Incubation period

Incubation period is the time elapsed between exposure to a pathogenic organism, a chemical or radiation, 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, 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 clinical latency, an infection is subclinical. With respect to viral infections, in clinical latency the virus is actively replicating.^[1] This is in contrast to viral latency, a form of dormancy in which the virus does not replicate.

Clinical latency occurs in:

• AIDS: persons infected with 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. These persons may be infectious.

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.

See also

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

References

1. ^ Sharara AI (1997). "Chronic hepatitis C". South. Med. J. 90 (9): 872–7. PMID 9305294.