Lipoarabinomannan (LAM) - a potential biomarker for the diagnosis of tuberculosis from the urine of infected elephants

Abstract

Abstract The spread of Tuberculosis (TB) in Asian countries is mainly due to co-existence and close association of humans with elephants and other domestic livestock. Infected animals tend to shed the organism in the preclinical period which risks the transmission of the infection from animals to humans and vice-versa. Since tuberculosis infection is chronic and lack specific clinical signs, diagnosis remains challenging. Present study focus on the utilization of Lipoarabinomannan (LAM) a glycolipid for the detection of TB infection in elephants. Usage of urine as the biological sample for the diagnosis makes it more advantageous. Seroprevalence of tuberculosis (TB) in elephants in Kerala were found to be 37.2 per cent (n = 86) using Chembio DPP VetTB assay. Nine (10.46 per cent) out of 86 elephants were positive for AFB and 29 (33.7 per cent) out of 86 elephants were positive for LAM antigen. On comparison of efficiency of LF-LAM assay with that of DPP VetTB assay, LF-LAM assay had a sensitivity of 90.63 per cent, specificity 100 per cent, positive predictive value 100 per cent, negative predictive value 94.7 per cent, accuracy 95.51 per cent and kappa statistic value 0.924 (p - value < 0.001). On comparison of LF-LAM with traditional acid fast staining method, LF- LAM assay had the sensitivity of 100 per cent, specificity 74.03 per cent, positive predictive value 31 per cent, negative predictive value 100 per cent, accuracy 76.74 per cent and kappa statistic value 0.374 (p - value < 0.001). The presence of Mycobacterium tuberculosis was confirmed in trunk wash sample using PCR targeting gene IS6110, at 245bp amplicon size and 25 seropositive elephants (78.2 per cent) were confirmed positive. Custom sequencing and phylogenetic analysis revealed that the isolate obtained were Mycobacterium tuberculosis. This study in elephants prove that TB LAM Ag (LF-LAM) can be used as potent biomarker for diagnosis of tuberculosis in elephants,