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From this, they were able to reconstruct “transmission pedigrees” that, for example, turned two previously separate Vienna / Korneuburg groups into one that belonged together. They also calculated that an average of 1,000 viruses are transmitted in case of infection. In the journal “Science Translational Medicine” they also report that viruses change in the patient.
A team led by Andreas Bergthaler from the Center for Molecular Medicine Research (CeMM) used the spread data (epidemiological data) from the official contact person tracking and sequenced the SARS-CoV-2 coronaviruses in the affected people. In this way, they were able to create family trees of viruses and thus partially improve the contact tracing data.
Merged cluster
In a group in Vienna and Korneuburg, it was already well known who had infected whom and that the virus had spread through a chain of infection through a spinning class in a gym (where those affected pedal together on bicycles static in a room). in addition to a cooking class, choirs, a funeral and children’s birthday parties, Bergthaler said. Additionally, there were repeat infections within intermediate family households. However, the researchers were able to add a second group from Korneuburg / Vienna to this group.
“Because of the mutations in the virus, we saw that the samples must belong to only one group because they were almost identical,” Bergthaler said. The researchers then called 17 of the affected people again and finally confirmed with this contact tracing that they were a related group and not two separate groups from Vienna / Korneuburg.
Mutation “in real time”
“We were also able to observe how a virus mutation suddenly appeared in the nine-generation chain of infection, which was then passed on to other infected people,” he reports. In this way, it was possible to track “in real time”, so to speak, how a mutation develops and is transmitted in the human population. However, it is not clear if it has any effect. “So far, we hardly have mutations in the world, we know what they really do,” said the researcher. Only a special change (D614G mutation) in the protein with which the virus attaches to lung cells (spike protein) would increase infectivity, at least in laboratory tests.
How many viruses are transmitted
The distribution of the different mutants of the virus between carriers (causing infections) and people infected by them (infected) also revealed to researchers how many viruses are transmitted from person to person when infected. If the infected person only carries some variants of the virus of the infection and is still sick, this means that it is already dangerous to come into contact with some viruses. If many variants of the contactor virus are found in the infected person, many viruses are necessary to trigger the disease.
“On average, there are 1,000 virus particles,” Bergthaler said. However, the spread is quite large, that is, with some “infected pairs” a small dose of virus was sufficient, with others it was much higher. “Now we want to see if different protective measures, such as wearing a mask, play a role here,” said the scientist.
The researchers also sequenced viruses from 31 intensive care unit patients every few days for three to four weeks. “We were able to see some mutations come up and then disappear again,” Bergthaler reported. With data from more patients, researchers now want to know if these mutations differ in different treatments. “That could give us clues to the extent to which the virus could adapt to certain treatments and develop resistance,” he said. However, since no truly effective therapies are available yet, the answer would only be of academic importance for now.
