Leptospira interrogans insoluble fraction as a potential antigen source for lateral flow immunochromatography

Abstract

BACKGROUND Leptospirosis is an emerging zoonosis that affects humans and animals worldwide. The mortality resulting from this disease is high and it is likely related to the delay in the differential diagnosis. Although it is not a gold standard, immunochromatography rapid test is widely used for early diagnosis of leptospirosis, but with low sensitivity and specificity in the acute phase. OBJECTIVES To evaluate of Leptospira interrogans insoluble fraction as a potential antigen source for lateral flow immunochromatography. METHODS Insoluble fraction derived from crude bacterial extract was obtained by serial centrifugation and polypeptide profile was determined by SDS-PAGE. Immune reactivity was assessed by Western Blotting and lateral flow immunochromatography (LFI) using 160 MAT-positive sera of patients in acute phase, 100 MAT-negative sera from patients with acute febrile illness and 45 patients with other infectious diseases. FINDINGS There was a predominance of low molecular mass-polypeptide bands, from 2 to 37 kDa, with antibody reactivity ranging from 13-50% between 10 and 38 kDa. Among MAT-positive sera of patients with leptospirosis in acute phase, 97% were also positive in LFI and the same pattern was observed among MAT-negative sera. Only 2% of cross-reactivity was detected, particularly in syphilis-positive sera. CONCLUSION The insoluble fraction might be an important antigen source for leptospirosis point-of-care diagnosis with high sensitivity and specificity.