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, or DNA techniques such as polymerase chain reaction. [edit] 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 in women. 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. [edit] 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] [edit] 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] [edit] 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: - Bordetella pertussis (Pertussis or whooping cough)[4]
- Chlamydia pneumoniae[5],
- Chlamydia trachomatis (Chlamydia)[6][7][8]
- Clostridium difficile[9]
- Cyclospora cayetanensis[10]
- dengue virus[11],
- Dientamoeba fragilis[12]
- Entamoeba histolytica[13],
- enterotoxigenic Escherichia coli[14],
- Epstein-Barr virus[15],
- Group A streptococcal infection[16],
- Helicobacter pylori[17]
- HIV-1 (AIDS)[18],
- Legionella pneumophila (Legionnaires' disease)[19],
- measles viruses[20],
- Mycobacterium leprae (leprosy)[21],
- Mycobacterium tuberculosis (tuberculosis)[22],
- Neisseria gonorrhoeae (gonorrhoea)[23][24],
- Neisseria meningitidis (Meningitis) [25],
- nontyphoidal Salmonella[26],
- noroviruses[27],
- Poliovirus (Poliomyelitis)
- rhinoviruses (Common cold)[28],
- Salmonella enterica serovar Typhi (Typhoid fever)[29],
- Staphylococcus aureus[30],
- Streptococcus pneumoniae (Bacterial pneumonia)[31],
- Treponema pallidum (syphilis)[32].
- ^ Miller MR, White A, Boots M. (2005) The evolution of host resistance: tolerance and control as distinct strategies. J Theor Biol. 236:198-207. PubMed
- ^ Boots M, Bowers RG. (2004) The evolution of resistance through costly acquired immunity. Proc Biol Sci. 271(1540):715-23. PubMed
- ^ Romero R, Espinoza J, Chaiworapongsa T, Kalache K. Infection and prematurity and the role of preventive strategies. Semin Neonatol 2002; 7:259-74. PubMed
- ^ Klement, E., Grotto, I., Srugo, I., Orr, N., Gilad, J. Cohent, D. (2005) "Pertussis in soldiers, Israel". Emerg Infect Dis. 11: 506-508 PubMed
- ^ Muller, J., Moller, D. S., Kjaer, M., Nyvad, O., Larsen, N. A. Pedersen, E. B. (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: 704-712 PubMed
- ^ Cecil, J. A., Howell, M. R., Tawes, J. J., Gaydos, J. C., McKee, K. T., Jr., Quinn, T. C. Gaydos, C. A. (2001) "Features of Chlamydia trachomatis and Neisseria gonorrhoeae infection in male Army recruits". J Infect Dis. 184: 1216-1219 PubMed
- ^ Korenromp, E. L., Sudaryo, M. K., de Vlas, S. J., Gray, R. H., Sewankambo, N. K., Serwadda, D., Wawer, M. J. Habbema, J. D. (2002) "What proportion of episodes of gonorrhoea and chlamydia becomes symptomatic?" Int J STD AIDS. 13: 91-101 PubMed
- ^ Sutton, T. L., Martinko, T., Hale, S. Fairchok, M. P. (2003) "Prevalence and high rate of asymptomatic infection of Chlamydia trachomatis in male college Reserve Officer Training Corps cadets". Sex Transm Dis. 30: 901-904 PubMed
- ^ Rivera, E. V. Woods, S. (2003) "Prevalence of asymptomatic Clostridium difficile colonization in a nursing home population: a cross-sectional study". J Gend Specif Med. 6: 27-30 PubMed
- ^ Chacin-Bonilla, L., Mejia de Young, M. Estevez, J. (2003) "Prevalence and pathogenic role of Cyclospora cayetanensis in a Venezuelan community". Am J Trop Med Hyg. 68: 304-306 PubMed
- ^ Burke, D. S., Nisalak, A., Johnson, D. E. Scott, R. M. (1988) "A prospective study of dengue infections in Bangkok". Am J Trop Med Hyg. 38: 172-180 PubMed
- ^ Peek, R., Reedeker, F. R. van Gool, T. (2004) "Direct amplification and genotyping of Dientamoeba fragilis from human stool specimens". J Clin Microbiol. 42: 631-635 PubMed
- ^ Blessmann, J., Ali, I. K., Nu, P. A., Dinh, B. T., Viet, T. Q., Van, A. L., Clark, C. G. Tannich, E. (2003) "Longitudinal study of intestinal Entamoeba histolytica infections in asymptomatic adult carriers". J Clin Microbiol. 41: 4745-4750 PubMed
- ^ Wenneras, C. Erling, V. (2004) "Prevalence of enterotoxigenic Escherichia coli-associated diarrhoea and carrier state in the developing world". J Health Popul Nutr. 22: 370-382 PubMed
- ^ Pegtel, D. M., Middeldorp, J. Thorley-Lawson, D. A. (2004) "Epstein-Barr virus infection in ex vivo tonsil epithelial cell cultures of asymptomatic carriers". J Virol. 78: 12613-12624 PubMed
- ^ Ozturk, C. E., Yavuz, T., Kaya, D. Yucel, M. (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: 271-272 PubMed
- ^ Kul S, Sert B, Sari A, Arslan M, Koşucu P, Ahmetoğlu A, Dinç H. (2008). Effect of subclinical Helicobacter pylori infection on gastric wall thickness: multislice CT evaluation. Diagn Interv Radiol. 14(3):138-42. PMID 18814135
- ^ Mummidi, S., Ahuja, S. S., Gonzalez, E., Anderson, S. A., Santiago, E. N., Stephan, K. T., Craig, F. E., O'Connell, P., Tryon, V., Clark, R. A., Dolan, M. J. Ahuja, S. K. (1998) "Genealogy of the CCR5 locus and chemokine system gene variants associated with altered rates of HIV-1 disease progression". Nat Med. 4: 786-793 PubMed
- ^ Flournoy, D. J., Guthrie, P. J., Lawrence, C. H., Silberg, S. L. Beaver, S. (1990) "Incidence of Legionella pneumophila infections among Oklahoma pulmonary disease patients". J Natl Med Assoc. 82: 25-29 PubMed
- ^ Anlar, B., Ayhan, A., Hotta, H., Itoh, M., Engin, D., Barun, S. Koseoglu, O. (2002) "Measles virus RNA in tonsils of asymptomatic children". J Paediatr Child Health. 38: 424-425 PubMed
- ^ Beyene, D., Aseffa, A., Harboe, M., Kidane, D., Macdonald, M., Klatser, P. R., Bjune, G. A. Smith, W. C. (2003) "Nasal carriage of Mycobacterium leprae DNA in healthy individuals in Lega Robi village, Ethiopia". Epidemiol Infect. 131: 841-848 PubMed
- ^ Dye, C., Scheele, S., Dolin, P., Pathania, V. Raviglione, M. C. (1999) "Consensus statement. Global burden of tuberculosis: estimated incidence, prevalence, and mortality by country. WHO Global Surveillance and Monitoring Project". Jama. 282: 677-686 PubMed
- ^ Cecil, J. A., Howell, M. R., Tawes, J. J., Gaydos, J. C., McKee, K. T., Jr., Quinn, T. C. Gaydos, C. A. (2001) "Features of Chlamydia trachomatis and Neisseria gonorrhoeae infection in male Army recruits". J Infect Dis. 184: 1216-1219 PubMed
- ^ Korenromp, E. L., Sudaryo, M. K., de Vlas, S. J., Gray, R. H., Sewankambo, N. K., Serwadda, D., Wawer, M. J. Habbema, J. D. (2002) "What proportion of episodes of gonorrhoea and chlamydia becomes symptomatic?" Int J STD AIDS. 13: 91-101 PubMed
- ^ Yazdankhah, S. P. Caugant, D. A. (2004) "Neisseria meningitidis: an overview of the carriage state". J Med Microbiol. 53: 821-832 PubMed
- ^ Sirinavin, S., Pokawattana, L. Bangtrakulnondh, A. (2004) "Duration of nontyphoidal Salmonella carriage in asymptomatic adults". Clin Infect Dis. 38: 1644-1645 PubMed
- ^ Gallimore, C. I., Cubitt, D., du Plessis, N. Gray, J. J. (2004) "Asymptomatic and symptomatic excretion of noroviruses during a hospital outbreak of gastroenteritis". J Clin Microbiol. 42: 2271-2274 PubMed
- ^ van Benten, I., Koopman, L., Niesters, B., Hop, W., van Middelkoop, B., de Waal, L., van Drunen, K., Osterhaus, A., Neijens, H. Fokkens, W. (2003) "Predominance of rhinovirus in the nose of symptomatic and asymptomatic infants". Pediatr Allergy Immunol. 14: 363-370 PubMed
- ^ Parry, C. M., Hien, T. T., Dougan, G., White, N. J. Farrar, J. J. (2002) "Typhoid fever". N Engl J Med. 347: 1770-1782 PubMed
- ^ Kenner, J., O'Connor, T., Piantanida, N., Fishbain, J., Eberly, B., Viscount, H., Uyehara, C. Hospenthal, D. (2003) "Rates of carriage of methicillin-resistant and methicillin-susceptible Staphylococcus aureus in an outpatient population". Infect Control Hosp Epidemiol. 24: 439-444 PubMed
- ^ Malfroot, A., Verhaegen, J., Dubru, J. M., Van Kerschaver, E. Leyman, S. (2004) "A cross-sectional survey of the prevalence of Streptococcus pneumoniae nasopharyngeal carriage in Belgian infants attending day care centres". Clin Microbiol Infect. 10: 797-803 PubMed
- ^ Singh, A. E. Romanowski, B. (1999) "Syphilis: review with emphasis on clinical, epidemiologic, and some biologic features". Clin Microbiol Rev. 12: 187-209 PubMed
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