Another example is when the sampler accidentally dabs a spot where there is usually not a lot of RNA, e.g. B. deep in the nose after a person's symptoms have subsided, which can lead to a false negative result. If the amount of viral RNA is very small, as is likely when a person is late in the illness, it could be just at the threshold where the test cuts reporting from positive to negative – which is a negative test The next day the day turns into a positive sample with a different swab and a little more RNA.
“It is plausible to me that when patients are recovering, false negative tests are more likely to be carried out, since the previous data indicate that the viral load is very low. After the symptoms have subsided, these patients probably only have anyway very small amounts of viral RNA in their swabs, ”says Rasmussen.
In this scenario, the viral RNA seems unlikely to be very low. Menachery explains that one person excretes the virus significantly enough to infect others, although further research is needed to know for sure.
Experts are considering whether the virus can hide in the body and then reactivate.
Another possibility experiment It is investigated whether SARS-CoV-2 could simply stay in the body and replicate again at a later point in time. This is a legitimate thought because it is known to be the case with some other viruses.
"Some viruses can exist in a host in a latent state … quietly in a host cell without actively replicating," explains Rasmussen. Viruses that do this are generally DNA viruses, while SARS-CoV-2 is an RNA virus. DNA viruses include the herpes viruses, which can cause sores in the mouth or genitals, and the chickenpox virus. Let's take the last one as an example to examine how this mechanism really works.
Chickenpox caused by the varicella zoster virus (also known as VZV) hides some of the viruses produced during the infection in a place called the dorsal root ganglia, which are nerve cell clusters in the Act near the spinal cord. When replicated in these cells, virus replication stops. The viruses "turn off most viral gene expression and effectively hide from the immune system," says Rasmussen. "VZV can remain latent in the neurons for years until it is reactivated, everything turns on again, new ones [viruses] are produced and shingles are caused." Rasmussen also notes that we don't know exactly what causes the reactivation. According to the Mayo Clinic, shingles risk factors can be over 50 years old and an immune deficiency. As NPR reported, some experts believe that a weakened immune system could allow SARS-CoV-2 to "recover" from someone who is "recovering" and has dropped to an undetectable level of the virus.
The catch is that this mechanism of latency and reactivation has never been observed in coronaviruses, the experts say. “It is not clear which cell type they would go latent in and which machines they would use to make this possible. I am skeptical that this would happen, ”says Menachery.
Rasmussen also found that both a renewed infection and such a rapid reactivation appear biologically unlikely. "That would depend on people not developing protective immunity at all," she says, "and after all the data released so far, most recovered COVID patients seem to have at least an increasing antibody response." Still, she admits that we have a lot to learn about immunity to this infection.
Experts are not sure whether a "chronic infection" is possible.
Chronic infection is similar to latency, but the virus does not necessarily sleep within a host cell. "There are other mechanisms by which RNA viruses cause chronic infections," says Rasmussen. Think more of the example of HIV, which can multiply in the body over a longer period of time. According to the National Institute of Allergy and Infectious Diseases, HIV converts its viral RNA into DNA, which it then integrates into the host's DNA to make copies of the HIV RNA. Symptoms often appear two to four weeks after exposure, according to the CDC, when the virus is at a stage of "clinical latency" and multiplies in small amounts for years without causing symptoms. The situation is similar with hepatitis C, another RNA virus that can cause either an acute or a chronic infection. "The hepatitis C virus can just hang around, replicate in small quantities, and infectiously manipulate the host's response to [be]just enough to fly under the radar of the immune system," says Rasmussen. If anything, it can take up to 1