Important Questions on Why do we fall ill
What are the two conditions which are essential for being free of disease ? 
What determines the severity of disease manifestation? What are the basic principles of preventing an infectious disease ? Why there is no use of giving vaccine of hepatitis A virus ? We are normally advised to take bland and nourishing food when we are sick. Why is it so? It is said that, "if you had smallpox once, there was no chance of suffering from it again." Why is it so ? It is a known fact that, "milkmaids who had cowpox did not catch smallpox even during epidemics". Why is it so ? Why HIV infection is considered very fatal? 
