There are two ways to treat an infectious (communicable) disease. These are:
(i)
To reduce the effects of the disease : It can be done by providing
symptomatic treatment. We can provide treatment that will reduce
the symptoms. For instance, we can take medicines that bring down fever,
reduce pain or loose motions. We can also have bed rest to conserve our
energy. These steps will enable us to focus on healing. However, such a
symptom-directed treatment by itself is not sufficient as it will not
remove the disease-causing microbes from the body. To cure the disease,
we need to kill the microbes.
(ii) To kill the cause of the disease,
i.e., pathogens : The most common method to kill disease-causing
microbes is to use medicines that kill microbes. The disease-causing
microbes are classified into different groups such as viruses, bacteria,
fungi and protozoans. Each of these groups of microbes have some
essential biochemical life processes which are peculiar to that group
and not shared with the other groups. Our cells have different pathways
than the ones used by these microbe groups. Therefore, we find a drug
that blocks; for example, the bacterial biochemical path way without
affecting our own. This is what is achieved by antibiotics.
Similarly, there are drugs that kill protozoans, e.g., malarial parasite.