13. Parasitology & Malaria

Question 1

define a parasitic relationship

Answer 1

one in which the organism lives off another organism (the host) harming it and possibly causing death

Question 2

what are protozoa

Answer 2

single celled organism

Question 3

what are helminths

Answer 3

worms, multicellular, often produce eggs

Question 4

give an example of a protozoan parasite

Answer 4

plasmodium
leishmania
giardia

Question 5

give an example of a helminth

Answer 5

schistosomes

roundworm

Question 6

how can we directly diagnose a parasite

Answer 6

visualising the parasite or a compound of the parasite (its DNA)

Question 7

What is an indirect way of diagnosing a parasite

Answer 7

using clinical diagnosis, biochemical and serological tests

Question 8

what are useful samples that can be taken to diagnose parasites

Answer 8

blood and stool

Question 9

what does sensitivity mean

Answer 9

the proportion of true positives identified

Question 10

what does specificity mean

Answer 10

the proportion of true negatives identified

Question 11

how can we figure out sensitivity

Answer 11

true positives / false negatives + true positives

Question 12

how can we figure out specificity

Answer 12

true negatives / false positives + true negatives

Question 13

what does a good test have in terms of sensitivity and specificity

Answer 13

high sensitivity and specificity (>90%) - although there is often a trade off

Question 14

in a life threatening situation, what is more important:

sensitivity or specificity

Answer 14

sensitivity - more important to known who truly has it

Question 15

if treatment is expensive with serious side effects, what Is more important:
sensitivity or specificity

Answer 15

specificity = more important to know that only those who truly have it are being treated

Question 16

what is the main species that causes human malaria

Answer 16

plasmodium falciparum

Question 17

how does malaria transmission occur

Answer 17

the bite of female anopheles mosquito

Question 18

are there any known reservoirs of plasmodium?

Answer 18

no significant reservoirs, except P. knowlsei in macaque monkeys

Question 19

how many malaria deaths per year

Answer 19

400,000

Question 20

where are most malaria cases

Answer 20

in africa

Question 21

what % of cases is P. falciparum responsible for

Answer 21

50% of cases

Question 22

describe the erythrocytic cycle of P. falciparum

Answer 22

merozoites invade RBCs to evade the host’s immune system

here they undergo an asexual reproduction cycle which produces trophozoites

Question 23

why is the erythrocytic cycle important in diagnosis

Answer 23

examining blood films to detect the stages of infection are key in diagnosis

Question 24

what is the second most prevalent plasmodium

Answer 24

P. vivax

Question 25

how many cases is p. vivax responsible for

Answer 25

43%

Question 26

why is it difficult to diagnose malaria from clinical diagnosis alone

Answer 26

no unique set of symptoms for malaria

Question 27

what is the gold standard diagnostic test for malaria

Answer 27

thick and thin blood films

Question 28

why conduct both thick and thin blood films

Answer 28

thick film = sensitivity - detects parasitaemia

thin film = specificity - identifies and counts species

Question 29

what stains are used in thick and thin blood films

Answer 29

giesma or leishmans

Question 30

describe how antigen detection tests work for malaria

Answer 30

detect the presence of histidine-rich protein 2 (in paracheck tests)

(produced by P. falciparum)

Question 31

what is a disadvantage of antigen detection tests

Answer 31

histidine rich protein 2 is only produced by P. falciparum

and NOT by other plasmodium species, e.g. p. vivax

Question 32

what are the 3 stages of malaria fever

Answer 32

1. cold stage = shivers, rise in temp
2. hot stage = peripheral vasodilation (flushed appearance, rapid pulse)
3. sweating stage = copious sweating = drop in temp