In humans, it can cause arteritis, keratitis, and periorbital cellulitis.[8] This has previously been thought to be a rare disease with only 28 cases reported in the literature up to 1996.[9] However, keratitis due to Pythium may be more common than previously thought, accounting for a proportion of cases that were due to unidentified pathogens.[10] Although this disease was first reported in 1884[11] the species infecting humans - Pythium insidiosum - was only formally recognised in 1987.[12] Diagnosis can be difficult in part because of a lack of awareness of the disease.[13] It does not appear to be transmissible either animal to animal or animal to human.