Incubation period

Incubation period (also known as the latent period or latency period) is the time elapsed between exposure to a pathogenic organism, a chemical, or radiation, and when symptoms and signs are first apparent.Lesson 1, Section 9: Natural History and Spectrum of Disease, Principles of Epidemiology in Public Health Practice, Third Edition, An Introduction to Applied Epidemiology and Biostatistics, Centers for Disease Control and Prevention, May 18, 2012 In a typical infectious disease, the incubation period signifies the period taken by the multiplying organism to reach a threshold necessary to produce symptoms in the host.

While latent or latency period may be synonymous, a distinction is sometimes made whereby the latent period is defined as the time from infection to infectiousness. Which period is shorter depends on the disease. A person may carry a disease, such as Streptococcus in the throat, without exhibiting any symptoms. Depending on the disease, the person may or may not be contagious during the incubation period.

During latency, an infection is subclinical (also called asymptomatic). With respect to viral infections, in incubation the virus is replicating. This is in contrast to viral latency, a form of dormancy in which the virus does not replicate. An example of latency is HIV infection. HIV may at first have no symptoms and show no signs of AIDS, despite HIV replicating in the lymphatic system and rapidly accumulating a large viral load. People with HIV in this stage may be infectious.

Intrinsic and extrinsic incubation period The terms "intrinsic incubation period" and "extrinsic incubation period" are used in vector-borne diseases. The intrinsic incubation period is the time taken by an organism to complete its development in the definitive host. The extrinsic incubation period is the time taken by an organism to develop in the intermediate host.

For example, 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 ranges from 10 to 28 days, depending on the parasite species and the temperature. This is the extrinsic incubation period of that parasite. If a female mosquito does not survive longer than the extrinsic incubation period, then she will not be able to transmit any malaria parasites.

But if a mosquito successfully transfers the parasite to a human body via a bite, the parasite starts developing. The time between the injection of the parasite into the human and the development of the first symptoms of malaria is its intrinsic incubation period.

Determining factors The specific incubation period for a disease process is the result of multiple factors, including: Dose or inoculum of an infectious agent Route of inoculation Rate of replication of infectious agent Host susceptibility Immune response

Examples for diseases in humans Due to inter-individual variation, the incubation period is always 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.

For many conditions, incubation periods are longer in adults than they are in children or infants.

Disease between and Cellulitis caused by Pasteurella multocida 0 daysCellulitis, kidshealth.org. Accessed 2012-05-28.1 day Chicken pox 9 days21 days Cholera 0.5 days4.5 days Common cold 1 dayCommon cold, The Mayo Clinic, mayoclinic.com. Accessed 2012-05-28.3 days COVID-19 2 days 11.5/12.5/14 days Dengue fever 3 days14 days Ebola 1 dayAre the Ebola outbreaks in Nigeria and Senegal over?, World Health Organization, who.int. Accessed 2014-10-21.21 (95%), 42 (98%) days Erythema infectiosum (Fifth disease) 13 days18 days Giardia 3 days 21 days HIV 2 weeks to months, or longer3 weeks to months, or longer Infectious mononucleosis (glandular fever) 28 daysMacnair, Trisha, Glandular fever, BBC, bbc.co.uk. Accessed 2012-05-28.42 days Influenza 1 daySeasonal Influenza (Flu), Centers for Disease Control and Prevention, cdc.gov. Accessed 2012-05-28.3 days Kuru disease 10.3 years (mean)13.2 years Leprosy 1 year20 or more years Marburg 5 daysQuestions and Answers About Marburg Hemorrhagic Fever , Centers for Disease Control and Prevention, cdc.gov. Accessed 2012-05-28.10 days Measles 9 daysMeasles, American Osteopathic College of Dermatology, aocd.org. Accessed 2012-05-28.12 days MERS 2 days14 days Mumps 14 daysMumps Disease, Questions & Answers , vaccineinformation.org. Accessed 2012-05-28.18 days Norovirus 1 dayNorovirus, Centers for Disease Control and Prevention, cdc.gov. Accessed 2012-05-28.2 days Pertussis (whooping cough) 7 daysPertussis, GPnotebook, gpnotebook.co.uk. Accessed 2012-05-28.14 days Polio 7 daysPolio, GPnotebook, gpnotebook.co.uk. Accessed 2012-05-28.14 days Rabies 1 month, but may vary from <1 week to rarely >1 year.3 months Rocky Mountain spotted fever 2 daysRocky Mountain Spotted Fever , About.com. Accessed 2012-05-28.14 days Roseola 5 days15 days Rubella (German measles) 14 days21 days Salmonella 12 days24 days Scarlet fever 1 day4 days SARS 1 dayWorld Health Organization (WHO), Severe acute respiratory syndrome, www.who.int. Accessed 2012-05-28.10 days Smallpox 7 daysSmallpox Disease Overview , Centers for Disease Control and Prevention, cdc.gov. Accessed 2012-05-28.17 days Tetanus 7 days21 days Tuberculosis 2 weeks12 weeks Typhoid 7 days 21 days

Incubation period

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