Pythium insidiosum

Pythium insidiosum is a species of Pythium and a member of the class oomycota. Pythium insidiosum is mainly found in standing water and occasionally soil. Unlike most Pythium species, which are generally pathogens of terrestrial plants, Pythium insidiosum is a pathogen of mammals. It causes pythiosis, mainly in horses, dogs and humans. It is a rarely occurring, non-transmissible disease. Infection can occur in healthy mammals. The pathogen is well-adapted to mammalian body temperature, with an optimum temperature for growth of 34-36 °C.

The cells walls of Pythium insidiosum are composed of β-glucans (compared to the chitin walls of fungi), and their cytoplasmic membranes lack sterols.