6. Parasitic Protists Flashcards
Define parasite
An organism which lives in or on another organism (its host) and benefits by deriving nutrients at the other’s expense
An example of a diplomonad
- giardia lamblia
- one agent of ‘traveller’s’ diarrhea
- one of the most common parasite infection worldwide
What are diplomonads?
The diplomonads (Greek for “two units”) are a group of flagellates, most of which are parasitic.
How is Giardia lamblia trasmitted?
- 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
What is trophozoite
A growing stage in the life cycle of some sporozoan parasites, when they are absorbing nutrients from the host.
Biology of Giardia lamblia
- trophozoite has 2 nuclei and associated sets of paired flagella
- have mitochondrial remnants but no mitochondria (to make iron-sulfur proteins)
What is one of the most common parasite infections in the world?
Giardia lamblia
What are parabasalids?
Parabasalids (phylum Parabasalia) are anaerobic flagellated protists
Physiology of parabasalids
- anaerobic
- converts glucose to pyruvate by glycolysis
- convert pyruvate to acetate in an organelle known as the hydrogenosome
What is hydrogenosome
- organelle found in parabasalids
- derived from mitochondria
- independent evolution in Trichomonas and other microbes, some still with DNA
Kinetoplastids examples
•leishmania •Trypanosoma
Kinetoplastids structure and name
- name given for clump of DNA at the anterior end of the mitochondrion
- VSG coat constantly changing, avoiding immune recognition
What are kinetoplastids?
- 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
Diseases caused by kinetoplastids
- swim in the blood stream
- chagas disease
- African sleeping sickness (spread by tsetse flies)
- leishmaniasis
What is the method of combating kinetoplastids?
- 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
What are ciliates?
- group of protozoans characterised by the presence of hair-like organelles called cilia
- cilia for motility and capturing food
Do ciliates cause disease?
- one species causes human disease
* balantidium coli
What disease is caused by entamoeba histolytica?
- causes the disease amebiasis
- 3rd worst parasite
- dysentery (colitis), spread in blood, and eventual liver abcess
Transmission of Entamoeba hystolytica
- transmission by faecal contamination of food or water
- cysts last several months
- cysts form trophozoites in intestine after ingestion
Phylum apicomplexa examples
All intracellular parasites
• toxoplasma gondii
• plasmodium spp. (malaria)
• cryptosporidium spp.(causes diarrhea)
What is the apical complex and where are they found?
- 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
What is the function of the apical complex?
• used to burst out of a used host cell and to invade
Who is at risk of being affected from toxoplasma gondii?
- fatal in immunocompromised individuals
- developmental defect in infected foetus (why pregnant women shouldn’t clean kitty litter)
- otherwise, usually not severe in humans
Who is the host of toxoplasma gondii?
Definitive host is cat and common risk of exposure is in kitty litter
What was the irish potato famine caused by?
Phytopthora infestans
What disease is casued by plasmodium spp?
- malaria
- infects red blood cells and liver cells
- each plasmodium species only affects one host (or a small number)
Vector of plasmodium
mosquitoes
What is the first drug developed against malaria?
- Quinine
* from plant in Peru to prevent shivering
Malaria resistance?
- quinine and several derivatives have lost potency
* emergence of resistance strains in much of Africa and Asia
What are the 6 examples of protist groups that have evolved parasitic lifestyles?
- diplomonads
- parabasalids
- kinetoplasmids
- ciliates
- amoebozoa
- apicomplexa
Parabasilids examples
trichomonas
Amoebozoa examples
Entamoeba histolytica
Apicomplexa example
- Toxoplasmi gondii
* plasmodium
Features of protist genomics
- overlap with the size of human pathogenic fungi
* key protist genomes have not yet been sequenced
What is the largest protist genome to date?
Trichomonas vaginalis
