How Do Antiviral Drugs Work?

Introduction

Antiviral medications alleviate symptoms and shorten illnesses caused by viruses like the flu by destroying these viruses from the body. They cannot fully eliminate chronic infections like HIV, hepatitis, and herpes but they can inhibit the virus from replicating in the host's body, aiding in the management of these conditions.

A virus is a minuscule, infectious organism carrying genetic material (DNA or RNA) enclosed in a protein coat. Unlike bacteria or living cells, viruses can't replicate on their own; they rely on infecting host cells to reproduce. This often leads to the death of the host cell, causing harm to the host organism. Common human diseases caused by viruses include AIDS, COVID-19, measles, and smallpox.

Antiviral drugs work by disrupting specific stages of the viral replication process. Despite being limited in approval due to potential side effects or reduced effectiveness, these medications hold tremendous significance. They are critical in treating severe infections such as HIV, hepatitis B, hepatitis C, and herpes, playing a crucial role in managing these conditions and significantly improving the quality of life for affected individuals.¹

The mechanism of antiviral medications varies based on the specific drug and type of virus. These medications can:

• Prevent viruses from attaching to and infiltrating healthy cells by blocking receptors
• Enhance the immune system's ability to combat viral infections
• Reduce the viral load, which refers to the quantity of active virus in the body

This article explores the modes of viral spread and cell penetration, distinguishes between antibiotics and antivirals, and delves into the pivotal role of antivirals in preventing viral transmission. Furthermore, it touches upon how environmental changes could trigger new viral threats.

How do viruses spread?

Viruses can disseminate through various modes, which vary based on the type of virus:

• Bodily fluids such as blood, urine, faeces, vomit, semen, and saliva that have been contaminated
• Insect bites where the virus is transferred from the insect's saliva into a person's bloodstream
• Skin-to-skin contact, including sexual activity

How do viruses get inside cells?

Viruses start infections by binding to specific spots on the surface of our cells, acting like keys fitting into locks. Understanding this mechanism is important because it helps viruses get into cells and spread, making it crucial knowledge for developing better treatments and vaccines against viruses.

Viruses have different ways of attaching to cells, which depend on their shapes and structures. Some viruses have spike-like parts that help them stick to specific spots on cells, which we call receptors, while others don’t have these spikes, so they use different ways to attach to cells. These differences significantly affect how viruses interact with and stick to cells when they cause infections.

Scientists have been exploring how viruses connect with and enter cells by studying cell receptors. Some viruses have an envelope, a protective layer around their genetic material. These enveloped viruses directly merge with cell membranes (the protective coating around a human cell) or follow specific paths into cells. In contrast, non-enveloped viruses need cell receptors to get inside. Recognition of these initial connections is vital for cells to prepare for a viral invasion and illustrates how various viruses employ different methods to enter our cells.

Studies at the atomic scale have uncovered how viruses attach to receptors, unveiling similarities across different viruses. This helps us grasp how viruses have evolved and how they interact with receptors, marking a significant leap forward in developing more effective strategies to combat viruses.

Most virus receptors belong to two main groups: cellular adhesion molecules (CAMs) and phosphatidylserine receptors (PtdSer). This similarity in receptor types implies that viruses share common methods to attach to cells, enter them, and initiate signals. Despite this straightforward pattern, these shared strategies significantly influence how viruses spread and cause diseases in different hosts.²

How do antibiotics differ from antivirals?

Antibiotics help combat bacterial infections, which typically occur outside cells, making them accessible to medication. They're effective against various bacterial infections but don't impact viruses.

On the other hand, each antiviral specifically targets one virus. Since viruses replicate inside cells, developing antivirals is more complex. Antivirals are more challenging to develop because there are more viruses than available drugs to treat them.

What side effects might antivirals have?

The potential side effects of antivirals vary depending on the specific drug and its dosage. People may experience:

• Dry mouth
• Headaches
• Nausea and vomiting
• Cough
• Diarrhoea
• Dizziness
• Fatigue
• Insomnia
• Joint pain or muscle pain
• Skin rash

Do antivirals have the ability to cure viral infections?

Antiviral medications can alleviate symptoms and reduce the duration of illnesses caused by viruses such as the flu and Ebola. They're capable of eliminating these viruses from your body.

However, chronic viral infections like HIV, hepatitis, and herpes cannot be eliminated by antivirals; these viruses persist in your body. Nevertheless, antiviral drugs can induce viral latency, rendering the virus inactive, often resulting in fewer or milder symptoms. Symptoms that occur while taking antivirals might be less severe or resolve more rapidly.

Can antivirals help prevent the spread of viral infections?

Yes, antiviral drugs can help prevent certain viral infections in individuals after a suspected or known exposure. For instance, taking specific antivirals:

• During pregnancy, antivirals reduce the risk of a mother passing HIV to her newborn (babies also receive antiviral medicine after delivery)
• Daily lowers the risk of transmitting herpes or HIV to others or getting HIV from an infected partner
• Within 72 hours of a potential HIV exposure antivirals can reduce the chances of getting infected
• Within 48 hours of exposure to the flu virus antivirals have the potential to prevent an individual from falling ill

What are the limitations and practical challenges of using antivirals?

Persistent viruses such as HIV, HBV, or herpes viruses can't be fully cured yet, but viruses causing short-term infections can be eliminated. However, with quick-moving infections like influenza or COVID-19, there's a brief window for antiviral treatments due to how rapidly these diseases progress. Timing matters significantly, and using antivirals right after exposure to the virus is most effective, though this timing challenge can limit practical application.¹

How do environmental changes trigger new viral threats?

Given the challenges in treating viruses, exploring how environmental changes trigger new viruses is crucial for scientists. Understanding this connection helps merge the current knowledge in treating viruses with preparing for future threats.

Around 10,000 viruses infectious to humans largely reside in wild animals without causing harm. Environmental alterations, such as warmer climates and changes in land use, could facilitate the interaction and exchange of viruses between different animal species. The mixing of viruses between different animal species might bring about new diseases in humans.

Scientists anticipate these exchanges occurring more often in specific areas: high-altitude regions, places with various animal species, and densely populated areas in Asia and Africa. Models estimate that this interaction could cause roughly 4,000 instances of viruses moving between animals. Bats, known for their role in spreading viruses, might significantly contribute to this process.

Even with climate change mitigation, the exchange of viruses between species may persist. Scientists strongly recommend closely monitoring animal viruses and tracking animal movement, especially in warm regions with a high risk of diseases that could potentially affect humans.³

Summary

Antiviral medications are critical in limiting viral replication and alleviating symptoms in infections like herpes, HIV, and influenza. Unlike antibiotics that target bacteria, antivirals specifically aim at individual viruses. They come with various side effects, including headaches, nausea, and fatigue, and while they can reduce symptoms and the duration of certain viral illnesses, they can't eliminate persistent viruses like HIV and herpes.

Antivirals are effective in preventing the spread of specific infections, especially when administered shortly after exposure. Environmental changes, such as warmer climates and alterations in land use, may facilitate the exchange of viruses between animal species, potentially leading to new viral threats for humans. Monitoring animal viruses and understanding their movement is crucial to predict and prevent potential outbreaks in certain regions.