Development of an Immunochromatographic Test for Rapid Serodiagnosis of Human Pythiosis

Human pythiosis is an emerging and life-threatening infectious disease caused by the fungus-like organism Pythium insidiosum. High rates of morbidity and mortality for patients with pythiosis are exacerbated by the lack of early diagnosis and an effective treatment. Here, we developed and evaluated an immunochromatographic test (ICT) for the diagnosis of human pythiosis, in comparison to a standard serological test of immunodiffusion (ID). Culture filtrate antigen of P. insidiosum was used to detect human anti-P. insidiosum antibody. Sheep anti-human immunoglobulin G-colloidal gold conjugate was used to generate an ICT signal. Thirty-three sera from patients with vascular (n = 27), ocular (n = 4), and cutaneous (n = 2) pythiosis and 181 control sera from healthy blood donors (n = 100), as well as patients with a variety of infectious (n = 56) and noninfectious (n = 25) diseases, were included in the test evaluation. The turnaround time for generating a result by the ICT was less than 30 min, while that for ID was similar to 24 h. Based on the results for all sera of pythiosis patients and the control groups, the ICT showed 88% sensitivity and 100% specificity and ID showed 61% sensitivity and 100% specificity. By both tests, false-negative results for sera from all ocular pythiosis patients were obtained. In addition, the ID test yielded false-negative results for sera from eight patients with vascular pythiosis and one patient with cutaneous pythiosis. It was concluded that the ICT is a rapid, user-friendly, and reliable serological test for the early diagnosis of vascular and cutaneous pythiosis.