Which is the most effective and harmful microbe?

HIV/AIDS, the Global Tragedy
The Human Immunodeficiency Virus or HIV causes the disease we know as AIDS. AIDS is a pandemic—a disease outbreak that is happening all over the world.

The Flu Virus—

Sure, every year during what’s called "the flu season" tens of thousands of people get the flu. Despite feeling all achy and lousy for several days, most people eventually beat the virus and recover just fine.