Visualisation and detection of latent DNA deposited by pangolin scales onto plastic packaging materials

We report on the detection and visualisation of latent DNA from pangolin scales deposited onto a plastic packaging material through the use of a nucleic acid staining dye. This latent DNA deposited by pangolin scales was subsequently isolated and analysed using DNA barcoding method. Pangolins are the most illegally traded mammalian species due to the demand for their scales and meat. The demand for their scales were mostly fuelled by its use in traditional medicines. The scales are usually packed into bags and transported globally via sea routes. This is the first report detailing the detection of trace latent DNA from processed wildlife products, on surfaces of bags that they were packaged in. Prior to this report, it was not known if the dried pangolin scales contained transferable quantities of biological material for DNA analyses. To address this, scales were removed from a roadkill Sunda pangolin (Manis javanica), processed by drying and packaged into one of five plastic bags. The presence of pangolin latent DNA was detected on the surface of the plastic bags and visualised using Diamond™ nucleic acid dye. Swabs were then used to recover the stained biological material from various locations in the five bags. The DNA was isolated and quantified using a newly designed quantitative PCR (qPCR) specific to M. javanica to amplify a fragment of the mitochondrial DNA cytochrome b gene. There was a positive correlation between the number of stained particles and DNA quantity, and a greater number of stained particles were found at the bottom of the bag than were found at the top. Conventional PCR targeting part of the cyt b gene amplified a product from all 30 samples taken from the bags and in all cases, sequence data generated matched that of the Sunda pangolin, as expected. All negative controls yielded no results. The method described here is the very first use of a nucleic acid staining dye to detect latent DNA from a mammalian species, other than humans, and highlights the opportunity for further use of Diamond™ nucleic acid dye in wildlife forensic science. It is anticipated that this method will be invaluable in retrieving latent DNA deposited by wildlife products from the environment in which they were contained, to determine the presence of these illegal wildlife products even when previously hidden, inaccessible, or no longer present physically. Further research is required to understand if the use on non-human mammalian wildlife species is feasible.