Scientists studying bats have found dozens of new members of a virus family linked to human disease, and warned of possible exposure as the winged mammals are driven out of forests into the cities.

Sixty-six new species of paramyxoviruses, the viral group that causes measles and mumps and is behind three cattle diseases, have a natural host in bats, they said.

It is not yet known if any of the newly-discovered viruses are a threat or are even transmissible to humans, but the experts urged caution.

Virologist Christian Drosten of Germany's University of Bonn and a team of international scientists used mathematical modelling to trace the root of paramyxoviruses among wild animals.

They found "the highest likelihood" that bats are the original, ancestral hosts, a reservoir where these viruses hole up, Drosten told AFP of the findings published in the journal Nature Communications.

The research discovered 66 new species that can be added to the paramyxovirus clan.

"The genetic range has really been doubled," Drosten told AFP. "We know the source now, the point where the viruses came from."

The findings hold important implications for tracking outbreaks of disease and for vaccination campaigns, the researcher said.

"If you want to investigate where the next pandemic virus (will hit), how it could look like, you have to look in the reservoir, the source of the viruses," he said.

"The decision to enter vaccination campaigns needs ... really clear knowledge that there is no reservoir, but now it seems clear that for a whole group of viruses there is indeed a reservoir, we just didn't know it. So we may have to think again."

The study found "a very large range and diversity" of viruses related to the pathogen that causes rinderpest, a cattle-killing disease declared eradicated last year, Drosten said.

The deadly Hendra and Nipah viruses, which are transmitted to livestock and then to humans, are also part of this family and may have originated in Africa.

Drosten said people were coming in contact with bats more and more as the animals' natural habitats become depleted, especially in Africa, and they entered urban areas.

"Now we have them sitting in the big cities and we know their faeces is full of viruses. This may be one of the reasons why we are experiencing more and more epidemics of novel viruses," he suggested.

"This is something we will have to monitor closely in the future. There are consequences of the invasion of humans into primary habitats."

He stressed it was unfeasible to consider eradicating bats -- and foolish to even try. Bats are a vital help for humans by eating mosquitos or acting as pollinators.

Many pathogens that affect humans have a reservoir in nature.

The AIDS virus, for instance, is believed to have leapt the species barrier from chimps to humans in centre-west Africa about a century ago, possibly through an animal bite or by the handling of infected "bushmeat."