Rhodococcus hoagii (formerly Rhodococcus equi) is a facultative pathogen organism in soil or horse faeces. R. hoagii is the most frequent causative agent of severe pneumonia with high fatility rates in foals aged 3 weeks to 6 months. Entry and predilection site is the lung (abscessation!), from where haematogenous spread to other organs and, through swallowing, a dissemination into the gastrointestinal tract (ulcera, diarrhoea, source of infection!) are possible. Umbilical infections occur as well. Moreover, R. hoagii shows an affinity for bones and joints.