Final answer:
Pathogens normally become better suited to infect and transmit by evolving traits that enhance their transmission and infectivity through natural selection, often by improving their ability to spread during periods when they're likely to encounter new hosts.
Step-by-step explanation:
Over time, a pathogen normally gets better suited to infect and transmit by evolving traits that enhance its transmission and infectivity. This occurs through a process of natural selection, where the pathogens that have mutations allowing them to spread more effectively and reproduce in the host will outcompete those that do not. These more 'fit' pathogens are then more likely to survive and pass on their genes to the next generation of pathogens, thus spreading these advantageous traits through the population.
It's also important to consider the mechanisms of disease transmission. Pathogens can be transmitted via different routes, including airborne transmission, direct contact, fecal-oral transmission, and more. A pathogen that evolves to be more contagious during a period when it is likely to come into contact with other potential hosts (e.g., the prodromal period for respiratory infections) will have greater success at transmitting itself to new hosts. However, too severe an infection may harm the host excessively, impairing the pathogen's chance to spread – thus, the evolution of transmission traits is a balance.