A team of U.S. scientists have completed five-year multi-million dollar project mapping nearly all the microbes that inhabit healthy human bodies, including bacteria viruses, and fungi.

The scientists collected 5,000 samples taken from different body parts of 250 volunteers of both sexes.

Experts have known for years that the human body plays host to trillions of microorganisms in what is called a microbiome.

They have determined that about 10,000 species of microbes are part of this microbiome. Some of the microbes cause diseases in some people while exist harmlessly in others.

The scientists plan to study a normal microbiome to try to understand the changes that take place when people get sick and how microbes can live peacefully in some people and not in others.

The team's study appears in the journals Nature and The Public Library of Science.