Malaria - 5 (10/11) Flashcards Preview

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1

Malaria

distribution

endemic in parts of

  • Asia
  • Africa
  • Latin America
  • Oceania

 global warming = insect vector's range broadening

  • 41% of the world's population live in areas where malaria is transmitted
  • 219 million cases in 2010
  • 0.6-1.2 million deaths in 2010
    • 75% are kids in Africa
    • most are kids under 5
  • 1800-3300 deaths per day OR 1-2 deaths per minute 
  • malaria is 4th leading cause of death after perinatal conditions, pneumonia and diarrheal diseases
    • may argue the major one because spread by only 1 organism

 

2

Malaria

transmission

  • causative agent is transmitted in the saliva of pregnant female mosquitoes (Anopheles) during blood feeding
    • mosquitoes (male/female) → vegetarian, feed on nectar, fruit juice, etc.
  • 30-40 different Anopheles speceis transmit the pathogen
    • Anopheles gambiae best known as it transmits the most common type of malaria

 

3

Malaria

superfunfaxxxx

  • mosquitoes are responsible for killing half the humans who have ever lived
    • 45 billion out of 90 billion
  • malaria
  • yellow fever
  • dengue fever
  • falariasis

 

4

Malaria

transmission

associated with

  • associated with "still" water
    • especially swamps
    • any puddle will do
  • mosquitoes utilize naturally occurring water bodies for breeding

 

5

Malaria 

causative agent

disease caused by Apicomplexa

  • protozoan parasites
  • genus Plasmodium
  • Apicomplexan = large diverse phylum (>5000 named species)

includes

  • Babesia
  • Theileria
  • Cryptosporidium

 

6

Causative agent

Cryptosporidium

  • lives in GI tract
  • fecal-oral transmission
  • can live in humans and a whole raft of other mammalian vectors
    • eg in cows
      • poo with oocysts into water supplies
  • in mammals attach to intestinal cells and induce fusion of microvilli → encapsulation
    • doesn't invade cells but promotes encapsulation of microvilli to surround parasite itself
  • in humans causes cryptosporidiosis
    • watery diarrhea (actually self-limiting)
  • important in immuno-compromised patients
  • problem in the UK - major cause of water-borne food poisoning

7

Causative agent

Toxoplasma

  • primary host - cat
  • intermediate host - rodents/birds
  • in human parasite infects macrophages anywhere in the body and form a cyst
    • can form in the brain 
    • can change personality if parasite lodged in wrong part of the brain
    • schizophrenia, attention deficit disorder, bipolar, Parkinson's disease
  • transmission from intermediate to primary host = ingestion 
    • predator-prey
  • transmission from primary to intermediate host = fecal-oral
  • humans are accidental host
    • via fecal-oral or eating under-cooked meat
  • in humans - congenital transmission
  • disease is self-limiting
  • can be fatal to fetus or immunocompromised people

8

Causative agent

Babesia

 

  • single-celled eukaryotes
    • phylum Apicomplexan
    • all obligate parasites
  • transmitted by ticks
  • in mammals infects red blood cells
  • causes hemolytic infection called Babesiosis
    • mild fevers, diarrhea to severe anemia, organ failure
    • ticks → mammals
  • rare in humans, often confused with malaria
  • major problem in livestock

 

9

Causative agent

Theileria

  • transmitted by ticks
  • in mammals infects red and white blood cells
  • major problem in livestock (cattle, sheep, etc.)
  • infection called Theileriosis
    • fever, enlarged lymph nodes, GI tract problems, diarrhea
  • unlike Babesia and malaria - invades WBC and RBC

 

10

Apicomplexan parasites caused by cell biology

contain:

  • apicoplast
  • inner membrane complex
  • apical complex

 

11

Apicoplast

  • non-photosynthetic plastid related to chloroplasts
  • involved in synthesis pathways
    • fatty acid
    • isoprenoids
    • heme
  • chloroplast with lost ability to perform photosynthesis
  • drugs can target this because we don't have it
  • taken up as secondary endosymbiotic event

 

12

Inner membrane complex

  • pellicle of 3 membrane layer (alveolar structure)
  • series of membranous structures under the membrane
  • protects cell
  • allows cell to retain shape during locomotion
  • involved in cell invasion in myosin motors
    • allows cell to move/glide over certain surfaces
    • stick to particular cell type and glide over
  • also RBC invasion

 

13

Apical complex

composed of

  • conoid and polar rings
  • microtubules
  • rhoptry
  • micronemes
  • dense granules
  • sescretory bodies

 

  • series of secretory molecules
  • for introducing molecules on the outside and cell evasion, gliding

 

14

Apicomplexan parasites

(picture)

A image thumb
15

In humans, 4 different Plasmodium species cause malaria

  • Plasmodium falciparum
    • ​clinically most important
    • 15% of malaria infections
    • 90% of deaths
    • causes severe complications in terms of its pathology that can affect virtually every organ in the patient's body and cause it to break down
  • Plasmodium vivax
    • ​most common
    • 80% of malaria infectous
  • Plasmodium malariae
  • Plasmodium ovale

16

Malaria life cycle

1. sporozoites

in saliva → blood

  • found in mosquito's salivary gland
  • stage transmitted by mosquitoes
    • mosquito takes blood meal
    • saliva into patient as well as sporozoite form of parasite
    • single cell
    • through epidermis
  • once in the blood the sporozoites will find vessels of the circulatory sytem
  • travel to the liver
    • must go through liver before can get into RBC
    • in liver sinusoids (liver blood supply) sporozoites glide over endothelial cells
    • circumsporozoite released from apical complex
    • parasite surface circumsporozoite protein interacts with sulfated heparin secreted by stellate cells
    • glides over by breaking and reforming heparin-sporozoite interaction
    • parasite crosses sinusoid layer by invading and transverse across Kupffer cells (macrophages) 
      • sporozoite invades it and uses it to cross the epithelial layer to be delivered into hepatocytes that lie below the space between the epithelial layer and hepatocytes that 
      • taken up, transferred into hepatocyte

17

Malaria life cycle

1. sporozoite

in liver

 

  • travel to the liver
    • must go through liver before can get into RBC
  • in liver sinusoids (liver blood supply) sporozoites glide over endothelial cells
  • circumsporozoite released from apical complex
    • parasite surface circumsporozoite protein interacts with sulfated heparin secreted by stellate cells
    • glides over by breaking and reforming heparin-sporozoite interaction
  • parasite crosses sinusoid layer by invading and transverse across Kupffer cells (macrophages) 
    • sporozoite invades it and uses it to cross the epithelial layer to be delivered into hepatocytes that lie below the space between the epithelial layer and hepatocytes that 
    • taken up, transferred into hepatocyte

18

Malaria life cycle

1. sporozoites

hepatocytes

  • sporozoites transverse several hepatocytes until it becomes established in one
    • once in hepatocyte can move amongst them until finds one it likes
  • parasite found in a parasitophorous vacuole

 

19

Malaria life cycle

bite → hepatocyte invasion takes

30-60 minutes

20

Malaria life cycle

2. liver schizont

definitions - schizogony, schizont

  • sporozoite develops into a liver (or exoerythrocytic) schizont
  • schizogony - nucleus divides asynchronously without cytoplasmic division
  • schizont - a multinucleated parasite

21

Malaria life cycle

2. liver schizont 

1 schizont →

liver exoerythrocytic schizont develops into merozoites

  • schizont undergoes budding producing many mononucleated merozoites
    • form of asexual reproduction
  • 1 schizont → thousands of merozoites

22

Malaria life cycle

3. Merozoites 

  • budding - migration of nucleus and other organelles to cell membrane, becomes incorporated into merging merozoite
  • hepatocyte becomes packed out with budded versions of itself - merozoites
  • merozoites cause the hepatocyte to die to form a merosome

23

Malaria life cycle

4. Merosome

  • dying hepatocytes release membrane-bound aggregates of merozoites (merosomes) into the bloodstream
    • merozoites associated with membranous material from the hepatocyte to form a merosome
  • merosomes - may protect merozoites from phagocytosis by Kuffper cells
  • merosomes break up releasing individual merozoites
    • membrane material breaks down
    • parasite is released into the bloodstream where merozoites go on to infect RBC

24

Malaria life cycle

dormant stage

  • in some P. vivax and P. ovale infections, sporozoites don't immediately form schizonts
  • in livers tage parasite becomes dormant part way through schizogony
  • infection enters dormant - hypnozoite - stage
  • hypnozoite can reactivate and undergo schizony resulting in relapse

25

Malaria life cycle

3. merozoites - continued

merozoite facts

  • small (~1nm diameter)
  • pear-shaped
  • pointed (apical) end contains apical complex
  • specifically infects erythrocytes
  • infection is rapid (~20 seconds)

 

parasite: mosquito → liver → RBC

  • merozoites designed to invade RBC
  • process of RBC invasion has 4 stages

 

 

26

Malaria life cycle

4. merozoites

RBC invasion - 4 steps

  1. attachment
  2. reorientation
  3. junction formation
  4. invasion
  • reorient because anywhere on spherical body but need apical end to be in contact with RBC membrane
  • parasite talking with RBC by secreting effectof molecules that form a tight junction
    • tight junction can split and pass up and over parasite, invade

27

Malaria life cycle

merozoites 

1. attachment

  • intial interaction - random collision
  • involves reversible interactions between merozoite "adhesins" and erythrocyte ligand

 

interaction between:

  • GPI-anchored merozoite surface protein-1 (MSP-1)
  • Band 3 (anion transporter)

 

other interactions between:

  • erythrocyte binding antigen (EBAs) and
  • reticulocyte-binding-like (RBL) proteins
  • bind to glycosylated (sialic) proteins on erythrocyte surface

^ P. falciparum 5xEBAs and 6xRBLs

eg EBA-175 binds to glycophorin A

28

Malaria life cycle

merozoites

1. attachment

different attachment pathways operate in different parasite lines/geographical locations

EBL-175/glycophorin A pathway predominates in India/Gambia

EBL-175/glycophorin A pathway only in a minority of cases in Brazil

29

Malaria life cycle

merozoites

2. reorientation

  • stick anywhere across parasite cell surface
  • must move itself around such that the apical end comes into contact with RBC membrane
  • parasite linked via adhesin to receptor on RBC membrane
  • parasite adhesins undergo proteolysis
  • at that point the link between parasite and RBC is broken
  • parasite shifts slightly
    • wobbles a bit and promotes slight movement of parasite in one direction so that next adhesin contacts adjacent/subsequent effector
  • adjacent parasite adhesins interact with adjacent RBC ligands
  • "apical end" makes contact with erythrocyte membrane
  • effectively rotates by proteases snapping the adhesin on the parasite surface → rotation of parasite so apical end contacts the erythrocyte membrane

30

Malarial life cycle

3. junction formation

  • secretory bodies release contents
  • parasite protein complexes insert into erythrocyte membrane while components of complex remaining bound to the parasite
  • bridge between host and pathogen cells called tight junction
  • appears as electron-dense zone at parasite/erythrocyte boundary

 

  • apical end contacts RBC membrane then forms junction
  • the parasite secretes membrane complexes - some of which are inserted into the erythrocyte membrane, some of which are held on to by the parasite itself
  • the complexes that held on to by the parasite by itself interact with complexes when it's produced and inserted into erythrocyte membrane

 

31

Malaria life cycle

merozoites

3. junction formation

tight junction proteins include

rhoptry neck proteins - RON2, 4, 5

  • RONs inserted in erythrocyte membrane to form RON complex
  • inserted at point of contact into erythrocyte membrane

 

apical membrane antigen-1 (AMA-1)

  • transmembrane protein (crosses parasite membrane)
  • extracellular region binds to RON complex
  • inner cellular region interacts with aldolase in parasite cytoplasm
    • aldolase binds to F-actin
    • actin interacts with myosin located in inner membrane complex
    • fixes the parasite onto the RBC surface at the apical end to promote junction formation

 

  • the AMA-1 C-terminuses exposed in the cytoplasm of the parasite
    • interacts with aldolase
    • aldolase interacts with actin
    • actin can interact with myosin
    • myosin can then sit on the inner membrane complex (interacts with) which is all around the cell
  • actually linked RBC membrane to the underlying structure within parasite unlerlying cell membrane of the parasite
  • myosin acts as ATP-driven motor
    • flips back and forth across surface of actin
    • this drives the parasite into the RBC

 

32

Malaria life cycle

merozoites

4. invasion

  • tight junction formation causes invagination of erythrocyte membrane
  • parasite forcibly enters through invagination
  • tight junction functions as biological (myosin) motor
  • as invasion progresses, tight junction forms a "ring of contact" with erythrocytes
  • eventually parasitophorous vacuole formed within which the parasite lives
  • as invasion progresses, components of tight junction are degraded by serine protease, PfSUB2 ("sheddase")

33

Malaria life cycle

5. asexual cycle

trophozoite

  • merozoite differentiates into a trophozoite stage
  • young trophozoite called ring stage because of Giemsa staining pattern
  • ring morphology disappears as parasite feeds on hemoglobin

34

Malaria life cycle

5. asexual cycle 

trophozoite

feeeeeding

  • ring stage trophozoite
    • hemoglobin taken up by pinocytosis over whole parasite surface
  • mature trophozoite
    • hemoglobin taken up by endocytosis via cytosome
    • hemoglobin-containing vesicles fuse to form food vacuole
    • food vacuole acidifies (pH 5-5.4) and recruits several distinct classes of proteases

 

35

Malaria life cycle

5. asexual cycle

trophozoites

digesting the noms

proteases digest hemoglobin in semi-ordered, sequential process

  • plasmepsins (aspartic acid proteases) make initial cleavage
  • release heme and globin
  • proteases digest globin to peptides then to amino acids
  • peptides and amino acids transported from food vacuole to parasite cytoplasm
  • used to make new proteins/energy source

 

 

36

Malaria life cycle

5. asexual cycle

trophozoites

heme watchu doin son?

  • heme (toxic) polymerizes to hematin
  • hematin polymerizes to hemozoin (inert)
  • chloroquine blocks polymerization

 

37

Malaria life cycle

5. asexual cycle

trophozoite stage ends when...

  • trophozoite stage ends when schizogony (nuclear division) starts
  • trophozoite differentiates into erythrocytic schizont
  • schizont formation involves 3-5 rounds of nuclear division
  • budding occurs - producing mononucleated merozoites
  • erythrocytes burst, releasing merozoites into the bloodstream
  • invade new erythrocyte
  • starts new asexual cycle
  • asexual cycle is usually synchronous in a given host
  • simultaneous rupture of erythrocytes and release of merozoites
  • antigens (host and parasite) and waste products cause relapsing fever
  • P. falciparum mature trophozoite- and schizont-infected erythrocytes adhere to capillary endothelial cells
    • leads to severe malaria pathologies

 

 

38

Malaria life cycle

6. Sexual cycle

  • some merozoites - upon invading the erythrocyte - develop into gametocytes
    • micro-gametocytes 
    • macro-gametocytes
  • do not cause pathology
  • cleared from bloodstream if not taken up by mosquito

 

  • in mosquito gut RBC breaks down
  • gametocytes released, differentiate into gametes (gametocytogenesis)
  • micro-gametocytes → micro-gametes
  • macro-gametocytes → macro-gametes

 

39

Malaria life cycle

6. sexual cycle

gametocytes

micro-gametocytes undergo

  • 3 x nuclear division
  • flagella formation (exflagellation)

 

macro-gametocytes - no morphological changes

40

Malaria life cycle

6. sexual cycle

zyote formation

  • micro-gamete (nucleated flagella) separate
  • fuse with macro-gamete → diploid zygote
  • zygote develops into motile ookinete
  • ookinete crosses mosquito gut lining/wall, emerging on basal side of epithelium

41

Malaria life cycle

6. sexual cycle

ookinete

  • zygote develops into motile ookinete

  • ookinete crosses mosquito gut lining/wall, emerging on basal side of epithelium

  • ookinete develops into oocyst → insect stages

 

42

Malaria life cycle

7. insect stages

oocyst

  • ookinete develops into oocyst
  • oocyst undergoes meiosis followed by binary fission (sporogony)
  • produces thousands of sporozoites

43

Malaria life cycle

7. insect stages

sporozoites

  • oocyst ruptures releasing spozoites into hemocel
  • motile sporozoites have specificity to the salivary gland
  • transverse the salivary gland epithelial cells, reside in lumen

44

Malaria life cycle

8. re-infection

  • mosquito is primary or definitive host
    • host where parasites rewaches maturity and sexually reproduces
  • mammals/humans are intermediate hosts​​
    • used to get from insect to insect

 

45

Primary/definitive host

host where parasite reaches sexual maturity and sexually reproduces

46

Intermediate host

used to get from insect to insect 

(between primary/definitive hosts)

47

Malaria pathology

1. onset

after infection and pre-patent time

  • 6-18 days after infection by mosquito parasites appear in blood
  • pre-patent time
    • time to complete liver stage
    • no symptoms with liver infection

 

48

Malaria pathology

1. onset

different plasmodium species have different pre-patent times

P. falciparum → 6-9 days

P. vivax → 8-12 days

P. ovale → 10-14 days

P. malariae → 15-18 days

49

Malaria pathology

1. onset

incubation period

the time between RBC infectoin and onset of symptoms

50

Malaria pathology

1. onset

different plasmodium species - different incubation periods

  • P. falciparum → 7-14 days
  • P. vivax → 12-17 days
  • P. ovale → 16-18 days
  • P. malariae → 18-40 days

51

Malaria pathology

2. development

classical symptoms

last 4-8 hours

  • chills/rigor
    • intense feeling of cold but displaying elevated temperature
    • vigorous shivering
  • fever
    • intense heat + severe headache
    • fatigue
    • dizziness
    • nausea
  • sweating 
  • fever starts to decline
  • patient exhausted, falls asleep, wakes up well

symptoms repeated every 2/3 days

52

Malaria pathology

2. development

cyclical nature of fever

  • P. vivax and P. ovale - every 2 days
  • P. malariae - every 3 days
  • P. falciparum - almost continous fever

 

53

Malaria pathology

2. development

cyclical nature of fever

why cyclical?

  • synchronous development of parasites in human host
  • all parasites in RBC at approximately same stage of development

 

54

Malaria pathology

2. development

cyclical nature of fever

symptoms

  • lysis of infected RBC
  • parasite antigens released into bloodstream
  • stimulate macrophages + immune effector cells to produce TNF-α and other cytokines
  • causes febrile episodes

 

symptoms become less severe as patient gets older (immunity)

55

Malaria pathology

2. development

further symptoms

  • symptoms intensify
  • irregular high fever
  • anxiety, delirium, other mental problems
  • sweating, increased pulse rate, severe exhaustion
  • worsening GI symptoms
  • enlarged spleen/liver

56

Malaria pathology

3. severe malaria

  • 10% falciparum cases
  • up to 50% mortality rate
  • several manifestations can arise simultaneously or sequentially
    • cerebral malaria
    • severe anemia

 

57

Malaria pathology

3. severe malaria

cerebral malaria

  • non-specific fever followed by loss of consciousness
  • severe headache
  • drowsiness
  • neurological abnormalities
  • convulsions
  • vomiting
  • coma

 

58

Malaria pathology

3. severe malaria

severe anemia

  • drop in hematocrit
    • destruction of RBCs (infected)
    • non-infected RBCs destroyed
    • reduced RBC formation (cytokines, etc.)
  • poor oxygen supply for organs and tissues

 

59

Severe malaria pathology

sequestration/cytoadherence

ring stages

  • P. falciparum infections only 
  • ring stage parasite found in peripheral blood

 

60

Severe malaria pathology

sequestration/cytoadherence

schizonts

mature trophozoite- and schizont-infected erythrocytes are "sicky" and attach to the endothelium of venules (cytoadherence)

 

mature trophozoite- and schizont-infected erythrocytes not found in peripheral blood (sequestration)

61

Severe malaria pathology

sequestration/cytoadherence

rosetting

adherence of infected RBCs to non-infected RBCs

62

Severe malaria pathology

sequestration/cytoadherence

clumping

adhesion between infected RBCs

63

Severe malaria pathology

sequestration/cytoadherence

rosetting and clumping

  • first observed in in votro culturing
  • observed in 50% of field isolates and correlates strongly with disease severity

 

64

Severe malaria pathology

sequestration/cytoadherence

mature trophozoite-infected and schizont-infected erythrocytes have

altered surface morphology

  • electron-dense protrusions (knobs)

 

65

Severe malaria pathology

knobs contain parasite proteins

 

  • PfEMP1 - P. falciparum Erythrocyte Membrane Protein 1
  • PfEMP2 - P. falciparum Erythrocyte Membrane Protein 2
  • KAHRP - knob-associated histidine rich protein

all produced and secreted by parasite then transferred toward erythrocyte surface

 

66

Severe malaria

knobs

PfEMP2 and KAHRP

  • not exposed on outer surface of erythrocyte
  • localized toward erythrocyte cytoplasm
  • function unknown - reorganizing erythrocyte cytoskeleton?

 

67

Severe malaria

knobs

PfEMP1

  • is exposed to the outer surface of the erythrocyte
  • functions as ligand to bind receptors on host epithelial cels 
  • is immunogenic
  • expressed by var gene family
  • parasite genome contains 40-60 var genes
  • at least 40-60 immunogenic PfEMP1 isoforms

 

68

Severe malaria

knobs

Pfemp1 

(picture)

A image thumb
69

Severe malaria

knobs

PfEMP1

  • 40-60 PfEMP1s exhibit high degree of sequence variability
  • have similar overall conserved, multi-domain structure
  • NTS = N-terminal segment
  • cysteine rich domains
  • TM - transmembrane domains
  • duffy binding like (DBL)
  • cysteine-rich interdomain regions (CIDR)
  • number and order of DBLs and CIDRs varies between PfEMP1 isoforms

70

Severe malaria

knobs

PfEMP1

different DBLs and CIDRs bind to different host cell receptors

CD36 complement receptor 1 - ICAM1

  • variable domain composition and extensive sequence polymorphism thought to provide great flexibility in binding properties

 

71

Severe malaria

knobs

PfEMP1

allelic exclusion

  • out of 40-60 var genes only 1 expressed by a population (allelic exclusion)
  • knobs only contain 1 PfEMP1 isoform
  • each PfEMP1 isoform is antigenically distinct
  • in response to immune system parasites switch to new PfEMP1 variants (antigenic variation)
  • switching is promoter-driven
  • switching frequency of ~2% of the population switch per cycle
  • switching to new, antigenically distinct PfEMPs results in new infected erythrocyte having different adhesion phenotype

72

Severe malaria pathology

sequestratio/cytoadherence

anemia

  • cytoadherence - non-infected and infected RBCs stick to each other AND the blood vessel endothelium (PfEMP1 mediated)
  • blood vessels become clogged and hemorrhage (common in cerebral malaria)
  • induces production of cytokines 
    • causes expression of endothelial adhesins and makes endothelial cells more "sticky"
  • reduces blood flow → anemia

 

73

Malaria

acquired immunity

  • people living in endemic areas acquire immunity through natural exposure to the parasite
  • acquired (or natural) immunity occurs only after continued exposure from multiple infections over time
  • acquired immunity limits high-density parasitemia
    • however it does not lead to sterile protection
  • clinical immunity provides protection against severe effects of malaria but fails to provide strong protection against infection with malaria parasites

explains why kids and people from non-malarious regions are more susceptible to malaria

74

Malaria

diagnosis

microscopy

  • thin/thick blood films
  • tell 4 species apart

antigen

  • can't distinguish between all types of malaria
  • rapid diagnostic tests

PCR

  • expensive

 

75

Malaria 

drugs

  • quinine
  • chloroquine
  • mefloquine (Lariam)
  • sulfadoxine-pyrimethamine (Fansidar)
  • atovaquone-proquanil (Malarone)
  • doxycycline
  • artemisin

 

MAJOR PROBLEM IS COUNTERFEIT DRUGS

COMPOUNDS SOLD AS ANTI-MALARIAL WITH NO/REDUCED ACTIVE INGREDIENT

 

76

Malaria

control measures

insecticide sprays

  • adult insects/larval stages
  • ecological considerations

bed nets containing insecticide

  • cheap
  • insecticide is "contained"

drainage

  • ecological considerations

wear socks

  • mosquitoes like smelly feet

 

77