Why is it so difficult to develop agents that are selectively toxic to viruses?

Answer 1

A bacterium is a single-celled organism. It's very small and rather simple as living things go. It contains within itself all the bio-chemical machinery necessary to eat, extract energy from food and reproduce itself. It contains in its DNA a complete blueprint for the manufacture of a copy of itself, and the cell is equipped with all the special chemicals needed to decode the blueprint properly and to make the copy.

A drug that is intended to destroy or at least render harmless a bacterium can be designed to attack almost any of the processes that the organism uses. Any process used by the bacterium that is not used by the human body, or that is used in a radically different way, can be targetted by a drug.

A virus is a quite different thing. It is much smaller than a bacterium. It is not a cell. It has no machinery to eat or reproduce itself. It is little more than naked DNA; about the only part of it that has a function other than to be a blueprint for its copying is a protein that helps it enter a cell.

Once a virus enters a cell it hijacks the reproductive machinery in the cell. A little bit like the cuckoo's egg in the nest, it substitutes its DNA for the DNA in the nucleus of the animal cell, so the cell makes copies of the virus. There is no "enough already" code on the virus DNA, so the cell copies the virus until there is so much of it in the host cell that the cell bursts, and new viruses flood through the body looking for new targets.

The fundamental problem in developing a drug against viruses is this :- you can't attack a virus's metabolic processes because it doesn't have any. You can't attack its reproductive system because it doesn't have any. It uses the machinery of the human cells. Easy to attack these, and kill them, but that kills the patient too.

Answer 2

It is hard to make antiviral medicines because viruses have a high tendency to mutate rapidly. Antiviral medications like the flu vaccine, are tailored specifically to one strain of the virus. As soon as the virus mutates it is no longer the same strain, thus rendering the antiviral ineffective.

Answer 3

The reason is due to the way in which viruses work. Antimicrobial agents are simple, since in many cases the agent simply disrupts the cell membrane. If a cell has a disrupted membrane, then its contents will leak out, and it will die. Other agents damage the membrane while it is originally being constructed. Still others make the DNA from inside the bacterial cell unable to replicate. Etc.

A virus is much different. Viruses do not have a cell membrane. Instead, many are formed and housed inside a small capsid, which is not susceptible to attacks like those used for bacteria. Since viruses use the hosts cells exclusively for reproduction, it is very difficult to find a way to kill the virus without killing the host cells. As such, the best method to be able to attack the virus is to inhibit its reproduction by inactivating a protein in the virus. This protein must be very specific, essential to the function of the virus, and totally unlike any proteins in the host. As genetic sequencing and understanding about how DNA/RNA works have increased, the understanding about how to create such a drug has improved. However, since it is so very targeted, each antiviral will only work on a very small set of actual viruses. Given the amount of time and effort (and expense) that goes into creating, testing, retesting, verifying, producing, and at long last marketing an antiviral agent, very few have actually been produced as of right now. However, many corporations are currently investing in discovering new antiviral agents. The number of these agents should soon (as in, within the next decade) increase dramatically.

Answer 4

viruses dont have mtabolism.Drugs must stop one of the steps of replication but that ocurre inside the host cell.Viruses mutate faster than bacteria creatin generation that are resistant to antiviraltherapy or difficult to find one.

Answer 5

Since antibiotics are not used on viruses and we have to use chemicals of one sort or another, we can be damaged by those chemicals as well.