Study on endotoxin in indoor environment: research at equine-related facilities in Japan

In recent years, endotoxins have received considerable attention as substances associated with allergic diseases. Endotoxins are cell wall components of gram-negative bacteria that are widely present in the living environment. Endotoxin concentrations are particularly high in environments where animals are housed. However, while the status of endotoxin concentrations in the general environment is becoming clearer, there remains a scarcity of studies in environments with potentially higher concentrations. In this study, we measured indoor endotoxin concentrations in buildings in Japan that are strongly associated with horses. The target buildings include a “Magariya,” an old Japanese house, an accommodation facility connected to a horse stable, and a stable specifically for thoroughbreds. Air and dust samples were collected at these measurement targets and analyzed for air and dust concentrations. Airborne concentrations were higher in buildings with horses present than in buildings without horses, and the presence/absence of horses is thought to have a significant effect on the airborne concentration of endotoxin. Additionally, as the density of horses increases, endotoxin concentrations also tend to increase. Dust concentration had different values in different rooms even in the same building. These results suggest that dust concentrations may be affected by floor materials, frequency of cleaning, and frequency of human traffic from areas of high concentrations. Endotoxin concentrations were high in the stable during the work because of the replacement of the dried straw in the stalls and the removal of horse excrement. These results are expected to be useful in controlling endotoxin concentrations in indoor environments of various building types.