Definition of incubation time
The "incubation period" is defined as the interval between the invasion of the body by a microorganism - be it a bacterium, a virus or a fungus - and the manifestation of the first symptom of the disease that derives from it. In disease vectors (eg flies, mosquitoes, ticks, etc.), the incubation time refers to the time interval that elapses between the entry of the virus or the bacterium into the vector and the moment in which it is in able to transmit the disease to a human host.
Generally, during the incubation period, the pathogen is NOT contagious; however, in some diseases, the infecting agent can also be transmitted during this phase.
In most cases, therefore, infectivity begins later than infection.
The duration of the incubation period, expressed in time intervals, is not a constant in all diseases: in fact, every pathological discomfort is characterized by its own specific incubation time, variable from a few hours (as happens, for example, for a cold) to a few weeks.
Some diseases have a very long incubation time, estimated around a few years: it is the case of the infection supported by the HIV virus. The longer the incubation period, the greater the chance of diagnostic delay; in turn, the delayed ascertainment of the disease complicates the prognosis, given that therapy is started late, often when it is now too late.
Examples
Now let's see some incubation times of the most known diseases:
- Salmonellosis → 6-72 hours
- cholera, flu, cold, scarlet fever → 1-3 days
- Haemophilus influenzae meningitis → incubation time not perfectly established. It is assumed to be 2-4 days
- legionellosis → 2-10 days
- dengue → 3-14 days
- poliomyelitis, pertussis, malaria transmitted by P. falciparum → 7-14 days
- measles → 9-12 days
- mumps → 12-25 days
- smallpox → 7-17 days
- tetanus → 7-21 days
- chickenpox → 14-16 days
- rubella → 14-21 days
- mononucleosis → 28-42 days
- tuberculosis → 28-84 days
- malaria transmitted by P. vivax → 8-10 months
- HIV and leprosy → 1-15 years
Note: the incubation time can vary not only from disease to disease, but also as a function of the form in which the same disease occurs.
The duration of the incubation period is conditioned by:
- Specific pathogen involved
- Number of infecting microorganisms
- Resistance capacity of the guest
- Pathogenic degree of pathogen (or virulence)
Food poisoning and incubation time
Even for food-borne diseases (diseases due to food intake polluted with bacteria and their toxins) it is possible to talk about incubation time, whose duration is generally less than 24 hours. The incubation period varies according to the type of infection; in some forms, the pathogen enterotoxin is processed OUT of the host, therefore directly into the food. According to these words, it is possible to understand the speed with which the symptoms manifest themselves. This is the case of toxinfections sustained by Staphylococcus aureus and Bacillus cereus, whose incubation period normally varies from one hour to six hours.
Different speech for the bacteria that process the toxin INSIDE the subject: Clostridium perfingens, synthesizes the toxin in the digestive tract, consequently the presence of the pathogen is indispensable for the manifestation of symptoms. In this case, the incubation time is longer (estimated between 8 and 20 hours).
As for the common fish poisoning, the incubation period is generally estimated between 15 and 90 minutes; salmonellae are an exception, since, taking root in the intestinal mucosa, they have a longer incubation time (of 6-24 hours).
- As we know, every food-borne infection is characterized by specific symptoms, which often allow us to hypothesize, from the earliest moments, the type of pathogen involved. In addition to symptoms, however, incubation time is also a fundamental element to guide us towards an infection rather than another: often, in fact, patients complain of symptoms by exposing the time and day when a meal was consumed potentially infectious.
Considering all these elements, it is therefore possible to quantify the duration of the incubation period of the different food-borne diseases.
