W2 LECT 9: Malaria

Question 1

what are the species of malaria?

Answer 1

-Plasmodium falciparum
– >95% of cases in southern Africa
– most important species causing severe or fatal
malaria
* Plasmodium ovale
* Plasmodium malariae
* Plasmodium vivax
* Plasmodium knowlesi (only in SE Asia)
* (P. simium, P. cynomolgi, P. brasilianum)

Question 2

explain the life cycle of malaria

Answer 2

1. Infectious Stage:
   
   • Infected Anopheles mosquito bites a human.
   • Sporozoites enter the human bloodstream.
2. Liver Stage:
   
   • Sporozoites travel to the liver.
   • They infect liver cells and mature into schizonts.
3. Blood Stage:
   
   • Schizonts rupture, releasing merozoites into the bloodstream.
   • Merozoites invade red blood cells (RBCs).
4. Asexual Replication:
   
   • Merozoites inside RBCs develop into trophozoites.
   • Trophozoites mature into schizonts, which rupture and release more merozoites.
   • Cycle repeats, causing symptoms of malaria.
5. Sexual Stage:
   
   • Some merozoites develop into sexual forms called gametocytes.
   • Gametocytes circulate in the bloodstream.
6. Transmission to Mosquito:
   
   • Another mosquito bites the infected human, ingesting gametocytes.
   • Gametocytes develop into gametes in the mosquito’s gut.
7. Mosquito Stage:
   
   • Gametes fuse to form zygotes, which develop into ookinetes.
   • Ookinetes penetrate the mosquito’s gut wall and form oocysts.
   • Oocysts grow, rupture, and release new sporozoites.
8. Cycle Repeats:
   
   • Sporozoites migrate to the mosquito’s salivary glands.
   • The mosquito becomes infectious and can transmit malaria to another human host.

Question 3

explain the pathogenesis of falciparum malaria

Answer 3

-Parasitised red blood cells (PRBCs) adhere to capillary wall
by sticky ‘knobs’
* sequestration of PRBCs containing mature parasites in
internal organs
* PRBCs: less deformable, rosetting, clumping - impaired
microcirculation
* malarial antigens stimulate release of inflammatory
cytokines

Question 4

what are the outcomes of malaria?

Answer 4

• asymtomatic
• fever
• severe, complicated malaria
• death

Question 5

what are the transmission scenarios of malaria?

Answer 5

• Stable transmission:
  – prevalence of infection is high
  – high levels of population immunity develop
• Unstable transmission
  – population immunity is low
  – epidemics likely to occur

Question 6

what are the manifestations of malaria

Answer 6

• anaemia
• cerebral malaria
• renal failure
• respiratory failure
• acidosis
• hypoglycaemia
• liver dysfunction
• bleeding, blackwater fever

Question 7

name the non- mosquito malaria transmission

Answer 7

Needlestick
* Transfusion
* Whole blood and blood components
* Minimised by donor screening and exclusion/deferment
* Congenital malaria
* Hyperendemic areas: cord blood parasitaemia frequent,
seldom results in clinical malaria in neonate
* Because of foetal haemoglobin, maternal antibodies?

Question 8

what is odyyssean malaria?

Answer 8

• Malaria acquired from the bite of an imported Anopheles
  mosquito
• No history of travel involving malaria endemic areas
• No history of blood transfusions, injections, needle sharing

Question 9

what are the diagnostic problems?

Answer 9

-Absence of travel history
* Non-specific symptoms and signs
* Automated laboratory technology: blood smears not routinely examined
– Delayed or missed diagnosis
– High morbidity and mortality: 15% vs. <1.5% for ordinary malaria

Question 10

Name the 3 factors acting on severity of malaria

Answer 10

• Parasite factors
• Host factors
• Environmental factors