vi. Malaria I and II Flashcards
Malaria I and II=
History:
History: Ancient disease that co-evolved w Homo sapiens
1880 Laveran discovered malaria parasite in Algeria —> 1897 Ross discovered _____ _____ in India —> 1972 Tu Youyou isolated artemisinin in China
mosquito vector
Global Disease burden:
- 85 malaria ______ countries; 2020 - estimated 241 million cases globally
- WHO African region - 2020 estimated malaria cases 228 million accounts for ____% global burden; ___% deaths in this region = children under 5yrs
- Since 2000 malaria case incidence reduced from 368 to 222 cases per 1000 pop @ risk in 2019 before _______ to 233 in 2020 owing to disruptions during Covid-19 pandemic
endemic
95%; 80%
increasing
The Parasite and the vector
Parasite =
Vector =
Plasmodium species: P. Falciparum; P. Ovals; P. Vivax; P. Malariae; P. Knowlesi
Female Anopheles mosquito
*Apical prominence =
*Apical prominence = place where merozoite attaches to RBC
Process of Parasite Invasion Proteins: (4)
- Attachment to RBCs = Merozoite surface protein MSP-1
- Junction formation = proteins secreted from micro eyes and rhoptries + erythrocyte binding antigen EBA-175
- Complex regulation of sequential release of invasion proteins
- Molecular interaction w host RBC receptors = glycosylated membrane proteins
Host RBC Membrane Receptors
P. Vivax —
P. Falciparum —
- P. Vivax — Duffy blood group antigen / IL8 which is only present on young RBCs therefore only invades young RBC
- P. Falciparum — several receptor pathways; Shalicious acid dep and indep (glycoproteins, Band 3, Basigin); P. Falciparum invades RBC of all ages
What is the process of remodelling of Host RBC? (4)
- New transport pathways: nutrient entry and waste prod disposal; movement across 3 membranes; parasitophorous duct
- Exports several hundred proteins into RBC
- Modification of host RBC proteins
- Insertion of parasite proteins into RBC membrane
Haemoglobin Degradation
- 95% of soluble RBC protein is haemoglobin; 25-75% haemoglobin = ____ ____ ______; 25% utilized for AAs; rest exported for volume control
- Haemoglobin ingested by parasite via ______ — fusion w acidic digestive vacuole — digestion by parasite specific protease — Release of _______ haemoglobin from globin —
auto-oxidation to toxic ferriprotoporphyrin — ________________ into inert haemoglobin
degraded by parasite
cystoscome
ferrous
bicrystallisation
How does the malaria parasite evade the host immune system? (3)
- Parasite growth alters pRBC surface — triggers an immune response
- Decreased deformability of parasitized RBC causes splenic trapping and destruction
- P. Falciparum parasites evade host immune system and spleen
- sequestration/ cytoadherence
- variation of exposed antigens
Cytoadherence: adhesion of pRBC to vascular endothelium
- Mature asexual P. Falciparum ________
- Immature P. Falciparum _______
parasites
gametocytes
What is Autoagglutination?
Adhesion of pRBC to other pRBC
What is Resetting?
Adhesion of pRBC to uninflected RBC
Parasite Cytoadherence Ligands:
Knobs:
protrusions on RBC membrane surface; host RBC spectrum, actin, protein 4.1 and 4.9; PfKAHRP; PfEMP 1,2 and 3
Parasite Cytoadherence Ligands:
Parasite ligands:
PfEMP1; Modified host band 3
Host Receptors for Cytoadherence: (5)
Parasite Antigenic Variation:
PfEMP 1 - most NB determinant; Encoded by fam of var genes; 50-150 copies of var gene per genome; Each parasite expresses a single var gene Invasion proteins: ______; ______
MSP 1; EBA 175
Release of Merozoites:
2 step mechanism:
parasitophorous vacuole membrane ruptures — parasite liberates proteases into RBC — proteolytic cleavage of RBC membrane — pressure driven explosion of RBC — rapid
discharge of merozoites
What is Gametocytogenesis? (8)
Gametocytogenesis
In mosquito:
- rapid gamete formation to avoid ______ detection
- rapid fertilization and ______ formation
- limited invasion of ookinetes in mosquito midgut
- limited number of ________ in the salivary glands
- Infected mosquitoes bite more
- Trade off btw rapid optimal transmission to human host and killing the _______ host
immune
ookinete
sporozoites
mosquito
Parasite Survival Strategies: Within human RBC = (4)
- metabolism adapted to host RBC environment
- Detoxifies haemoglobin
- regulates vol of RBC
- Induces alterations of RBC membrane
Parasite Survival Strategies:
Immune Evasion = (3)
- cytoadherence to escape destruction in spleen
- Antigenic variation to escape immune response
- Minimum time outside RBC to evade detection
Parasite Survival Strategies:
Other:
- gametocyte formation to ensure _______
- Regulates ________ to protect human host-apoptosis
- Drug resistance
transmission
parasitaemia
Survival stategies of human host
Malaria hypothesis Haldan 1949:
to explain the high incidence of hereditary Angelia in regions where malaria was endemic
Survival stategies of human host
Balanced polymorphism -
Balanced polymorphism - selection of a deletorious gene by survival advantage for another disease
Survival stategies of human host
Inherited genetic defects or polymorphisms:
haemoglobinopathies; enzymopathies; RBC membrane protein defects; blood groups and antigens
Haemoglobinopathies:
1. Sickle cell haemoglobin: (7)
What are the Haemoglobinopathies?
- Sickle cell haemoglobin
- HaemoglobinC
- Other haemoglobinopathies
Haemoglobinopathies:
2. HaemoglobinC: (2)
Haemoglobinopathies:
3. Other haemoglobinopathies: (3)
HBE and HbF:
- decreased parasite growth
- Increased immune clearance by phagocytosis
- Stable HbF tetramer is poor substrate
What are Thalassemias? (4)
- Imbalance of globin chain synthesis
- Decreased parasite growth
- Increased phagocytosis and oxidative damage
- Impaired rosetting
What are Enzymopathies? (2)
- G6PD Deficiency
- Pyruvate Kinase (PK) Deficiency
Enzymopathies
1. G6PD Deficiency: (4)
Enzymopathies
2. Pyruvate Kinase (PK) Deficiency: (3)
- PK catalyses an essential step in anaerobic glycolysis
- critical for ATP production in erythrocytes which lack mitochondria
- PK deficient red cells show marked in vitro resistance to P. Falciparum invasion and growth
RBC Membrane Protein Defects:
1. South East Asian Ovalocytosis
- V high ______ in South East Asia
- Homozygote = ______
- 9 AA deletion in band 3
- Inhibits parasite invasion
- Decreases ________
- protects against ______ malaria
prevalence
lethal
cytoadherence
cerebral
Blood group Antigens:
P Falciparum -
P Vivax -
- P Falciparum - absence oof glycophorins/ hybrid glycophorins; decreased invasion/ growth of parasites; protection not complete, can use multiple receptors
- P Vivax - Duffy antigen receptor; 100% Duffy negative in parts of west Africa; absence of P. Vivax
ABO blood groups:
- current ABO distribution due to ______ ______ from malaria
- Blood group O protects against _____ P. Falciparum malaria
- Reduced cytoadherence/ resetting of group O _____
- O>A in endemic malaria areas; A>O in non-malaria areas
selective pressure
severe
pRBC
Blood group Antigens:
- Hereditary Spherocytosis (HS)
- Hereditary Elliptocytosis (HE)
- Decreased parasite growth ____ ______
in vitro
Symptoms of P. Falciparum Malaria:
What is Acute Febrile Illnesses?
Can rapidly progress to severe disease and death; initial symptoms non specific: fever, chills, perspiration, headache, myalgia, tiredness, loss of appetite, poor feeding (young children), nausea, vomiting, diarrhoea, abdominal discomfort; spleen omega lay (areas of high transmission)
Symptoms of P. Falciparum Malaria
Severe Malaria:
- Impaired consciousness; prostration (unable to sit/ stand/ walk w/o assistance; multiple convulsions (more than 2 in 24hrs); respiratory distress; acidotic breathing; acute pulmonary edema; auria; jaundice; abnormal bleeding
Pathogenesis of P. Falciparum Malaria:
Fever and chills =
- haemolysis of infected RBCs every __ hrs
- release of ______ which infect new RBCs
- Release of haemoglobin an _____
- Endothelial cell injury and _______ damage
- _____ release, inflammatory response, fever
48
merozoites
toxins
oxidative
Cytokine
Severe Anaemia:
- Haemolysis of infected RBCs every 48hrs and of _______ bystander RBCs
- Destruction of infected RBCs in ____
- Impaired _________
uninflected
spleen
erythropoietin’s
What is Pathogenesis of P. Falciparum Malaria?
- Fever and chills
- Severe Anaemia
- Hypoglycemia and metabolic acidosis
- Organ damage and cerebral malaria
Pathogenesis of P. Falciparum Malaria:
Hypoglycemia and metabolic acidosis =
- Increased anaerobic glycolysis in infected ____
- ________ and increased lactic acid prod
- metabolic _____
RBCs
Hypoglycemia
acidosis
Organ damage and cerebral malaria:
- cytoadherence/ agglutination/ resetting _____ RBCs
- Obstruction of capillaries and small blood vessels
- Reduced blood flow and _____
- Endothelial cell injury and _______ damage
- Decreased nitric oxide, impaired _______
- cytokine storm and inflammatory response
infected
hypoxia
oxidant
vasoregulation
Diagnosis of Malaria: (4)
- Microscopy of blood smears
- Rapid diagnostic tests (RDT)
- PCR
- Automated diagnosis
[Clinician has to request malaria test, clinical suspicion or travel history required]
Diagnosis of Malaria:
1. Microscopy:
What are the differences between a thin blood smear and a thick blood smear?
(3 x 3)
Diagnosis of Malaria:
1. Microscopy
Advantages or Disadvantages: (5 x 4)
Diagnosis of Malaria:
2. RDT - rapid antibody-based dipstick tests/ lateral flow immunoassay; malaria antigens pHRP/ pLDH
Advantages or Disadvantages: (3 x 6)
Diagnosis of Malaria:
3. PCR - molecular test
Advantages or Disadvantages: (4 x 6)
What test is used to calculate percentage parasitaemia?
SYSMEX Analyser:
Number of infected RBC (MI-RBC 103/ul) % parasitaemia (MI-RBC %)
Full blood count
Automated Diagnosis of Malaria:
- Haematology analysers; __________ based on cell size and complexity
- Indirect measurement of WBCs w haemoglobin; laser light differentiates btw diff WBCs Intraerythrocytic parasites produce ________
Monocytes ingest parasitized erythrocytes; monocytes scattered abnormally Haemozoin is _________ and depolarizes laser light
- Direct measurement of parasites in RBCs
- ________ can also be detected
scattergrams
haemozoin
birefringent
Gametocyte
What are the anti-malaria drugs? (10)
Pharmacological Therapy:
Uncomplicated P.
Falciparum malaria in non-pregnant patients:
- Fixed dose artemisinin-based combination therapy (ACT), artemether-lumefantrine (Coartem) 6 doses + low dose primaquine
- When artemether-lumefantrine is not available or is contraindicated (history of allergy to artemisinins/lumefantrine), uncomplicated malaria can be treated w/ oral quinine plus either doxycycline or clindamycin
Pharmacological Therapy:
Complicated/Severe malaria:
Intravenous artesunate at 0.12 and 24 hours, then daily until Pt s able to tolerate oral treatment (Coartem)
Pharmacological Therapy:
Non falciparum malaria: (2)
- Artemether-lumefantrine (Coartem)
- For P. Vivax or P. Ovale, a follow-on treatment course on primaquinine is essential to eradicate residual hepatic phase to prevent relapse
Artemisinin Resistance:
What are the Prophylactic Measures?
ABCDE
A: Awareness and assessment of malaria risk
B: Avoidance of bites (insecticide treated bed nets, mosquito repellants, long sleeve clothes at night etc.)
C: Chemoprophylaxis
D: Early detection and diagnosis
E: Effective treatment
Other strategies: Indoor residual spraying (IRS), larvicides
Vaccines:
Challenges w/ vaccine dev & admin:
dif parasite stages express dif antigens, incredible antigenic variation of parasite proteins, parasites can establish asymptomatic chronic infection in an immune-competent host
Vaccines:
Vaccine approaches:
Anti-infection vaccine (target sporozoites or liver stages eg. CSP), anti disease/mortality vaccine (target asexual RBC stage eg. MSP 1), Anti-transmission/
mosquito vaccine (target gametocytes/gametes/ookinetes)
Vaccines:
Strategies for Vaccine Design: (2)
- Antigens must be accessible to immune system, induce a protective immune response
Vaccines should combine antigens from dif parasite stages, combine several antigens from single parasite stage, elicit correct type of immune - Response for stage of parasite, elicit antibody & cell-mediated immune response, simple & inexpensive
What is the GSK RTS,S AS01 Vaccine?
Molecular Research Advances:
Genome sequences:
- Human: Homo Sapiens around 3 billion bp, ______ genes
- Parasite: P. Falciparum with 23 million bp, around _____ genes
- Mosquito: Anopheles gambiae, 280 million bp, ___-_______ genes
25 000
5300
13-14 000
Molecular Research Advances:
P. Falciparum can be cultured __ _____, protein biochem and cell biology
- Advanced molecular biology tech: gene transfection, gene knockout, ____-________ genome editing, RNAi - controversial, Microarrays, transcriptome sequencing, proteomics
- Enhances our knowledge of biology of _____, enables rational design of new drugs and vaccines
in vitro
CRISPR-Cas9
parasite
