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'''Pathogen avoidance''', also referred to as, '''parasite avoidance''', '''pathogen [[disgust]]''', refers to theory that the [[disgust]] response, in humans, is an adaptive system that guides behavior to avoid infection caused by parasites such as [[Virus|viruses]], [[bacteria]], [[Fungus|fungi]], [[protozoa]], [[Helminth|helminth worms]], [[Arthropod|arthropods]] and [[Social parasitism (biology)|social parasites]] <ref>{{Cite journal|last=Sarabian|first=Cecile|last2=Curtis|first2=Val|last3=McMullan|first3=Rachel|date=2018-07-19|title=Evolution of pathogen and parasite avoidance behaviours|url=https://royalsocietypublishing.org/doi/10.1098/rstb.2017.0256|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|language=en|volume=373|issue=1751|pages=20170256|doi=10.1098/rstb.2017.0256|issn=0962-8436|pmc=PMC6000144|pmid=29866923}}</ref><ref>{{Cite journal|last=Curtis|first=Val|last2=de Barra|first2=Mícheál|date=2018-07-19|title=The structure and function of pathogen disgust|url=https://royalsocietypublishing.org/doi/10.1098/rstb.2017.0208|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|language=en|volume=373|issue=1751|pages=20170208|doi=10.1098/rstb.2017.0208|issn=0962-8436|pmc=PMC6000136|pmid=29866921}}</ref><ref>{{Cite book|last=author.|first=Curtis, Valerie 1958-|url=http://worldcat.org/oclc/935021890|title=Don't look, don't touch, don't eat the science behind revulsion|isbn=978-0-226-13133-7|oclc=935021890}}</ref>. Pathogen avoidance is a psychological mechanism associated with the [[behavioral immune system]]. More specifically, Joshua M. Tybur outlines pathogen avoidance as one of the three domains of disgust which also include sexual disgust and moral disgust. <ref>{{Cite journal|last=Tybur|first=Joshua M.|last2=Lieberman|first2=Debra|last3=Kurzban|first3=Robert|last4=DeScioli|first4=Peter|date=2013-01-XX|title=Disgust: Evolved function and structure.|url=http://doi.apa.org/getdoi.cfm?doi=10.1037/a0030778|journal=Psychological Review|language=en|volume=120|issue=1|pages=65–84|doi=10.1037/a0030778|issn=1939-1471}}</ref>
== Evolutionary significance ==
In nature, controlling or the avoidance of pathogens is an essential fitness strategy because disease-causing agents are ever-present. <ref>{{Cite journal|last=Hart|first=Benjamin L.|date=2011-12-12|title=Behavioural defences in animals against pathogens and parasites: parallels with the pillars of medicine in humans|url=https://royalsocietypublishing.org/doi/10.1098/rstb.2011.0092|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|language=en|volume=366|issue=1583|pages=3406–3417|doi=10.1098/rstb.2011.0092|issn=0962-8436|pmc=PMC3189355|pmid=22042917}}</ref>. Pathogens reproduce rapidly at the expense of their hosts' fitness, this creates a coevolutionary arms race between pathogen transmission and host avoidance. <ref>{{Cite book|last=W.|first=Ewald, Paul|url=http://worldcat.org/oclc/45093039|title=Evolution of infectious disease|date=1996|publisher=Oxford University Press|isbn=0-19-511139-7|oclc=45093039}}</ref><ref>{{Cite book|last=C.|first=Nesse, Randolph M.; Williams, George|url=http://worldcat.org/oclc/1090912898|title=Why We Get Sick : the New Science of Darwinian Medicine|date=2012|publisher=Knopf Doubleday Publishing Group|isbn=978-0-307-81600-9|oclc=1090912898}}</ref> For a pathogen to move to a new host, it must exploit regions of the body that serve as points of contact between current and future hosts such as the mouth, the skin, the anus and the genitals.<ref>{{Cite journal|last=Tybur|first=Joshua M.|last2=Lieberman|first2=Debra|last3=Kurzban|first3=Robert|last4=DeScioli|first4=Peter|date=2013-01-XX|title=Disgust: Evolved function and structure.|url=http://doi.apa.org/getdoi.cfm?doi=10.1037/a0030778|journal=Psychological Review|language=en|volume=120|issue=1|pages=65–84|doi=10.1037/a0030778|issn=1939-1471}}</ref> To avoid the cost of infection, organisms require counteradaptations to prevent pathogen transmission, by defending entry points such as the mouth and skin and avoiding other individual's exit points and the substances exiting these points such as feces and sneeze droplets<ref>{{Cite journal|last=Tybur|first=Joshua M.|last2=Lieberman|first2=Debra|last3=Kurzban|first3=Robert|last4=DeScioli|first4=Peter|date=2013-01-XX|title=Disgust: Evolved function and structure.|url=http://doi.apa.org/getdoi.cfm?doi=10.1037/a0030778|journal=Psychological Review|language=en|volume=120|issue=1|pages=65–84|doi=10.1037/a0030778|issn=1939-1471}}</ref>. Pathogen avoidance provides the first line of defense by physically avoiding conspecifics, other species, objects or locations that could increase vulnerability to pathogens. <ref>{{Cite journal|last=Tybur|first=Joshua M.|last2=Lieberman|first2=Debra|last3=Kurzban|first3=Robert|last4=DeScioli|first4=Peter|date=2013-01-XX|title=Disgust: Evolved function and structure.|url=http://doi.apa.org/getdoi.cfm?doi=10.1037/a0030778|journal=Psychological Review|language=en|volume=120|issue=1|pages=65–84|doi=10.1037/a0030778|issn=1939-1471}}</ref>
The pathogen avoidance theory of disgust predicts that behavior that reduces contact with pathogens, will have been under strong selection throughout the evolution of free-living organisms and should be prevalent throughout the ''Animalia'' kingdom <ref>{{Cite book|last=Claude.|first=Combes,|url=http://worldcat.org/oclc/59478910|title=Parasitism : the ecology and evolution of intimate interactions|date=2001|publisher=University of Chicago Press|isbn=0-226-11446-5|oclc=59478910}}</ref>. Compared to the alternative, facing the infectious threat, avoidance likely provides a reduction in exposure to pathogens and in energetic costs associated with activation of the physiological [[immune response]]<ref>{{Cite journal|last=Schulenburg|first=Hinrich|last2=Ewbank|first2=Jonathan J.|date=2007|title=The genetics of pathogen avoidance in Caenorhabditis elegans|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2958.2007.05946.x|journal=Molecular Microbiology|language=en|volume=66|issue=3|pages=563–570|doi=10.1111/j.1365-2958.2007.05946.x|issn=1365-2958}}</ref>. These behaviors are found throughout the animal literature, particularly amongst social animals<ref>{{Cite journal|last=Curtis|first=Val|last2=de Barra|first2=Mícheál|date=2018-07-19|title=The structure and function of pathogen disgust|url=https://royalsocietypublishing.org/doi/10.1098/rstb.2017.0208|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|language=en|volume=373|issue=1751|pages=20170208|doi=10.1098/rstb.2017.0208|issn=0962-8436|pmc=PMC6000136|pmid=29866921}}</ref>.
* Hygiene: The detection of displays of or physical evidence of unhygienic behavior.
* Animals or Insect: Typically, animal or insect disease vectors such as mice or mosquitoes are recognized as cues.
* Sex: Behavior related to promiscuity of sexual activities
* Atypical appearance: Infection cues in other individuals such as abnormal body shape, deformity, auditory cues such as coughing and contextual cues related to circumstances of increased risk of infection such as homelessness.
=== Computational structure model ===
Tybur proposed a model of how an information processing system might be structured. In this model, perceptual systems (vision, olfaction, etc.) monitor the environment for cues to pathogens<ref>{{Cite journal|date=2016-02-01|title=Human pathogen avoidance adaptations|url=https://www.sciencedirect.com/science/article/pii/S2352250X15001670|journal=Current Opinion in Psychology|language=en|volume=7|pages=6–11|doi=10.1016/j.copsyc.2015.06.005|issn=2352-250X}}</ref>. Then, a mechanism integrates cues from the different perceptual systems and estimates a pathogen index, an internal estimation of the probability that pathogens are present based on reliability and detection of cues. Finally context-dependent avoidance can only occur if additional information is taken as input- if other mechanisms exist that function to trade off pathogen presence against other fitness-impacting dimensions across various contexts. <ref>{{Cite journal|date=2016-02-01|title=Human pathogen avoidance adaptations|url=https://www.sciencedirect.com/science/article/pii/S2352250X15001670|journal=Current Opinion in Psychology|language=en|volume=7|pages=6–11|doi=10.1016/j.copsyc.2015.06.005|issn=2352-250X}}</ref> The expected value of contact is a downstream index that integrates other indexesindices relevant to the costs and benefits of contact which then regulates the approach versus avoidance in an adaptive manner. This model is consistent with several empirical findings of how additional variables such as sexual value, nutrient status, kinship status, hormonal status and immune function also influence responses to pathogen cues. <ref>{{Cite journal|last=Borg|first=Charmaine|last2=de Jong|first2=Peter J.|date=2012-09-12|title=Feelings of Disgust and Disgust-Induced Avoidance Weaken following Induced Sexual Arousal in Women|url=http://dx.doi.org/10.1371/journal.pone.0044111|journal=PLoS ONE|volume=7|issue=9|pages=e44111|doi=10.1371/journal.pone.0044111|issn=1932-6203}}</ref><ref>{{Cite journal|last=Hoefling|first=Atilla|last2=Likowski|first2=Katja U.|last3=Deutsch|first3=Roland|last4=Häfner|first4=Michael|last5=Seibt|first5=Beate|last6=Mühlberger|first6=Andreas|last7=Weyers|first7=Peter|last8=Strack|first8=Fritz|date=2009|title=When hunger finds no fault with moldy corn: Food deprivation reduces food-related disgust.|url=http://dx.doi.org/10.1037/a0014449|journal=Emotion|volume=9|issue=1|pages=50–58|doi=10.1037/a0014449|issn=1931-1516}}</ref><ref>{{Cite journal|last=Case|first=Trevor I.|last2=Repacholi|first2=Betty M.|last3=Stevenson|first3=Richard J.|date=2006-09|title=My baby doesn't smell as bad as yours|url=http://dx.doi.org/10.1016/j.evolhumbehav.2006.03.003|journal=Evolution and Human Behavior|volume=27|issue=5|pages=357–365|doi=10.1016/j.evolhumbehav.2006.03.003|issn=1090-5138}}</ref><ref>{{Cite web|last=Tybur|first=Joshua M.|last2=Jones|first2=Benedict C|last3=DeBruine|first3=Lisa Marie|last4=Ackerman|first4=Joshua|last5=Fasolt|first5=Vanessa|date=2020-08-21|title=Preregistered replication of “Sick body, vigilant mind: The biological immune system activates the behavioral immune system”|url=http://dx.doi.org/10.31234/osf.io/m6ghr|access-date=2021-05-07|website=dx.doi.org}}</ref><ref>{{Cite journal|last=Fleischman|first=Diana S.|last2=Fessler|first2=Daniel M.T.|date=2011-02|title=Progesterone's effects on the psychology of disease avoidance: Support for the compensatory behavioral prophylaxis hypothesis|url=http://dx.doi.org/10.1016/j.yhbeh.2010.11.014|journal=Hormones and Behavior|volume=59|issue=2|pages=271–275|doi=10.1016/j.yhbeh.2010.11.014|issn=0018-506X}}</ref>
=== Imperfections in pathogen detection ===
Signaling detection errors are prevalent in the pathogen avoidance system; there are two types of errors: a false alarm, where a pathogen avoidance response is deployed needlessly or a miss, where a pathogen avoidance was not deployed in the presence of infection risk, they depend on whether pathogens are present or not. <ref>{{Cite journal|date=2016-02-01|title=Human pathogen avoidance adaptations|url=https://www.sciencedirect.com/science/article/pii/S2352250X15001670|journal=Current Opinion in Psychology|language=en|volume=7|pages=6–11|doi=10.1016/j.copsyc.2015.06.005|issn=2352-250X}}</ref> The costs for not mounting an avoidance response in the presence of infection risk is assumed to be greater, suggesting that selection may be favoring a greater sensitivity to cue pathogens at the expense of specificity. <ref>{{Cite journal|date=2016-02-01|title=Human pathogen avoidance adaptations|url=https://www.sciencedirect.com/science/article/pii/S2352250X15001670|journal=Current Opinion in Psychology|language=en|volume=7|pages=6–11|doi=10.1016/j.copsyc.2015.06.005|issn=2352-250X}}</ref> This is thought to explain the [[law of contagion]] wherein, objects in contact with an infectious cue are themselves treated as infectious.<ref>{{Cite journal|last=Rozin|first=Paul|last2=Millman|first2=Linda|last3=Nemeroff|first3=Carol|date=1986|title=Operation of the laws of sympathetic magic in disgust and other domains.|url=http://dx.doi.org/10.1037/0022-3514.50.4.703|journal=Journal of Personality and Social Psychology|volume=50|issue=4|pages=703–712|doi=10.1037/0022-3514.50.4.703|issn=1939-1315}}</ref><ref>Rozin, P., Haidt, J., & McCauley, C. R. (2008). ''Disgust.'' In M. Lewis, J. M. Haviland-Jones, & L. F. Barrett (Eds.), ''Handbook of emotions'' (p. 757–776). The Guilford Press.</ref>
== Known factors of influence ==
=== Sex ===
Females consistently demonstrate higher disgust sensitivity than men. <ref>{{Cite journal|last=Curtis|first=Val|last2=Aunger|first2=Robert|last3=Rabie|first3=Tamer|date=2004-05-07|title=Evidence that disgust evolved to protect from risk of disease|url=https://royalsocietypublishing.org/doi/10.1098/rsbl.2003.0144|journal=Proceedings of the Royal Society of London. Series B: Biological Sciences|language=en|volume=271|issue=suppl_4|doi=10.1098/rsbl.2003.0144|issn=0962-8452|pmc=PMC1810028|pmid=15252963}}</ref>. Evidence suggests that females respond more sensitively to specifically disease threatthreats than men<ref>{{Cite journal|last=Curtis|first=Val|last2=Aunger|first2=Robert|last3=Rabie|first3=Tamer|date=2004-05-07|title=Evidence that disgust evolved to protect from risk of disease|url=https://royalsocietypublishing.org/doi/10.1098/rsbl.2003.0144|journal=Proceedings of the Royal Society of London. Series B: Biological Sciences|language=en|volume=271|issue=suppl_4|doi=10.1098/rsbl.2003.0144|issn=0962-8452|pmc=PMC1810028|pmid=15252963}}</ref><ref>{{Cite journal|last=Quigley|first=John F.|last2=Sherman|first2=Martin F.|last3=Sherman|first3=Nancy C.|date=1997-05-XX|title=Personality disorder symptoms, gender, and age as predictors of adolescent disgust sensitivity|url=http://dx.doi.org/10.1016/s0191-8869(96)00255-3|journal=Personality and Individual Differences|volume=22|issue=5|pages=661–667|doi=10.1016/s0191-8869(96)00255-3|issn=0191-8869}}</ref><ref>{{Cite journal|last=Fessler|first=Daniel M.T.|last2=Navarrete|first2=C.David|date=2003-11|title=Domain-specific variation in disgust sensitivity across the menstrual cycle|url=http://dx.doi.org/10.1016/s1090-5138(03)00054-0|journal=Evolution and Human Behavior|volume=24|issue=6|pages=406–417|doi=10.1016/s1090-5138(03)00054-0|issn=1090-5138}}</ref>. This is hypothesized to be consistent with the enhanced evolutionary role in women for protecting their offspring.<ref>{{Cite journal|last=Curtis|first=Val|last2=Aunger|first2=Robert|last3=Rabie|first3=Tamer|date=2004-05-07|title=Evidence that disgust evolved to protect from risk of disease|url=https://royalsocietypublishing.org/doi/10.1098/rsbl.2003.0144|journal=Proceedings of the Royal Society of London. Series B: Biological Sciences|language=en|volume=271|issue=suppl_4|doi=10.1098/rsbl.2003.0144|issn=0962-8452|pmc=PMC1810028|pmid=15252963}}</ref>
=== Sexual behavior ===
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