How viruses give us clues about their origins

Now it's hard to believe that it's been almost two years since a pandemic was declared for a new virus that could cause serious respiratory disease. Although the virus has changed and caused several waves of infections since early 2020, the debate around where the original virus came from continues to rage on…

Julia - While the initial focus of these investigations honed in on trying to find the animal intermediates from which the virus jumped through to get to humans. More recently, talks of a lab leak have started to surface. So, which theory is right? Well, we have to start back at the beginning

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Julia - Throughout history, we have faced constant threat from disease outbreaks. Tiny pathogens, invisible to the naked eye, can hijack our systems, use our cells as breeding grounds to increase their numbers, and leave devastation in their wake.

Chris - Each one of these outbreaks from a global pandemic to a few cases in a community, leaves a trail though, a clue as to where it's come from. And that is its genetic material. And for the SARS-CoV-2 virus, which causes COVID 19, this code has been at the centre of trying to crack how and where this virus originated.

David - SARS-Cov-2 is a kind of virus known as an RNA virus

Julia - That is David Matthews, a professor of virology at the university of Bristol, who specialises in the study of coronaviruses.

David - We were working on coronaviruses before the pandemic started. So we immediately made requests to see if we get a hold of SARS-Cov-2 and start to chip in our expertise.

Chris - Like a recipe book, genetic material encodes the instructions for life. From humans, to dogs, to mice, plants, bacteria, and viruses. SARS-Cov-2 is generated from a 30,000 letter long set of instructions that are written using a form of genetic material that's a chemical relative of DNA that's called RNA.

Julia - And just as the human genome project has helped to reveal how our cells work, the coronavirus RNA code can tell us about the properties of SARS-Cov-2. But reading the viral genetic code is not as simple as opening that recipe book at a certain page and scanning through. It requires specialist equipment and experts like David to translate its meaning.

Chris - As well as using genetic material as a blueprint to predict how a virus might act, it can also be used to trace where it came from. Like humans, a virus has a family tree, a line from which it was descended. And if you look at your parents or siblings or cousins or grandparents, your genetic code will be more similar to those members of your family than it would be to say a stranger in the street.

Julia - Although we are all human and our genetic instructions contain the same recipes, small spelling mistakes - a changed letter here and there - generates different outcomes when these instructions are followed.

Chris - Those spelling mistakes or mutations are more similar between family members than strangers. Meaning we can trace our lineage by comparing our genetics and viruses are just the same.

David - What happened at the beginning of course is, they extracted the RNA from the early patients and sequenced it. And what you do then is you compare the sequence of the genome that you've got with all the other genomes of all other known viruses.

Chris - David Matthews. And that is how you track down the closest relatives of a new virus to find out where it may have come from and how it emerged. Aris Katzourakis from the University of Oxford works on how this trail of genetic breadcrumbs can be used to lead us back up the evolutionary tree to find the ancestors and therefore, the sources of diseases like COVID19

Aris - Evolution leaves imprints that can be deciphered when we read the genome of a virus. By comparing sequence data from different species, we can try and work out where different viruses may have come from, what kind of species they may have crossed from. Let's say you see a virus in a human, and it's incredibly similar in terms of sequence data to a virus in a mouse, you may conclude that there has been some source of transmission between those two species in recent history,

Julia - The more similar a virus' code the more closely related they are. And if we find the parent, we can crack the mystery of where this virus SARS-Cov-2, which caused one of the most significant pandemics in our history, originated.