Generating human STR DNA profiles from blood ingested by leeches

Abstract

Aquatic crime scenes may include the presence of annelids, such as leeches, which may have ingested human blood and can potentially aid in the identification of a victim and/or suspect. In this research, human blood from one male donor was fed to 35 North American medicinal leeches. These leeches were then euthanized at various periods (0, 1, 2, 4-, 6-, 12-, and 24-hours post-feed). Blood from their midguts (crop) was amplified using three methods. First, the tip of each Copan microFLOQ® Direct Swab was dipped into the midgut of the individual leeches and amplified directly. Second, Copan microFLOQ® Direct Swabs were utilized to sample the crop, concentrating crop blood followed by direct amplification. Third, 4N6 FLOQSwabs® forensic collection devices collected, extracted, and amplified remaining crop blood. The aim was to determine if blood found in the midgut of leeches can be used in revealing human identity. This research can aid in unique forensic cases where annelids might be present at a crime scene. Autosomal STR profiles were generated using PowerPlex Fusion 6 C System and GlobalFiler Express. Y-STR profiles were obtained with PowerPlex® Y23 System and Yfiler® Plus amplification kits. Complete and partial, concordant, and consistent, autosomal, and Y-STR profiles were observed between 420 autosomal and 420 Y-STR profiles. All three methods can be used to generate DNA profiles from blood ingested by leeches when collected within a 24-hour period. The results indicate that blood ingested by annelids can serve as a valuable source of evidence in unique crime scene cases.