Evidence of Stray Dogs as Possible Origin of COVID-19 Pandemic

Stray Dog Dirty Street

Ever since the outbreak of COVID-19 (the disease caused by the SARS-CoV-2 coronavirus), scientists have been scrambling to identify the species of origin to understand how the new coronavirus first leapt from its animal hosts to humans, causing the current pandemic infecting more than a million people worldwide.

Scientists have been looking for an intermediate animal host between bats, which are known to harbor many coronaviruses, and the first introduction of SARS-CoV-2 into humans.

Many animals, beginning with snakes and most recently, pangolins, have all been put forth as the likely intermediate, but the viruses isolated from them are too divergent from SARS-CoV-2, suggesting a common ancestor too far back in time — living in the 1960s[1].

Now, University of Ottawa biology professor Xuhua Xia, tracing coronavirus signatures across different species, has proposed that stray dogs — specifically dog intestines — may have been the origin of the current SARS-CoV-2 pandemic.

“Our observations have allowed the formation of a new hypothesis for the origin and initial transmission of SARS-CoV-2,” said Xia. “The ancestor of SARS-CoV-2 and its nearest relative, a bat coronavirus, infected the intestine of canids, most likely resulting in a rapid evolution of the virus in canids and its jump into humans. This suggests the importance of monitoring SARS-like coronaviruses in feral dogs in the fight against SARS-CoV-2.”

The findings appear in the advanced access online edition of the journal Molecular Biology and Evolution.

Xia has long-studied the molecular signatures of viruses in different hosts. When viruses invade a host, their genomes often bear the battle scars from fighting off and evading the host’s immune system through changes and adaptations found within their genomes.

Humans and mammals have a key antiviral sentinel protein, called ZAP, which can stop a virus in its tracks by preventing its multiplication in the host and degrading its genome. The viral target is a pair of chemical letters, called CpG dinucleotides, within its RNA genome. CpG dinucleotides act as a signpost that a person’s immune system uses to seek and destroy a virus. ZAP patrols human lungs, and is made in large amounts in the bone marrow and lymph nodes, where the immune system first primes its attack.

But it’s been shown that viruses can punch back. Single-stranded coronaviruses, like SARS-CoV, can avoid ZAP by reducing these CpG signposts, thus rendering ZAP powerless. A similar examination of HIV, another RNA virus, shows that it has also exploited this evolutionary trick to lose CpG in response to human antiviral defenses. One implication of this is that the remaining CpG dinucleotides on the viral genome are likely functionally important for the virus and could serve as target of modification to attenuate virulence in vaccine development.

“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,” said Xia. “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.”

To perform the study, Xia examined all 1252 full-length betacoronavirus genomes deposited into GenBank to date. Xia found that SARS-CoV-2 and its most closely related known relative, a bat coronavirus (BatCoV RaTG13), have the lowest amount of CpG among its close coronavirus relatives.

“The most striking pattern is an isolated but dramatic downward shift in viral genomic CpG in the lineage leading to BatCoV RaTG13 which was reported to be sampled from a bat (Rhinolophus affinis) in Yunnan Province in 2013 but only sequenced by Wuhan Institute of Virology after the outbreak of SARS-CoV-2 infection in late 2019,” said Xia. “This bat CoV genome is the closest phylogenetic relative of SARS-CoV-2, sharing 96% sequence similarity.”

“In this context, it is unfortunate that BatCoV RaTG13 was not sequenced in 2013, otherwise the downshifting in CpG might have served as a warning due to two highly significant implications,” said Xia. “First, the virus likely evolved in a tissue with high ZAP expression which favors viral genomes with a low CpG. Second and more importantly, survival of the virus indicates that it has successfully evaded ZAP-mediated antiviral defense. In other words, the virus has become stealthy and dangerous to humans.”

Xia applied his CpG tool to reexamining the camel origin of MERS, and found those viruses infecting camel digestive system also had lower genomic CpG than those infecting camel respiratory system.

When he examined the data in dogs, he found that only genomes from canine coronaviruses (CCoVs), which had caused a highly contagious intestinal disease worldwide in dogs, have genomic CpG values similar to those observed in SARS-CoV-2 and BatCoV RaTG13. Second, canids, like camels, also have coronaviruses infecting their digestive system with CpG lower than those infecting their respiratory system (canine respiratory coronavirus or CRCoV belonging to BetaCoV).

In addition, the known cellular receptor for SARS-CoV-2 entry into the cell is ACE2 (angiotensin I converting enzyme 2). ACE2 is made in the human digestive system, at the highest levels in the small intestine and duodenum, with relatively low expression in the lung. This suggests that mammalian digestive systems are likely to be a key target infected by coronaviruses.

“This is consistent with the interpretation that the low CpG in SARS-CoV-2 was acquired by the ancestor of SARS-CoV-2 evolving in mammalian digestive systems and interpretation is further corroborated by a recent report that a high proportion of COVID-19 patients also suffer from digestive discomfort,” said Xia. “In fact, 48.5% presented with digestive symptoms as their chief complaint.”

Humans are the only other host species Xia observed to produce coronavirus genomes with low genomic CpG values. In a comprehensive study of the first 12 COVID-19 patients in the U.S., one patient reported diarrhea as the initial symptom before developing fever and cough, and stool samples from 7 out of 10 patients tested positive for SARS-CoV-2, including 3 patients with diarrhea.

Canids are often observed to lick their anal and genital regions, not only during mating but also in other circumstances. Such behavior would facilitate viral transmission from the digestive system to the respiratory system and the interchange between a gastrointestinal pathogen and a respiratory tract and lung pathogen.

“In this context, it is significant that the bat coronavirus (BatCoV RaTG13), as documented in its genomic sequence in GenBank (MN996532), was isolated from a fecal swab. These observations are consistent with the hypothesis that SARS-CoV-2 has evolved in mammalian intestine or tissues associated with intestine.”

Another finding of Xia’s study involves viruses recently isolated from pangolins. Nine SARS-CoV-2-like genomes have recently been isolated and sequenced from pangolin and deposited in GISAID database (gisaid.org). “The one with the highest sequence coverage (GISAID ID: EPI_ISL_410721) has an ICpG value of 0.3929, close to the extreme low end of the CpG values observed among available SARS-CoV-2 genomes. Thus, SARS-CoV-2, BatCoV RaTG13 and those from pangolin may either have a common ancestor with a low CpG or have convergently evolved low CpG values.”

Based on his results, Xia presents a scenario in which the coronavirus first spread from bats to stray dogs eating bat meat. Next, the presumably strong selection against CpG in the viral RNA genome in canid intestines resulted in rapid evolution of the virus leading to reduced genomic CpG. Finally, the reduced viral genomic CpG allowed the virus to evade human ZAP-mediated immune response and became a severe human pathogen.

“While the specific origins of SARS-CoV-2 are of vital interest in the current world health crisis, this study more broadly suggests that important evidence of viral evolution can be revealed by consideration of the interaction of host defenses with viral genomes, including selective pressure exerted by host tissues on viral genome composition,” said Xia.

Reference: “Extreme genomic CpG deficiency in SARS-CoV-2 and evasion of host antiviral defense” by Xuhua Xia, 14 April 2020, Molecular Biology and Evolution.
DOI: 10.1093/molbev/msaa094


[1] Here is Dr. Xia’s explanation on why SARS-CoV-2 couldn’t have jumped directly from bats or pangolins into humans.

If we contrast early SARS-CoV-2 collected from December 24, 2019 to January 5, and late ones collected in March 1-13, 2020, with an average of 66.5844 days between the early and late groups, and use synonymous substitution rate as an approximation to substitution rate, then the substitution rate is 0.0278 substitutions per genome per day. The average distance between bat CoV RaTG13 and SARS-CoV-2 is 0.0365, or 1073.8158 substitutions per genome (for aligned length of 29409 sites). The time to the common ancestor of SARS-CoV-2 and bat’s RaTG13 is 19296.2808 days (= 1073.8158/2/0.0278) or about 53 years. So their common ancestor lived around 1966. The same method would date the common ancestor of SARS-CoV-2 and pangolin/Guangdong/1 back to around 1882.

19 Comments on "Evidence of Stray Dogs as Possible Origin of COVID-19 Pandemic"

  1. With all the discussion about where the virus came from there needs to be more done about what to do since the coronavius is here. Here is some thought for us all to consider.
    The advise I have to give is that is is easy to help stop the spread of Coronavirus. I read yesterday on the internet that some scientist somewhere took some copper and shot laser beams at it to see what would happen. The scientist discovered that after he treated the copper with the laser beam that the copper had ridges on it that enabled the copper to catch the Coronavirus and shread the virus apart thus killing the virus! The trick to stopping the spread of the Coronavirus is to make just about everything thing we touch with laser treated copper. I mean laser treated copper doorknobs, door handles, door plates to push, railings, banisters, seats, plumbing handles, elevator panels and buttons, table tops, bar tops, door mats and everything else that we touch or walk on. Big and long laser treated copper mats going into stores and hospitals and all other businesses would surely slow the transfer of this Coronavirus as well as many other viruses and germs. Having hand wash sinks at the font area of every business would also help stop the spread of many different viruses and germs. We need to also make face mask made of laser treated copper and other material to stop the virus from getting into our bodies. In some way we need to make gloves of this laser treated copper. If we can we should try giving laser treated copper supplements pills or capsules to those with the Coronavirus or other flu or virus infection. WE should try giving laser coppered spray in ventilators and inhalers that those that have asthma use. Try even laser coppered blood transfusions or blood cleaning. Run someone’s blood through a machine that has laser treated copper filters that filter out the virus in the blood. Speaking of filters we have to have all of the buildings air filters to be changed to a new kind of filter that will have laser treated copper in it to trap viruses and germs. Also face mask will be made with laser treated copper.
    So that is how we are going to stop this Coronavirus as well as many other germs and viruses, We are going to end up with a healthier world after we do this because this will also stop the spread of the flu and colds. Doing this will insure we have a better chance of stopping this spread of the Coronavirus. Are you with me America! Let’s all get started and use laser treated copper on most everything we touch!

  2. And there is a common human habit of letting dogs ‘kiss’ the faces of those who take them in & look after them….it makes me shudder every time I see that, and altho I do adore some dogs just as any humans can, I NEVER let a dog lick my face – so stupid – we all know what they were licking just before your face !!! So if this new research does anything maybe it will teach humans the stupidity of their habits !

  3. seriously a Chinese scientist wanting to blame dogs for this, how original. try blaming yourselves

    • patsy beeler | May 5, 2020 at 12:51 am | Reply

      we dont eat dogs like china does also humans have more germs in there mouth than dogs do / mike row on tv did test / humans had more germs than dog even after dog lick his butt a fact look it up or do your own test looking at slides. There are 84 wet markets in new york u.s.a sad fact in this day and age and nothing is being done to get rid of these places.

  4. This may be slightly off the topic of the common origin of SARS-CoV-2 and bat’s RaTG13; but addresses the comment of Rod McCune, and espouses a method to kill the SARS-CoV-2 virus. I believe that Convalescent Plasma, at this time, is the best way to defeat the virus, and provide enough immunity so that we can stop sequestering and return to some sense of normality in the workplace. The only problem is getting the infrastructure created for the many blood transfusions (for plasma) from recovered patients, and the treatment of the blood to separate the plasma and antibodies for injection into those still fighting COVID-19. China has shown, initially, the curing of 5 patients who were on ventilators (by the the time ventilation is needed the chance of a patient living is 20% or lower)so a cure of people who were on ventilators is saying much as to the effectiveness of using Convalescent Plasma as a cure. The US and Canada are still testing this method, rather than ramping up it’s use to heal the sick, by believing that it works, and starting it’s use with the critically (ventilated) ill (like those in the Chinese experiment)immediately. This “testing before allowing CP’s use” is wasting precious time, as many deaths are occurring while testing is taking place; the results of employing it immediately with the critically ill would show if it works, and would give many who have no other chance of living what they need to fight off the virus. What have we got to lose? A vaccine may be over a year away; and no other method, that doesn’t involve drugs with dangerous side effects, is available. So what are we waiting for: a Magic Bullet? Our economies are tanking, and people are going to start breaking out of social distancing soon, and then watch the numbers of the dead rise! So let’s use a method that will work, and start setting it up now to increase immunity, and help make more recoveries, so we will will have even more antibodies to share, though convalescent plasma! This is not an ad–it is the product of an analytical mind that has searched through every possible method that it could find and calculated the best path to our success in getting this disease under control.

  5. I sent a link to this excellent story to Dr. Tedros at W.H.O. CBC Canada ran a story today about Dr. Tedros discussing a “missing link” between the virus’s bat source and humans! I hope that SciTechDaily gets some credit for posting the complete, and excellent article. The idea is now shared around the internet, but other articles are very lacking in the logistics of how the connections were made. I am very proud of the article’s Ottawa source, and the fact that a fellow Canuck got this information out where it might do some good, perhaps in finding a vaccine!

  6. arpita bhattacharya | May 17, 2020 at 3:16 am | Reply

    Bullshit. Every other day new fake information

  7. The virus came from a bat in the laboratory in Wuhan because the scientist was an idiot! Dogs did not transmit this virus! You people are complete idiots🤪

  8. Name calling does nothing. Perhaps PJ should present his evidence rather than name calling?

  9. Interesting….the 2019/2020 flu vaccine was grown on a dog cell line established back in 1958…The Madin-Darby Canine Kidney cell line(MDCK) was deemed more efficient, and cost effective than the ethod of growing the vaccine on fertilized eggs used for the last 40years. My understanding is that the dog cell line used is contaminated with Hela cells, the world’s first and oldest immortal human cell line(derived from the cervical cancer of Henrietta Lacks)….established in February of 1951. The immortal HeLa cells once established were then shared with scientists around the world. HeLa cells are considered a lab contaminant and have tainted many of the most famous established lab cell lines. I have been asking since the beginning of this pandemic if we are not dealing with a contamination problem disseminated through the new 2019/2020 flu vaccine. The 2020-2021 flu vaccine will be the same. So this paper speaking of “stray dogs” as a possible intermediate host…well one should look at the kidney cell line of a 62 year old dead cocker spaniel contaminated with the immortal cervical cancer cells of a 69 year old dead black woman, and the use of this cell line as a means to grow a flu vaccine used worldwide.

  10. I have had it with this crap. Now you are trying to get people to kill their poor animals or next you will be pushing deadly vaccines on our animals. Covid-19 is a false flag.A year later and I have never been sick and neither has my cat. I have not seen a covid patient anywhere in a year!!! Anyone tries to touch my animal in the name of this plandemic is not going to make it out of my house.Take your fake false positive tests and your depopulation vaccines and shove them in your corrupt… Thousands of censored doctor’s are blowing the whistle on this false flag. This lock down is to crash the economy because greedy elites put the world in debt…Again…So now we need the great reset and us little people have everything stolen from us while the rich get richer. I put my forced isolation to good use. I investigated this lie. It seems you crazy freaks want to replace humans with AI, and synthetics, robot? You trying to live forever because you know what is waiting for you. I found on NASA’s website a plan that is in action now to depopulate us.They have openly waged war on us. Then they go on to name the technology they plan to use to murder most of us. Then Bill Gates website, world economic forum, a step by step plan to depopulate the earth using covid-19 and vaccines amongother thing’s. . I 1st saw this 50 year plan 2 years ago, so I knew this covid false flag was coming. Not to mention these dumb asses kept telling us it was coming. They stand to make trillions off forced deadly vaccines. I just almost died from the flu vaccine last fall so the government will have to murder me another way. The high levels of Mercury broke through the blood brain barrier. Brain shocks and seizures, lost the use of my arm and more.I read under the Obama care, you all can hang us, shoot us, behead us,electrocute us, lethal injection, same as vaccines. This shit is not for prisoners, it’s for the law abiding citizens of America. You pieces of shit are not as smart and savy as you think you are.Some of us still have some brain cells left, even though you try and kill us with medications, vaccines, you poison our food,our water and our air. My spiritual connection is strong despite your evil satanic bull shit. You all are really bad liars. If covid does exist, you guys tampered with it, it’s man made, like everything else you all do to get rich and kill us. A pandemic every damn year. Bio weapons. It’s all from our government and these satanic elites,bankers. The whole government, every single government agency especially the FDA and the CDC, FEMA,CIA,FBI,the WHO, everyone is evil, satanic and corrupt.Nothing any of you say is true.Are any of you ruling over us even human? Because you don’t act like you’re human.Those holograms keep glitching. You all may want to get better programs. If any of you told the truth, your heads would explode. The mainstream media should be executed for their psychological warfare against humanity. Pieces of shit! I tell you what,I am not going to just roll over and let you all kill me and your not getting near my animal with a fucking mask or vaccines. You are trying to turn the sheeple against their animal’s. I’m going to go hug my cat and kiss her silky kitty head. Then I’m going to go hug as many people as I can and I am going to keep acting like a human being. Not a synthetic robot or a clone…You weirdos are the one’s that need to be depopulated.You’re the one’s raping and killing babies, not us. We will probably lose this battle since the military is in on this betrayal too but I’m going to go out fighting, helping people and animal’s and being true to myself, no matter how scared I am. You can have this shit hole of a world. The good soul’s will cross over and be free of it. This place is as close to hell as I ever want to get.Looking forward to the next false flag, another terrorist attack? What’s it going to be? The only thing attacting us is our own lame shitty government. I’m sure my true comment won’t be approved. Truth is not acceptable these day’s. For those who are a part of this that are human,they will all devour you too as soon as you are used up. None of you are safe from each other.

    • Wow,Shelly, I think your tinfoil hat is on a little bit too tight. You might want to put down the meth pipe and stop believing everything you see on YouTube. Nobody is coming after you or your cat. My 4 cats have assured me that they are fully aware of the current pandemic, and they are pretty sure it’s the dogs that are to blame. I asked both of my dogs and they deny everything. But,they look guilty. Won’t make eye contact, just keep licking their butts. I think we’ll be fine as long as we keep our feline overlords happy.

  11. Very interesting! But are there any stray dogs left in China? Aren’t they considered free food with festivals dedicated to eating dogs?

  12. After reading the preface to the article which admittedly states that there is no proof dogs (stray or not) are con a source of covid. I had to ask myself WHY was the article published? Supporting your article with speculation and theory provides NO justification for the space taken for printing and time taken reading it. Removing stray animals by feeding on someone’s fears and anxieties is reckless. More documented evidence linking Covid-19 to laboratory studies than anything else. I feel that if dogs encountered this was through forced injection and their release for the purpose of research. Shame on you!

  13. At the start of the article, it was said that iys a new hypothesis not a full fledged theory. But as a survey was conducted, please make a bigger survey as by the estimates published,home delivery from supermarkets is a bigger threat. Also please look into the fact that whether reverse zoonosis occured or not. Also practicing good hygine habits is a better option and a win-win situation for all humans and the animals we come in contact with or coexist with. God and Science bless all living beings no matter what or who they are. Regards.

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