Virologist Claire Crossan (Crossan Claire) from Caledonian University of Glasgow in Scotland has revealed the most likely reason why Spanish researchers found the first traces of the emergence of the coronavirus SARS-CoV-2 to Spain in the spring of 2019. According to the scientist, the truth is that the results of tests conducted by specialists of the University of Barcelona, can be wrong. Read more in the article published in the Conversation.
In the study, which is now criticized by the scientific community, the researchers analyzed frozen samples of wastewater, which contains particles of human faeces collected in the period from January 2018 to December 2019. The virus was present in the samples, dated January 15, 2020, at least 45 days before the first official case of infection with coronavirus in Barcelona. All other samples were negative except one that was collected on March 12, 2019. PCR analysis showed that it was present one of the three genes of SARS-CoV-2 — RDRP are. Based on this result, scientists came to the conclusion that the coronavirus could appear in the world much before the official deadline.
PCR analysis is a technique which is polymerase chain reaction (PCR), when selected and purified genetic material is copied many times (amplificate) with the participation of specific enzymes. In the case of coronavirus carried out PCR with reverse transcription, when RNA of the pathogen is translated first into DNA and then amplificarea in a series of cycles. Soon fragments of the original gene becomes high enough to be detected using specific markers.
Researchers have documented the presence of two key fragments of the gene RDRP are approximately at the 39th cycle of amplification. It should be noted that with increasing number of cycles, the method becomes less reliable due to accumulated errors in copying, therefore PCR is sometimes used for making changes to genes. For testing is usually performed about 40 cycles.
According to Crossan, there are several explanations for the result. First, the virus is really present in the wastewater at a low level. Second, in the laboratory it is sometimes difficult to prevent contamination of the samples, a minor amount of another sample. Finally, the sample can be RNA, which was very similar to the desired gene fragment to give a positive result at the 39th cycle of amplification.
The first option is unlikely, because seriously at odds with the epidemiological data, and the authors provided evidence of a sharp increase in respiratory diseases during the period of selection of positive samples. In addition, in later samples, no traces of the virus, although the presence of the pathogen in the wastewater with a volume of 800 milliliters should speak of its high prevalence in the population. Thus, the findings of scientists at the University of Barcelona that SARS-CoV-2 could be present in Spain long before the first official outbreak of the disease should be treated with caution until further research would be undertaken, concludes Crossan.
Video, photo All from Russia.