In human medicine, epidemiologists have become indispensable intracking down the causes of certain clusters of diseases -- AIDS,Legionnaire's disease, toxic shock syndrome and so on. Animal epidemiologists use the same principles to study disease outbreaks in animal populations. Their goals are to discover the causes of the outbreaks and to prevent additional cases and future outbreaks. In a Wednesday afternoon session, July 31, UC Davis assistant professor Dr. Philip Kass will discuss the basics of investigating disease outbreaks, including the reasons why certain studies succeed and others are doomed to failure. To illustrate these principles, associate professor Dr. David Hird will describe the investigation of a 1985 listeriosis outbreak in Los Angeles that was linked to Mexican-style soft cheese manufactured in the city. Associated with the bacterium Listeria monocytogenes, the disease can cause death in infants, the elderly and people with weak immune systems. The team of investigators, which included Hird, speculated but could not prove that raw milk may have carried the guilty bacteria. Although not conclusive, their investigation has helped other countries identify and control listeria outbreaks caused by contaminated soft cheeses.