Evaluation of lateral flow devices for rabies diagnosis in decomposed animal brain samples.

Abstract

Background: The Direct Fluorescent Antibody Test (DFAT), the standard rabies confirmatory test, is less sensitive when used with decomposed brain samples, a frequent issue in rabies-endemic regions. This study evaluates the diagnostic accuracy of the ADTEC lateral flow device (LFD) for rabies post-mortem diagnosis using decomposed brain samples.

Methods: We used 34 animal heads submitted with a cold chain to an animal diagnostic laboratory located in central Philippines including 26 DFAT-positive and eight DFAT-negative samples. After defrosting the heads, the entire brain was extracted and left at room temperature to induce decomposition. The decomposition status was scored after 1 day, 3 days, and 4 days at room temperature. DFAT and LFD were performed using the brain samples at each timepoint to evaluate the diagnostic accuracy. The day of animal head submission to the laboratory was defined as day 0, and the DFAT results were used as the reference. Image analysis was performed to measure the intensity of the LFD-positive bands.

Results: The decomposition scores dropped by day 3 and day 4, with all samples exhibiting signs of advanced decomposition. The sensitivity of DFAT was 96.2% (95% confidence interval 80.4-99.9) on day 1, but dropped to 61.5% (P < 0.01) by day 3 and further decreased to 38.5% (20.2-59.4) by day 4. In contrast, the sensitivities and specificities of LFD on day 1, day 3, and day 4 were consistently 100% (86.3-100) and 100% (63.1-100), respectively. Visual examination of the test band intensity on the LFD suggested that the intensity of the positive bands increased as decomposition progressed.

Conclusions: ADTEC LFDs demonstrated consistently high sensitivity and specificity with decomposed brain samples observed up to day 4, making them a reliable screening tool for rabies post-mortem diagnosis in decomposed brain samples, particularly in resource-limited settings. Furthermore, LFD positive bands became more distinct as decomposition advanced.