Final answer:
Pathogens are transmitted from one host to another through various means including direct contact, airborne droplets, or via biological vectors like insects. After leaving the infected host, the pathogen must enter and bypass the defenses of a new host to cause disease. The severity of the disease correlates with the number of pathogens in the host.
Step-by-step explanation:
Pathogen Transmission from Infected Host to Another Host
Pathogens are transmitted from an infected host to another potential host through several stages: exposure, adhesion (colonization), invasion, and infection. Transmission may occur via direct contact, airborne droplets, and biological vectors. Specifically, in the case of biological transmission, an organism, often an insect, acts as an intermediary in spreading the pathogen. For instance, mosquitoes are known vectors that can transmit the malaria parasite to humans. The pathogen grows and reproduces within the vector before being passed onto a new host.
Pathogens can exit the infected host through various portals of exit, such as respiratory droplets during coughing or sneezing, or through blood extracted by a biting insect. These expelled pathogens are then encountered by another host, potentially leading to a new infection if they can successfully bypass the host's immune response and replicate within their tissues to cause disease.
It's important to understand that for a pathogen to cause disease it must not only find a way into a new host but also overcome the host's defenses and induce damage. The severity of the disease often correlates with the number of pathogens that successfully invade and multiply within the host.