Viruses are basically a part of DNA or RNA that
gets built into a DNA of a host cell and replicates. Sometimes the host cell
gets ruined, sometimes immune cells of the organism destroy it and sometimes it
survives for some time. Important is that unlike bacteria viruses don’t have
cell walls and primitive organelles that can be affected by antibiotics, so
what antivirals do – they don’t usually destroy viruses – they block their
replication and adhesion to the cells instead.
The most specific tool against viruses ever invented by humanity is vaccines. Vaccines teach immune system to recognize specific virus and attack it. If virus can be recognized and killed by immune cell – it does not stand a chance, for it is very primitive and does not have elaborated defense systems like bacteria.
Many other antiviral substances are not specific. Popular group with non specific action is called immunomodulatory drugs. That kind of activity has, for example, interferon. Interferon is a natural immune system alert to invasion, it causes inflammation – increased blood flow (pain as a result), swelling, increases body temperature (interferon is the reason why we have high temperature when sick), etc. Many nasal sprays contain interferon, for it does not attack one specific virus – it alerts everyone else that there is something wrong going on and makes better conditions for immune cells to come and kill whatever is there.
Only some viruses have been developed specific chemical treatment against them. Antiretroviral therapy includes chemicals like azidothymidine (zidovudine), which inhibits virus transcription. If started in the first month – treatment can slow down the progression of the disease and win a lot of time for a patient.
Herpes – can be suppressed by acyclovir. Although it can never be cured, for the medication would not reach inside the nervous cells, it can suppress the virus enough to get rid of the symptoms.
Flu can only partially be treated medicinally. The reason for that is that flu has many varieties and it can mutate faster than we can develop medication. Remantadine and midantane can be effective against A2 stem of flu, ointment with oxoline can suppress influenza virus on the mucosa (nose, eyes). Every year virologists try to predict the stem of the flu that is going to be spreading this season and vaccinate against it. The vaccine is in form of drops and is probably the most effective prevention tool, the trick is to predict the type of flu correctly.
Often when a doctor diagnoses a patient with flu, measles or other viral infections the antibiotics are prescribed. That does not mean that antibiotics are effective against viruses. Viruses tend to break cells, weaken immune system and exhaust organism, leaving a great field for bacteria. Antibiotics are prescribed against complications of viral infections and not against viruses themselves. Recent pandemics have shown us how little antiviral drugs can do without vaccination, with time the number of viruses will only increase.
Antibiotics have won the battle against bacteria, but bacteria have evolved mechanisms to fight antibiotics. Germs can live in colonies and share a mucous capsule that prevents antibiotics from getting to them, some of them can produce beta lactamases and dissolve penicillin, and they can lose their shell for some time and live without it in so-called L-forms for some time, avoiding being ruined by the antibiotics that attack that shell. To crown it all bacteria can exchange their DNA, they can learn from each other – one bacteria that knows how to fight penicillin can teach millions.
Viruses are less complex but that gives them a significant advantage – they can mutate faster and adjust even faster than bacteria. Viruses can be extremely contagious and what they lack in complexity they also compensate in their numbers – they are much more numerous than bacteria.
Anti-viral drugs can only target replication of the virus, for the opportunity to destroy the DNA or RNA of a virus without harming the DNA of a human is very rare.
Antivirals can block the receptors on the cell, the same receptors used by the virus to get inside the cell. They can also inhibit the uncoating of the virus inside the cell or impede the virus transcription and multiplication.
Anti-Viral medication can successfully suppress the virus to the point when there will be no symptoms of it. The best example of that is above-mentioned acyclovir. Most of us are carriers of regular herpes, some can have more dangerous genital (type 2) herpes. There is no cure, but if we treat the symptoms – the individual will be completely healthy although remain to be a carrier.
Finally, Anti-Viral medication can fight certain specific viruses, like Remantadine can fight A2 influenza type. If you have different type of virus (Adenovirus can cause similar symptoms), or even different type of flu – Remantadine will not make any difference.