Nisse said:
We're told in school that the only way to catch an STD is to have intimate relations with someone who's already infected.
If that really is the case, then how can these diseases have started in the first place? There must, logically, be some other way of contracting them.
The diseases could have begun in humans in a number of ways. They could have been microbes, bacteria or fungi that lived harmlessly on humans (or animals or even plants that entered the human body) and then mutated.
Diseases mutate, like other life forms, their success is then a matter of selection by survival, propagation etc. Indeed, syphillis, for example, has mutated significantly since it was first recorded in humans in Europe from an outbreak in troops at the siege Naples in the Middle Ages. Then, the body became covered in pustules, flesh fell away from the body and death ensued within a few months.
There is a theory that diseases (and harmful parasites too) are life forms trying to achieve co-existence with their hosts (as has been done by harmless or beneficial bacteria that we carry today, "dust mites", etc. They keep mutating in order to achieve that as it is not in their interests to wipe out their hosts. On the other hand, diseases try to survive attack too, so mutations arise that are resistant to antibiotics, for example. Mutations may also be successful by transferring to another species (e.g. from animals to humans and vice versa)
Standard modern treatment is to isolate the source of infection and to kill off all the pathogens before they can mutate, also maintaining high levels of hygiene. For a number of reasons this has rarely been successful.
Another treatment has been to boost the defence of the patient from secondary infection and promote her own healing -- this probably results in less harmful mutations of the disease but they may be longer-lasting (or permanent).
Phages are an interesting treatment which were being developed in the USSR but around not a lot of work is being done at the moment (drugs are simpler to produce and more profitable). The theory is that for every life-form another will evolve to prey on it and may already be in existence. The best place to find that preying life-form is in the vicinity of sources of infection. Once the disease-killer is identified through laboratory testing, it can be tested and, if thought safe, administered in a heavy dose to the patient. This seems likely to be the most effective form of treatment for epidemics of new diseases or mutations, providing it is backed by sufficient resourcing.
Helping the disease to mutate to a less harmful form may be tried in the future.