Question: What is it that makes diseases caused by viruses and bacteria hard to treat?

Susan Cartwright answered on 15 Jun 2015:

– Health warning: I’m a physicist, not a physician. Treat this answer with caution! –

I think that the principal reason is that both viruses and bacteria multiply very very quickly. If you don’t get them under control soon enough, they quickly overwhelm your natural defences.

That said, viral diseases are much harder to treat than bacterial diseases, although it is not clear that this state of affairs is permanent. The reason is that we have chemicals – antibiotics – that are very effective at killing bacteria, but we do not have equally effective antiviral chemicals. Hence, the best treatment for many viral diseases is vaccination – don’t try to treat the disease, but prime your body’s immune system so that it will respond fast enough to prevent the disease from taking hold in the first place. With many viral diseases, once they have become established, all you can do is treat the symptoms, so that the patient stays alive until the disease has run its course. Fortunately, the commonest viral diseases are quite mild, as it is often best for the virus *not* to make its host really ill, because if the host feels well enough to carry on socialising with other people, it makes it easier for the virus to get passed on. Hence many viruses, e.g. the common cold, have evolved to cause only mild – but very hard to treat – disease.

Bacterial diseases used to be equally lethal, but since the introduction of penicillin have become much easier to treat. Many modern surgical procedures, such as hip replacements, would be very dangerous if we did not have effective antibiotics to prevent bacterial infection. One of the big dangers facing us at the moment is that resistance to common antibiotics is spreading rapidly amongst bacteria, and thus diseases that used to be quite easy to treat, such as tuberculosis, are becoming killers again.

You can help to stop this! Please don’t ask your doctor to prescribe antibiotics for things like colds and sore throats which are caused by viruses – it won’t help, and it will give bacteria more chance to evolve resistance. And if you are prescribed antibiotics, take the whole course: don’t stop taking the pills when you start to feel better. Obviously, the last bacteria to die are the ones that are most resistant to the antibiotic: if you stop taking the pills, there’s a good chance that some bacteria are still alive, and they will pass on to their descendants their resistance to that antibiotic.
Finally, campaign against the use of antibiotics as growth promoters in farm animals: this is an idiotic practice that just gives the bugs a massive helping hand in developing resistance. (End of rant!)