Answer :
Final answer:
The elements that lead to infection include a source of the agent, a way for it to transmit, and a susceptible host. The infectious agent departs its reservoir through a portal of exit and enters the host through a portal of entry, with transmission often facilitated by fomites or other means. Correct option is a.
Explanation:
The key elements that can lead to the occurrence of an infection are a source of the infectious agent, its mode of transmission, and a susceptible host. Correct option is a.
An infection cycle starts with the pathogen leaving its reservoir through the portal of exit, moving via a mode of transmission, and then entering a new host via the portal of entry. The different modes of transmission may include direct droplet contact, indirect contact through fomites (like contaminated objects), and vectors such as mosquitoes.
A susceptible host is typically a person or organism whose immune status allows for infection; they can vary from being immune, susceptible, to already being infected. Environmental factors can influence this process by affecting the pathogen's survival outside its host or by impacting the exposure level and susceptibility of the host population.
