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Man's best friend could be responsible for the deadliest pandemic in decades, scientists have claimed in a bombshell study.

New research from Canada suggests that stray dogs in China transmitted coronavirus to humans after eating discarded bat meat.

Experts have been scrambling to find the "intermediary animal" which passed the Covid-19 disease to humans since the start of the outbreak in December.

Now a team from the University of Ottawa claim stray dogs may have caused the virus to leap to humans.

Almost two million patients have now been infected worldwide, while more than 125,000 have died.

Lead author of the study Professor Xuhua Xia suggests that "the coronavirus first spread from bats to stray dogs eating bat meat".

(Image: Getty Images/EyeEm)

He added that the specific origins of Covid-19 are "of vital interest in the current world health crisis".

Professor Xia, a biologist at the University of Ottawa, went on: "Our observations have allowed the formation of a new hypothesis for the origin and initial transmission.

"The ancestor of Covid-19 and its nearest relative, a bat coronavirus, infected the intestine of dogs, most likely resulting in a rapid evolution of the virus and its jump into humans.

"This suggests the importance of monitoring SARS-like coronaviruses in feral dogs in the fight against Covid-19."

Pangolins – a scaly mammal that looks like an anteater – were previously believed to have provided the key "staging post".

But a study of Covid-19 mutations has ruled both them out as the "human reservoir" – as well as bats.

The finding published in Molecular Biology and Evolution is based on chemical signatures across a variety of species including bats, pangolins, dogs, snakes and humans.

(Image: Getty Images/iStockphoto)

When viruses invade a host, "battle scars" are left from fighting off and evading the immune system through changes and adaptations within their genomes.

Covid-19 began in bats according to the hypotheses of many scientists. They have been around for millions of years and have picked up a lot of viruses that have killed people — including Ebola, rabies and Sars.

But humans and bats don't interact — so another animal is usually involved. Finding out what it is is crucial to eradicating Covid-19.

(Image: Getty Images)

So Professor Xia and colleagues looked at a key antiviral protein, called ZAP, which can stop a virus in its tracks by preventing its multiplication and degrading its genome.

The viral target is a pair of chemical letters, called CpG dinucleotides, within bits of DBNA called RNA.

Professor Xia said: "Think of a decreased amount of CpG in a viral pathogen as an increased threat to public health, while an increased amount of CpG decreases the threat of such viral pathogens.

"A virus with an increased amount of CpG would be better targeted by the host immune system, and result in reduced virulence, which would be akin to natural vaccines."

(Image: AFP via Getty Images)

He found only genomes from dog coronaviruses have CpG values similar to those observed in Covid-19.

They also affect their digestive system and enter via a protein called ACE2 which is also made in humans' intestines.

Professor Xia said: "This is consistent with the interpretation the low CpG in Covid-19 was acquired by the ancestor evolving in mammalian digestive systems.

(Image: Getty Images)

Dogs often lick their anal and genital regions, not only during mating but also in other circumstances.

Such behaviour would transmit the virus from the digestive to the respiratory system. It also fits the picture of a pathogen that causes gastrointestinal, respiratory and lung disease.

Professor Xia added: "In this context, it is significant the bat coronavirus (BatCoV RaTG13) was isolated from a faecal swab."

The disease started in December at a seafood market in Wuhan, China, where wild animals including marmots, birds, rabbits, bats and snakes, are traded illegally.