• 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.
• A latent viral infection is an infection 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.
• As opposed to active infections, where a virus is actively replicating and potentially causing symptoms, latent 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
• Latent viral infections can be reactivated into a lytic form (the replication of a viral genome). The ability to move back and forth from latent to lytic infections helps the virus spread from infected individuals to uninfected individuals”
• 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.
A latent infection vs. a persistent viral infection:
• A latent viral infection occurs when the virus is present within an infected cell but dormant and not multiplying. In a latent virus, the entire viral genome is present, and infectious virus can be produced if latency ends and the infections becomes active. The latent virus may integrate into the human genome – as does HIV, for example – or exist in the nucleus as a self-replicating piece of DNA called an episome.
• A latent virus can reactivate and produce infectious viruses, and this can occur months to decades after the initial infection.
Mains Paper 2: Health
Prelims level: Latent viral infection
Mains level: Difference between latent infection and persistent viral infection