Context
- Ever since cases of ‘reinfection’ — people who had tested negative for COVID-19 testing positive again after a while — emerged in early January, the question of latency of the SARS-CoV-2 virus is being hotly debated.
More details
- A latent infection is when the virus in the body is dormant and does not replicate within the host.
- It however possesses the capacity to be reactivated at some point, causing a flare-up of the disease much later.
What is a latent viral infection?
- A latent viral infection is an infection that is inactive or dormant.
- As opposed to active infections, where a virus is actively replicating and potentially causing symptoms, latent (or persistent; but not chronic) infections are essentially static which last the life of the host and occur when the primary infection is not cleared by the adaptive immune response.
- Examples are Herpes simplex viruses type 1 and 2, varicella-zoster virus, HIV, Epstein-Barr virus (human herpesvirus 4), and cytomegalovirus.
- They are known to cause typical latent infections in humans.
Types of Virus
- Viruses fall into two broad categories: chronic and acute.
- A chronic virus will infect its host for extended periods of time, often through the lifetime of the host.
- An acute infecting virus, such as influenza and rotavirus, is cleared from the body after a few days or weeks.
- 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 herpes virus infects a cell, its genome can remain in that cell as long as that cell is alive.
- Many viruses can survive at the mucosal level in spite of immunity. “A classic example is the polio virus, which, like SARS-CoV-2, is also a positive sense, single strand RNA (ribonucleic acid).