Final answer:
Infectious diseases, caused by pathogens, can be transmitted from person to person, while non-infectious diseases cannot and are instead typically related to genetics and lifestyle. The mode of transmission is the primary difference between the two, and infectious diseases progress through various stages with variable contagiousness.
Step-by-step explanation:
An infectious disease is caused by the direct effect of a pathogen such as bacteria, viruses, fungi, parasites, viroids, or prions, and can be spread from person to person, while a non-infectious disease is generally due to genetic, lifestyle, and environmental factors and cannot be transmitted between individuals. Infectious diseases can be categorized into various types, including zoonotic, which are transmitted from animals to humans; nosocomial, which are acquired in healthcare settings; and iatrogenic, which result from medical procedures. These diseases can be spread through direct or indirect contact or vector transmission, and their contagiousness varies based on how the pathogen is transmitted. Acute infectious disease often progresses through stages: the incubation period, prodromal period, period of illness, period of decline, and convalescence. The risk of transmission varies at different stages, depending on the pathogen and disease. For example, viral meningitis is contagious at the onset of the prodromal period, while bacterial meningitis can be contagious during the incubation period, continuing up to a week before the prodromal period begins.