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Malaria

Malaria. A scourge of mankind from time immemorial. History. Descriptions known from classical times e.g. Chinese writings; Hippocrates; Roman writings. Variously described as:- “swamp fever” “marsh fever” “Roman fever” “malaria” (literally “bad air”).

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Malaria

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  1. Malaria A scourge of mankind from time immemorial

  2. History • Descriptions known from classical times e.g. Chinese writings; Hippocrates; Roman writings

  3. Variously described as:- “swamp fever” “marsh fever” “Roman fever” “malaria” (literally “bad air”)

  4. Characteristics of the disease • Periodic fevers with interspersed periods of remission • Tertian fever - every 3 days (48h remission) • Quartan fever - every 4 days

  5. Discovery of the disease agent • Laveran - French army surgeon in Algeria, 1880 • saw “pigmented bodies” in blood of malaria patients and recognised these to be parasites • In a fresh smear he noted “at the periphery, motile filaments of an animated nature”.

  6. Parasites causing quartan fever in Italy were named:- Plasmodium malariae • Golgi predicted that benign tertian fever was caused by a different form of the parasite. This he proved and it was named:- P. vivax

  7. Subsequently 2 other types of malaria were classified:- • Malignant tertian malaria - P. falciparum • P. ovale - tertian fevers (50h) with relapses up to 20-30 years later

  8. Plasmodium spp. Species Periodicity Range P. falciparum 48 h cosmopolitan P. vivax 48 h cosmopolitan P. ovale 50 h W. Africa P. malariae 72 h widespread/local

  9. How is transmission achieved? • Sir Patrick Manson first showed that insects could transmit diseases (filarial nematodes) • He speculated a similar mechanism for malaria in 1894

  10. Ronald Ross • Indian Army Medical Service • Saw that more parasites “exflagellated” in mosquitoes than in blood smears • Working with birds in 1898 he showed infections were bite transmitted • Traced larval parasites to mosquito salivary glands

  11. Vectors are Anopheles spp. • Up to 50 species implicated • A. gambiae most important in sub-Saharan Africa

  12. Malaria vectors in Afrotropical region (Region 7) • Anopheles arabiensis • A. funestus • A. gambiae • A. melas • A. merus • A. moucheti • A. nili • A. pharoensis

  13. Malaria vectors in Malaysian region (Region 10) A. campestris A. dirus A. conaldi A. flavirostris A. donaldi A. jeyporiensis A. letifer A. leucosphyrus A. nigerrimus A. ludlowae A. whartoni A. maculatus A. acconitus A. mangyanu A. balabacensisA. minimus A. philippiensis A. subpictus A. sundaicus (19 species)

  14. Acquired Immunity • This is seen in endemic areas • Adults ARE infected, but morbidity low • High prevalence in infants associated with high morbidity/mortality • In peripheral areas, immunity doesn’t build up. Also, if people leave endemic areas, immunity may be lost (i.e. NOT lifelong)

  15. Epidemiological considerations • Strain variation (implications for immunity) • Vector transmission (complicates dynamics) • Some acquired immunity • Long term of infection (2-4 years +) • Reservoir hosts (P. malariae only)

  16. Summary • Malaria occurs in 4 forms • Most serious - P. falciparum • Vectors are Anopheles mosquitoes • Acquired immunity is seen • Strain variation and drug resistance are widespread

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