amudu: "Dose" of coronavirus one can get, and its connection to the severity of COVID-19

Monday, March 30, 2020

"Dose" of coronavirus one can get, and its connection to the severity of COVID-19

The average number of viral particles needed to establish infection is known as the infectious dose. We don’t know what this is for covid-19 yet, but given how rapidly the disease is spreading, it is likely to be relatively low – in the region of a few hundred or thousand particles, says Willem van Schaik at the University of Birmingham, UK.

Viral load, on the other hand, relates to the number of viral particles being carried by an infected individual and shed into their environment. “The viral load is a measure of how bright the fire is burning in an individual, whereas the infectious dose is the spark that gets that fire going,” says Edward Parker at the London School of Hygiene and Tropical Medicine.

If you have a high viral load, you are more likely to infect other people, because you may be shedding more virus particles. However, in the case of covid-19, it doesn’t necessarily follow that a higher viral load will lead to more severe symptoms.

For instance, health workers investigating the covid-19 outbreak in the Lombardy region of Italy looked at more than 5,000 infected people and found no difference in viral load between those with symptoms and those without. They reached this conclusion after tracing people who had been in contact with someone known to be infected with the coronavirus and testing them to see if they were also infected.

Similarly, when doctors at the Guangzhou Eighth People’s Hospital in China took repeated throat swabs from 94 covid-19 patients, starting on the day they became ill and finishing when they cleared the virus, they found no obvious difference in viral load between milder cases and those who developed more severe symptoms.

Although it is difficult to draw firm conclusions at this stage, such studies “may impact our assumptions about whether a high number of viral particles predisposes to a more serious disease”, says van Schaik.ring the "dose" of coronavirus one can get, and its connection to the severity of COVID-19

Some young healthcare workers with a serious disease -- a result of a big viral dose?

But three questions deserve particular attention because their answers could change the way we isolate, treat, and manage patients.

First, what we can learn from the "dose-response curve" for the initial infection --- that is, can we quantify the increase of the risk of infection as people are exposed to higher doses of the virus?

Second, there is a relationship between the initial "dose" of the virus and the severity of the disease - that is, does more exposure result in graver illness?

And third, are the quantitative measures of how the virus behaves in infected patients (e.g. the peak of your body's viral load, the patterns of its rise and fall) that predict the severity of their illness and how infectious they are to others?

So far, in the early phases of the COVID19 pandemic, we have been measuring the spread of the virus across people. As the pace of the pandemic escalates, we also need to start measuring the virus within people.

Cecile G. Tamura