Plasmodium and Malaria Flashcards
How prevalent/important is Malaria? Deaths? 00:30
- Most important tropical disease; affecting 207 million worldwide
- 3 billion at risk worldwide
- > 600,000 people die from malaria every year; mainly children U5 years old; one death a minute.
» Preventable and curable
Who should be assessed for possible malaria infection?
- Any patient w/recent history of travel to an endemic country (luggage can be vector too) or been in an international airport presenting WITH FEVER should be assessed
- Malaria can present up to a year after travel to an endemic area
Who is at risk of contracting malaria?
- Any person; regardless of age, gender, ethnicity or country of birth
What is the UK stance on malaria?
Notifiable disease (Health Protection Regulation 2010)
What are the main causative agents of human malaria, and the respective strain they cause?
- Plasmodium falciparum (malaria subtertiana)
- Plasmodium ovale (malaria tertiana)
- Plasmodium vivax (malaria tertiana)
- Plasmodium malariae (malaria quartana)
- Plasmodium knowlesi; still considered zoonotic though (malaria quotidiana)
»> This one not diagnosed by RDT, difficult by microscopic tests (from monkeys in SE Asia)
What is the vector malaria is spread by, and what is their typical habitat?
- Plasmodium spread by Anopheles (genus) mosquito; the vector
- Anopheles deposits eggs in stagnating waters e.g. rice paddies, swamps, marshes for egg maturation
What is the life cycle of the Anopheles spp. mosquito?
- Adult female mosquito takes a blood meal, then lays eggs; 50-200 at a time (only females transmit malaria)
- The eggs are laid onto still water, developing into aquatic larvae (close to the surface; have breathing tubes)
- Over 8-10 days; the larvae go through 4 stages of development called instars.
- During the last larval instar, the larvae develop into pupae
- After 1-2 days, the adult mosquito emerges from the water.
»> Development time is 10-14 days (depending on species and ambient temperature; greater temperature = shorter time, but too low a temperature and Plasmodium do not develop)
Why do countries like Norway/Siberia/North Africa have the malaria vector Anopheles spp., but no incidence of malaria?
- Non-tropical/sub-tropical areas
- Plasmodium does not develop in lower temperatures
Some sub-species of Anopheles spp. mosquito are zoophilic; what does that mean?
- Some sub-species of Anopheles spp. in (primarily in) Europe are primarily zoophilic; preferring to feed on animals such as cattle or birds
- But most species are not exclusively anthropophilic or zoophilic; thus will feed on humans if needs be etc.
»> Climate change may bring malaria back to Europe
What is the lifecycle for the malaria parasite?
Exo-erythrocytic Cycle:
1) During a blood meal (essential before laying eggs), a malaria-infected female Anopheles injects anti-coagulant (its saliva) into the human first, so it can get the blood - the saliva contains the Plasmodium, inoculating sporozoites into the human host)
2) Kuppfer cells of the liver take up Plasmodium (sporozoites) into the hepatocytes (liver cell), which divide and replicate…
3) Maturing into schizonts, which rupture…
4) Releasing merozoites (1000s); killing the hepatocyte cell.
Erythrocytic Cycle:
(responsible for clinical manifestations of disease)
5) These merozoites then infect RBCs (hiding from immune system in RBCs)
6) Ring-stage (immature) trophozoites then mature into schizonts, which then rupture, releasing more merozoites (starting Erythrocytic Cycle again, 5)
7) Some parasites differentiate into sexual erythrocytic stages; gametocytes.
8) The male and female (micro/macro-) gametocytes are ingested by an Anopheles spp. during a blood meal
Sporogenic Cycle:
- The parasite (malaria) multiplies in the mosquito, gametocytes > zygotes > ookinetes > oocysts > sporozoites; which make their way to mosquito’s salivary glands.
»> 1) Inoculation of the sporozoites into a new human host kicks off the malaria life cycle again.
What are sporozoites thin and slender in shape?
To fit in the salivary glands of the Anopheles spp. mosquito.
What are the symptoms associated with malaria infection?
- No symptoms associated with liver stage (exo-erythrocytic)
- Symptoms occur when RBC stages (erythrocytic cycle) rupture cells and release malaria ‘toxins’ and pyrogens (which in turn induce fever)
Common symptoms:
- Fever (can be w/o)
- Anaemia (loss of RBCs)
- Splenomegaly (dead RBCs trapped in spleen; becomes enlarged)
- Jaundice (sub-optimal liver function)
- Diarrhoea (non-specific)
- Vomiting (non-specific)
What is unique WRT malaria tertiana (P. vivax/P. ovale) life cycle?
- They have an extra step in the Exo-erythrocytic cycle (liver stage)
- Hypnozoites (a dormant stage) can persist in the liver and cause relapses by invading the bloodstream weeks/years later
What is malarial fever caused by?
- Caused by host cytokines (IL-6) released in response tp released pyrogens from lysed RBC
What are the classical stages of malarial fever?
Do all malaria infection follow this pattern?
- Cold stage; patient shivers or shows rigor (15-60 min)
- Hot stage; patient becomes flushed, has rapid pulse and high temperature (41 degrees C) for hours (2-6 hrs)
- Sweating stage; patient sweats abundantly (as a result of high temp in Hot stage), temperature drops (2-4 hours, evaporation of sweat)
> > > Particularly w/P. vivax
But there can serious cases of malaria infection w/o fever
