RESEARCHES STILL ON CORONAVIRUS WILDLIFE SOURCE

                The race is on to find out how the deadly Coronavirus jumped from animals to humans, Helen Briggs looks at how scientists are trying to trace the source of the outbreak. Somewhere in China, a bat flits across the sky, leaving a trace of Coronavirus in its droppings, which fall to the forest floor. A wild animal, possibly a pangolin snuffling for insects among the leaves, picks up the infection from excrement, the novel Covid-19 circulates in wildlife, eventually an infected animal is captured and a person somehow catches the disease, then passes it on to workers at a wildlife market.
A global outbreak is born, scientists are attempting to prove the truth of this scenario as they work to find wild animals harboring the Coronavirus. Finding the sequence of events is a bit of a detective story, says Prof Andrew Cunningham of Zoological Society London ZSL, A range of wild animal species could be the host, in particular bats which harbor a large number of different Coronavirus. So how much do we know about the spillover event as it's known in the trade, when scientists cracked the genetic code of the new Covid-19, taken from the body of a patient, bats in China were implicated.
The mammals gather in large colonies, fly long distances and are present on every continent, they rarely get sick themselves but have the opportunity to spread pathogens far and wide. According to Prof Kate Jones of University College London, there is some evidence bats have adapted to the energetic demands of flight and are better at repairing DNA damage, this might enable them to cope with a higher burden of viruses before getting sick but this is just an idea at present. There's no doubt that the behavior of bats allows viruses to thrive. When you consider the very way that they live, then they are going to have a large array of viruses and because they are mammals there's a possibility that some of them can infect humans either directly or through an intermediate host species. Says Prof Jonathan Ball from the University of Nottingham. The second part of the puzzle is the identity of the mystery animal that incubated the virus in its body and possibly ended in the market at Wuhan, one suspect for the smoking gun is the pangolin. The ant devouring scaly mammal, said to be the most widely trafficked mammal in the world is threatened with extinction, the animal's scales are in high demand in Asia for use in traditional Chinese medicine, while pangolin meat is considered a delicacy by some. Coronavirus have been found in pangolins, some claimed to be a close match to the novel human virus. Could the bat virus and pangolin virus have traded genetics before spreading to humans! Experts are cautious about drawing any conclusions, full data on the pangolin study has not been released, making the information impossible to verify.
Prof Cunningham says the provenance and number of pangolins examined for the research is especially important, for example, were there multiple animals sampled directly in the wild in which case the results would be more meaningful, or was a single animal from a captive environment or wet market sampled in which case conclusions about the true host of the virus could not be robustly made. Pangolins and other wild species, including a variety of species of bat are often sold in wet markets, he says, providing opportunities for viruses to move from one species to another. Wet markets, crate ideal conditions for the spillover of pathogens from one species to another including to people. The market in Wuhan, which was closed down after the outbreak had a wild animal section, where live and slaughtered species were on sale, including body parts of camels, koalas and birds. The Guardian reports that an inventory at one shop listed live wolf pups, golden cicadas, scorpions, bamboo rats, squirrels, foxes, civets, hedgehogs, salamanders, turtles and crocodiles. As far as we know, bats and pangolins were not listed but authorities in China will have intelligence on what animals were being sold, says Prof Ball, if the spillover is happened once, you want to know whether or not this sort of thing can happen again, because it's important from a public health standpoint, so you need to know exactly what species of animal it is in and also were the risks that grave rise to that spillover event. Many of the viruses we have become familiar with recent years have crossed over from wild animals, this is the story of Ebola, HIV, Severe Acute Respiratory Syndrome SARS and now Coronavirus, Prof Jones says the rise in infectious disease events from wildlife might be because of our increasing ability to detect them, growing connectivity to each other or more encroachment into wild habitats, thereby changing landscapes and coming into contact with new viruses the human population hasn't seen before. If we understand the risk factors, we can take steps to prevent it happening in the first place without adversely affecting wild animals, says Prof Cunningham. Conservationists are at pain to point out that although bats are thought to carry many viruses, they are also essential for ecosystems to function, Insectivorous bats eat huge volumes on insects such as mosquitoes and agricultural pets, while fruit bats pollinate trees and spread their seeds. It's imperative that these species are not culled through misguided disease control measures.
After SARS caused by very similar Coronavirus to the one now emerging in China and beyond, there was a temporary ban on wild animal market, but the market quickly sprang again across China, Vietnam and other parts of South East Asia. China has again suspended the buying and selling of wild animal products, which are commonly used for food, fur and in traditional medicines. Reports suggest this may be made permanent, while we may never know exactly how or where the disease responsible for many deaths made the leap into humans, Prof Diana Bell of the University of East Anglia says we can prevent another perfect storm, we are bringing together animals from different countries, different habitats, different lifestyles in terms of aquatic animals, arboreal animals and so on, mixing them together and it's a kind of melting pot and we've got to stop doing it.
Researchers at the South China Agricultural University in Guangzhou suggested the same thing about pangolins as the animal source at a press conference on February 7. They had found a Coronavirus in smuggled pangolins that was a 99% genetic match to the virus circulating in people, but the result didn't actually refer to the entire genome, in fact it related to a specific site known as the receptor binding domain RBD, say the study's authors as they report, the result of an embarrassing miscommunication between the bioinformatics group and the lab group of the study, explains parasitologiste Xiao Lihua, a whole genome comparison found that the pangolin and human virus share 90.3% of their DNA. The RBD is a crucial part of Coronavirus, which allows them to latch on to and enter a cell, even a 99% similarity between the RBDs of the two viruses is not necessarily enough to link them, says Linfa Wang, a virologist at Duke National University of Singapore Medical School who was part of the team that found the origin of the SARS Virus. Three similar comparison studies found that Coronavirus in frozen cell samples from illegally trafficked pangolins shared between 85.5% and 92.4% of their DNA with the virus found in patients, Two other papers published from groups in China, also studied Coronavirus from smuggled pangolins, the viruses were 90.23% similar, respectively to the virus that causes Covid-19.
The genetic similarity should be higher than reported in these studies before the host can identified, says Arinjay Banerjee, who studies Coronavirus at McMaster University in Hamilton, Canada. He notes that the SARS virus shared 99.8% of its genome with a civet Coronavirus, which is why wivets were considered the source, if pangolins are the origin of the current outbreak. So far, the closest match to the human Coronavirus has been found in a bat in China's Yunnan province, a study published on February 3 found that the bat Coronavirus shared 96% of its genetic material with the virus that causes Covid-19, bats could have passed the virus to humans but there are key differences between the RBD sites in the two viruses. This suggests that this specific bat Coronavirus did not directly infect people, but could have been transmitted it to people through an intermediate host. The papers raise more questions than they answer, says Jiang Zhigang, an  ecologist at the Chinese Academy of Sciences Institute of Zoology in Beijing, if pangolins are the source of the virus and they came from another country, why haven't there been reports of people being infected in that location?
Sarah Platto, who studies animal behavior at Jianghan University in Wuhan, worries that all the speculation about pangolins being the source could drive people to kill them, civets were killed en masse after the SARS outbreak. The problem is not the animals, it's that we get in contact with them.