L3 Parasites affecting the host Flashcards
How do parasites cause harm?
Parasites take energy and nutrients from the host.
GI helminths- take food
Hookworms - feed off host
Malaria - destroys RBC
Energetic cost of immune responses/repairing damage
Costs dependent on intensity of infection
How do hookworms cause anaemia?
hookworms feed on blood causing iron loss
1 Necator americanus - 50microlitres per day
1 Ancylostoma 200 microlitres per day
Huge effect when over 100 worms in population
Density dependent effects growth and cognitive development, seen in comparisons of children w and wo infection.
how does STH- soil transmitted helminthiasis affect children?
Negative relationship btw infection and cognitive performance.
De-worming improves cognitive performance and school attandence
Describe Hb and how sickled cell Hb differs`
Hb consists of 4 globin molecules with 4 haem groups.
1 Hb carried 1 O2.
Sickle cell Hb- HbS, mutation in B globin combined with a normal globin.
If someone has 2 HbS globins, v severe, RBC sickle shape. Low life expectancy, adhere to vasculature causing organ failure and joint pain.
If 1 HbS, they are phenotypically normal, not diseased. V commin in subsaharan africa 30% of people in Tropical africa have it.
Affects of the sickle cell trait, 4
childhood survival rates
< Malaria parasite replication
Why had the sickle cell trait been selected for?
the disease has a cost always
Trait has a benefit sometimes.
protection from malaria - heterozygote advantage
Only advantageous in presence of malaria
In N hemisphere, no malaria so no advantage, not selected for.
Which genotypes of thalassaemia are advantageous
Thalassaemia is an inherited condition affecting Hb
Normal: aa,aa -a,-a –,aa
Lethal: –,–
[- = absence of function of gene product]
Advantageous: -a,-a –,aa as there is an inhibitor effect on the malaria parasite.
describe overdispersion of ascaris infection
FEC and worm counts following treatment
High correlation - 0.787, of infected people between time periods. There are ‘wormy’ and ‘non wormy’ people
What does ascaris worm load tell you about its effect on the host?
about 40% of worm load variation is due to host genetics.
Strong genetic effect of host genotype on ascaris Infection implies that ascaris is a strong selective force on host.
Do parasites evolve towards virulence?
Used to be thought that they would evolve to avirulence, as if too many, will use up resources and kill host, giving a negative effect.
Now thought they evolve with an optimal virulence.
recent work suggests vertical transmission leads to less virulent parasites, whereas horizontal = more virulent.
