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Medicine: The arms race between viruses and humankind ☢️
[MEDICINE] Pathology: The arms race between viruses and humankind ☢️
Viruses infamously outsmart the human body regularly. For example, influenza vaccinations have to be changed each year to fit whichever strain is predicted to be most prevalent. You may have heard of the new BA.2.86 Covid variant, which can render previously-acquired immunity less effective. One of the key reasons for this dynamic nature is the rate at which viruses reproduce. While human generations last about 20 years, viruses can reproduce 200 times in 30 minutes (such as bacteriophage T4). This increased rate of replication opens the door for more frequent mutations and more phenotypic variation to arise in a viral population, some of which may be advantageous to the virus and thus, are positively selected. With our relatively slow replication rate, viruses would naturally out-compete our adaptations with ease. However, we have modern medicine on our side, such as antiviral pharmaceuticals and, more commonly, induced immunity (in the form of a vaccination). These protect us at the point of use, however, also provide a selection pressure to these rapidly mutating viruses, meaning they can evolve to withstand our treatment attempts. Evading this is fundamentally difficult and viruses may always outsmart us…
💡 Things to consider
The advanced machinery and choreographed attack procedure of viruses: The fast turnover rate of viruses allows them to possess a range of attack strategies, despite their small and simple composition. They hijack body cells to exploit their replication machinery at that cell’s expense, acting as a passive protection from immune surveillance. The number of ways that viruses have adapted to overcome our immune system is almost too many to list. Examples include the production of vIL-10 (vIL = viral interleukin: a glycoprotein that regulates immune response) from EBV, which directs the immune system to a response that is less potent against viruses (Th2 polarisation). Membrane modification then allows cell-cell viral spread without it having to enter the extracellular space, where it can more easily be spotted by immune cells.
What affects how well-equipped a virus is?: It goes without saying that some viruses naturally adapt more rapidly than others: you have a measles vaccine (MMR) when you’re very young and you’re set for life, but influenza needs an annual vaccine. The stability of viruses affects to what extent they can outcompete human defence: those that are less stable acquire more mutations that may allow them to evade any attempt kill them. Factors that affect how stable a virus is includes whether it is enveloped or not, its size, and its genome (DNA/RNA, single/double-stranded…).
Why don’t we use antivirals as much as antibiotics?: Earlier, I alluded to antiviral medications. While most people can name a few antibiotics or have at least been prescribed them at some point, antivirals are seemingly harder to come by. There are a number of reasons for this. First of all, the success of viral vaccination programmes and herd immunity means that most people are able to fight off a viral infection easily, without the need for drugs, given the higher amount of virus-specific immune cells circulating in their blood (memory T-lymphocytes). Another, arguably more important reason, is the difference in how bacteria and viruses act in the body. Bacteria are self-contained organisms, while viruses enter our body cells to hijack replicative machinery. Antibiotics can therefore target bacteria - and just the bacteria - while antivirals may have to kill infected body cells, leading to more severe side effects.
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That’s it for this week! We’d like to thank this week’s writer: Rob Folkard (Medicine).
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