Species Interactions and Immunity to Malaria Parasites

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Species Interactions and Immunity to Malaria
Parasites

• Marian Bruce, Christl Donnelly, Michael Alpers,
• Mary Galinski, John Barnwell, David Walker,
• Karen Day

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(No Transcript)
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Study Design

• Village of Gonoa, Madang Province, Papua New
  Guinea
• 34 asymptomatic children
• Parasite sampling from fingerpricks at 3 day
  intervals for 60 days
• Dynamics of P. falciparum, P. vivax and P.
  malariae from blood smears
• Dynamics of P. falciparum and P. vivax genotypes

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P. falciparum Genotyping
3D7HB3
HB3
HB3
3D7
m
m 0 3 9 12 15 18 24 27 33 36 42 m
m 0 3 6 9 12 15 18 24 27 33 36 42 51 60
m
EthBr ICI FC27
EthBr ICI FC27
m 0 6 9 12 15 18 21 24 27 30 33 36 39 42 51 54
57 60 m
EthBr ICI FC27
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P. vivax Genotyping
PCR/RFLP analysis at the polymeric Msp3? locus
child day
HhaI
AluI
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Correlation of Multiplicity and Prevalence
P. falciparum genotype
P. vivax genotype
proportion of samples P. vivax smear positive
proportion of samples P. falciparum smear positive

• 4 yrs

• 5-9 yrs

• 10-14 yrs

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10000 1000 100 10 1
total density (parasites/?I)
0 3 6 9 12 15 18 21 24 27 30 33 36 39
42 45 48 51 54 57 60
proportion of each species making total density
P. falciparum genotypes
0 3 6 9 12 15 18 21 24 27 30 33 36 39
42 45 48 51 54 57 60
P. vivax genotypes
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10000 1000 100 10 1
total density (parasites/?I)
0 3 6 9 12 15 18 21 24 27 30 33 36 39 42
45 48 51 54 57 60
proportion of each species making total density
P. falciparum genotypes
0 3 6 9 12 15 18 21 24 27 30 33 36 39
42 45 48 51 54 57 60
P. vivax genotypes
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Stability of Parasite Density
parasites/?I
parasites/?I
proportion
proportion
parasites/?I
parasites/?I
proportion
proportion

• P. vivax

• P. malariae

• total parasite density

• P. falciparum

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Regulation of Multiple Malaria Populations
10000 1000 100 10
threshold
parasite density (parasites/?I)
detection limit
suppression
antigenic variation
days
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Bulmers Test

• children with gt50 smears positive
• no autocorrelation in total density data
• n 19
• 16/19 data conforms with model of
• density-dependence
• 9/13 significance reduced or abolished
• applied to data from each species

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Mechanisms Underlying Density Dependent Regulation

• competition
• antigenic variation
• antibody-dependent cellular immunity (ADCI)
• fever
• innate immune mechanisms

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Species Interactions

• Evidence for parasite interactions
• Deficit of mixed species infections in
  cross-sectional surveys - associated with
  children
• - associated with high transmission rates
• Reciprocal seasonality in the prevalence of
  species
• - associated with the dominance of P. falciparum

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Pattern of Infection with Multiple Species

• Longitudinal
• number of infections with each species as
  expressed from prevalence of each
  (Chi-square1.60 p0.449)
• Cross-sectional
• deficit of mixed infections (Chi-square9.06
  p0.028)
• Peaks of episodes
• peaks did not coincide as often as expected by
  chance
• (Chi-square6.56 p0.01)

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Sequential Episodes of Infection

• sequential pattern of infection is a result of
  density dependent regulation
• during cross-sectional sampling this appears as
  a deficit of mixed infections

density
slide detection level
time
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Conclusions

• density dependent regulation of parasite density
  is species- and genotype-transcending
• acts to enhance sequential nature of infection
  with each species
• sequential pattern of infection underlies
  parasite interaction observed as mixed
  infection deficits

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Acknowledgements

• The people of Gonoa
• Mike Packer PNG Institute of Medical Research
• Moses Lagog
• Georges Snounou Imperial College
• Wellcome Trust
• European Commission
• British Medical Research Council

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statistical analysis of density-dependence

• Bulmers test
• distinguishes random changes from return
  tendency
• bootstrap variance test
• tests the independence of the dynamics of each
  species

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Parasite Detection Thresholds
1013 total red blood cells 2 litres
number of parasites log scale
1010 fever
108 microscopy
107 PCR
104 liver
101 from mosquito
parasite growth
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Comparison of Human Malarias
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Immunity Regulating Malaria Parasite Density

• Humans Species Specificity
• Ciuca et al., 1934 Boyd Kitchen, 1936
• Taliaferro, 1939 Jeffrey, 1966
• Animal models Species and Genotype Specificity
• P. knowlesi in Rhesus monkey Brown Brown, 1965
• P. chabaudi in mouse Jarra Brown, 1985
• P. fragile in toque monkey Handunnetti et al.,
  1987
• P. falciparum in Saimiri monkey Fandeur
  Chalvet, 1998

(Cross-reactions only in very closely related
species)