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TM: Vector borne diseases - Malaria lifecycle + epidemiology (ii)…
TM: Vector borne diseases - Malaria lifecycle + epidemiology (ii)
Plasmodium lifecycle
sporozoites (spore-like infective form) from mosquito salivary glands (saliva = anaesthetic)
sporozoite becomes trophozoite (growing stage), lives on Hb
sporozoites invade hepatocytes + multiply as schizonts (replicate form - divide by schizogony) - forms merozoites (daughter cells)
some 1st become hypnozoites (P vivax + ovale) + become schizonts months later (dormant then relapse)
liver schizont ruptures, trophozoites enter RBCs + develop into schozonts again
RBC schizonts rupture, cause haemolytic anaemia + jaundice due to bilirubin release, invade other RBCs
some become sexual forms (gametocytes) which get ingested by mosquito during blood meal
gametes fuse, form zygote called an ookinete, develops on mosquito's stomach wall into an oocyst (can be seen microscopically on dissection)
oocyst ruptures, motile sporozoites migrate to salivary glands
3 cycles
sporogonic (mosquito stage)
exo-erythrogenic (human liver stage)
erythrogenic (human blood stage)
Lab Dx
gold standard = detecting + identifying parasites microscopically in stained blood films
thick (more sensitive but less specific)
thin
Leishman's/Giemsa/Field's stain
RDT
detects malaria antigen (e.g. HRP2 - histamine rich protein)
takes 20 mins
if +ve do film to confirm + detect type
if -ve rule out malaria
QBC
direct + rapid
based on acridine orange staining of centrifuged peripheral blood samples in a microhaematocrit tube + examination under UV light (fluorescence microscopy)
PCR (research only)
Epidemiology
mortality fallen by 42% globally since 2000 + by 49% in the WHO African region
most deaths in African children (1 per min)
rates have reduced by 54% since 2000
103 countries with ongoing transmission - 40% of world's pop @ risk
90% of cases in SSA
75% of death in under 5s
MDR + insecticide resistance
Mosquito control
there's evidence to show that this reduces malaria incidence
Larvae
larvivorous fish
larval control using parasites + pathogens
physical control - covering water pots, filling in/draining swamps, container removal
environmental manipulation (release of water from damns quick to flush out larvae)
chemical control. oils (e.g. on top of septic tank), Paris Green, insecticides
Adults
screens/bed nets impregnated with insecticide (works well)
Room sprays
impregnated tablets for electric sockets
repellents (DEET = best, but resistance occurring)
aerosols
mists
fogs
ultra low volume techniques for pesticides
residual house spray - toxicity + resistance
genetic control (sterile males - not yet proven to work @ pop level)