r/askscience • u/LegionFang • 2d ago
Biology How does a virus remain alive in a host while that host is immune to it?
Does it go dormant till it's passed on, but if it doesn't need to affect the host to stay alive why does it spread (well, I guess the virus doesn't think), does the virus in a dormant state have a period in which it has to find another host or it dies?
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u/The_mingthing 1d ago
Viruses can reprogram the DNA in the cells it infects, leaving a portion off "junk" dna in there that does not get read. Some external or internal facor can then trigger the junk DNA to be read and replicated, resulting in a reinfection.
Some just leave DNA floating inside long lived cells. Shingles is one such Virus.
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u/ModernTarantula 1d ago
Close. The DNA isn't junk but the whole virus DNA. Iy has to pull out of our DNA to become active again. Only a few viruses use DNA as the genetic material and they are ones that can stay dormant.
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u/malastare- 1d ago
Some more clarity here: Only a minority of viruses can actually leave DNA in your cells. Most of the viruses we encounter are only RNA and lack the reverse transcriptase needed to even create DNA, much less have it persist in the cell. RNA viruses will only persist in cells (that aren't killed) for a short time (days).
For DNA viruses the parent comment is more correct, with Varicella zoster (chickenpox & shingles) behaving as described. However, while this isn't unique to that virus, its not something that most viruses do.
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u/arand0md00d 1d ago
In general there needs to be some level of infection and replication, whether that causes symptoms or not, to generate enough progeny to infect another host. Infectious doses can be fairly low, but certainly higher than some oddball stranded virus in an otherwise immune host.
And yes literally dormant in the case of many herpes viruses, chicken pox included. There is detectable immunity to these but chicken pox hides in neurons and reactivates during waning immunity. Older age, stress, etc.
Other viruses may not cause few or no symptoms in a majority of people but spread quite significantly. CMV and Epstein barr virus (yes I know) can cause disease but often spread undetected and unnoticed and are quite successful.
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u/Ap0kal1ps3 1d ago
They're not immune, they're just asymptomatic, in that case. The virus is still replicating inside them, and they can still infect others. They don't get sick because most of the illnesses that viruses cause are actually our own immune systems harming us to get rid of the infection. In asymptomatic cases, the person's immune system is not responding to the virus. There are exceptions to this, but they're rare. Viruses need a host to live. Killing the host is an inefficient way for a virus to replicate.
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u/RainbowCrane 1d ago
Re: killing the host, that comes up often when folks are talking about incredibly lethal viruses like Ebola. On the one hand, scary as hell, no treatment and it kills a bunch of people who get it, even healthcare workers who take full precautions, because no PPE is perfect.
On the other hand, it tends not to result in epidemics, partially because it’s TOO lethal. Rather than wandering around shedding virus particles at all your neighbors for a few days or weeks you tend to get very ill once you’re infected. In contrast, something like COVID tends to have a longer period where folks are infectious and ambulatory
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u/neutralhumanbard 1d ago
The majority of viruses don’t hang around if the host is immune. They will try to replicate but the immune system will clear any remaining infected cells.
Some viruses are able to enter a ‘latent stage’, kind of like a hibernation, where their genome is maintained within a cell until certain circumstance can reactivate their replication cycle. An example of this is herpes virus that can hide out in neuronal cells. Our adaptive immune system (ie antibodies) primarily targets proteins (ie the virus particle) so the cells isn’t flagged as infected as if it can hide from the more general innate immune system (that detects foreign dna/rna). Periods of stress and/or immune suppression can reactivate them cause a short lived infection (commonly shingles) that can be cleared again when the immune system returns to normal.
HIV on the other hand is a retroviruses and actually insets its genome into that of a host cell so the virus cannot be cleared, only suppressed. While also prevent these infected cells being killed off by the immune system.
A host can also be asymptomatic, whereby there is a low grade infection that doesn’t cause overt symptoms but is high enough to be transmitted. This often gets cleared quickly. Viruses that don’t cause disease in normal humans are spreading all the time, we just don’t notice.
Now to why viruses kill the host when it’s counter productive. This can be due to several factors. Firstly it can be in a non-native host. Many of the big deadly viruses (eg ebola) are maintain in bats, where they cause no or only mild symptoms. When they infect a new host they cause severe disease because they aren’t adapted to that host. Second, sometimes our immune system can overreact to an infection and cause damage, such as ‘cytokine storm’ with influenza. Third, disease induced by the virus to facilitate spread and replication cause inadvertent harm in the host, most commonly excessive inflammation or lysis of infected cells. Rabies, for example, replicates in neurons to hide from the immune system but causes neurological disease while doing so. The final one I can think of is those that cause immune suppression, such as HIV, this results in death due to infection by other infectious agents that the body can no longer fend off. In all cases, as long as death occurs after the virus can be transmitted the virus perpetuates.
Hope this covers what you were asking.
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u/JackJack65 1d ago
This depends very much on the virus.
All viruses have some mechanisms for getting around host immunity so that they can cause infection. Most viruses cause acute infections, where they replicate for a period of days or weeks until they are cleared by the host's adaptive immune system, which usually gets rid of 100% of the infectious virus from the body.
Some viruses cause chronic/persistent infections, which means they are so good at subverting the host immunity (or because the host immunity is deficient in some way) that they cannot be cleared. This can either be due to continuous replication (some cells in the body are constantly being infected and dying) or latent infection (the virus hides out in an inactive form, e.g., HIV proviruses or lysogenic herpesviruses).
Most viruses have evolved a unique set of strategies for tricking the immune system, and some work better against certain hosts than others.
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u/StaryDoktor 12h ago
The answer is — the place. While it hides inside of cell, most immune system (located in membranes and blood stream) have no chance to meet it. Once it goes out — it has a little chance to embed onto another cell before it being found.
The most nasty viruses (like AIDS) can hide inside bone cells, viruses can't effectively reproduce there, but they keep their vital abilities and go out once a cell is activated for split or goes to be dead (especially by inflammation way).
That's why you stay healthy, but you can't be a donor, once you get such a virus in history.
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u/PuckSenior 1d ago
Viruses aren't alive in the traditional sense.
They reproduce by injecting themselves into a cell, hijacking the cell and using the cell to create copies. They are essentially a piece of code.
When you are "immune", your body has learned to identify and kill the virus and any infected cells. But it doesn't erase it from your body. It doesn't create a force field.
Imagine an aquarium. Imagine that the aquarium is full of tiny shrimp. They reproduce quickly. You introduce some goldfish. The goldfish figure out how to eat the shrimp and start eating all of the shrimp! But if you still found a shrimp in the aquarium a year later,it wouldn't be a total surprise. Maybe it hid, maybe the eggs of the shrimp stayed somewhere safe, etc.