8 results
Inflammation, infection and depression: an evolutionary perspective
- Caroline Doyle, Walker A. Swain, Holly A. Swain Ewald, Paul W. Ewald
-
- Journal:
- Evolutionary Human Sciences / Volume 1 / 2019
- Published online by Cambridge University Press:
- 09 December 2019, e14
-
- Article
-
- You have access Access
- Open access
- HTML
- Export citation
-
The evolutionary basis for clinical depression is not well understood. A growing body of literature that is not based on evolutionary logic links inflammation to depression. Integration of these findings with an evolutionary framework for depression, however, needs to address the reasons why the body's inflammatory response would be regulated so poorly that it would result in incapacitating depression. Pathogen induction of inflammation offers an explanation, but the extent to which the association between inflammation and depression can be attributed to general inflammation as opposed to particular effects of pro-inflammatory pathogens remains unclear. This paper reports a study of sexually transmitted pathogens, which addresses this issue. Although several sexually transmitted pathogens were associated with depression according to bivariate tests, only Chlamydia trachomatis and Trichomonas vaginalis were significantly associated with depression by a multivariate analysis that accounted for correlations among the pathogens. This finding is consistent with the hypothesis that infection may contribute to depression through induction of tryptophan restriction, and a consequent depletion of serotonin. It reinforces the idea that some depression may be caused by specific pathogens in specific evolutionary arms races with their human host.
7 - Evolutionary insights for immunological interventions
- from Part III - Evolution and Medicine
- Edited by Aldo Poiani, Monash University, Victoria
-
- Book:
- Pragmatic Evolution
- Published online:
- 05 April 2012
- Print publication:
- 10 November 2011, pp 115-132
-
- Chapter
- Export citation
-
Summary
An evolutionary perspective reveals why immune processes are intricately interconnected with each other and with other biological processes within multicellular organisms. This web-like interconnectedness has important implications for medical interventions. Evolutionary considerations suggest that direct manipulation of molecules and processes within the immune system are inevitably going to be associated with detrimental side-effects that result from the web-like interconnectedness. Manipulations of the immune system's exposure to threats, however, has led to many of the most successful achievements of medical science, because this sort of manipulation takes advantage of the inherent strengths of an intact immune system, by giving the immune system the upper hand in its attempts to control these threats. Evolutionary considerations also offer a new way to complement the intact operation of immune systems – by designing health interventions, such as vaccination strategies, to control the evolution of pathogen virulence.
Evolution of immune systems
One of the problems the first multicellular organisms encountered was the need for protection against unicellular organisms (e.g. bacteria) or subcellular agents (e.g. viruses). Although the mechanisms of this parasitism were probably similar to those involved in parasitism of unicellular hosts, multicellular organisation posed some additional vulnerabilities. Multicellular organisms required time to develop from a single cell and evolved cellular specialisation for different tasks. The longer time associated with multicellular development created a vulnerability, because any parasite that could circumvent the defences of a single cell could have immediate potential access to the host's other genetically identical cells. To restructure the genetic basis for its defences, the multicellular host would have to await development to maturity when sexual reproduction could create genetically different cells (Hamilton, 1980). A host's cells might still be able to rely on the defences that unicellular hosts have against parasites, such as destruction within phagosomes, but competition between multicellular organisms favours specialisation of cells for different purposes, such as neuronal conduction, support, sensing stimuli, proliferation and reproduction. Maintaining the entire suite of defensive armaments within each cell would compromise the ability of cells to be superior at their specialised functions.
29 - Evolutionary Medicine and the Causes of Chronic Disease
- Edited by Michael P. Muehlenbein, Indiana University, Bloomington
-
- Book:
- Human Evolutionary Biology
- Published online:
- 05 August 2012
- Print publication:
- 29 July 2010, pp 502-517
-
- Chapter
- Export citation
-
Summary
The current integration of evolution with medicine is artificially narrow because it reflects the biases of medicine as a whole and the specializations of particular investigators. If evolutionary principles are to offer a fundamental framework for understanding medical issues they should help identify these biases and the areas over which integration needs to be broadened. The chapter discusses this problem as it relates to evolutionary interpretations of chronic diseases. It also illustrates how an evolutionary perspective can provide a broader framework for resolving the causes and control of chronic diseases, focusing on the greatest killers in prosperous societies – atherosclerosis and cancer.
OVERVIEW OF CHRONIC DISEASES
Chronic diseases account for about 70% of the mortality in the United States and other wealthy countries. Most of this disease-induced mortality is attributable to heart attacks, strokes, and cancer. In spite of this importance, the causes of chronic diseases remain largely unresolved. This situation represents a major short-coming of modern medicine because understanding the causes of disease enables prevention, and prevention is the most effective way of eliminating the damage inflicted by disease. We can therefore expect that a better understanding of the causes of chronic diseases will yield some of the most valuable contributions that any discipline can make to improvements in health.
Chronic diseases can be defined broadly as diseases that persist within individuals for a long time. The US National Center for Health Statistics considers “long” to mean persistence for at least three months.
Pathogen survival in the external environment and the evolution of virulence
- Bruno A. Walther, Paul W. Ewald
-
- Journal:
- Biological Reviews / Volume 79 / Issue 4 / November 2004
- Published online by Cambridge University Press:
- 08 November 2004, pp. 849-869
- Print publication:
- November 2004
-
- Article
- Export citation
-
Recent studies have provided evolutionary explanations for much of the variation in mortality among human infectious diseases. One gap in this knowledge concerns respiratory tract pathogens transmitted from person to person by direct contact or through environmental contamination. The sit-and-wait hypothesis predicts that virulence should be positively correlated with durability in the external environment because high durability reduces the dependence of transmission on host mobility. Reviewing the epidemiological and medical literature, we confirm this prediction for respiratory tract pathogens of humans. Our results clearly distinguish a high-virulence high-survival group of variola (smallpox) virus, Mycobacterium tuberculosis, Corynebacterium diphtheriae, Bordetella pertussis, Streptococcus pneumoniae, and influenza virus (where all pathogens have a mean percent mortality [ges ]0.01% and mean survival time >10 days) from a low-virulence low-survival group containing ten other pathogens. The correlation between virulence and durability explains three to four times of magnitude of difference in mean percent mortality and mean survival time, using both across-species and phylogenetically controlled analyses. Our findings bear on several areas of active research and public health policy: (1) many pathogens used in the biological control of insects are potential sit-and-wait pathogens as they combine three attributes that are advantageous for pest control: high virulence, long durability after application, and host specificity; (2) emerging pathogens such as the ‘hospital superbug’ methicillin-resistant Staphylococcus aureus (MRSA) and potential bioweapons pathogens such as smallpox virus and anthrax that are particularly dangerous can be discerned by quantifying their durability; (3) hospital settings and the AIDS pandemic may provide footholds for emerging sit-and-wait pathogens; and (4) studies on food-borne and insect pathogens point to future research considering the potential evolutionary trade-offs and genetic linkages between virulence and durability.
Systematic reappraisal of Coniella and Pilidiella, with specific reference to species occurring on Eucalyptus and Vitis in South Africa
- Jan M. VAN NIEKERK, J. Z. ‘Ewald’ GROENEWALD, Gerard J. M. VERKLEY, Paul H. FOURIE, Michael J. WINGFIELD, Pedro W. CROUS
-
- Journal:
- Mycological Research / Volume 108 / Issue 3 / March 2004
- Published online by Cambridge University Press:
- 05 May 2004, pp. 283-303
- Print publication:
- March 2004
-
- Article
- Export citation
-
The genus Pilidiella, including its teleomorphs in Schizoparme, has a cosmopolitan distribution and is associated with disease symptoms on many plants. In the past, conidial pigmentation has been used as a character to separate Pilidiella (hyaline to pale brown conidia) from Coniella (dark brown conidia). In recent years, however, the two genera have been regarded as synonymous, the older name Coniella having priority. To address the generic question, sequences of the internal transcribed spacer region (ITS1, ITS2), 5.8S gene, large subunit (LSU) and elongation factor 1-α gene (EF 1-α) were analysed to compare the type species of Pilidiella and Coniella. All three gene regions supported the separation of Coniella from Pilidiella, with the majority of taxa residing in Pilidiella. Pilidiella is characterised by having species with hyaline to pale brown conidia (avg. length[ratio ]width >1.5), in contrast to the dark brown conidia of Coniella (avg. length[ratio ]width [les ]1.5). Pilidiella diplodiella, which is a pathogen associated with white rot of grapevines, was shown to be an older name for C. petrakii. To delineate species in the P. diplodiella species complex, isolates were also compared based on histone (H3) gene sequences. Analyses derived from these sequence data separated P. diplodiella from a newly described species, P. diplodiopsis. The new species P. eucalyptorum sp. nov. is proposed for isolates formerly treated as C. fragariae and associated with leaf spots of Eucalyptus spp. This species clustered basal to Pilidiella, and may represent yet a third genus within this complex. Pilidiella destruens sp. nov. is newly described as anamorph of Schizoparme destruens, which is associated with twig dieback of Eucalyptus spp. in Hawaii. A key based on morphological characteristics is provided to separate the taxa treated in this study.
19 - Units of selection and the evolution of virulence
-
- By Paul W. Ewald, Department of Biology, University of Louisville, Gregory M. Cochran, Department of Anthropology, University of Utah, Salt Lake City
- Edited by Rama S. Singh, McMaster University, Ontario, Marcy K. Uyenoyama, Duke University, North Carolina
-
- Book:
- The Evolution of Population Biology
- Published online:
- 08 January 2010
- Print publication:
- 15 January 2004, pp 377-390
-
- Chapter
- Export citation
-
Summary
Introduction
In his classic paper on the units of selection Richard Lewontin, following Williams (1966), emphasized that natural selection for characteristics that benefited individual organisms was stronger than selection for characteristics that benefited groups of organisms. One of the most important generalizations from this insight is that natural selection will tend to favor characteristics that benefit the survival and reproduction of individuals (individual selection) over characteristics that benefit group survival or productivity (group selection) when these two benefits are contradictory (Williams 1966, Lewontin 1970). Lewontin went on to suggest that group selection might be particularly strong for parasites because the parasites within a host are a well-defined group and the transmission of such groups may be highly dependent on the characteristics of the group, such as the overall level of harm that the group of parasites imposes on the host; consequently if one wishes to evaluate whether group selection is important in nature, parasites would be appropriate objects for study (Lewontin 1970).
One reason for this expectation derives from the theory of inclusive fitness, which emphasizes how characteristics that benefit other group members can be favored even when they impose a cost on the individual possessing the characteristic as a result of the positive effects of the characteristic on other individuals that harbor the same genetic instructions (Hamilton 1964).
28 - Virulence Management in Humans
- Edited by Ulf Dieckmann, International Institute for Applied Systems Analysis, Austria, Johan A. J. Metz, Universiteit Leiden, Maurice W. Sabelis, Universiteit van Amsterdam, Karl Sigmund, Universität Wien, Austria
-
- Book:
- Adaptive Dynamics of Infectious Diseases
- Published online:
- 15 January 2010
- Print publication:
- 11 April 2002, pp 399-412
-
- Chapter
- Export citation
-
Summary
Conceptual Basis for Virulence Management
Studies of virulence evolution have attracted attention in part because of the potential for practical applications to health problems. One of these potential applications involves forcing disease organisms to evolve toward low virulence (Ewald 1988,1991a, 1994a). If evolutionary interventions to control virulence are feasible they may be especially cost-effective solutions, because they may control entire classes of diseases through interventions considered valuable for other reasons. In particular, interventions that favor reduced frequency of infection may simultaneously favor evolutionary reductions in the inherent harmfulness of infectious agents (referred to hereafter as “pathogen virulence”).
Evolutionary considerations and the current state of empirical investigation suggest that one class of such interventions, potentially capable of tipping the competitive balance in favor of milder pathogen strains, involves alterations in the mode of pathogen transmission. This chapter assesses the current state of investigation into options for the virulence management of diarrheal diseases, as well as of other categories of disease for which transmission may be relatively independent of host mobility. For each category of disease I discuss interventions that may foster virulence management through the alteration of transmission mode. Finally, I broaden the argument to include virulence management through vaccination strategies. A thorough evaluation of these ideas requires a long series of hierarchically organized tests, so the current state of evidence represents work in progress, which may require decades to fully develop.
Virulence Management of Diarrheal Diseases
Principles of virulence management seem especially applicable to diarrheal disease for several reasons.
2 - Alternative Transmission Modes and the Evolution of Virulence
- Edited by Ulf Dieckmann, International Institute for Applied Systems Analysis, Austria, Johan A. J. Metz, Universiteit Leiden, Maurice W. Sabelis, Universiteit van Amsterdam, Karl Sigmund, Universität Wien, Austria
-
- Book:
- Adaptive Dynamics of Infectious Diseases
- Published online:
- 15 January 2010
- Print publication:
- 11 April 2002, pp 10-25
-
- Chapter
- Export citation
-
Summary
Introduction: Historical Background
For most of the 20th century, medical scientists writing about the evolution of infectious diseases generally concluded that parasites are expected to evolve toward states of benign coexistence with their hosts (reviewed in Ewald 1994a). According to this line of reasoning, parasites that harm their hosts are harming their own long-term chances of survival, and are therefore at a disadvantage over evolutionary time. Theory developed since the 1980s emphasizes that this traditional viewpoint is based on faulty assumptions about the level at which natural selection acts. Specifically, natural selection is a process by which organismal variants that contribute more of their genetic instructions into future generations become increasingly represented in the gene pool of future generations. When applied to parasite virulence, the appropriate focus is therefore on the short-term competitive processes among parasite variants rather than on the characteristics that would allow a particular parasite species to persist most stably over the long term. According to this reasoning, by the time any variants reap such long-term benefits, they would already have been displaced by the variants that held the short-term advantage. Any increases in long-term survival of the parasite species associated with benignity are therefore of little if any relevance to the evolution of virulence if benign strains lose the short-term competition.