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1. Plasmodium
Dr. Himanshu Khatri
E-mail: himanshubkhatri@yahoo.co.in

2. • Plasmodium belongs to the phylum
Apicomplexa
• They are the causative agents of malaria

3. Phylum Apicomplexa
• Phylum Apicomplexa have a cellular structure called apical
complex, which helps in the penetration inside host cells
• Organs of locomotion like pseudopodia, cilia or flagella are
usually absent (except in some male gamete forms)
• Life cycle has asexual phase (schizogony) and sexual phase
(sporogony), and this is termed as alternation of generation
• Alternation of generation can take place in a single host
(monogenetic) or separate hosts (digenetic)
• It forms reproductive cells called sporozoites, which have a
protective layer
• Obligate endoparasites
• Examples include Plasmodium, Toxoplasma, etc.,

4. Epidemiology of malaria
• Mal: bad; aria: air
• Eradicated in North America, Europe and
Russia
• Malaria eradication failed in 1976 after
mosquitoes developed resistance to DDT

5. Causative agent and vector
• Caused by 4 species of Plasmodium
P. falciparum
P. vivax
P. malariae
P. ovale
• Transmitted by Anopheles mosquito
Anopheles is a biological vector

7. Life cycle
• Humans (Intermediate host)
• Mosquito (Definitive host)

9. In Humans
• Forms in liver
• Forms in RBC

10. Forms in liver
• Sporozoites
• Merozoites

11. Sporozoites
• Morphology
slender
banana shaped
9-12 microns
• Infective form for humans
• Enter blood through bite of infected
mosquitoes
• Reach liver  multiply by schizogony 
merozoites

12. Merozoites
• End products of schizogony
• Released into blood by lysis of hepatocytes
• Infective stage for RBC to initiate erythrocytic
schizogony
• 1 sporozoite—40,000 merozoites

13. Forms in RBC (erythrocytic schizogony)
• Trophozoites
• Schizonts
• Merozoites
• Gametocytes

14. Trophozoites (Greek;trephein-to feed)
• Merozoitestrophozoites
• Types of trophozoites:
1) young: ring forms (they have vacuole in the
center)
The size of the ring forms increase
Also,the cytoplasm shows amoeboid movementso it
is irregular in stained preparations
The food vacuole gradually reduces in size and finally
disappears
2) old: amoeboid forms

15. Schizonts (Greek; schizein-dividing)
• Trophozoiteasexual multiplication (i.e.
schizogony)schizonts
1) immature schizont: nucleus divides but cytoplasm
does not divide
2) mature schizont: cytoplasm condenses around the
nucleus
• When schizonts are covered by cell membrane, they
are called merozoites

16. Merozoites (mero-part)
• 0.5-2.5 micron in diameter
• Number in RBC: 8-32
• The number depends on the species of
Plasmodium
• Infect other RBC to repeat schizogony

17. Merozoites lysing the RBC

18. Gametocytes
• Some merozoites, after transforming into immature
trophozoites, instead of undergoing erythrocytic
schizogony, undergo gametogony and form
gametocytes
• This occurs probably after immunity develops
• Gametocytes are exit forms
• 2 types
macrogametocyte (female)
microgametocyte (male)
• But syngamy takes place only in mosquitoes

19. Parasitic numbers
• Usually 1-2% RBCs are infected
• Life threatening: when > 5%
• In P. falciparum: upto 30% are infected,
therefore most serious

20. Forms in mosquitoes
• Gametes
• Ookinete
• Oocyst
• Sporozoites

22. Gametes
• Gametocyte mature in midgut of mosquitoes
to form gametes
• 1 macrogametocyte forms 1 macrogamete
• But 1 microgametocyte, by process of
exflagellation forms 6-8 microgametes

23. Ookinete
• 1 microgamete + 1macrogamete= zygote
• Zygote
1) elongates to 10-12 microns
2) becomes motile
to become ookinete

24. Oocyst
• Ookinete
It penetrates gut wall to reach haemocel
It gets covered by an electron dense capsule
to form oocyst
It matures and enlarges to upto 60 micron

25. Sporozoites
• Oocyst undergo meiosis and mitosis to form
haploid sporozoites
• Sporozoites break out of oocyst in haemocel
to reach the salivary glands
• They can now infect humans during bite

26. Species variations in trophozoite form
stage
• Cytoplasmic ring: uniform in P. falciparum, thick
opposite nucleus in the other three
• Chromatin dots: 2 in P.falciparum, 1 in other three
• Location of rings: inside or surface (accole) in
P.falciparum, always inside in other three
• Size of infected RBC:enlarged in P.vivax, oval in
P.ovale, no change in other two
• Band and basket forms in P.malariae

27. Gametocyte
• In P. falciparum: crescentic
• In P. vivax, ovale and malariae: spherical

35. Duration of each stage
• The injected sporozoites disappear from the
blood stream of within an hour
• Pre-erythrocytic schizogony : 6-9 days
• Erythrocytic schizogony: 48 hours (except P.
malariae: 72 hours)
• After an indeterminate number of
erythrocytic schizogony cycles, gametogony
takes place
• Gametocytes are formed within 96 hours

36. Prepatent and incubation period
• Prepatent period
• Intrinsic incubation period
• Extrinsic incubation period

37. Pre-patent period
• It is the time taken for the malarial parasite to be
first detected in blood after infection
• The patient is asymptomatic
• It takes 5-13 days

38. Intrinsic incubation period
• It is the time taken for signs and symptoms of
malaria to appear
• It takes 12 to 30 days

39. Extrinsic incubation period
• It is the time taken by the mosquitoes to
become infective after a blood meal
• It is the time taken by the parasites to develop
inside the mosquitoes
• It takes 9-28 days

40. Recurrence of malaria
• Recrudescence
• Relapse

41. Recrudescence (Latin;crudus:raw)
• In P.falciparum / P.malariae (Mnemonic: FM)
• Erythrocytic form evades immunity
survives then multiplies and increases in
number reappearance of symptoms
• In P. falciparum -within a year or two
in P. malariae -after decades

42. Relapse
• In P.vivax / P.ovale
• Some sporozoites invade liver do not enter
schizogony, but remain dormant (cryptobiotic
phase)—called hypnozoites
• These hypnozoites are activated from time to
time to initiate pre-erythrocytic schizogony

43. Clinical features
• Characteristic features
 fever at regular intervals i.e. tertian (after 48 hours)
in P. vivax, P.falciparum and P.ovale; and quartan
(after 72 hours) in P.malariae
 cycle of ‘chill-fever-sweating’
• Additional features
 Anaemia
 Splenomegaly

45. Special features of P.falciparum
pathogenicity
• RBCs infected with P.falciparum have protuberances
(knobs)
• Knobs have adhesive proteins (PfEMP-1)
• PfEMP-1 mediates adhesion to receptors on
endothelium
• Also, infected RBCs attach to other RBCs forming
rosettes
• Capillaries in organs are blocked involvement of
brain and heart are most serious life threatening
complications

46. Severe/pernicious/malignant malaria
caused by P. falciparum
• Severe anemia
• Cerebral (diffuse symmetric encephalopathy)
• Blackwater fever
• Renal failure due to plugging of renal capillaries
• Cardiac failure Pulmonary edema and shock
• Algid malaria: severe malaria + shock (algid means
‘cold’, and implies cold and clammy extremities seen
in circulatory shock)
• DIC (?due to adherence of platelets to RBC rosettes)
• Hypoglycemia (due to liver involvement)

47. Cerebral malaria
• Diffuse symmetrical encephalopathy develops
• Focal neurological signs are absent
• Intially there can be abnormal behaviour or
delirium
• This may progress to coma
• Mortality, despite treatment, is high (20%)

48. Blackwater fever
• Anti-erythrocytic
antibodies are
produced
• Massive hemolysis
occurs
• Hemoglobinuria ensues
• This results in dark red
to black urine
(blackwater fever)

49. Other immune mediated
complications
• Malarial nephropathy
• Tropical splenomegaly

50. Malarial nephropathy
• After chronic or repeated P.malariae infection
• Immune-complex mediated
• Nephrotic syndrome
• Does not respond to anti-malarial treatment

51. Tropical splenomegaly
• Seen in endemic areas like Africa or Indian
subcontinent
• Exaggerated immune response due to repeated
attacks of malaria over long period of time
• Large amounts of IgM antibodies are secreted
against CD8+ suppressor cells
• Due to lack of suppressor activity, excessive B-cells
proliferation takes place
• Therefore spleen is increased in size, and symptoms
of hypersplenism like anemia and thrombocytopenia
are seen

52. • In most cases, malarial parasites are not found
in peripheral smear as their number is
minimal
• It responds to anti-malarial treatment
• Prophylactic treatment to prevent recurrent
attacks is given

53. Spleen rate
• Proportion of individuals with splenomegaly in
endemic area
• Measured in children 2-9 years, and adults
 hypoendemic: spleen rate in children 10% or <
 Mesoendemic: spleen rate in children 11-50%
 Hyperendemic:spleen rate in children51-75%, adults
> 25%
 Holoendemic: spleen rate in children > 75%,
adults=low

54. Transfusion malaria
• Merozoites are infective forms
• No intrahepatic schizogony
• Short incubation period

55. Laboratory diagnosis
• Peripheral blood smear (PBS) (most common)
• Rapid Detection Tests (RDT) (widely used)
• Quantitative Buffy Coat (QBC) (if facilities
available)
• IF, IHA, EIA
• ELISA,RIA,DNA probes
• Culture

56. Timing of blood collection
• In P. falciparum, late trophozoites and schizonts are
not seen in peripheral blood
• Only early ring forms are seen in blood
• Early ring forms appear in blood after merozoites
invade new RBCs
• This happens only after a paroxysm of fever
• Therefore blood is collected after a paroxysm of
fever

57. Peripheral Blood Smear
• Thick films
 for detecting Plasmodium
 40 times more sensitive than thin smear
• Thin films
 species identification
 % of parasitized RBCs
 To find late trophozoites and schizonts of P.
falciparum
 Malarial pigment: indicative of recent malarial
infection

59. Stains for PBS
• Giemsa (best): cytoplasm-blue, nucleus-red
• Leishman’s
• Wright’s
• Field’s
• JSB

60. Rapid Diagnostic Test
• Detection of histidine rich protein 2 (PfHRP-2)
of P. falciparum and plasmodium lactate
dehydrogenase (pLDH) of all plasmodium
species
• Takes 20 minutes

62. Quantitative Buffy Coat
• When blood is
centrifuged, it forms
three layers
1. Upper layer of plasma
2. Lower layer of RBCs
3. Middle layer of WBCs
and platelets called the
buffy layer (as it is buffy
in color)

63. • A smear is prepared
from this layer and
stained with acridine
orange
• acridine orange stains
DNAobserved under
fluorescent microscopy
• Advantage: More
sensitive than PBS
• Disadvantage: Less
accurate for species
identification(90%)

64. Culture (Rarely done)
• Studying antigenic structure
• Vaccine preparation
• Drug sensitivity test

65. Thank you

66. Questions?