ESR scientist Dr Wendy Williamson describes how modern molecular polymerase chain reaction (PCR) tools have made it possible to detect viruses in the environment. Previously used methods of detection, such as culture, work well in a medical situation but are unable to detect viruses in the environment. PCR also makes it possible to distinguish between even closely related viruses.
DR WENDY WILLIAMSON
The ability to actually detect viruses has been difficult due to their very small size and because so many of them were not necessarily culturable. The classical methods for detecting the viruses has been culture, and that means you have specific types of cells that are cultured up, that you then put the viruses in, and you use those cells to indicate the presence of viruses because they will infect the cells, and then, with time, they will lyse the cells – that means they will burst them apart as they go through the viral replication – they burst the cells apart, and they infect the next cells beside them. So what you tend to get is a small area of cells that are highly damaged and they die. And that is what we actually see is the consequences of the viruses in those. This can take a lot of work and often quite a few days to do. And while that might work well for a type… medical or relatively pure samples, it breaks down when we start using environmental samples, because, first of all, the numbers again are very low, but also there are other viruses in there and other bacteria in there that can, in fact, contaminate our sample, and we are no longer sure that's what is causing the damage to the cells is only the virus of what we are interested in. So it can indicate that there are infectious viruses in there, but it doesn't necessarily tell us exactly who is doing the infecting. So we are trying to develop new assays now using molecular biology tools – PCR type of tools – to amplify the genetic material of viruses. The other advantage of using the new molecular tools is that many of the viruses that we suspect cause human disease are not necessarily able to be cultured yet, and so if we can't culture it by the old system, we cannot confirm that it’s actually there and causing disease. Hepatitis E is a good example of that because it is not what one would call a culturable virus, so it’s hard to study it and understand its dynamics. But by using molecular tools, we can understand a lot more techniques, can concentrate viruses from faecal samples, and so you can get a fairly pure sample of virus. We design what is called primers and probes for the PCR, and they are often very specific to certain parts of the organism of the virus, and we use those with other probes, which we put a fluorescent tag on, and they will detect, for example, Hepatitis E but not Hepatitis A. So really, it’s been the advent of molecular biology that's enabled us to detect the genetic material of these viruses. It’s meant that we can actually work with them now, produce standards, recognise their impact good and bad within the environment.
Dr. Maria-Lucia Rácz, Institute of Biomedical Sciences, University of São Paulo
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