Lecture 16 + 17 - Malaria

Question 1

Age group most represented in malaria deaths

Answer 1

Children under 5

Question 2

Phylum of malaria

Answer 2

Apicomplexia

Question 3

Genus of malaria

Answer 3

Plasmodium

Question 4

Plasmodium species that infect humans
1)
2)
3)
4)

Answer 4

1) Falciparum
2) Vivax
3) Ovalae
4) Malariae

Question 5

Primate - human plasmodium pathogen

Answer 5

Plasmodium knowlesi

Question 6

How does plasmodium gain access to hepatocytes?

Answer 6

Kupfer cell

Question 7

3 places where plasmodium live

Answer 7

Mosquito, human hepatocytes, human erythrocytes

Question 8

Example of the strength of anti-malarial selective pressure

Answer 8

Sickle-cell anaemia alleles are maintained in sub-Saharan Africa, as being heterozygous for this reduces susceptibility to malaria

Question 9

Difference in P. vivax and P. falciparum infection

Answer 9

Vivax causes more severe morbidity, but is less likely to kill

Question 10

Number of malaria deaths per year

Answer 10

~650,000

Question 11

What are the gold crystals observed in malaria-infected erythrocytes?

Answer 11

Haemozin
Parasite eats haemoglobin, but haem is toxic.
Crystallises haem to haemozoin

Question 12

Malaria definitive host

Answer 12

Mosquito (where sexual reproduction of gametocytes occurs)

Question 13

Why are malarial infections comparable between Latin America and sub-Saharan Africa, but sub-Saharan Africa has much higher mortality rates?

Answer 13

P. vivax more common in Latin America.

P. falciparum more common in sub-Saharan Africa

Question 14

Estimated number of malaria cases per year

Answer 14

300 - 500 million

Question 15

Amount of household spending on malaria in Africa

Answer 15

Estimated 10% of household spending (mosquito nets, medication ,etc)

Question 16

P. falciparum life cycle
1) a, b, c
2) a, b
3) a, b
4)

Answer 16

1) Mosquito stage (in mosquito gut)
a) Gamete
b) Zygote
c) Ookinete

MOSQUITO BITES HUMAN

2) Hepatocyte stage
a) Sporozoites infect hepatocytes
b) Merozoites form, exit hepatocytes

3) Blood stage
a) Merozoites infect erythrocytes, divide rapidly
b) Gametocytes form

4) Mosquito ingests gametocytes from human host, sexual reproduction in mosquito

Question 17

When does malaria cause illness?

Answer 17

During merozoite stage

Hepatocyte stage is asymptomatic

Question 18

Number of infected erythrocytes directly after hepatocyte stage Vs number of infected erythrocytes after merozoite expansion

Answer 18

10^3 infected erythrocytes Vs 10^11 infected erythrocytes

Question 19

What does merozoite release coincide with?

Answer 19

Periodic fever, cytokine storm

Question 20

Basic overview of three stages of malarial infection

Answer 20

Mosquito stage - Sexual reproduction
Hepatocyte stage - Asexual reproduction
Erythrocyte stage - Asexual reproduction, major amplification stage

Question 21

Where does the sexual stage occur, and for how long?

Answer 21

1 - 2 weeks in female Anopheles mosquito

Question 22

How long does it take for injected sporozoites to enter hepatocytes from skin?

Answer 22

~30 minutes

Question 23

How long does the asexual liver stage last for?

Answer 23

~1-2 weeks

Question 24

How long after infection does disease occur?

Answer 24

~1 month

Question 25

How long does the asexual erythrocyte stage last for?

Answer 25

~2-3 days, is quite synchronous

Question 26

Symptoms of malaria

Answer 26

Fever, chills, anaemia, coma

Question 27

Proportion of malaria deaths caused by P. falciparum

Answer 27

95%

Question 28

How does P. vivax cause relapsing malaria?

Answer 28

Hypnozoites in the liver

Question 29

What role does cytoadherence play?

Answer 29

Malaria doesn't want infected blood cells to enter the spleen, as they would be destroyed there. Instead, cause infected erythrocytes to adhere to vascular wall.

Question 30

What coincides most with malarial death?

Answer 30

Infected erythrocytes adhering to walls of blood vessels in brain. Exact mechanism of death not known. Not straight ischaemia

Question 31

What adheres infected erythrocytes to the vascular wall?

Answer 31

PfEMP1

Question 32

PfEMP1 role

Answer 32

Binds to molecules on microvascular endothelium

Question 33

Surface protein in the brain microvasculature that PfEMP1 binds to

Answer 33

ICAM1

Question 34

Number of different genomic copies of PfEMP1 in a malarial genome

Answer 34

Over 60

Question 35

Name of genes encoding PfEMP1

Answer 35

var genes

Question 36

How are different var genes expressed?

Answer 36

Epigenetic silencing of all var genes except for 1. | A parasite can change var gene expression

Question 37

What correlates with different waves of parasitaemia?

Answer 37

Expression of different PfEMP1 genes | Express different ones when an effective antibody response is launched against one

Question 38

Where are most var genes located?

Answer 38

Sub-telomeric regions of chromosomes

Question 39

Why do different P. falciparum parasites have a greater variety of var genes than expected? 1) 2) 3)

Answer 39

1) Chromosomes cluster at at nuclear periphery of parasite 2) Recombination between heterologous chromosomes that are clumped together, aligned 3) Results in great variation of var genes and expressed PfEMP1s

Question 40

Number of proteins that P. falciparum exports into erythrocyte cytoplasm

Answer 40

Hundreds

Question 41

KAHRP function

Answer 41

Knob formation. | Knob allows parasite to hang onto microvascular endothelium under flow pressure

Question 42

Evidence for KAHRP function

Answer 42

With KAHRP, infected RBC surface is rough, cell sticks to microvascular endothelium Without KAHRP, infected RBC surface is smooth, doesn't stay attached to vascular wall

Question 43

Motif allowing P. falciparum to export proteins into RBC cytoplasm

Answer 43

PEXEL motif

Question 44

Amount of P. falciparum proteome estimated to be exported out of parasite

Answer 44

~5%

Question 45

PEXEL motif role

Answer 45

Allow proteins to cross parasitophorous vacuole membrane

Question 46

Two important sites in P. falciparum protein export

Answer 46

1) Endoplasmic reticulum | 2) Parasitophorous vacuole membrane

Question 47

What is PEXEL?

Answer 47

A protease cleavage site | Cleaved by Plasmepsin IV

Question 48

What does plasmepsin IV cleave?

Answer 48

PEXEL motif, in the endoplasmic reticulum

Question 49

Where is PEXEL cleaved by plasmepsin IV?

Answer 49

RxLxE/Q/D --> RxL | xE/Q/D In the ER

Question 50

Where is plasmepsin IV present?

Answer 50

In the ER of P. falciparum

Question 51

PTEX

Answer 51

A putative translocon of PEXEL proteins

Question 52

``` Criteria for PTEX 1) 2) 3) 4) ```

Answer 52

1) Plasmodium-specific, in the correct location 2) Essential to blood-stages 3) Energy source, a protein-unfolding mechanism 4) Binds transiting cargo PEXEL proteins

Question 53

PTEX structure 1) 2) 3)

Answer 53

1) 5 proteins 2) HSP101 is an energy source, unfolds proteins so that they can fit through pore 3) EXP2 is a pore protein

Question 54

PTEX location

Answer 54

Parasitiphorous vacuole membrane in RBC

Question 55

How long does it take for a merozoite to enter an erythrocyte?

Answer 55

~30 seconds

Question 56

Possible anti-malarial drug targets 1) 2)

Answer 56

1) Plasmepsin IV | 2) PTEX

Question 57

Types of anti-malarial vaccine 1) 2) 3)

Answer 57

1) Pre-erythrocytic 2) Transmission-blocking 3) Blood-stage (anti-merozoite)

Question 58

Example of possible pre-erythrocytic vaccine

Answer 58

RTS, S | In stage III clinical trials

Question 59

Difficulty for anti-merozoite antibodies

Answer 59

Only have about 1.5 minutes when merozoites are susceptible to action. ~1.5 minutes between when merozoites exit former host cell, enter erythrocyte

Question 60

Primary interaction target of possible vaccine

Answer 60

Binding to cell

Question 61

``` Secondary interaction target of possible vaccines 1) 2) 3) 4) 5) ```

Answer 61

1) Actin/myosin motor 2) Surface protein shedding 3) Secondary ligand shedding 4) Resealing 5) Recovery from echinocytosis

Question 62

``` Problems with making an anti-malaria vaccine 1) 2) 3) 4) ```

Answer 62

1) Empirical vaccine techniques aren't working 2) Very little functional knowledge of individual antigens 3) Many antigens are identified, but which to target? 4) Vaccine must cover three major invasion pathways

Question 63

Target of P. vivax on erythrocytes

Answer 63

Duffy protein

Question 64

Adaptation of West Africans against P. vivax

Answer 64

Don't express Duffy protein on erythrocyte membrane As a result, no P. vivax in West Africa

Question 65

Families of surface proteins that bind erythrocytes in P. falciparum

Answer 65

1) EBA (erythrocyte-binding antigen) (5 members) | 2) PfRh (5 members)

Question 66

What does the W2mef strain of P. falciparum use to bind erythrocytes?

Answer 66

Can use EBA175 to bind sialic acid on GlyA

Question 67

What does W2mef strain do when RBCs have been depleted of sialic acid by neuraminidase?

Answer 67

Expresses a silaic acid-independent invasion phenotype using a different surface ligand (Rh4)

Question 68

Important targets of inhibitory antibodies

Answer 68

EBA, Rh proteins

Question 69

Why does P. falciparum use several invasion pathways? 1) 2)

Answer 69

1) Accommodate RBC polymorphism | 2) Immune avoidance

Question 70

Major invasion pathways now identified

Answer 70

Three major invasion pathways