Geographical distribution of human pythiosis in the USA

For more than 100 years, the infections caused by Pythium insidiosum have been well documented in horses. However, recently, pythiosis was also described in several species, including dogs, cats, cattle, zoo captive animals, and humans. Human pythiosis is a life-threatening infection requiring an early diagnosis for a successful management. The clinical picture of pythiosis mirrors the clinical features of infections caused by other pathogens, including filamentous fungi, making its diagnosis challenging. This fact had led to several misdiagnosed cases involving filamentous fungal pathogens. The first pythiosis human case in the USA was reported in 1989. Soon after, various pythiosis cases of orbital disease in children and on the limbs of adults were sporadically diagnosed. To investigate the geographical distribution of human pythiosis in the USA, we constructed a density USA map using a recent report of pythiosis in animals highlighting the known human cases. Our data showed that P. insidiosum human infections in the USA are diagnosed in the same geographic areas where animal pythiosis occur. Physicians handling clinical cases like those so far reported can use the geographic distribution of pythiosis human cases in this study as a guide in their clinical diagnosis and in the early management of putative cases.IMPORTANCEThe relevance of the study not only resides in the epidemiological distribution of animal human pythiosis in the USA (our team's recent publication), but also shows physicians the areas where Pythium insidiosum thrive in endemic areas. Our manuscript shows to the medical and veterinary communities the current areas of human and animal pythiosis, an event that could have a direct impact on the epidemiology, diagnosis, and management of pythiosis.