GENEVA (AP) -- A ballooning world population, intensive farming practices and changes in sexual behavior have provided a breeding ground for an unprecedented number of emerging diseases, the U.N. health agency said Thursday.

AIDS and 38 other new pathogens are afflicting mankind that were unknown a generation ago, the World Health Organization said.

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.

"We've urbanized a world. We have moved people and food around that world at ever increasing speed," Ryan said. "We're not saying that's a bad thing. What we're saying is that we must recognize the risk we create in the process and invest to manage those risks."

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, and bird flu.

Much of WHO's annual report on the state of the world's health was designed to convince governments to adhere to new, tighter International Health Regulations, providing the basis for the world to cooperate in combating frightening diseases.

WHO also said Thursday that it was working to fast-track improvements of food and products regulation in China, whose exports have become a source of safety concern in recent months.

"The Food and Safety department of the World Health Organization in Geneva has been working with the government of China to streamline their regulation of food and products," Chan said. "And actually they have been in touch with our colleagues again to take their initial discuss forward.

"The process has been going on for some time ... and recently we were approached to see in what way we can strengthen and fast-track that process."

Chan announced a special experts meeting in Beijing scheduled for mid-September.

"The government of China is committed to improving their system," she added.

Chinese exports have come under intense scrutiny, especially in the United States, China's most important export market. Regulators have turned up tainted pet-food ingredients, seafood and toothpaste with potentially dangerous chemicals and drugs.

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