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Incubation period

Incubation period

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Incubation period is the time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

 elapsed between exposure to a pathogenic organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

, a chemical or radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...

, and when symptoms and signs are first apparent. The period may be as short as minutes to as long as thirty years in the case of variant Creutzfeldt–Jakob disease.

While Latent or Latency period may be synonymous,
a distinction is sometimes made between Incubation period, the period between infection and clinical onset of the disease, and Latent period, the time from infection to infectiousness. Which is shorter depends on the disease.

A person may be a carrier of a disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...

, such as Streptococcus
Streptococcus
Streptococcus is a genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the lactic acid bacteria group. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek στρεπτος streptos, meaning...

in the throat
Throat
In vertebrate anatomy, the throat is the anterior part of the neck, in front of the vertebral column. It consists of the pharynx and larynx...

, without exhibiting any symptoms. Depending on the disease, the person may or may not be contagious
Contagious disease
A contagious disease is a subset category of infectious diseases , which are easily transmitted by physical contact with the person suffering the disease, or by their secretions or objects touched by them....

 during the incubation period.

During clinical latency, an infection is subclinical. With respect to viral infections, in clinical latency the virus is actively replicating. This is in contrast to viral latency, a form of dormancy
Dormancy
Dormancy is a period in an organism's life cycle when growth, development, and physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions...

 in which the virus does not replicate.

Clinical latency occurs in:
  • AIDS
    AIDS
    Acquired immune deficiency syndrome or acquired immunodeficiency syndrome is a disease of the human immune system caused by the human immunodeficiency virus...

    : persons infected with HIV
    HIV
    Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...

     may at first have no symptoms and show no signs of AIDS, despite HIV replicating in the lymphatic system
    Lymphatic system
    The lymphoid system is the part of the immune system comprising a network of conduits called lymphatic vessels that carry a clear fluid called lymph unidirectionally toward the heart. Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated...

     and rapidly accumulating a large viral load
    Viral load
    Viral load is a measure of the severity of a viral infection, and can be calculated by estimating the amount of virus in an involved body fluid. For example, it can be given in RNA copies per milliliter of blood plasma...

    . These persons may be infectious
    Infection
    An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

    .


Extrinsic incubation period: In a vector, it is the time between entrance of an organism into the vector and the time when that vector can transmit the infection. For Eg.: Once ingested by a mosquito, malaria parasites must undergo development within the mosquito before they are infectious to humans. The time required for development in the mosquito (the extrinsic incubation period) ranges from 10 to 21 days, depending on the parasite species and the temperature. If a mosquito does not survive longer than the extrinsic incubation period, then she will not be able to transmit any malaria parasites.

Examples of incubation periods


Incubation periods vary greatly, and are generally expressed as a range. When possible, it is best to express the mean and the 10th and 90th percentiles, though this information is not always available. The values below are arranged roughly in ascending order by number of days, although in some cases the mean had to be inferred.

For many conditions, incubation periods are longer in adults than they are in children or infants.
Disease Incubation period
Cellulitis
Cellulitis
Cellulitis is a diffuse inflammation of connective tissue with severe inflammation of dermal and subcutaneous layers of the skin. Cellulitis can be caused by normal skin flora or by exogenous bacteria, and often occurs where the skin has previously been broken: cracks in the skin, cuts, blisters,...

 caused by Pasteurella multocida
Pasteurella multocida
Pasteurella multocida is a Gram-negative, non-motile coccobacillus that is penicillin-sensitive and belongs to the Pasteurellaceae family . It can cause avian cholera in birds and a zoonotic infection in humans, which typically is a result of bites or scratches from domestic pets...

 
less than 1 day http://kidshealth.org/parent/infections/bacterial_viral/cellulitis_p2.html
Norovirus  1–2 days http://www.cdc.gov/NCIDOD/DVRD/revb/gastro/norovirus-factsheet.htm
Cholera
Cholera
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...

 
1–3 days http://www.cdc.gov/epo/dih/ddm/ch2_ch.htm
Influenza
Influenza
Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...

 
1–3 days http://www.cdc.gov/flu/professionals/diagnosis/,http://www.cdc.gov/flu/h2n2bsl3.htm
Scarlet fever
Scarlet fever
Scarlet fever is a disease caused by exotoxin released by Streptococcus pyogenes. Once a major cause of death, it is now effectively treated with antibiotics...

 
1–4 days http://www.emedicine.com/emerg/topic518.htm
Common cold
Common cold
The common cold is a viral infectious disease of the upper respiratory system, caused primarily by rhinoviruses and coronaviruses. Common symptoms include a cough, sore throat, runny nose, and fever...

 
1–3 days http://www.mayoclinic.com/health/common-cold/DS00056/DSECTION=symptoms
Ebola
Ebola
Ebola virus disease is the name for the human disease which may be caused by any of the four known ebolaviruses. These four viruses are: Bundibugyo virus , Ebola virus , Sudan virus , and Taï Forest virus...

 
2–21 days http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/Fact_Sheets/Ebola_Fact_Booklet.pdf
Rocky Mountain spotted fever
Rocky Mountain spotted fever
Rocky Mountain spotted fever is the most lethal and most frequently reported rickettsial illness in the United States. It has been diagnosed throughout the Americas. Some synonyms for Rocky Mountain spotted fever in other countries include “tick typhus,” “Tobia fever” , “São Paulo fever” or “febre...

 
2–14 days http://dermatology.about.com/cs/infectionvirus/g/incubation.htm
Dengue fever
Dengue fever
Dengue fever , also known as breakbone fever, is an infectious tropical disease caused by the dengue virus. Symptoms include fever, headache, muscle and joint pains, and a characteristic skin rash that is similar to measles...

 
3–14 days http://cmr.asm.org/cgi/content/abstract/11/3/480
SARS  up to 10 days http://www.who.int/csr/sars/archive/2003_05_07a/en/
Marburg  5–10 days http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/marburg/qa.htm
Roseola
Roseola
Exanthema subitum , also referred to as roseola infantum , sixth disease and baby measles, or three-day fever, is a disease of children, generally under two years old, although it has been known to occur in eighteen year olds, whose manifestations...

 
5–15 days http://www.drgreene.com/21_110.html
Polio  7–14 days http://www.gpnotebook.co.uk/cache/-1919287231.htm
Pertussis
Pertussis
Pertussis, also known as whooping cough , is a highly contagious bacterial disease caused by Bordetella pertussis. Symptoms are initially mild, and then develop into severe coughing fits, which produce the namesake high-pitched "whoop" sound in infected babies and children when they inhale air...

 
7–14 days http://www.gpnotebook.co.uk/cache/-1919287231.htm
Measles
Measles
Measles, also known as rubeola or morbilli, is an infection of the respiratory system caused by a virus, specifically a paramyxovirus of the genus Morbillivirus. Morbilliviruses, like other paramyxoviruses, are enveloped, single-stranded, negative-sense RNA viruses...

 
9–12 days http://www.aocd.org/skin/dermatologic_diseases/measles.html
Smallpox
Smallpox
Smallpox was an infectious disease unique to humans, caused by either of two virus variants, Variola major and Variola minor. The disease is also known by the Latin names Variola or Variola vera, which is a derivative of the Latin varius, meaning "spotted", or varus, meaning "pimple"...

 
7–17 days http://www.bt.cdc.gov/agent/smallpox/overview/disease-facts.asp
Generalized tetanus
Tetanus
Tetanus is a medical condition characterized by a prolonged contraction of skeletal muscle fibers. The primary symptoms are caused by tetanospasmin, a neurotoxin produced by the Gram-positive, rod-shaped, obligate anaerobic bacterium Clostridium tetani...

 
7–21 days http://www.emedicine.com/ped/topic3038.htm
Chicken pox  14–16 days http://dermatology.about.com/cs/infectionvirus/g/incubation.htm
Erythema infectiosum (Fifth Disease
Fifth disease
Erythema infectiosum or fifth disease is one of several possible manifestations of infection by erythrovirus, previously called parvovirus B19. The disease is also referred to as slapped cheek syndrome, slapcheek, slap face or slapped face. In Japan the disease is called 'apple sickness' or...

)
13–18 days http://dermatology.about.com/cs/infectionvirus/g/incubation.htm
Mumps
Mumps
Mumps is a viral disease of the human species, caused by the mumps virus. Before the development of vaccination and the introduction of a vaccine, it was a common childhood disease worldwide...

 
14–18 days http://www.vaccineinformation.org/mumps/qandadis.asp
Rubella
Rubella
Rubella, commonly known as German measles, is a disease caused by the rubella virus. The name "rubella" is derived from the Latin, meaning little red. Rubella is also known as German measles because the disease was first described by German physicians in the mid-eighteenth century. This disease is...

 (German measles)
14–21 days http://dermatology.about.com/cs/infectionvirus/g/incubation.htm
Infectious mononucleosis
Infectious mononucleosis
Infectious mononucleosis is an infectious, widespread viral...

 
28–42 days http://www.cnn.com/HEALTH/library/DS/00352.html
Kuru
Kuru (disease)
Kuru is an incurable degenerative neurological disorder that is a type of transmissible spongiform encephalopathy, caused by a prion found in humans...

 
mean between 10.3 and 13.2 years http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12094094&dopt=Citation

See also

  • Quarantine
    Quarantine
    Quarantine is compulsory isolation, typically to contain the spread of something considered dangerous, often but not always disease. The word comes from the Italian quarantena, meaning forty-day period....

  • Prodrome
    Prodrome
    In medicine, a prodrome is an early symptom that might indicate the start of a disease before specific symptoms occur. It is derived from the Greek word prodromos or precursor...

  • Window period
    Window period
    In medicine, the window period for a test designed to detect a specific disease is the time between first infection and when the test can reliably detect that infection...

    , the time between infection and when lab tests can identify the infection. The window period may be longer or shorter than the incubation period.