Lecture 8 - parasitology Flashcards
What is evolutionary evidence of endosymbiosis?
Mitochondria and Chloroplasts:
• Contain DNA
• Contain own ribosomes
• Sensitive to antibiotics
• Sequencing data demonstrates gene transfer
• Eukaryotic nucleus contains bacterial genes
What are protozoa?
Phylogenetically diverse group but all are
Single-celled, motile eukaryotes that lack chlorophyll
• 4 groups: divided according to their mode of motility
1. Amoebas (e.g. Entamoeba)
2. Ciliates (e.g. Paramecium)
3. Flagellates (e.g. Trypanosoma brucei; causes
African sleeping sickness)
4. Apicomplexans (e.g. Plasmodium; causes malaria)
What are amoebas?
Move by amoeboid movement – use
pseudopodia formed by cytoplasmic
extensions of the cell
• Usually no structural cell wall,
but can have shell comprised of CaCO3
What is Entamoeba histolytica?
causes amoebic dysentery • Amoeboid form 15-30 µm • Infects ~ 50 million humans (correlates w/poor sanitation) • Often asymptomatic • Severe cases: trophozoites enter intestine tissue causing dysentery and ulcers
What are ciliates?
Use cilia (hair-like projections) to aid propulsion & attract food • Ingest food through ‘mouth’ (deep oral groove) • Often contain endosymbionts (bacteria) • Up to 350µm in length • Abundant in marine and freshwater
What are flagellates?
move using a single flagellum or multiple flagella
Important parasitic infections of humans and other animals:
Trypanosoma causes sleeping sickness, Chagas disease
Leishmania causes Leishmaniasis
Giardia causes Giardiasis
Trichomonas causes Trichomoniasis
What is Trypanosoma brucei?
African Trypanosomiasis “Sleeping Sickness” • Threatens 60 million in 36 countries • Glossina “Tsetse fly” vector • Livestock animal reservoirs • No vaccines available • Current treatments are potentially lethal • Lethal if untreated
What is Trypanosoma cruzi?
American Trypanosomiasis “Chagas Disease” Threatens over 25 million • Reduviid “kissing bug” vector • Wild animal reservoirs • No vaccines available • Current treatments are limited • 30% develop severe heart disease
What are Leishmania species?
Leishmaniasis “kala azar” •Threatens 1/10 world in 98 countries • Phlebotomus “sandfly” vector • Domestic animal reservoirs • No vaccines available • Resistance to current treatments rising • Visceral leishmaniasis lethal if untreated
Describe sleeping sickness and its control measures
Rapid multiplication, spread from blood to CNS, neurological changes, coma • Acute form = weeks-months • Chronic form = years • Fatal if untreated, no vaccines Pills Tsetse control • DDT : Kills flies (amongst other things…..) • Artificial pheromones : Coat net in pheromone to trap females • Release of sterile males : Females only mate once
Describe human leishmaniasis
One of the most neglected tropical diseases, yet ranked 9th in
analysis of global burden of disease, with an associated
mortality amongst parasitic infections second only to malaria
§ 14M people infected, ~1.2M new cases annually, ~20-30,000
annual deaths, mostly of children and young adults; 1 billion
people at risk in 98 endemic countries (incl. the 15 poorest)
§ No vaccines currently available and severe side effects from
and resistance to available drugs an increasing problem
What are Apicomplexans (Sporozoans)?
Key features:
• Intracellular
• Relatively non-motile except gamete stage
• All obligate parasites causing serious disease
• Apical organelles (hence the name) enable parasites
to invade host cells
What is Toxoplasma gondii: toxoplasmosis?
Worldwide distribution
• Multiple vertebrate hosts
• Cats essential part of life cycle (asymptomatic host),
reproduces in intestine
• Shed oocysts remain viable for < 1 year
• Tachyzoite invade tissues (retina and CNS)
• Secondary host mounts an immune response : France ~90%+ve
• Problematic in immuno-suppressed individuals
• Danger during pregnancy to foetus (congenital toxoplasmosis)
What is malaria?
Characterised by cycles of fever and chills every 48hrs Related to synchronous bursting of RBC and release of parasites (merozoites) Each RBC releases 20 new merozoites plus toxic compounds If only 1% of RBC are infected then 100,000,000,000 parasites in an infected person Highly pathogenic: severe anaemia kills 50% of those infected
Why is P. falciparum so pathogenic?
Infected RBC develop ‘surface knob’ containing parasite proteins
• Causes RBCs to stick in blood vessels and block capillaries
• Results in liver & brain inflammation/damage, “cerebral malaria”
