Virus Latency, what is it and what does it mean?
Been seeing miscommunication about SARS-CoV-2 and latency, so here's a brief thread on what "latent" or "latency" means in virus infection.
Viruses fall into two broad categories: chronic and acute (1/11)
Been seeing miscommunication about SARS-CoV-2 and latency, so here's a brief thread on what "latent" or "latency" means in virus infection.
Viruses fall into two broad categories: chronic and acute (1/11)
A chronic virus will infect its host for extended periods of time, often the lifetime of the host. HIV and herpesviruses are examples of this.
An acute infecting virus, such as influenza and rotavirus, are cleared from the body after a few days or weeks (2/11)
An acute infecting virus, such as influenza and rotavirus, are cleared from the body after a few days or weeks (2/11)
A chronic virus can go into latency. This is when a virus is present within a cell, but not actively producing more infectious virus particles. For example, when a herpesvirus infects a cell, its genome can remain in that cell as long as that cell is alive. (3/11)
The virus inside the cell can reactivate from its latent state into what we call the lytic state. This is when the production of new virus particles occurs.
This is an intentional strategy by the virus to promote its survival. (4/11)
This is an intentional strategy by the virus to promote its survival. (4/11)
An example of this is chickenpox, caused by human herpesvirus 3 (aka varicella-zoster virus). Many of us got it when we were kids and developed chickenpox. The body responds, and then the virus goes into latency. Decades later it can re-activate, resulting in shingles (5/11)
HIV can also go into latency after infection. It integrates itself into the host chromatin, and can reactivate upon stimulation such as inflammation induced by co-infecting pathogens. This can lead to uncontrolled HIV replication and clinical AIDS (6/11)
So can SARS-CoV-2 go into latency like herpesviruses or HIV? No.
There's no evidence SARS-CoV-2 chronically infects a patient and goes into a latency. There might be long-term disabilities in patients, but there's no evidence the virus itself chronically infects a patient (7/11)
There's no evidence SARS-CoV-2 chronically infects a patient and goes into a latency. There might be long-term disabilities in patients, but there's no evidence the virus itself chronically infects a patient (7/11)
So what about someone who tests (+), then (-), and then (+) again? In virology, there's what we call a "limit of detection" of a virus. This is the threshold where a virus can be detected. A (-) SARS-CoV-2 test doesn't mean zero infection; it means no detectable infection (8/11)
It's entirely possible to have detectable, then non-detectable, and then detectable SARS-CoV-2 virus because of the limit of detection of our current testing. Also, a (+) SARS-CoV-2 test doesn't necessarily mean there is infectious virus. Testing for SARS-CoV-2 RNA... (9/11)
... on surfaces can yield a (+) result, but that simply means that there is some SARS-CoV-2 RNA present (it is an RNA virus). It doesn't necessarily mean the RNA is intact, or that the RNA is inside an infectious particle. So fragmented RNA can actually yield a (+). (10/11)
In sum, there's no evidence that SARS-CoV-2 enters latency or can chronically infect a patient as HIV does. Those who are spreading such rumors likely don't know what the term means, and are doing harm to #scicomm during this health crisis (11/11).
*** The test I'm referring to in this thread is the SARS-CoV-2 PCR test.
