6. Parasitic Protists

Question 1

Define parasite

Answer 1

An organism which lives in or on another organism (its host) and benefits by deriving nutrients at the other’s expense

Question 2

An example of a diplomonad

Answer 2

• giardia lamblia
• one agent of ‘traveller’s’ diarrhea
• one of the most common parasite infection worldwide

Question 3

What are diplomonads?

Answer 3

The diplomonads (Greek for “two units”) are a group of flagellates, most of which are parasitic.

Question 4

How is Giardia lamblia trasmitted?

Answer 4

• transmitted by cysts in food and water
• 14 billion cysts/day in faeces
• adheres to intestinal epithelium to absorb nutrients from the host
• not all people infected have symptoms

Question 5

What is trophozoite

Answer 5

A growing stage in the life cycle of some sporozoan parasites, when they are absorbing nutrients from the host.

Question 6

Biology of Giardia lamblia

Answer 6

• trophozoite has 2 nuclei and associated sets of paired flagella
• have mitochondrial remnants but no mitochondria (to make iron-sulfur proteins)

Question 7

What is one of the most common parasite infections in the world?

Answer 7

Giardia lamblia

Question 8

What are parabasalids?

Answer 8

Parabasalids (phylum Parabasalia) are anaerobic flagellated protists

Question 9

Physiology of parabasalids

Answer 9

• anaerobic
• converts glucose to pyruvate by glycolysis
• convert pyruvate to acetate in an organelle known as the hydrogenosome

Question 10

What is hydrogenosome

Answer 10

• organelle found in parabasalids
• derived from mitochondria
• independent evolution in Trichomonas and other microbes, some still with DNA

Question 11

Kinetoplastids examples

Answer 11

•leishmania •Trypanosoma

Question 12

Kinetoplastids structure and name

Answer 12

• name given for clump of DNA at the anterior end of the mitochondrion
• VSG coat constantly changing, avoiding immune recognition

Question 13

What are kinetoplastids?

Answer 13

• bloodstream parasites
• group of flagellated protists belonging to the phylum Euglenozoa,
• characterised by the presence of an organelle with a large massed DNA called kinetoplast

Question 14

Diseases caused by kinetoplastids

Answer 14

• swim in the blood stream
• chagas disease
• African sleeping sickness (spread by tsetse flies)
• leishmaniasis

Question 15

What is the method of combating kinetoplastids?

Answer 15

• very few effective drugs and bad side effects
• however, for African SS, disease mortality rate is 100% with 5% for the drug
• no known drug effective against Chagas disease
• therefore target the insect vectors

Question 16

What are ciliates?

Answer 16

• group of protozoans characterised by the presence of hair-like organelles called cilia
• cilia for motility and capturing food

Question 17

Do ciliates cause disease?

Answer 17

• one species causes human disease

* balantidium coli

Question 18

What disease is caused by entamoeba histolytica?

Answer 18

• causes the disease amebiasis
• 3rd worst parasite
• dysentery (colitis), spread in blood, and eventual liver abcess

Question 19

Transmission of Entamoeba hystolytica

Answer 19

• transmission by faecal contamination of food or water
• cysts last several months
• cysts form trophozoites in intestine after ingestion

Question 20

Phylum apicomplexa examples

Answer 20

All intracellular parasites
• toxoplasma gondii
• plasmodium spp. (malaria)
• cryptosporidium spp.(causes diarrhea)

Question 21

What is the apical complex and where are they found?

Answer 21

• A group of cytoskeletal structures and associated membrane-bounded organelles
• found at the anterior end of adult obligate intracellular protozoan parasites in the phylum Apicomplexa

Question 22

What is the function of the apical complex?

Answer 22

• used to burst out of a used host cell and to invade

Question 23

Who is at risk of being affected from toxoplasma gondii?

Answer 23

• fatal in immunocompromised individuals
• developmental defect in infected foetus (why pregnant women shouldn’t clean kitty litter)
• otherwise, usually not severe in humans

Question 24

Who is the host of toxoplasma gondii?

Answer 24

Definitive host is cat and common risk of exposure is in kitty litter

Question 25

What was the irish potato famine caused by?

Answer 25

Phytopthora infestans

Question 26

What disease is casued by plasmodium spp?

Answer 26

• malaria
• infects red blood cells and liver cells
• each plasmodium species only affects one host (or a small number)

Question 27

Vector of plasmodium

Answer 27

mosquitoes

Question 28

What is the first drug developed against malaria?

Answer 28

• Quinine

* from plant in Peru to prevent shivering

Question 29

Malaria resistance?

Answer 29

• quinine and several derivatives have lost potency

* emergence of resistance strains in much of Africa and Asia

Question 30

What are the 6 examples of protist groups that have evolved parasitic lifestyles?

Answer 30

• diplomonads
• parabasalids
• kinetoplasmids
• ciliates
• amoebozoa
• apicomplexa

Question 31

Parabasilids examples

Answer 31

trichomonas

Question 32

Amoebozoa examples

Answer 32

Entamoeba histolytica

Question 33

Apicomplexa example

Answer 33

• Toxoplasmi gondii

* plasmodium

Question 34

Features of protist genomics

Answer 34

• overlap with the size of human pathogenic fungi

* key protist genomes have not yet been sequenced

Question 35

What is the largest protist genome to date?

Answer 35

Trichomonas vaginalis