[scientizscht (OP)]

Hello!

Is viral pneumonia a result of an immune reaction to the virus or actual damage from the virus?

Thanks!

[chris]

Both.

Viruses are obligatory intracellular parasites, meaning that they rely on invading and hijacking our cells in order to replicate. When they do so, they usually compromise the cell, leading to its ultimate destruction. As such, viral infection leads directly to tissue damage; if this is in the lung, that's a pneumonia.

At the same time, viral replication in cells leads to the production of various cellular alarm signals called cytokines. These attract the immune system, which then sets about destroying virally-infected cells; but in the process it usually also causes bystander damage to adjacent healthy tissue. This is a pneumonitis.

Both phenomena will occur at the same time; usually the degree of damage is low, but in some cases it can be severe. The evidence we have is that the 1918 Spanish flu pandemic strain (H1N1) provoked just this sort of immune overdrive, leading to catastrophic lung damage, especially in people with healthy immune systems. This is, we believe, the main cause of death in these people.

[scientizscht (OP)]

Why then corticosteroids are not prescribed in viral bronchitis? If the damage from immune reaction is more prominent?

[chris]

Why then corticosteroids are not prescribed in viral bronchitis? If the damage from immune reaction is more prominent?

Sometimes we do administer steroids to damp down the immune response in a range of situations. I have seen reports indicating that doctors in China have been conducting small scale trials of steroids in some patients with Covid-19 to see if the immune bystander damage can be mitigated. One downside of doing this though is that it prolongs the illness and the period of time for which the patient remains infectious, which is not optimal.

[scientizscht (OP)]

Why then corticosteroids are not prescribed in viral bronchitis? If the damage from immune reaction is more prominent?

Sometimes we do administer steroids to damp down the immune response in a range of situations. I have seen reports indicating that doctors in China have been conducting small scale trials of steroids in some patients with Covid-19 to see if the immune bystander damage can be mitigated. One downside of doing this though is that it prolongs the illness and the period of time for which the patient remains infectious, which is not optimal.

The infectiousness should be managed with quarantine and not by refusing therapeutic means to patients!