The Covid-19 epidemic in Italy bears the signature of the 'European' B1 strain coronavirus, the one that arrived in Germany from Shanghai, while the original Wuhan strain seems to have a completely marginal role: this is indicated by the analysis of 59 new Italian SarsCoV2 genomes, made available to the international scientific community by researchers from the State University of Milan. The study, shared on the medRxiv website, significantly increases the number of sequences obtained in Italy from native infections.
"Our 59 samples come from patients from Lombardy, Veneto, Marche and Tuscany: of these, 58 belong to the European B1 strain, arrived from Germany: according to our phylogenetic analysis, it was already present in Italy at the beginning of February", explains Gianguglielmo Zehender, associate professor of hygiene at the State University. "Surprisingly, only one patient from the Veneto region, who did not report recent trips or contacts with people from China, was infected with the ancestral B virus of direct import from Wuhan."
This unique virus of Chinese origin represents a real puzzle for researchers. First of all, it is necessary to understand why it does not seem to have spread. "We still don't know if the Chinese strain is less contagious than the European virus, or if its run by us was hampered by the genetic characteristics of the human host," says Zehender. Another surprising element is that the B strain found in Veneto has a particular mutation of the Spike protein (the 614G mutation) which usually characterizes the European strain. "Spike's same mutation has also been found in some B-strain viruses isolated in Thailand, Turkey, Romania, Holland and Israel," recalls Zehender. "This tells us that it is a mutation of great interest: some speculate that it may have increased the contagiousness of the virus, but the debate is still open".
New answers may come from the expansion of the study, which so far has focused on the viral genomes isolated from the first days of the outbreak until the second half of April. The data made it possible to draw a picture of the evolution of the virus in Italy, which confirms and completes the results of the epidemiological analyzes. The reconstruction of the SarsCoV2 family tree shows that the virus was already present in Italy in early February, even though exponential growth occurred between the end of February and the middle of March, when the contagion index Rt it went from an initial value close to 1 to more than 2.3 and the doubling time of the epidemic decreased from 5 to 3 days. Only in the second half of March, the analysis shows a slight decrease in the values of Rt, probably in relation to the adoption of measures of social distancing.