Theory:

The infectious diseases can be treated in two ways. They are as follows:
  • By killing the infectious agents
  • By reducing the effects of the disease or reducing the symptoms
The symptoms can be reduced by providing treatment. These symptoms are mostly due to inflammation. For example, the high temperature during fever can be brought down by using medicines.
 
Similarly the pain and loose motions can also be reduced. The energy in our body can be conserved by taking bed rest so that more energy is available to focus on healing. But, all these treatments that are symptom directed will not make the microbe go away by itself.
The killing of microbes:
Microbes can be killed by using medicines. The different categories of microbes such as viruses, bacteria, fungi or protozoa have certain biochemical processes which are specific to their groups and are not shared by any other group.
 
These processes may be pathways for the synthesis of new substances or respiration. These processes are also not used by humans as the cells of humans make new substances by a mechanism different from that used by bacteria.
 
Hence, finding a drug that blocks the bacterial synthesis pathway without affecting our own is mandatory.
 
This is achieved by the antibiotics. In similar to this, there are also drugs that kill protozoa, such as the malarial parasite. Compared to these two, it is harder to produce medicines against viruses as the viruses have very few biochemical mechanisms of their own.
 
Viruses are pathogens enter the cells and use our machinery for their life processes. Thus, from this we can say that there are very few virus-specific targets to aim at. But despite these limitations, there are certain anti-viral drugs such as the drugs that keep HIV infection under control.