis is transmitted by the vector […]

Answer 39

Black flies

Question 40

Onchocerciasis is transmitted the parasite […]

Answer 40

Orchocerca Volvulus

Question 41

Describe how onchocerca volvulus accumulate in the individual.

Answer 41

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.

Question 42

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

Answer 42

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

Question 43

Onchocerciasis can lead to the disease […]

Answer 43

River blindness (accumulation in the eye necessary)

Question 44

Describe the geographic relationship between helminth infections and autoimmune disease.

Answer 44

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.

Question 45

Explain how helminth infections might be used for good. Give a specific example of a helminth that can be used.

Answer 45

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.

Question 46

For the 3 soil transmitted helminths, do the males or females release eggs, or both?

Answer 46

Ascaris: both
Trichuris: only females
Hookworm: both