R Equi Phneumonia: Airborne Exposure and Foal Immunity / Rhodococcus Equi Airborne Environmental Study

goals. The abstract should be a succinct, accurate and self-explanatory description of the proposed work. Pneumonia caused by the bacterium Rhodococcus equi is an important cause of morbidity and mortality among foals. Increasingly, there is evidence that foals become infected very early in life at an age when their immune systems are naIve or relatively immature. Many important questions pertaining to R. equi foal pneumonia remain unanswered. In particular, it remains unknown why certain farms are more likely to experience the disease, and why some foals develop the disease while most other foals from the same farm remain unaffected. Addressing these questions will require consideration of factors related to the agent, environment, and host. Our laboratories have demonstrated that a specific strain is not responsible for endemicity of disease at a farm: any virulent isolate has the potential to cause disease in foals. Thus, environmental and host factors likely playa dominant role. In the environment of young foals, our laboratories have demonstrated that exposure to virulent R. equi is widespread, both in feces of mares and soil samples from breeding farms. Recent evidence from other continents, however, indicates that airborne concentrations of virulent R. equi are positively correlated with incidence of R. equi pneumonia. The extent to which this association is either true in North America or causal is unknown. An objective of the proposed study is to better characterize the association of R. equi pneumonia with airborne concentration of virulent organisms at the levels of both farm and foal. The relative exposure in barns and paddocks The null hypotheses to be tested in the study are as follows: 1) airborne concentrations of R. equi (REACs) don't vary by time of day; 2) REACs don't vary between areas in a barn; 3) REACs during the perinatal period are similar among foals that later develop R. equi pneumonia (affected foals) and foals that remain unaffected (unaffected foals); 4) exposures are greater in barns than in paddocks; and, 5) incidence of R. equi pneumonia is not correlated with REACs at the farm level. The study will focus on the perinatal period because of evidence from our laboratories that most foals become infected at this age and because immunity of these foals is relatively naIve or immature. The extent of environmental exposure will be examined both at the level of farm and foal in this study.