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Why are antibiotics useful against bacterial infections but not most viral infections?

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Diagram showing the West Nile virus transmission cycle: a mosquito bites an infected bird (the primary reservoir host), then transmits the virus to humans or horses (incidental hosts) through subsequent bites. — infectious disease Birds are the primary reservoirs of West Nile virus. The virus is transmitted to humans and horses by mosquitoes that have bitten infected birds.

Antibiotics are ineffective against most viral infections because they are specifically designed to target the unique biological structures and metabolic processes of bacteria, which are living, single-celled organisms.12

In contrast, viruses are not living organisms; they function by hijacking the metabolic machinery of a host cell to replicate. Because viruses mimic the functions of the host's own cells, it is extremely difficult to develop chemical compounds that inhibit viral multiplication without also damaging or killing the host's healthy cells.12

Antibiotics work through mechanisms that do not exist in viruses, such as:
* Inhibiting cell wall synthesis: Many antibiotics, such as $β$ -lactams, target the specific assembly of the bacterial cell wall, leading to the death of the bacterium.3
* Disrupting protein synthesis: Antibiotics can selectively bind to bacterial proteins to prevent the growth of new bacterial cells.3
* Interfering with metabolic pathways: Some agents inhibit the synthesis of essential nutrients like folic acid within bacteria.3

Since viruses lack these distinct structures and pathways, antibiotics have no target to act upon.32