SARS-CoV-2 multiplied in the upper respiratory tract

Scientists have discovered that the SARS-CoV-2 is present and multiplies not only in the lungs but also in the upper respiratory tract and in the human gut. Testing for viral RNA in a smear from a throat efficiently in the first days of the disease when symptoms are mild. Based on the presence of whole virus particles in the various tests, the authors determined that to discharge patients from the hospital within ten days after the onset of symptoms, even if the sample in viral RNA they are still positive. Monitoring the dynamics of RNA SARS-CoV-2 in the sputum can help to predict worsening of symptoms of pulmonary infection. Article published in the journal Nature.

The new coronavirus SARS-CoV-2 are genetically similar to SARS-CoV that caused the outbreak of severe acute respiratory syndrome (SARS) in 2003. The main finding of these viruses in the body is a lightweight, so they are diagnosed based on the analysis of sputum. SARS-CoV-2 was detected in samples from the throat, but until now it was unknown whether the virus to multiply in the upper respiratory tract and how the manifestations of SARS are similar to COVID-19.

A group of scientists from Germany and the UK under the leadership of Roman Velvele (Roman Wölfel) from the Institute of Microbiology of the Bundeswehr investigated SARS-CoV-2 in the analyses of the nine volunteers who were treated at the hospital in Munich. All the patients were tested for SARS-CoV-2 due to the fact that they are in contact with carriers of the virus, not the appearance of specific signs of illness, so the study results cannot be linked to specific symptoms. The tests all participants were examined for the presence of pathogens of a number of other respiratory viral infections.

Viral RNA was determined by polymerase chain reaction (PCR) real-time strokes of Roto – and nasopharynx. Also traces of the virus searched for in samples of sputum, blood, urine and feces. To assess whether the virus can spread to others, in samples of isolated whole virus particles.

The researchers then determined whether to occur replication of the virus in the upper respiratory tract. To do this, in samples using real-time PCR were looking for subgenogroup messenger RNA. Such RNA is only active in an infected cell and are not part of the Mature virus particle, therefore, are present only in cells in which the virus actively multiplies. The researchers also conducted whole genome sequencing of RNA of SARS-CoV-2 in smears from throat and sputum samples.

Scientists have determined when the immune system of patients started producing antibodies to SARS-CoV-2: using immunofluorescence analysis, found antibodies to the protein shell of the virus and then tested the ability of antibodies to neutralize the virus.

The day of initial testing for SARS-CoV-2 in all patients the symptoms of the infection were weak or pronormality. The amount of viral RNA in the first days of the disease was high in the smear from the throat, the sputum and feces. Faster just the number of RNA decreased in smears from the throat, but in these samples traces of the virus were detected and in the second week of illness, when symptoms have already passed. The latest positive sample was taken on day 28 after the onset of illness. The amount of viral RNA in sputum and feces decreased more smoothly, and exceeded the detection threshold more than three weeks. In the blood and urine tests have not found the RNA of SARS-CoV-2.

The researchers were able to isolate the virus from the parts of the swabs and sputum specimens during the first seven days of illness. After that, despite the large number of RNA SARS-CoV-2, isolate the virus failed. Based on these data, the authors created a model that allows to predict the number of viral particles and, consequently, the infectiousness of the patient, depending on the day with the onset of the disease and the amount of viral RNA in the analyses. This model will help to determine when a person can be discharged from hospital and to lift the quarantine. The authors believe that patients are safe within ten days after the onset of the disease, the expectoration is less than 100 thousand copies of viral RNA per milliliter.

Subhanahu RNA detected in the samples only in the first five days of illness, so the virus replicates in this period of time. One of the patients in the genome of the virus that was isolated from smear from the throat, found the mutation, which was not in the RNA from sputum is further evidence that SARS-CoV-2 propagated independently in the throat and lungs.

In all patients the disease proceeded in the form of light. Only two people had symptoms of pulmonary infection, they coincided with the peak amount of viral RNA in the sputum, which is found on the tenth day only in these patients. It is necessary to conduct studies in patients with severe course of the disease, to establish whether it is possible to predict the development of symptoms to increase the amount of viral RNA in the lungs.

Half of the participants in the immune system has developed antibodies to SARS-CoV-2 on the seventh day of the disease, and the rest by the end of the second week. This is similar to the data on severe acute respiratory syndrome (SARS).

A swab from the throat will allow you to effectively diagnose the infection SARS-CoV-2 already with the appearance of early mild symptoms. It features a new virus from the SARS-CoV to detect it smears the upper airway was possible not always, and peak concentrations of viral RNA occurred later. A new virus is probably transmitted more actively in the early stages of the disease when the symptoms are more like a upper respiratory infection.

How to create a vaccine against the new coronavirus and how soon it will start to apply everywhere you can read in our text, “to Catch up and warn”.

Alice Bahareva

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