Viruses mutate and can become more pathogenic to humans. some viruses may originate in other animals, such as birds, bats or pigs and then become infectious to humans. an influenza pandemic is a global outbreak of disease that occurs when a new influenza a virus appears or "emerges" in the human population, causes serious illness, and then spreads easily from person to person worldwide. such a

Viruses may be defined as the organisms that shows the border line between the living and non living organisms. Viruses can only replicate when they enter in the body of a particular host.

Viruses are pathogenic for humans and can cause deadly diseases like AIDS. The pandemic condition of virus mainly depends on the the matter of time. The appearance of the disease condition before the occurrence of the another  disease.

unicellular organisms, like bacteria, are able to perform all life functions within one single cell. multicellular organisms need many different types of cells to carry out the same life processes. each of these special types of cells has a different structure that it perform a specific function.