Malria: diagnosis, treatment and prevention

Mind Map by maisie_oj, updated more than 1 year ago


Microbiology Mind Map on Malria: diagnosis, treatment and prevention, created by maisie_oj on 04/27/2013.

Resource summary

Malria: diagnosis, treatment and prevention
1 Diagnosis
1.1 Microscopy
1.1.1 thin or thick blood films
1.1.2 Can tell four species apart
1.2 Antigen
1.2.1 Cannot distinguish between all types of malaria
1.2.2 Serves as a rapid diagnostic tool
1.3 PCR
1.3.1 Expensive
2 Treatment
2.1 Quinine-based drugs
2.1.1 Act within the food vacuole
2.1.2 Quinine 1st treatment available for malaria Natural medicine Peruvian mexicans chewed the bark of the Cinchona plant to treat malaria Earkly 1600's it was used by the catholic missionaries (called it "Jesuit's powder") Purified in 1817 - Pelletier and Caventou First pharmaceutical agent = 4-methanol quinolone Could cause cinchonism Blurred vision, nausea, vomitting, imparied hearing and dizziness Active against RBC stage malaria Effective against chloroquine-resistant malaria Found in tonic water Pharmacokinetics Absorption Oral Distribution 70% is bound to protein Elimination Redily metabolised in liver (~80%) Metabolites inactive 20% in urine Half life of ~18hrs
2.1.3 Chloroquine 4-aminoquninolone Artificial analogue of quinine Developed in 1940's Cheap, stable and no serious side effects Active against RBC stages Used extensively in 60's and 70's (during erradication campaign) Lead to massive levels of resistance e.g. in Vietnam etc. No other anti-malarial has come close Pharmacokinetcs Absorption Oral Distribution 50-60% protein bound Elimination Partially metabolised in liver in to active de-ethylated metabolites Excreted in urine unchanged (45%) - but slowly Half life = 1-2 months
2.1.4 MOA of Qunine and Chloroquine e.g. during ring-stage Parasite trophozoite requires haemoglobin (Hb) to survive Hb taken up by cytosome (endocytosis) uptake -> transport vesicles - > fuse with food vacuole Hb in food vacuole Hb broken down to release amino acids (released into cytoplasm) and haematin (kept in food vacuole) AA's used by cell Haematin (toxic to parasite) is crystallised to form haemozoin (inert, non-reactive) Two haematin molecules dimerised with a propionate group of one haematin interacting with the Fe ion of a second (this de-toxfies the Fe) These dimers form crystalline structures with other dimers -> haemozoin Seen as the second solid structure during the ring phase (the other one is the nucleus) Dimer = 4-beta haematin Fe(3+) ion of haematin can generate free radicals Quinine and chloroquine accumulate in the food vacuole Prevent the formation of haemozoin crystals -> haematin builds up, generates free radicals and kills the parasite In the 60's chloroquine was heralded as a major success However chloroquine resistance was observed as early as 1959 in SE Asia and S. America Since then chloroquine resistance has spread to all endemic areas (1957 - spread through asia and oceana, 1959-60 spread through S. America) In 1978 resistance from Asia spread throughout sub saharan africa Resistance now common Molecular basis for resistance chloeroquine resistance develops slowly Spectrum (low-high) resistance seen Suggestions mechanism of resistance is complex Resistance at target level (unlikely) Target is haematin (synthesised by host - Hb) Cannot be altered by parasite) Resistance at drug level (likely) Less chloroqunine retained in parasite Either; reduced uptake or drug efflux In low-medium resistant strains Mutations detected (by PCR and sequencing) in parasite protein PfCRT (P. falciparum chloroquine resistance transporter) PfCRT is found in the membrane of the food vacuole Features 10 transmembrane domains Resistance-conferring mutatin (K76T) is localised in a region of the protein involved in substrate selectivity Mutation: K76T is a key diagnostic tool for resistance detection In non-resistant strains food-vacuolar chloroquine is positively charged (protonated) due to the low pH The lysine (K) residue at position 76 features a positive side chain which physically repels the chloroquine molecule - preventing its escape) Hence its accumulation to x20,000 the level of the plasma chloroquine concentration The mutation of K to threonine (T) at position 76 means that chloroquine is removed from the food vacuole as threonine has an uncharged side chain Chloroquine is eliminated from the food vacuole via PfCRT (efflux pump) In higher resistance strains Feature additional mutaiotns to K76T in PfCRT Resistance can be enhanced by a mutation in a second gene PfMDR (P.falciparum multi druig resistance) PfMDR is an ABC (ATP-binding casette) transporter - group of membrane transporter proteins MDRs in other organisms function to export hydrphobic drugs and indirectly regulate ionic gradients MDRs are responsible for drug resistance in cancer cells The Ca(2+) channel blocker verapamil (which reverses resistance of mammalian cells to anti-cancer cells) reverses chloroquine resistance PfMDR contains 12 transmembrane domains (TMDs) ATP interacting loops PfMDR (like the PfCRT) is located in the membrane of the food vacuole There are several known mutations unique to different geographical resistant strains E.g. N86Y (Africa); S1034C, N1042D and D1246Y (S. America) ALL RESISTANT STRAINS FEATURE K76T!!! The acidity of the food vacuole causes chloroquine to accumulate (due to protination -> become charged) to x20,000 the plasma [chloroquine]
2.1.5 Mefloquine Used in cases of chloroquine-resistant malaria Absorption Oral Distribution Can cross the BBB (cerebral malaria) Side effects Experienced in 1:10,000 patients (psychological effects, seizures, motor and CNS problems MOA is unknonw In food vacuole like other quinines? Resistance newly emerging (SE Asia) - different mechanism to chloroquine Molecular basis of mefloquine resistance Requires wild type PfMDR1 Mutation in PfMDR actually causes mefloquine sensitivity Mutation associated with overexpression of wild type PfMDR Can remove mefloquine faster from the food vacuole So mefloquine resistance occurs by a different method to chloroquine resistance Amplification of PfMDR (mefloquine) Mutataion in PfMDR (chloroquine)
2.2 Non-quinolone-based drugs
2.2.1 Sulfadoxine-pyrimethamine combinational therapy Second-line treatment in chloroquine resistance (after mefloquine) Active against the asexual cycle merozoite -> trophozoite -> merozoite Side effects (Rare) death from drug-induce dermatological conditions (toxic epidermal necrolysis; or Steven-Johnson syndrome (SJS) Many milder side effects: rash, photosensitivity, blood disorders (aplastic anaeamia, agranulocytosis), liver/lung damage Absorption Single oral dose (3 tablets for adults) Distribution 90% is protein-bound both cross the placental barrier and pass into the breast milk Pyrimethamine concentrates in blood cells (red and white) and crosses into the CNS fluids Elimination <5% of each drug is metabolised both excreted in urine (long half lives - both >100 hrs) MOA Targets multiple enzymes of the folate synthesis pathway Drugs act synergistically (complimentary) Reduce folate levels -> folate is essential for nucleotide (DNA) synthesis and metabolism of certain amino acids Humans lack components of this pathway and therefore rely on the diet for folate Sulfadoxine Type 1 anti-folate para-aminobenzioc acid (PABA) analogue Necessary in folate synthesis Target: Dihydropteroate synthase (DHPS) - missing in humans Competitive inhibition In Plasmodium, DHPS is part of a bifunctional enzyme with dihydroptero pyrophosphokinase = PPPK-DHPS Pyrimethamine Type 2 anti-folate Pyrimidine containing compound Target: Dihydrofolate reductase (DHFR) - present in humans Competitive inhibition Pyrimethamine binds x7,000 more strongly to DHFR than dihydro folate (natural substrate) In Plasmodium DHFR is in copmplex with another enzyme thymidylate synthase (TS) Resistance Basis of resistance due to difference in activity (pyrimethamine is more active than sulfadoxine) Due to point mutations in their respective enzymes Firstly in DHFR-TS (only DHFR domain affected) Then in PPPK-DHPS (only DHPS domain affected) After four mutations in DHFR (above) - A437G; and K540E cause sulfadoxine resistance Diagnostic mutation = S108N (always present in resistant strains) causes 100 fold increase in resistance Secondary mutations cause increased resistance (e.g. N51I; C59R; I164L)
2.2.2 Atovaquone Part of a combinational therapy (with proguanil - another Type 2 antifolate inhibitor [targets DHFR]) Active against liver and RBC stages Casual prophylaxis (taken 1 day before travel) Pharmacokinetics Absorption Oral (standard malarone tablet) Distribution 99% binds to serum albumin (extremely lipophilic) Elimination Not metabolised (slowly excreted in faeces, little in urine - half life = 48-72hrs) Side effects Very few Trade name = Malarone MOA Analogue of ubiquinone Ubiquinone: shuttles electrons from complexes 1 and 2 of the oxidative phosphorylation pathway to complex 3 (cytochrome b) Atovaquone inhibts the passing of electrons to (reduction of) complex 3 in the ETC Inhibits proton gradient production -> ATP production Resistance Can only arise through a point mutation (Y268N or Y268S) in the gene encoding cytochrome b Resistance is rare when using Malarone combinational therapy - first case reported in 2002 Tyrosine (Y) is a bulky hydrophilic amino acid that interacts with the hydrophobic atovaquone Substitution to a less bulky asparagine (N) or serine (S) causes a loss of drug binding ability
2.2.3 Doxycycline Absorption Oral Distribution 90% drug in plasma Elimination Not metabolised Excreted in urine/faeces Half life = 18hrs MOA Site of action is the apicoplast (prokaryote remenant that resembles a chloroplast - non-photosynthetic) Inhibits cell growth by inhibiting translation in the apicoplast Stops cell growth - doesnt kill Broad spectrum antibiotic Used as prophylaxis Active against asexual cycle Resistance not yet reported
2.2.4 Artemisinin From leaves of Artemesia annua Problem with supply Not enough plant material can be grown for demmand Made from a series of isoprene units with a peroxide bond Pharmacokinetics poorly understood (oral bioavailability is poor) Synthetic compounds (Artesunsate) produced with increased H2O solubility - can be injected Active against ring stage Used against MDR malaria Evidence of resistance in Cambodia already The way forward? Artemisinin combinational therapy with... Amodiaquine Active against all forms of malaria (falciparum, vivax, ovale, malariae) Active against chloroquine resistant strains >20 million cases of malaria treated as of (2009) ...Mefloquine Reduced mefloquine side effects WHO advise use for uncomplicated falciparum infection Not cosidered suitable for first line treatment in African malaria MOA Uknown whether one or multiple drug targets(?) Inhibiton of food vacuole cysteine protease activity Damage to parasite's ETC in the mitochondria Irreversible inhibition with an ATPase (PfATP6) that pumps Ca(2+) from the cytoplasm into the ER
2.3 Three points of malarial chemotherapy
2.3.1 stage to target Sporozoite Liver schizont Merozoite Trophozoite (ring stage) RBC schizont
2.3.2 In host Liver Blood
2.3.3 Species P. falciparum P. vivax P. ovale P. malariae
2.4 Anatomy of the infected RBC
2.4.1 RBC Parasite (cytoplasm) Site of action for sulfadoxine-pyrimethamine (combinational therapy) Digestive (food) vacuole The food vacuole is the site of action for quinine-base drugs Nucleus Mitochondrion Atovaquone targets the mitochonrion Apicoplast Apicoplast: target for doxycycline Cytosome uptake of haemoglobin
3 Prevention
3.1 Insecticide sprays - control of adult and larval stages
3.1.1 Particularly around breeding grounds (still water) Ecological considerations
3.2 Mosquito nets
3.2.1 Contain insecticide Cheap and insecticide is "contained"
3.3 Prophylactic treatment
3.4 Control of mosquito population (introduction of sterile males)
3.5 Drainage and removal of breeding grounds
3.5.1 Ecological considerations
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