You can find lot of information online. Whereas my opinion is different regarding the causative agents. All viral diseases which include dengue, hepatitis, prolong fevers, certain cancers etc always indicate a badly abused body. If you were very erratic about your dietary pattern, night sleep and physical activity, you were self sabotaging yourself. If a person always look at the negative aspect of a situation , immune system will be suppressed. Remember fear, phobia, sadness, lack of contentment, insecurity, poor relationship with parents and weak faith put you at the risk of killer diseases.
Viruses are like demons hidden in our body, waiting vigilantly for the right situation. In epidemics fear factor dominates and immunity crashes. In epidemic situations scholars should preach peace related religion aspects effectively to overcome the fear factor.
Keep in your virus can’t kill but fear can kill.