Final answer:
The statement provided is true. Infection occurs in a cycle involving various stages and components, from the presence of infectious agents in a reservoir to their transfer to new hosts via various transmission modes and entry portals.
Step-by-step explanation:
The statement is true; infection does occur in a cycle that involves the presence of infectious agents, reservoirs, a portal of exit, a mode of transmission, a portal of entry, and a susceptible host. Infectious agents are microorganisms such as bacteria, viruses, fungi, and protozoa. These agents need reservoirs where they can grow and multiply. Common reservoirs include humans, animals, and the environment. Once the microorganisms have multiplied, they exit the host through various portals such as the skin, respiratory tract, urinary tract, and gastrointestinal tract.
The pathogen employs different modes of transmission to reach a new host. These modes can be direct, such as through physical contact, or indirect, through vectors like insects or contaminated surfaces. Pathogens enter the new host through portals of entry, which include the same routes as the portals of exit. At this point, the host's susceptibility plays a crucial role in determining whether the infection will become established. For instance, if the host's immune system is robust, it might successfully fight off the pathogen. If the pathogen does manage to enter host tissue and multiply, it results in an infection, which can be local, focal, or systemic.
During different stages of the disease, such as the incubation and prodromal periods, the infected individual can transmit the pathogen to others. For instance, patients with bacterial meningitis are contagious during the incubation period, while those with viral meningitis become contagious during the prodromal period. Furthermore, following certain diseases, an individual may continue to shed the pathogen and pose a transmission risk even after symptoms have disappeared.
In summary, the cycle of infection involves the interplay between pathogens and their movement from one host to another, using different methods and pathways to infect and, as a result, sometimes lead to disease in a new host.