The new coronavirus SARS-CoV-2 may have been circulating in Europe longer than previously thought. The latest research shows that the virus was first circulating in Italy in December 2019. Even more surprising is that researchers at the University of Barcelona found traces of the virus when testing untreated wastewater samples dated March 12, 2019.
The research was recently published on the pre-print server medRxiv. Currently, the paper is undergoing rigorous review by external experts in preparation for publication in scientific journals. However, the evidence must be treated with caution before completing the peer review process.
So, how did the experiment take place, what did the scientists discover?
One of the early discoveries about SARS-CoV-2 was found in the stools of infected people. When the virus passes through the intestine (which may cause gastrointestinal symptoms), it loses its outer protein layer, but the genetic material called RNA survives and “sheds”
For now, as far as the current evidence is concerned, it is no longer contagious.
However, the fact that these fragments of coronavirus RNA can be found in untreated wastewater (called “influent”) is useful for tracking disease outbreaks. Indeed, they can predict where the outbreak will be a week to ten days before the official data appear-the reason is that people are infected with coronavirus before the symptoms appear.
Then, these “symptomatic” people must be sick enough to be examined, get results, and be admitted as a formal “case”, so it takes about a week.
As a result, many countries, including Spain, are monitoring the presence of coronavirus traces in wastewater. In this particular study, wastewater epidemiologists examined frozen samples of incoming water between January 2018 and December 2019 to understand when the virus first appeared in the city.
They discovered evidence of the virus on January 15, 2020, 41 days before the first official case was announced on February 25, 2020. All samples before this date are negative, but the samples on March 12, 2019 are positive. Results Coronavirus PCR was tested. PCR is a standard test method to detect whether someone is currently suffering from a disease.
PCR involves removing all unnecessary material from a sample that is considered latent by saliva, mucus, frozen wastewater, or any other virus, and then converting RNA (a single strand of genetic material) into DNA (a well-known double-stranded helix).
The DNA is then “amplified” in successive cycles until the key bits of the genetic material known to exist only in the specific virus are sufficient enough to be detected with fluorescent probes.
Not too specific
In coronavirus testing, scientists usually screen multiple genes. In this case, the researchers tested three. They obtained a positive result in one of the three tested genes (RdRp gene) in March 2019. They screened both regions of the gene, and they were only detected around the 39th cycle of amplification. (As the number of amplifications increases, the “specificity” of the PCR test decreases. Scientists usually use 40 to 45 rounds of amplification.)
There are several explanations for this positive result. One is that the content of SARS-CoV-2 is very low. The other is that the test reaction in the laboratory was accidentally contaminated by SARS-CoV-2. Sometimes this happens in the laboratory because it is necessary to process positive samples on a regular basis, so it is difficult to prevent a very small number of positive samples from contaminating other samples.
Another explanation is that there is other RNA or DNA in the sample that is sufficiently similar to the test target site that it is sufficient to produce a positive result in the 39th amplification cycle.
Further testing is required to conclude that this sample contains SARS-CoV-2, and that this number of findings needs to be separately replicated by independent laboratories.
The strange thing about this discovery is that it is different from the epidemiological data about the virus. The author did not cite reports of a surge in the number of respiratory disease cases in the local population after the sampling date.
Similarly, we know that SARS-CoV-2 has a very high transmission capacity at least in its current form. If this result is a truly positive result, it indicates that the virus has a high rate of presence in the population and can be detected in 800 ml of sewage samples, but in the absence of a control, the presence rate of this virus is nine Undetectable within a month. Measures are in place.
Therefore, it is best not to draw clear conclusions before conducting further research.
Claire Crossan is a researcher in virology at the University of Caledonia in Glasgow.
This article was republished from The Conversation under a Creative Commons license. Read the original article.