Editing Asymptomatic carrier (section)

== Infectious diseases ==
Asymptomatic carriers have furthered the spread of many infectious diseases. A common principle in epidemiology, the [[Pareto principle|80–20 rule]], speculates that 80% of the disease transmission is conducted by only 20% of people in a population.<ref>{{Cite web|url=http://www.eurekalert.org/pub_releases/2016-02/ehs-zio022516.php|title=Zeroing in on 'super spreaders' and other hidden patterns of epidemics|website=EurekAlert!|language=en|access-date=2018-11-12}}</ref>

=== Typhoid fever ===
[[Typhoid fever]] is an ailment caused by the bacterium ''Salmonella enterica'' ser. Typhi. An individual can acquire this infection from consuming risky foods or drinks, or by consuming foods or drinks prepared by an infected individual. Those who recover from this infection can still carry the bacteria in their cells, and therefore be asymptomatic.<ref>{{cite web|url=https://www.cdc.gov/nczved/divisions/dfbmd/diseases/typhoid_fever/|title=CDC – Typhoid Fever: General Information – NCZVED|publisher=Cdc.gov|access-date=2016-02-14}}</ref>

==== Typhoid Mary ====
[[File:Mary Mallon (Typhoid Mary).jpg|thumb|[[Typhoid Mary]] in a New York Hospital]]
[[Mary Mallon]], known as "Typhoid Mary", was an asymptomatic carrier of ''Salmonella enterica'' serovar typhi, the causative agent of [[typhoid fever]].<ref name=":3">{{cite web|title=Scientists get a handle on what made Typhoid Mary's infectious microbes tick |url=http://med.stanford.edu/ism/2013/august/typhoid.html |website=Med.stanford.edu |access-date=20 August 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130818111217/http://med.stanford.edu/ism/2013/august/typhoid.html |archive-date=18 August 2013 }}</ref> She was a cook for several families and soldiers in New York City during the late 1800s, and several cases of typhoid fever were traced to her by the Health Department. At the time, there was no way of eradicating the disease, and it was spread primarily through fecal-oral transmission. Most of Mary Mallon's transmission risk was thought to arise from her continued involvement in occupations involving food preparation and handling. New York City's public health officials initially sought to merely restrict her from such employment rather than permanently quarantining her. When she continued to be non-compliant, the Health Commission ordered that she be quarantined on one of the islands surrounding Manhattan. She remained there until her death.<ref>{{cite web | url=https://www.forbes.com/sites/kionasmith/2017/09/22/who-was-typhoid-mary/ | title=Who Was Typhoid Mary? | website=[[Forbes]] }}</ref>

Despite appearing perfectly healthy, it is estimated that Mallon infected about 50 people before she was quarantined on [[North and South Brother Islands (New York City)|North Brother Island]].<ref>{{Citation |last=von Csefalvay |first=Chris |title=Simple compartmental models |date=2023 |url=https://linkinghub.elsevier.com/retrieve/pii/B9780323953894000116 |work=Computational Modeling of Infectious Disease |pages=19–91 |access-date=2023-03-06 |publisher=Elsevier |language=en |doi=10.1016/b978-0-32-395389-4.00011-6 |isbn=978-0-323-95389-4|url-access=subscription }}</ref> Scientists calculate that between 1% and 6% of individuals infected with ''Salmonella typhi'' become chronic, asymptomatic carriers like Mary.<ref name=":3" />

===HIV===
{{main|Long-term nonprogressor}}
[[HIV infection]] has a long period during which the person is [[asymptomatic]].<ref>{{cite journal|last=Siliciano|first=Robert F.|title=HIV Latency|journal=Cold Spring Harbor Perspectives in Medicine|year=2011|volume=1|issue=1|pages=a007096|url=http://perspectivesinmedicine.org/content/1/1/a007096.full|publisher=Cold Spring Harbor Laboratory Press|doi=10.1101/cshperspect.a007096|pmid=22229121|pmc=3234450|access-date=20 August 2013}}</ref> Although the host may not be experiencing symptoms, the virus can still be passed on to others. It is also possible for the infection to become symptomatic after this incubation period. Whether the host is showing symptoms or not, opportunistic infections can take advantage of the weakened immune system and cause further complications.<ref>{{cite web|url=https://www.nlm.nih.gov/medlineplus/ency/article/000682.htm |title=Asymptomatic HIV infection: MedlinePlus Medical Encyclopedia |publisher=Nlm.nih.gov |date=2016-02-02 |access-date=2016-02-14}}</ref>

===Epstein–Barr virus===
Many carriers are infected with persistent viruses such as [[Epstein–Barr virus]] (EBV), a member of the herpes virus family. Studies show that about 95% of adults have antibodies against EBV, which means they were infected with the virus at some point in their life.<ref>{{cite web|url=http://www.medicinenet.com/script/main/art.asp?articlekey=89105 |title=The Broad Spectrum of Epstein-Barr Virus (EBV) Disease on |publisher=Medicinenet.com |access-date=2016-02-14}}</ref>

===''Clostridioides difficile''===
''[[Clostridioides difficile (bacteria)|Clostridioides difficile]]'' has also been shown to be spread by asymptomatic carriers, and poses significant problems in home-care settings.<ref name=":2" /> Reports indicating that over 50% of long-term patients present with fecal contamination despite a lack of symptoms have led many hospitals to extend the period of contact precautions until discharge.<ref name=":2" />

===Cholera===
For [[cholera]] the estimates of the ratio of [[asymptomatic]] to symptomatic infections have ranged from 3 to 100.<ref>{{cite journal |vauthors=King AA, Ionides EL, Pascual M, Bouma MJ | s2cid = 4408759 | title = Inapparent infections and cholera dynamics | journal = Nature | volume = 454 | issue = 7206 | pages = 877–880 | date = August 2008 | pmid = 18704085 | doi = 10.1038/nature07084 | bibcode = 2008Natur.454..877K | url = https://deepblue.lib.umich.edu/bitstream/2027.42/62519/1/nature07084.pdf | hdl = 2027.42/62519 | hdl-access = free }}</ref>

===Chlamydia===
[[Chlamydia]], an STI that affects both men and women, can also be asymptomatic in most individuals. Although the infection may not yield any obvious symptoms, it can still damage the reproductive system. If the infection goes unnoticed for a long time, infected individuals are at risk of developing [[pelvic inflammatory disease]] (PID). Like chlamydia, PID can also be asymptomatic.<ref>{{cite web|url=https://www.cdc.gov/std/chlamydia/stdfact-chlamydia.htm |title=STD Facts – Chlamydia |publisher=cdc.gov |access-date=2016-02-14}}</ref>

===Poliomyelitis===
A small number of asymptomatic carriers of [[polio]] (referred to as ''chronic excretors'') continue to produce active virus for years (or even decades) after their initial exposure to the oral [[Sabin vaccine]].<ref>{{cite journal|title=Update on Vaccine-Derived Polioviruses – Worldwide, January 2014–March 2015|author1=Ousmane M. Diop |author2=Cara C. Burns |author3=Roland W. Sutter |author4=Steven G. Wassilak |author5=Olen M. Kew |journal=Morbidity and Mortality Weekly Report |volume=64 |issue=23 |pages=640–646 |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6423a4.htm|pmid=26086635 |pmc=4584736 |year=2015 }}</ref> Carriers of the [[attenuated vaccine|attenuated]] virus unintentionally spread the attenuated virus, inoculating others, giving them [[contact immunity]]; however some adults with weak immune systems have [[polio vaccine#Vaccine-induced polio|contracted paralytic polio]] from contact with recently immunized children. Carriers of virulent strains spread polio, increasing the difficulty of [[poliomyelitis eradication]].<ref>{{cite web | url=https://www.cdc.gov/pinkbook/hcp/table-of-contents/chapter-18-poliomyelitis.html | title=Chapter 18: Poliomyelitis | date=17 August 2021 }}</ref>

=== Tuberculosis ===
[[Tuberculosis]] (TB) is an [[infectious disease]] usually caused by the bacterium ''[[Mycobacterium tuberculosis]]'' (MTB). Tuberculosis generally affects the [[lung]]s, but can also affect other parts of the body.<ref>{{Cite web|url=https://www.who.int/en/news-room/fact-sheets/detail/tuberculosis|title=Tuberculosis (TB)|website=World Health Organization|language=en-US|access-date=2018-11-12}}</ref> Active or symptomatic tuberculosis is spread from person to person through the air through bacterium spores that are released into the air following a cough or sneeze. Some individuals may be infected with the tuberculosis mycobacterium but never display symptoms.<ref name=":5">{{Cite web|url=https://www.who.int/tb/areas-of-work/preventive-care/ltbi_faqs/en/.|title=Latent tuberculosis infection (LTBI)|website=World Health Organization|language=en-GB|access-date=2018-11-12}}</ref> Called [[latent tuberculosis]], these cases, while uncontagious, are particularly problematic from a public health perspective, since approximately 10% of those diagnosed with latent TB will go on to develop an active (and contagious) case.<ref name=":5" />

=== COVID-19 ===
A 2021 paper estimated that at least 50% of SARS-CoV-2 infections were a result of exposure to asymptomatic carriers.<ref>{{cite journal |last1=Johansson |first1=Michael A. |last2=Quandelacy |first2=Talia M. |last3=Kada |first3=Sarah |last4=Prasad |first4=Pragati Venkata |last5=Steele |first5=Molly |last6=Brooks |first6=John T. |last7=Slayton |first7=Rachel B. |last8=Biggerstaff |first8=Matthew |last9=Butler |first9=Jay C. |title=SARS-CoV-2 Transmission From People Without COVID-19 Symptoms |journal=JAMA Network Open |date=7 January 2021 |volume=4 |issue=1 |pages=e2035057 |doi=10.1001/jamanetworkopen.2020.35057 |pmid=33410879 |pmc=7791354 |url=https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2774707 |issn=2574-3805}}</ref>