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Susceptibility of Anopheles stephensi to Plasmodium gallinaceum: a trait of the mosquito, the parasite, and the environment.

Hume JC, Hamilton H, Lee KL, Lehmann T - PLoS ONE (2011)

Bottom Line: Notably, the environment contributed 28%.These estimates are relevant only to the particular system under study, but this experimental design could be useful for other parasite-host systems.The prospects and limitations of the genetic manipulation of vector populations to render the vector resistant to the parasite are better considered on the basis of this framework.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America.

ABSTRACT

Background: Vector susceptibility to Plasmodium infection is treated primarily as a vector trait, although it is a composite trait expressing the joint occurrence of the parasite and the vector with genetic contributions of both. A comprehensive approach to assess the specific contribution of genetic and environmental variation on "vector susceptibility" is lacking. Here we developed and implemented a simple scheme to assess the specific contributions of the vector, the parasite, and the environment to "vector susceptibility." To the best of our knowledge this is the first study that employs such an approach.

Methodology/principal findings: We conducted selection experiments on the vector (while holding the parasite "constant") and on the parasite (while holding the vector "constant") to estimate the genetic contributions of the mosquito and the parasite to the susceptibility of Anopheles stephensi to Plasmodium gallinaceum. We separately estimated the realized heritability of (i) susceptibility to parasite infection by the mosquito vector and (ii) parasite compatibility (transmissibility) with the vector while controlling the other. The heritabilities of vector and the parasite were higher for the prevalence, i.e., fraction of infected mosquitoes, than the corresponding heritabilities of parasite load, i.e., the number of oocysts per mosquito.

Conclusions: The vector's genetics (heritability) comprised 67% of "vector susceptibility" measured by the prevalence of mosquitoes infected with P. gallinaceum oocysts, whereas the specific contribution of parasite genetics (heritability) to this trait was only 5%. Our parasite source might possess minimal genetic diversity, which could explain its low heritability (and the high value of the vector). Notably, the environment contributed 28%. These estimates are relevant only to the particular system under study, but this experimental design could be useful for other parasite-host systems. The prospects and limitations of the genetic manipulation of vector populations to render the vector resistant to the parasite are better considered on the basis of this framework.

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Related in: MedlinePlus

Infection prevalence and intensity in unselected lines of An. Stephensi.Anopheles stephensi prevalence and mean oocyst load in unselected lines over a total of 28 infection experiments. Overall mean is shown by the horizontal line. Number of experiments is shown above each box-whisker plot (sample size range per experiment 50–175, except n = 20 in one experiment with the NIH line). The differences among lines in overall prevalence was not significant (χ2 = 3.96, df = 2, P<0.137) as was the case for the oocyst load (ANOVA with Experiment treated as blocking factor: F2,2135 = 0.58, P>0.55).
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pone-0020156-g003: Infection prevalence and intensity in unselected lines of An. Stephensi.Anopheles stephensi prevalence and mean oocyst load in unselected lines over a total of 28 infection experiments. Overall mean is shown by the horizontal line. Number of experiments is shown above each box-whisker plot (sample size range per experiment 50–175, except n = 20 in one experiment with the NIH line). The differences among lines in overall prevalence was not significant (χ2 = 3.96, df = 2, P<0.137) as was the case for the oocyst load (ANOVA with Experiment treated as blocking factor: F2,2135 = 0.58, P>0.55).

Mentions: As part of the selection on the vector, an An. stephensi control line was maintained side by side with each selected line, keeping the number of mothers for each generation of selection the same to assess the effect of random drift and systematic environmental change. We did not subtract the control line from the selected line because the prevalence of control line remained stable 0–5% (Figures 3 and 4).


Susceptibility of Anopheles stephensi to Plasmodium gallinaceum: a trait of the mosquito, the parasite, and the environment.

Hume JC, Hamilton H, Lee KL, Lehmann T - PLoS ONE (2011)

Infection prevalence and intensity in unselected lines of An. Stephensi.Anopheles stephensi prevalence and mean oocyst load in unselected lines over a total of 28 infection experiments. Overall mean is shown by the horizontal line. Number of experiments is shown above each box-whisker plot (sample size range per experiment 50–175, except n = 20 in one experiment with the NIH line). The differences among lines in overall prevalence was not significant (χ2 = 3.96, df = 2, P<0.137) as was the case for the oocyst load (ANOVA with Experiment treated as blocking factor: F2,2135 = 0.58, P>0.55).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3111409&req=5

pone-0020156-g003: Infection prevalence and intensity in unselected lines of An. Stephensi.Anopheles stephensi prevalence and mean oocyst load in unselected lines over a total of 28 infection experiments. Overall mean is shown by the horizontal line. Number of experiments is shown above each box-whisker plot (sample size range per experiment 50–175, except n = 20 in one experiment with the NIH line). The differences among lines in overall prevalence was not significant (χ2 = 3.96, df = 2, P<0.137) as was the case for the oocyst load (ANOVA with Experiment treated as blocking factor: F2,2135 = 0.58, P>0.55).
Mentions: As part of the selection on the vector, an An. stephensi control line was maintained side by side with each selected line, keeping the number of mothers for each generation of selection the same to assess the effect of random drift and systematic environmental change. We did not subtract the control line from the selected line because the prevalence of control line remained stable 0–5% (Figures 3 and 4).

Bottom Line: Notably, the environment contributed 28%.These estimates are relevant only to the particular system under study, but this experimental design could be useful for other parasite-host systems.The prospects and limitations of the genetic manipulation of vector populations to render the vector resistant to the parasite are better considered on the basis of this framework.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America.

ABSTRACT

Background: Vector susceptibility to Plasmodium infection is treated primarily as a vector trait, although it is a composite trait expressing the joint occurrence of the parasite and the vector with genetic contributions of both. A comprehensive approach to assess the specific contribution of genetic and environmental variation on "vector susceptibility" is lacking. Here we developed and implemented a simple scheme to assess the specific contributions of the vector, the parasite, and the environment to "vector susceptibility." To the best of our knowledge this is the first study that employs such an approach.

Methodology/principal findings: We conducted selection experiments on the vector (while holding the parasite "constant") and on the parasite (while holding the vector "constant") to estimate the genetic contributions of the mosquito and the parasite to the susceptibility of Anopheles stephensi to Plasmodium gallinaceum. We separately estimated the realized heritability of (i) susceptibility to parasite infection by the mosquito vector and (ii) parasite compatibility (transmissibility) with the vector while controlling the other. The heritabilities of vector and the parasite were higher for the prevalence, i.e., fraction of infected mosquitoes, than the corresponding heritabilities of parasite load, i.e., the number of oocysts per mosquito.

Conclusions: The vector's genetics (heritability) comprised 67% of "vector susceptibility" measured by the prevalence of mosquitoes infected with P. gallinaceum oocysts, whereas the specific contribution of parasite genetics (heritability) to this trait was only 5%. Our parasite source might possess minimal genetic diversity, which could explain its low heritability (and the high value of the vector). Notably, the environment contributed 28%. These estimates are relevant only to the particular system under study, but this experimental design could be useful for other parasite-host systems. The prospects and limitations of the genetic manipulation of vector populations to render the vector resistant to the parasite are better considered on the basis of this framework.

Show MeSH
Related in: MedlinePlus