Researchers believe canines ate infected bat meat, causing the virus to develop into a more “stealthy and dangerous” disease to humans.
OTTAWA, Ontario — Scientists around the world are still scrambling to find the source and a vaccine for the coronavirus pandemic. The most common theory is the illness was spread by animals to humans; possibly by an infected bat. A new study now points to the virus jumping to dogs first, where it evolved and became even deadlier to humans.
University of Ottawa biology professor Xuhua Xia says SARS-CoV-2, the virus which causes COVID-19, likely originated in stray dogs. The biologist adds that coronavirus was likely transmitted to canines that ate infected bat meat, and then developed into a more dangerous disease in the dogs’ intestines.
“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,” Prof. Xia said in a statement.
How Coronavirus Evolved To Be “Stealthy And Dangerous”
According to the professor, a virus has certain “signposts” in their genes that are targeted by the human immune system. Those signs are called CpG dinucleotides and the more of them a virus has, the easier it is for our immune systems to find and destroy them.
Xia says humans and other mammals have antiviral proteins, called ZAP, which are in charge of finding the virus signposts and stopping them from multiplying in the body. Unfortunately, the fewer CpG a virus has, the harder it is to get rid of.
“Think of a decreased amount of CpG in a viral pathogen as an increased threat to public health,” Xia explained.
SARS-CoV-2 has one of the lowest amounts of CpG among the different versions of coronavirus. When comparing those results to virus information in dogs, the study found that only coronavirus genes in a dog’s digestive system have CpG amounts that low. Xia says the illness likely evolved in tissue where there is high levels of ZAP and learned to dodge them.
“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 warns.
COVID-19 May Start In The Digestive System
Although the most severe cases of COVID-19 have given patients pneumonia and forced many to use ventilators, the study points to COVID-19 actually targeting the human digestive system first. The study says coronavirus enters the cells through the ACE2 gene. That gene is made in the digestive system. Xia says nearly half of COVID-19 patients reported stomach discomfort as their biggest issue.
“These observations are consistent with the hypothesis that SARS-CoV-2 has evolved in mammalian intestine or tissues associated with intestine,” Xia added.
Officials say the pandemic has now affected over two million people worldwide.
The study is published in the online edition of the journal Molecular Biology and Evolution.