Subclinical infection
A subclinical infection—sometimes called a preinfection or inapparent infection—is an infection by a pathogen that causes few or no signs or symptoms of infection in the host.[1] Subclinical infections can occur in both humans and animals.[2] Depending on the pathogen, which can be a virus or intestinal parasite, the host may be infectious and able to transmit the pathogen without ever developing symptoms;[3][4] such a host is called an asymptomatic carrier.[3] Many pathogens, including HIV, typhoid fever, and coronaviruses such as COVID-19 spread in their host populations through subclinical infection.[3][4][5]
Not all hosts of asymptomatic subclinical infections will become asymptomatic carriers. For example, hosts of Mycobacterium tuberculosis bacteria will only develop active tuberculosis in approximately one-tenth of cases;[6] the majority of those infected by Mtb bacteria have latent tuberculosis, a non-infectious type of tuberculosis that does not produce symptoms in individuals with sufficient immune responses.[7]
Because subclinical infections often occur without eventual overt sign, in some cases their presence is only identified by microbiological culture or DNA techniques such as polymerase chain reaction (PCR) tests.[8][9]
Transmission
In humans
Many pathogens are transmitted through their host populations by hosts with few or no symptoms, including
In animals
Some animal pathogens are also transmitted through subclinical infections. The A(H5) and A(H7) strains of avian influenza are divided into two categories: low pathogenicity avian influenza (LPAI) viruses, and highly pathogenic avian influenza (HPAI) viruses.[13] While HPAI viruses have a very high mortality rate for chickens,[14] LPAI viruses are very mild and produce few, if any symptoms; outbreaks in a flock may go undetected without ongoing testing.[14]
Wild
Pathogens known to cause subclinical infection
The following pathogens (together with their symptomatic illnesses) are known to be carried asymptomatically, often in a large percentage of the potential host population:
- Baylisascaris procyonis[17]
- Pertussis or whooping cough)[18]
- Chlamydia pneumoniae[19]
- Clostridium difficile[23]
- Cyclospora cayetanensis[24]
- Dengue virus[25]
- Dientamoeba fragilis[26]
- Entamoeba histolytica[27]
- Enterotoxigenic Escherichia coli[28]
- Epstein–Barr virus[29]
- Group A streptococcal infection[30]
- Helicobacter pylori[31]
- oral herpes, genital herpes, etc.)[32]
- Influenza (strains)
- Legionella pneumophila (Legionnaires' disease)[34]
- Measles viruses[35]
- Mycobacterium leprae (leprosy)[36]
- Mycobacterium tuberculosis (tuberculosis)[37]
- Neisseria meningitidis (Meningitis)[38]
- Nontyphoidal Salmonella[39]
- Noroviruses[40]
- Poliomyelitis)
- Plasmodium (Malaria)
- Rabies lyssavirus (Rabies)
- Rhinoviruses (Common cold)[41]
- Salmonella enterica serovar Typhi (Typhoid fever)[42]
- SARS-CoV-2 (COVID-19)[43] and other coronaviruses[44]
- Staphylococcus aureus[45]
- Streptococcus pneumoniae (Bacterial pneumonia)[46]
- Treponema pallidum (syphilis)[47]
See also
References
- ISBN 978-0-19-997672-0.[page needed]
- PMID 16389321.
- ^ a b c d "Principles of Epidemiology | Lesson 1 - Section 9". www.cdc.gov. 2021-12-20. Retrieved 2023-01-26.
- ^ a b Bogoch, Isaac (16 May 2020). "The Term 'Asymptomatic' Is More Complicated Than It Seems When It Comes To Coronavirus Infections". Forbes.
- ^ "Questions and Answers | Typhoid Fever | CDC". www.cdc.gov. 2020-11-16. Archived from the original on 2016-06-08. Retrieved 2023-01-26.
- ^ "Tuberculosis (TB) Detailed Explanation". National Institute of Allergy and Infectious Diseases. 2009-03-06. Archived from the original on 2010-04-11. Retrieved 2023-01-26.
- ^ PMID 30021818.
- PMID 15172342.
- PMID 29955859.
- PMID 11181126.
- S2CID 78523832.
- PMID 33071595.
- ^ a b c CDC (2022-03-09). "Avian Influenza in Birds". Centers for Disease Control and Prevention. Retrieved 2023-01-26.
- ^ a b "Avian influenza: assessing the pandemic threat" (PDF). WHO. 2005. Retrieved 2023-01-26.
- ^ "Avian influenza in Canada". Ducks Unlimited Canada. Retrieved 2023-01-26.
- ^ Government of Canada, Canadian Food Inspection Agency (2021-02-26). "Protect your flock from bird flu". www.inspection.gc.ca. Retrieved 2023-01-26.
- PMID 28726612.
- PMID 15789494.
- S2CID 43211363.
- ^ PMID 11598849.
- ^ S2CID 33926189.
- S2CID 43394485.
- PMID 12813999.
- PMID 12685635.
- .
- PMID 14766828.
- PMID 14532214.
- PMID 15663170.
- PMID 15507648.
- PMID 15623954.
- PMID 18814135.
- PMID 7643884.
- S2CID 30305043.
- PMID 2304095.
- S2CID 40754266.
- PMID 14596524.
- PMID 10517722.
- .
- PMID 15156460.
- PMID 15131210.
- PMID 14641606.
- S2CID 5059045.
- Wikidata Q84106604.
- PMID 32172672.
- S2CID 27801815.
- PMID 15355410.
- PMID 10194456.
Further reading
- Endara, Pablo; Trueba, Gabriel; Solberg, Owen D.; Bates, Sarah J.; Ponce, Karina; Cevallos, William; Matthijnssens, Jelle; Eisenberg, Joseph N.S. (April 2007). "Symptomatic and Subclinical Infection with Rotavirus P[8]G9, Rural Ecuador". Emerging Infectious Diseases. 13 (4): 574–580. PMID 17553272.