BEIJING (Xinhuanet) -- Humans are at greater risk of being infected by diseases from the animal world, according to researchers who have documented illnesses that have made that jump over the past 25 years.

The researchers disclosed that 38 new human pathogens have emerged in the past 25 years. Three quarters of these, including Aids, avian flu, Sars and new variant CJD, originated as animal diseases.

The survey, led by Mark Woolhouse, of the University of Edinburgh, has identified more than 1,400 pathogens that can cause disease in human beings, at least 800 of which crossed the species barrier from animals.

The human population is accumulating new pathogens from animals at a rate of one or two per year. "This does not seem to be sustainable over evolutionary timescales; we would be overwhelmed with pathogens," said Prof Woolhouse.

Rapid changes in the way people interact with the environment, such as bushmeat hunting, intensive agriculture, the ease of long-distance travel and global warming, are probably responsible.

Two-thirds of the pathogens that have moved most recently into humans are "RNA viruses", Prof Woolhouse said. This type of virus, including flu, HIV and Sars, has the advantage of being genetically variable and fast mutating, so it can adapt quickly to a new host. "We have to recognize that there is really only one medicine," Dr. Woolhouse said. "Pathogens don't distinguish between humans and animals, but we do with our distinction between medicine and veterinary medicine. We can't afford to go on like that. Vets and medics need to work together."