BEIJING, Aug 24 (Xinhuanet) -- Changes in sexual habits, a burgeoning world population and intensive farming practices are reasons for an unprecedented number of emerging diseases, the World Health Organization said Thursday.

    The United Nations health agency said AIDS and 38 other new pathogens that were unknown a generation ago are afflicting mankind.

    Though advances in science could account for the discovery of existing pathogens that were previously unidentified, WHO epidemics expert Dr. Mike Ryan said changes in human behavior and practices have produced more new diseases.

    "We've seen a shift in trend that reflects a transition of human civilization," Ryan said. "The relationship to the animal kingdom, our travel, our social, sexual and other behaviors have changed the nature of our relationship with the microbial world and the result of that is the emergence of new pathogens and the spread of those pathogens around the world."

    He noted that in the late 19th century, scientists discovered a range of agents causing ancient scourges such as anthrax, staphylococcus, tuberculosis and tetanus.

    In the 1970s and '80s it wasn't pathogens experts were discovering but new syndromes: children getting sick with rashes and fever in the suburban areas of the Americas, people suffering from liver and renal disease after consuming undercooked meat.

    WHO Director-General Dr. Margaret Chan said one of the changes affecting human health was increasingly intensive poultry farming, which may account for the global spread of bird flu.

    "It should not come as a surprise that we are seeing more and more disease outbreaks coming from the animal sector," Chan said.

    She said the majority of the 39 new diseases came from animals, including Ebola, SARS, or bird flu.

    (Agencies)