The time interval between the entry of the disease agent into the body and the appearance of first sign or symptom of the disease is–

Correct option is A

Sol. The incubation period is the time between the exposure to an infectious agent and the onset of symptoms. This period varies depending on the disease. For example, influenza has an incubation period of 1–3 days, while hepatitis B may take weeks. Knowing the incubation period helps in disease surveillance and outbreak control.
Explanation of each option:
· (a) Incubation period – Correct Answer. Refers specifically to the "silent" period after exposure but before symptoms appear. Crucial for contact tracing and isolation timing.
· (b) Transmission – Refers to how the disease spreads from person to person or animal to human. It is not a time interval but a process.
· (c) Infection – Describes the invasion and multiplication of pathogens in the body. May occur before, during, or after symptoms develop but is not a defined time period.
· (d) Epidemic – A large-scale outbreak of disease in a population. It’s a public health term referring to the spread, not to timing between exposure and symptoms.