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Pak D, Kamiya T, Greischar MA. Proliferation in malaria parasites: How resource limitation can prevent evolution of greater virulence. Evolution 2024; 78:1287-1301. [PMID: 38581661 DOI: 10.1093/evolut/qpae057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Revised: 03/28/2024] [Accepted: 04/04/2024] [Indexed: 04/08/2024]
Abstract
For parasites, robust proliferation within hosts is crucial for establishing the infection and creating opportunities for onward transmission. While faster proliferation enhances transmission rates, it is often assumed to curtail transmission duration by killing the host (virulence), a trade-off constraining parasite evolution. Yet in many diseases, including malaria, the preponderance of infections with mild or absent symptoms suggests that host mortality is not a sufficient constraint, raising the question of what restrains evolution toward faster proliferation. In malaria infections, the maximum rate of proliferation is determined by the burst size, the number of daughter parasites produced per infected red blood cell. Larger burst sizes should expand the pool of infected red blood cells that can be used to produce the specialized transmission forms needed to infect mosquitoes. We use a within-host model parameterized for rodent malaria parasites (Plasmodium chabaudi) to project the transmission consequences of burst size, focusing on initial acute infection where resource limitation and risk of host mortality are greatest. We find that resource limitation restricts evolution toward higher burst sizes below the level predicted by host mortality alone. Our results suggest resource limitation could represent a more general constraint than virulence-transmission trade-offs, preventing evolution towards faster proliferation.
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Affiliation(s)
- Damie Pak
- Department of Ecology and Evolutionary Biology, Cornell University, 215 Tower Rd, Ithaca, NY 14853, United States
| | - Tsukushi Kamiya
- Center for Interdisciplinary Research in Biology (CIRB), Collège de France, Paris, France
- HRB Clinical Research Facility, University of Galway, Ireland
| | - Megan A Greischar
- Department of Ecology and Evolutionary Biology, Cornell University, 215 Tower Rd, Ithaca, NY 14853, United States
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Herbert Mainero A, Spence PJ, Reece SE, Kamiya T. The impact of innate immunity on malaria parasite infection dynamics in rodent models. Front Immunol 2023; 14:1171176. [PMID: 37646037 PMCID: PMC10461630 DOI: 10.3389/fimmu.2023.1171176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2023] [Accepted: 07/07/2023] [Indexed: 09/01/2023] Open
Abstract
Decades of research have probed the molecular and cellular mechanisms that control the immune response to malaria. Yet many studies offer conflicting results on the functional impact of innate immunity for controlling parasite replication early in infection. We conduct a meta-analysis to seek consensus on the effect of innate immunity on parasite replication, examining three different species of rodent malaria parasite. Screening published studies that span four decades of research we collate, curate, and statistically analyze infection dynamics in immune-deficient or -augmented mice to identify and quantify general trends and reveal sources of disagreement among studies. Additionally, we estimate whether host factors or experimental methodology shape the impact of immune perturbations on parasite burden. First, we detected meta-analytic mean effect sizes (absolute Cohen's h) for the difference in parasite burden between treatment and control groups ranging from 0.1475 to 0.2321 across parasite species. This range is considered a small effect size and translates to a modest change in parasitaemia of roughly 7-12% on average at the peak of infection. Second, we reveal that variation across studies using P. chabaudi or P. yoelii is best explained by stochasticity (due to small sample sizes) rather than by host factors or experimental design. Third, we find that for P. berghei the impact of immune perturbation is increased when young or female mice are used and is greatest when effector molecules (as opposed to upstream signalling molecules) are disrupted (up to an 18% difference in peak parasitaemia). Finally, we find little evidence of publication bias suggesting that our results are robust. The small effect sizes we observe, across three parasite species, following experimental perturbations of the innate immune system may be explained by redundancy in a complex biological system or by incomplete (or inappropriate) data reporting for meta-analysis. Alternatively, our findings might indicate a need to re-evaluate the efficiency with which innate immunity controls parasite replication early in infection. Testing these hypotheses is necessary to translate understanding from model systems to human malaria.
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Affiliation(s)
- Alejandra Herbert Mainero
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Philip J. Spence
- Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Sarah E. Reece
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
- Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Tsukushi Kamiya
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
- Centre for Interdisciplinary Research in Biology, Collège de France, Paris, France
- HRB, National University of Ireland Galway, Galway, Ireland
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Greischar MA, Childs LM. Extraordinary parasite multiplication rates in human malaria infections. Trends Parasitol 2023; 39:626-637. [PMID: 37336700 DOI: 10.1016/j.pt.2023.05.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2023] [Revised: 05/18/2023] [Accepted: 05/19/2023] [Indexed: 06/21/2023]
Abstract
For pathogenic organisms, faster rates of multiplication promote transmission success, the potential to harm hosts, and the evolution of drug resistance. Parasite multiplication rates (PMRs) are often quantified in malaria infections, given the relative ease of sampling. Using modern and historical human infection data, we show that established methods return extraordinarily - and implausibly - large PMRs. We illustrate how inflated PMRs arise from two facets of malaria biology that are far from unique: (i) some developmental ages are easier to sample than others; (ii) the distribution of developmental ages changes over the course of infection. The difficulty of accurately quantifying PMRs demonstrates a need for robust methods and a subsequent re-evaluation of what is known even in the well-studied system of malaria.
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Affiliation(s)
- Megan A Greischar
- Department of Ecology & Evolutionary Biology, Cornell University, Ithaca, NY, USA.
| | - Lauren M Childs
- Department of Mathematics, Virginia Tech, Blacksburg, VA, USA
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Rodriguez T, Dobrovolny HM. Estimation of viral kinetics model parameters in young and aged SARS-CoV-2 infected macaques. ROYAL SOCIETY OPEN SCIENCE 2021; 8:202345. [PMID: 34804559 PMCID: PMC8595996 DOI: 10.1098/rsos.202345] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Accepted: 10/25/2021] [Indexed: 06/13/2023]
Abstract
The SARS-CoV-2 virus disproportionately causes serious illness and death in older individuals. In order to have the greatest impact in decreasing the human toll caused by the virus, antiviral treatment should be targeted to older patients. For this, we need a better understanding of the differences in viral dynamics between SARS-CoV-2 infection in younger and older adults. In this study, we use previously published averaged viral titre measurements from the nose and throat of SARS-CoV-2 infection in young and aged cynomolgus macaques to parametrize a viral kinetics model. We find that all viral kinetics parameters differ between young and aged macaques in the nasal passages, but that there are fewer differences in parameter estimates from the throat. We further use our parametrized model to study the antiviral treatment of young and aged animals, finding that early antiviral treatment is more likely to lead to a lengthening of the infection in aged animals, but not in young animals.
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Affiliation(s)
- Thalia Rodriguez
- Department of Physics and Astronomy, Texas Christian University, Fort Worth, TX, USA
| | - Hana M. Dobrovolny
- Department of Physics and Astronomy, Texas Christian University, Fort Worth, TX, USA
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Kamiya T, Davis NM, Greischar MA, Schneider D, Mideo N. Linking functional and molecular mechanisms of host resilience to malaria infection. eLife 2021; 10:e65846. [PMID: 34636723 PMCID: PMC8510579 DOI: 10.7554/elife.65846] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Accepted: 08/16/2021] [Indexed: 12/30/2022] Open
Abstract
It remains challenging to understand why some hosts suffer severe illnesses, while others are unscathed by the same infection. We fitted a mathematical model to longitudinal measurements of parasite and red blood cell density in murine hosts from diverse genetic backgrounds to identify aspects of within-host interactions that explain variation in host resilience and survival during acute malaria infection. Among eight mouse strains that collectively span 90% of the common genetic diversity of laboratory mice, we found that high host mortality was associated with either weak parasite clearance, or a strong, yet imprecise response that inadvertently removes uninfected cells in excess. Subsequent cross-sectional cytokine assays revealed that the two distinct functional mechanisms of poor survival were underpinned by low expression of either pro- or anti-inflammatory cytokines, respectively. By combining mathematical modelling and molecular immunology assays, our study uncovered proximate mechanisms of diverse infection outcomes across multiple host strains and biological scales.
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Affiliation(s)
- Tsukushi Kamiya
- Department of Ecology and Evolutionary Biology, University of TorontoTorontoCanada
| | - Nicole M Davis
- Department of Microbiology and Immunology, Stanford UniversityStanfordUnited States
| | - Megan A Greischar
- Department of Ecology and Evolutionary Biology, Cornell UniversityIthacaUnited States
| | - David Schneider
- Department of Microbiology and Immunology, Stanford UniversityStanfordUnited States
| | - Nicole Mideo
- Department of Ecology and Evolutionary Biology, University of TorontoTorontoCanada
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Wait LF, Kamiya T, Fairlie-Clarke KJ, Metcalf CJE, Graham AL, Mideo N. Differential drivers of intraspecific and interspecific competition during malaria-helminth co-infection. Parasitology 2021; 148:1030-1039. [PMID: 33971991 PMCID: PMC11010048 DOI: 10.1017/s003118202100072x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Revised: 04/14/2021] [Accepted: 05/04/2021] [Indexed: 11/05/2022]
Abstract
Various host and parasite factors interact to determine the outcome of infection. We investigated the effects of two factors on the within-host dynamics of malaria in mice: initial infectious dose and co-infection with a helminth that limits the availability of red blood cells (RBCs). Using a statistical, time-series approach to model the within-host ‘epidemiology’ of malaria, we found that increasing initial dose reduced the time to peak cell-to-cell parasite propagation, but also reduced its magnitude, while helminth co-infection delayed peak cell-to-cell propagation, except at the highest malaria doses. Using a mechanistic model of within-host infection dynamics, we identified dose-dependence in parameters describing host responses to malaria infection and uncovered a plausible explanation of the observed differences in single vs co-infections. Specifically, in co-infections, our model predicted a higher background death rate of RBCs. However, at the highest dose, when intraspecific competition between malaria parasites would be highest, these effects of co-infection were not observed. Such interactions between initial dose and co-infection, although difficult to predict a priori, are key to understanding variation in the severity of disease experienced by hosts and could inform studies of malaria transmission dynamics in nature, where co-infection and low doses are the norm.
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Affiliation(s)
- L. F. Wait
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, USA
| | - T. Kamiya
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | | | - C. J. E. Metcalf
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, USA
| | - A. L. Graham
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, USA
| | - N. Mideo
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
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