Paws for a moment: Investigation of bi-directional transfer of human DNA during a short human–dog interaction and subsequent indirect transfers

DNA transfer events have been well researched in the context of commonly found items at crime scenes. However, whilst animals are a common feature of most households, transfer events involving companion animals have been understudied. Recent research has shown that dogs and cats are a reservoir of human DNA that can transfer to a hand or sterile object after a short contact. It is now of interest to explore how and where this DNA on dogs can transfer during normal human-animal interactions. In order to assess this aspect of DNA transfer, 5 dogs were paired with 5 visitors that were unknown to one another. The dogs were contacted by the visitor for 5 min and the first 5 items contacted immediately were sampled. Additionally, the first 3 items the visitor touched on return home, a number of pre-determined items they were instructed to touch, and both hands, were also targeted. Finally, the dog and the items that the animal contacted in an hour post contact were also analysed. 

The results showed that DNA of the visitor or visitor's housemate persisted on the dog up to an hour later in 50 % of the samples but was not detected on any of the items an animal contacted. Dog owner's DNA transferred from the dog to the visitor and visitor related items and surfaces, including the car and the house, in 31 % of the samples. These results provide a valuable insight for forensic investigators on the potential origins of DNA found at a crime scene and also add to the body of research indicating that companion animals may be used as evidence to identify who had been in contact with a dog.