It's known that all mammals and most vertebrates (or creatures with backbones) possess retroviruses -- such as HIV that have the ability to incorporate their genetic material into that of their hosts -- in their genomes.

To get a broader picture of how deeply retroviruses have invaded genomes, a team of scientists in Sweden analysed the first sequenced carnivore genome, that of a female dog of the boxer breed.

They found that "endogenous" retroviruses only seem to make up 0.15 per cent of the dog genome, six times less than humans, LiveScience reported.

It's because dogs may have better mechanisms to protect their genomes against retroviruses, or their genomes may house unknown types of retroviruses that current techniques can't yet detect, the researchers said.

Intriguingly, they discovered a novel group of retroviral material in dogs that is highly similar to endogenous retroviruses seen in humans. They belong to a type of virus known as gammaretroviruses, the most frequent type found in mammals to date.

This specific group of retroviruses seems to have invaded the dog genome relatively recently. This suggests that dogs and humans may have passed these germs to each other due to close interactions during our thousands of years of history together -- a phenomenon known as "lateral transmission", the researchers said. However, it remains uncertain how such transmission might have occurred -- perhaps from wet "doggie kisses", for instance, the researchers reported in the journal PLoS ONE.

"We need to stress that we can only say potential for possible lateral transmission between dog and human," said researcher Goran Andersson, a molecular geneticist at the Swedish University of Agricultural Sciences.

To shed light on if, when and how much this happened, "DNA from more dogs will be analyzed," said Andersson.

Such research might not only discover evidence for such lateral transmission, but also could reveal how dogs might be protecting themselves against retroviruses.

Such knowledge might help lead to therapies against retroviruses, including perhaps HIV, Andersson said.