Advances in the study of DNA transfer, persistence, prevalence, and recovery (TPPR) continue to expand our understanding of how DNA transfers and persists in real world environments. As forensic DNA methods grow increasingly sensitive, the need to evaluate indirect pathways of DNA transfer has become more critical. Companion animals, particularly dogs and cats, live in close physical contact with humans yet are rarely considered within the framework of DNA TPPR. This research explores the potential for human DNA to be deposited on, persist on, and be transferred by companion animals, their owners and visitors to their environments  under conditions reflective of everyday interactions and possible forensic scenarios.

A series of controlled and semi controlled studies examined the prevalence of  human DNA from owners and unknown individuals on various areas of a dog and cat bodies following routine handling and brief or extended contact. Additionally, the studies assessed DNA movement through indirect routes, where contacts are made my multiple individuals in turn. These studies also assessed how long DNA may persist on a dog after contact, with collection occurring immediately, 1 hour and 6 hours post contact. Furthermore, microscopic examination of dog hairs was used to assess the presence of human cellular material.

Across studies, companion animals were found to carry quantifiable human DNA, with certain areas on the body consistently exhibiting higher quantities of both owner and unknown DNA. Short interactions were sufficient to generate detectable transfer, and bidirectional exchange of human cellular material between people and animals was observed. Behavioural patterns, such as the way animals’ are approached and handled in a typical interaction, helped identify areas where transfer is most likely and can inform practical sampling strategies.

Extended interaction and scenario based experiments indicated that indirect transfer involving animals can occur, with human DNA transferring from animals to individuals or objects they subsequently contact. However, tertiary transfer to objects appeared less common and more variable. The presence of human cells on individual animal hairs suggests that even the collection of animal hairs may provide informative profiles.

Overall, these findings demonstrate that companion animals can act as both reservoirs and vectors of human DNA which can provide informative profiles of owners, known handlers and unknown intruders, where contact with an unknown and in some cases a known person is suspected, and this may become a relevant consideration during activity level evaluations.

Authors

• Heidi Monkman (Flinders University, College of Science and Engineering, Australia)
• Roland van Oorschot (Office of the Chief Forensic Scientist, Victoria Police Forensic Services Department, Australia)
• Luke Volgin (Forensic Science South Australia, Australia)
• Mariya Goray (Flinders University, College of Science and Engineering, Australia)