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Subclinical infection
Nearly or completely asymptomatic infection From Wikipedia, the free encyclopedia
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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]
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Transmission
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In humans
Many pathogens are transmitted through their host populations by hosts with few or no symptoms, including sexually transmitted infections such as syphilis and genital warts.[10] In other cases, a host may develop more symptoms as the infection progresses beyond its incubation period.[3][7] These hosts create a natural reservoir of individuals that can transmit a pathogen to other individuals. Because cases often do not come to clinical attention, health statistics frequently are unable to measure the true prevalence of an infection in a population. This prevents accurate modeling of its transmissibility.[11][12]
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 ducks and other waterfowl are asymptomatic carriers of avian influenza, notably HPAI, and can be infected without showing signs of illness.[13][15] The prevalence of subclinical HPAI infection in waterfowl has contributed to the international outbreak of highly lethal H5N8 virus that began in early 2020.[13][16]
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Pathogens known to cause subclinical infection
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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]
- Bordetella pertussis (Pertussis or whooping cough)[18]
- Chlamydia pneumoniae[19]
- Chlamydia trachomatis (Chlamydia)[20][21][22]
- Clostridioides 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]
- Herpes simplex (oral herpes, genital herpes, etc.)[32]
- HIV-1 (HIV/AIDS)[33]
- Influenza (strains)
- Legionella pneumophila (Legionnaires' disease)[34]
- Measles viruses[35]
- Mycobacterium leprae (leprosy)[36]
- Mycobacterium tuberculosis (tuberculosis)[37]
- Neisseria gonorrhoeae (gonorrhoea)[20][21]
- Neisseria meningitidis (Meningitis)[38]
- Nontyphoidal Salmonella[39]
- Noroviruses[40]
- Poliovirus (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]
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See also
References
Further reading
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