Prof. Dr. Jürgen K. Rockstroh, Infectious disease specialist & current president of The European AIDS Clinical Society is walking us through the current state of knowledge about SARS-CoV-2 virology.
Hi, my name is Jürgen Rockstroh. I'm an infectious disease doctor from the Department of Medicine University Hospital in Bonn, Germany. I want to talk to you today about some of the ongoing issues and discussion points around the recent COVID-19 epidemic.
Now, coronaviruses are a large family of viruses which may cause illnesses in animals or humans. COVID-19 now is the name which was given to the infectious disease caused by the most recent discovered novel coronavirus called SARS-CoV-2. Now, this new virus and disease were really completely unknown before the outbreak began in Wuhan, China- end of December 2019.
If we're talking about the incubation period, most studies so far suggest that the time from exposure to symptom onset is about five days. However, studies have also shown that symptoms could appear as early as three days after exposure to as long as 13 days later. Now, these two weeks where you can have symptoms are important, because they continue to support the general recommendation of self-quarantine and monitoring of symptoms for 14 days post-exposure. If you compare the incubation period for SARS-CoV-2 to other commonly known viruses, for example, common flu, seasonal influenza, it's very different. That is typically around two days, so it's shorter. The incubation period for other coronaviruses for SARS is two to seven days, for MERS it's five days.
How does the newly discovered coronavirus spread? It is believed that the coronavirus mainly spreads from person to person. Now, this can happen between people who are in close contact with one another. Droplets that are produced when an infected person coughs or sneezes may land on the mouths or noses of people who are nearby, or possibly inhaled into their lungs. Recent research was able to show that the virus can remain viable: in the air for up to three hours, on copper for up to four hours, on cardboard up to 24 hours, and on plastic and stainless steel up to 72 hours. So another possible transmission pathway could be the touching of services where the virus is present, and then subsequently touching your nose or mouth, and that can lead to infection. However, the virus being detectable on surfaces does not mean it's infectious, so that's one of the open questions, how likely infection from surfaces where the virus can be found is. At this time point, it looks more like most of the infections occurred through person to person contact.
It is known that COVID-19 enter cells via the angiotensin 1 converting enzyme 2, ACE2, which is also present in the lung, and that is where recursively patients who develop more severe manifestations of disease have viral infection.
Now, very interestingly, most recently a paper on the virological characteristics of the COVID-19 infection was described in Nature1. This group from Germany was able to show that very early on there is extreme pharyngeal virus shedding, which is very high during the first week's symptoms. And this may explain why infectiousness in this asymptomatic phase is actually quite high, because of the high amount of virus which can be found in the upper respiratory tract. Infectious virus was readily isolated from throat and lung direct samples, however, not from stool samples, in spite of high virus RNA concentration. Now, other groups have demonstrated that virus per se is detectable in stool samples, but it's not necessarily infectious, so that is probably a different issue, and that is important, because then probably transmission just from stool becomes a less likely probability. In this analysis of the German patients, blood and urine never yielded virus. Now, interestingly, shedding of viral RNA from sputum outlasted the end of symptoms, and there was a drop in the amount of viral load over time from the throat samples. Serologic investigations show that seroconversion occurred after seven days in 50% of patients, and after 14 days all patients showed antibodies. But this was not followed or associated with a rapid decline in viral load, so that sort of limits probably the diagnostic value of serologic determinations in patients who present with active disease.
One important question which is being discussed is whether potentially when warmer seasons arrive, the transmission rates will go down. We know that some of the common cold viruses as well as influenza transmit less likely in the summer period. However, remember that parts of the COVID-19 outbreaks occurred in very warm places like Hong Kong and Singapore, suggesting that this may not really be the case. So please remember this is a new virus, and you cannot translate knowledge from other viruses immediately into this new virus presentation.