CANBERRA (Reuters) - Research into the common rat has revealed how people and certain diseases migrated around the ancient world, Australian scientists said on Friday.

A study of DNA from 165 Black Rat specimens from 32 countries has found six distinct family groups, with each group coming from a different part of Asia.

"It has been unclear why certain rodent-borne diseases are more common in some places than others," said head researcher Ken Alpin, from Australia's top science research body, the CSIRO.

"But our work raises the possibility that the different lineages of black rats each carry a different set of diseases."

The black rat, Rattus rattus, is also known as the house rat or ship rat, and is one of the most common of the 56 species of rat. It is found throughout Africa, Asia, Australia, Europe and the Americas carries diseases including the plague and typhus.

Alpin said the six different rat lineages originated in India, East Asia, the Himalayas, Thailand, the Mekong Delta and Indonesia.

The Indian lineage spread to the Middle-East around 20,000 years ago, then later to Europe and eventually Africa, the Americas and Australia.

The East Asian lineage moved from Taiwan to Japan, the Philippines, and Indonesia, arriving in Micronesia about 3,500 years ago, he said. The other four lineages have not moved as far, but could spread further in future.

He said the study found a good match between the spread of each rat lineage and ancient routes of human migration and trade, giving some new clues to spread of humans across the world.

But more study was needed.

"We need to know more about what types of black rats are moving around the world and what disease risks each of them might pose," he said.

He also said genetic evidence pointed to there being more than one species of black rat.

"But more work is needed before we can say exactly how many species there are."