Subclinical infection

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Typhoid Mary in a 1909 was a famous case of a subclinical infection of Salmonella enterica serovar Typhi, the infectious agent of typhoid fever

A subclinical infection is the asymptomatic (without apparent sign) carrying of an (infection) by an individual of an agent (microbe, intestinal parasite, or virus) that usually is a pathogen causing illness, at least in some individuals. Many pathogens spread by being silently carried in this way by some of their host population. Such infections occur both in humans and nonhuman animals. An example of an asymptomatic infection is a mild common cold that is not noticed by the infected individual. Since subclinical infections often occur without eventual overt sign, their existence is only identified by microbiological culture, electromagnetic frequency detection or DNA techniques such as polymerase chain reaction.

Infection transmission

An individual may only develop signs of an infection after a period of subclinical infection, a duration that is called the incubation period. This is the case, for example, for subclinical sexually transmitted diseases such as AIDS and genital warts. Individuals with such subclinical infections, and those that never develop overt illness, creates a reserve of individuals that can transmit an infectious agent to infect other individuals. Because such cases of infections do not come to clinical attention, health statistics can often fail to measure the true prevalence of an infection in a population, and this prevents the accurate modeling of its infectious transmission.

Evolution of host tolerance

Fever and sickness behavior and other signs of infection are often taken to be due to them. However, they are evolved physiological and behavioral responses of the host to clear itself of the infection. Instead of incurring the costs of deploying these evolved responses to infections, the body opts to tolerate an infection[1] as an alternative to seeking to control or remove the infecting pathogen.[2]

Hidden costs

Subclinical infections are important since they allow infections to spread from a reserve of carriers. They also can cause clinical problems unrelated to the direct issue of infection. For example, in the case of urinary tract infections in women, this infection may cause preterm delivery if she gets pregnant without proper treatment.[3]

List of subclinical infections

The following pathogens (together with their symptomatic illnesses) are known to be carried asymptomatically, often in a large percentage of the potential host population:

Notes

  1. ↑ Miller MR, White A, Boots M (September 2005). "The evolution of host resistance: tolerance and control as distinct strategies". J. Theor. Biol. 236 (2): 198–207. doi:10.1016/j.jtbi.2005.03.005. PMID 16005309. 
  2. ↑ Boots M, Bowers RG (April 2004). "The evolution of resistance through costly acquired immunity". Proc. Biol. Sci. 271 (1540): 715–23. doi:10.1098/rspb.2003.2655. PMC 1691655. PMID 15209105. 
  3. ↑ Romero R, Espinoza J, Chaiworapongsa T, Kalache K (August 2002). "Infection and prematurity and the role of preventive strategies". Semin Neonatol 7 (4): 259–74. doi:10.1053/siny.2002.0121. PMID 12401296. 
  4. ↑ Klement E, Grotto I, Srugo I, Orr N, Gilad J, Cohent D (March 2005). "Pertussis in soldiers, Israel". Emerging Infect. Dis. 11 (3): 506–8. PMID 15789494. 
  5. ↑ Müller J, Møller DS, Kjaer M, Nyvad O, Larsen NA, Pedersen EB (2003). "Chlamydia pneumoniae DNA in peripheral blood mononuclear cells in healthy control subjects and patients with diabetes mellitus, acute coronary syndrome, stroke, and arterial hypertension". Scand. J. Infect. Dis. 35 (10): 704–12. doi:10.1080/00365540310016538. PMID 14606608. 
  6. ↑ 6.0 6.1 Cecil JA, Howell MR, Tawes JJ, et al. (November 2001). "Features of Chlamydia trachomatis and Neisseria gonorrhoeae infection in male Army recruits". J. Infect. Dis. 184 (9): 1216–9. doi:10.1086/323662. PMID 11598849. 
  7. ↑ 7.0 7.1 Korenromp EL, Sudaryo MK, de Vlas SJ, et al. (February 2002). "What proportion of episodes of gonorrhoea and chlamydia becomes symptomatic?". Int J STD AIDS 13 (2): 91–101. doi:10.1258/0956462021924712. PMID 11839163. 
  8. ↑ Sutton TL, Martinko T, Hale S, Fairchok MP (December 2003). "Prevalence and high rate of asymptomatic infection of Chlamydia trachomatis in male college Reserve Officer Training Corps cadets". Sex Transm Dis 30 (12): 901–4. doi:10.1097/01.OLQ.0000091136.14932.8B. PMID 14646638. 
  9. ↑ Rivera EV, Woods S (2003). "Prevalence of asymptomatic Clostridium difficile colonization in a nursing home population: a cross-sectional study". J Gend Specif Med 6 (2): 27–30. PMID 12813999. 
  10. ↑ Chacin-Bonilla L, Mejia de Young M, Estevez J (March 2003). "Prevalence and pathogenic role of Cyclospora cayetanensis in a Venezuelan community". Am. J. Trop. Med. Hyg. 68 (3): 304–6. PMID 12685635. 
  11. ↑ Burke DS, Nisalak A, Johnson DE, Scott RM (January 1988). "A prospective study of dengue infections in Bangkok". Am. J. Trop. Med. Hyg. 38 (1): 172–80. PMID 3341519. 
  12. ↑ Peek R, Reedeker FR, van Gool T (February 2004). "Direct Amplification and Genotyping of Dientamoeba fragilis from Human Stool Specimens". J. Clin. Microbiol. 42 (2): 631–5. doi:10.1128/JCM.42.2.631-635.2004. PMC 344490. PMID 14766828. 
  13. ↑ Blessmann J, Ali IK, Nu PA, et al. (October 2003). "Longitudinal Study of Intestinal Entamoeba histolytica Infections in Asymptomatic Adult Carriers". J. Clin. Microbiol. 41 (10): 4745–50. doi:10.1128/JCM.41.10.4745-4750.2003. PMC 294961. PMID 14532214. 
  14. ↑ Wennerås C, Erling V (December 2004). "Prevalence of enterotoxigenic Escherichia coli-associated diarrhoea and carrier state in the developing world". J Health Popul Nutr 22 (4): 370–82. PMID 15663170. 
  15. ↑ Pegtel DM, Middeldorp J, Thorley-Lawson DA (November 2004). "Epstein-Barr Virus Infection in Ex Vivo Tonsil Epithelial Cell Cultures of Asymptomatic Carriers". J. Virol. 78 (22): 12613–24. doi:10.1128/JVI.78.22.12613-12624.2004. PMC 525079. PMID 15507648. 
  16. ↑ Ozturk CE, Yavuz T, Kaya D, Yucel M (December 2004). "The rate of asymptomatic throat carriage of group A Streptococcus in school children and associated ASO titers in Duzce, Turkey". Jpn. J. Infect. Dis. 57 (6): 271–2. PMID 15623954. 
  17. ↑ Kul S, Sert B, Sari A, et al. (September 2008). "Effect of subclinical Helicobacter pylori infection on gastric wall thickness: multislice CT evaluation". Diagn Interv Radiol 14 (3): 138–42. PMID 18814135. 
  18. ↑ Wald A, Zeh J, Selke S, Ashley RL, Corey L (September 1995). "Virologic characteristics of subclinical and symptomatic genital herpes infections". N. Engl. J. Med. 333 (12): 770–5. doi:10.1056/NEJM199509213331205. PMID 7643884. 
  19. ↑ Mummidi S, Ahuja SS, Gonzalez E, et al. (July 1998). "Genealogy of the CCR5 locus and chemokine system gene variants associated with altered rates of HIV-1 disease progression". Nat. Med. 4 (7): 786–93. doi:10.1038/nm0798-786. PMID 9662369. 
  20. ↑ Flournoy DJ, Guthrie PJ, Lawrence CH, Silberg SL, Beaver S (January 1990). "Incidence of Legionella pneumophila infections among Oklahoma pulmonary disease patients". J Natl Med Assoc 82 (1): 25–9. PMC 2625929. PMID 2304095. 
  21. ↑ Anlar B, Ayhan A, Hotta H, et al. (August 2002). "Measles virus RNA in tonsils of asymptomatic children". J Paediatr Child Health 38 (4): 424–5. doi:10.1046/j.1440-1754.2002.t01-1-00029.x. PMID 12174013. 
  22. ↑ Beyene D, Aseffa A, Harboe M, et al. (October 2003). "Nasal carriage of Mycobacterium leprae DNA in healthy individuals in Lega Robi village, Ethiopia". Epidemiol. Infect. 131 (2): 841–8. doi:10.1017/S0950268803001079. PMC 2870027. PMID 14596524. 
  23. ↑ Dye C, Scheele S, Dolin P, Pathania V, Raviglione MC (August 1999). "Consensus statement. Global burden of tuberculosis: estimated incidence, prevalence, and mortality by country. WHO Global Surveillance and Monitoring Project". JAMA 282 (7): 677–86. doi:10.1001/jama.282.7.677. PMID 10517722. 
  24. ↑ Yazdankhah SP, Caugant DA (September 2004). "Neisseria meningitidis: an overview of the carriage state". J. Med. Microbiol. 53 (Pt 9): 821–32. doi:10.1099/jmm.0.45529-0. PMID 15314188. 
  25. ↑ Sirinavin S, Pokawattana L, Bangtrakulnondh A (June 2004). "Duration of nontyphoidal Salmonella carriage in asymptomatic adults". Clin. Infect. Dis. 38 (11): 1644–5. doi:10.1086/421027. PMID 15156460. 
  26. ↑ Gallimore CI, Cubitt D, du Plessis N, Gray JJ (May 2004). "Asymptomatic and Symptomatic Excretion of Noroviruses during a Hospital Outbreak of Gastroenteritis". J. Clin. Microbiol. 42 (5): 2271–4. doi:10.1128/JCM.42.5.2271-2274.2004. PMC 404621. PMID 15131210. 
  27. ↑ van Benten I, Koopman L, Niesters B, et al. (October 2003). "Predominance of rhinovirus in the nose of symptomatic and asymptomatic infants". Pediatr Allergy Immunol 14 (5): 363–70. doi:10.1034/j.1399-3038.2003.00064.x. PMID 14641606. 
  28. ↑ Parry CM, Hien TT, Dougan G, White NJ, Farrar JJ (November 2002). "Typhoid fever". N. Engl. J. Med. 347 (22): 1770–82. doi:10.1056/NEJMra020201. PMID 12456854. 
  29. ↑ Kenner J, O'Connor T, Piantanida N, et al. (June 2003). "Rates of carriage of methicillin-resistant and methicillin-susceptible Staphylococcus aureus in an outpatient population". Infect Control Hosp Epidemiol 24 (6): 439–44. doi:10.1086/502229. PMID 12828322. 
  30. ↑ Malfroot A, Verhaegen J, Dubru JM, Van Kerschaver E, Leyman S (September 2004). "A cross-sectional survey of the prevalence of Streptococcus pneumoniae nasopharyngeal carriage in Belgian infants attending day care centres". Clin. Microbiol. Infect. 10 (9): 797–803. doi:10.1111/j.1198-743X.2004.00926.x. PMID 15355410. 
  31. ↑ Singh AE, Romanowski B (April 1999). "Syphilis: Review with Emphasis on Clinical, Epidemiologic, and Some Biologic Features". Clin. Microbiol. Rev. 12 (2): 187–209. PMC 88914. PMID 10194456. 

See also

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