“Know thy enemy: How do viruses infect their hosts?”

Have you ever imagined tiny particles entering your nose every time you breathe? Have you also experienced a situation when a person suddenly sneezed in front of you, and these tiny particles feel like they’re getting absorbed by your skin? Scary (and gross) isn’t it? Specially during this pandemic. I know everyone is getting paranoid of anything around us (who doesn’t?) because we are scared of getting infected. We are scared of facing something which we cannot see.

So how do viruses infect their hosts (like for real)? Let’s have a quick discussion on the pathogenicity of viruses. Pathogenicity means the ability to produce pathogenic changes or diseases. Remember that it is important to know these things so we won’t be easily fooled by what we see on our newsfeeds/social media. Okay, let’s start! 🙂

There are two ways a virus may undergo to infect its host (which indirectly means “reproducing more viruses to cause diseases”): (1) lytic and (2) lysogenic cycles. Let me first show you the diagram of each cycle. I bet you can easily understand the difference just by looking at these figures.

The Lytic Cycle
The Lysogenic Cycle

Okay, so did you notice any difference between the two cycles? Hmm.. The obvious difference is one cycle involves cell disruption, while the other does not. What does it mean? Let me discuss individually. The lytic cycle involves five steps for viral reproduction to happen. Step 1 is ENTRY. This is the portal of entry where the virus enters the host (e.g., inhalation, droplets). Step 2 is ATTACHMENT and PENETRATION. Remember the “spikes”? That’s the part of the cycle where spikes are needed. Viruses need to attach to the cell so reproduction can start. Step 3 is ASSEMBLY where the virus hijacked the host. Basically, the virus commands the host (and all inside the host) to “assemble” viral particles. Remember we mentioned in the last post that viruses cannot reproduce on its own. They need the help of the hosts since they have all the materials needed to create these viruses. So you can imagine, the assembly step is like the manufacturing of new viruses. Step 4 is MATURATION where the final viral particles are being prepared (including the spikes and protein coat with few host’s materials integrated). And finally, step 5 is RELEASE. As you may notice in the diagram, the cell bursts (lyses) and the new viral particles are released and are now ready to infect new cells. That’s why lytic cycle is called lytic cycle. In the end, the cell bursts.

Next, the lysogenic cycle. Here, you may notice that no cell lysis happens. Instead, the viral nucleic acid was integrated with the host’s nucleic acid, which resulted to replication of “infected cells”. Let me again discuss each step. Lysogenic cycle involves four steps. Steps 1 and 2 are similar to the lytic cycle (please refer to the previous paragraph). Step 3 is VIRAL INTEGRATION. This step involves the combination of viral and host’s nucleic acids, which we call here the “infected cell”. Step 4 is CELL DIVISION. Unlike lytic cycle, no cell lysis happens. The “infected cell” keeps on dividing. So you can imagine, the host is slowly piling up infected cells resulting to diseases.

Between the two cycles, somehow you can say that the lytic cycle is more morbid than lysogenic cycle. 😀 The lysogenic cycle, on the other hand, can be described as “killing a host softly”. It makes sense right?

I hope you learned the basic pathogenesis of viruses. 🙂

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