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. ==See also==