Human pythiosis is characterized by the formation of subcutaneous lesions and the invasion of the main arteries. If not treated the infection is fatal. The majority of the cases have been diagnosed in Thailand. The disease has been also reported in Australia, Haiti, India, and the USA. The organism is acquired through traumatic implantation and remains localized or spreads to infect other tissues, especially arteries. The diagnosis of the disease in humans is based in culture, serology, and histopathology. In all cases hyphae of this oomycete are present in the infected tissues. Serological test such as ID and ELISA have proved to be of value for its early diagnosis.

The main clinical forms of the disease includes: keratitis, orbital disease (in children), arterial pythiosis, and a subcutaneous form on the limbs and other anatomical areas. Keratitis is difficult to differentiate from cases of keratitis caused by the hyaline filamentous fungi. The clinical manifestations and the microscopic characteristic of the clinical samples sent to the laboratory are identical. Culture is the only tool to make the appropriate diagnosis. The problem is that only few laboratories are familiar with this organism. So, mast cases are misdiagnosed. Something similar had happened with orbital pythiosis in USA children. Since zygomycetous fungi can also cause orbital disease, and their filamentous hyphae are very similar to that developed by P. insidiosum in the infected tissues, some cases has been in the past misdiagnosed as cases of zygomycosis. Arterial pythiosis is more frequently diagnosed in Thailand.

Treatment The treatment of human subcutaneous pythiosis on limbs, in which the arteries have been involved, consists of the amputation in the affected extremity. Iodides and other drugs have been used with questionable results. More recently the vaccine used to treat equine pythiosis, was successfully used in cases of human pythiosis with 55% cure rate. In addition, a combo of itraconazole and terbinafine cure a Tennessee boy with orbital disease. However, this combination had failed in other similar cases of pythiosis in humans and animals.