Fluorescence videography for the rapid and automated in-clinic detection of microfilariae

Heartworm infection is a serious cause of both morbidity and mortality in canids. Current guidelines from professional bodies recommend annual testing using both molecular (ELISA/PCR/Lateral Flow) and microscopic (detection of microfilariae in blood) testing. The inconvenience of the latter, however, presents a barrier to some clinicians towards adherence to these guidelines. We have recently developed a fully automated, rapid and hands-free test that uses videography coupled to computer vision analysis to detect and enumerate blood-borne microfilariae.

Here we describe the performance of this test compared to a common clinical option - the 20 μL wet mount. Multiple counts were conducted by both methods on serially diluted infected blood to determine count correlations and on highly diluted and negative samples to compare sensitivities and specificities.

Automated counts correlated well (R² = 0.9851) at microfilarial concentrations of up to 1000 microfilariae/mL, after which the automated counts began to plateau as microfilariae began to overlap and became more difficult to distinguish from each other. Within the linear range, the automated method counted more than 10-times as many microfilariae in the same blood samples than the manual method; this translated to a sensitivity of 100% at approximately 50 microfilariae/mL compared to 60% for the manual wet mount. After a further 2-fold dilution the sensitivity of the manual method dropped to 10% while that of the automated remained at 100%.

These results indicate that the automated system is a viable option to replace current manual options in-clinic while combining superior sensitivity with greater convenience.