Origin of sexually transmitted diseases

[Nisse]

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.

[negitron]

Mutations. An airborne pathogen has a gene accidentally switched off or switched on or transposes a couple base pairs and, BAM, you've got a blood-borne pathogen, instead.

[Borek]

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.

Please elaborate, I can't see a logic conection.

[Nisse]

Please elaborate, I can't see a logic conection.

If the only way to contract a disease is by coming into contact with an already-infected person, how did the first person contract it?

[f95toli]

If the only way to contract a disease is by coming into contact with an already-infected person, how did the first person contract it?

As negitron has already pointed out: Mutations.
In the simplest case one could imagine someone carrying a harmless virus that mutates in his/her body and becomes an STD that can then be transmitted.
In reality it is more complicated than that; but this is the basic idea.

[Borek]

If the only way of getting flu is to contact someone with the flu, how did the first person got it?

Do you see that it is not a problem with STD, but with any contagious disease?

[Astronuc]

If the only way of getting flu is to contact someone with the flu, how did the first person got it?

Do you see that it is not a problem with STD, but with any contagious disease? STDs require more intimate contact than one requires to get the flu. STDs are not airborne, but usually require gential-oral/genital/anal intercourse.

In fact, I have heard sometime in the past, that humans (mainly males of the species) may have contracted venereal disease through intercourse with domesticated animals, e.g. sheep or pigs, then simply passed it on to human females or other males.

Certainly promiscuous behavior will increase the risk of being exposed to an STD.

There is a practical side to abstinence and monogamy. It simply reduces or mitigates the risk of STD.

[tchitt]

There's actually an animal porn industry (google it, if you dare.) so I don't see why it's unbelievable that people didn't pick up these diseases from intercourse with animals. I doubt this is the only explanation for all STD's though... You don't necessarily need to engage in sexual intercourse to catch herpes.

[KingNothing]

I'm willing to bet my ex-girlfriend is the source of most STDs.

[Borek]

STDs require more intimate contact than one requires to get the flu. STDs are not airborne, but usually require gential-oral/genital/anal intercourse.

I think you have missed the point - problem reported by OP is not a problem of STDs, but of every contagious disease no matter how it does spread. Before someone else could be infected, someone has to contract the ilness first. As there are many contagious diseases obviously there must be some flaw in the OP understanding of the problem - and I tried to show it by reductio ad absurdum.

[Nisse]

Thank you to everyone for clearing that up for me (no pun intended).

I only used STDs as an example because that's what first got me thinking about this. I'm not a medical person and the question has been bothering me for ages, and you're the first people to give me a sensible answer, so thanks again.

[Astronuc]

I think you have missed the point - problem reported by OP is not a problem of STDs, but of every contagious disease no matter how it does spread. Before someone else could be infected, someone has to contract the ilness first. As there are many contagious diseases obviously there must be some flaw in the OP understanding of the problem - and I tried to show it by reductio ad absurdum. Unicellular organisms have been around longer than multi-cellular organisms. I was responding to the origin of STD's in humans specifically. It is very difficult to determine the precise origin of each disease.

An interesting book on the subject Microcosmos (http://books.google.com/books?id=VeiwSEETa2wC&pg=PA141&lpg=PA141).

[vibjwb]

This may help you understand how aids was introduced to humans.

http://en.wikipedia.org/wiki/Origin_of_AIDS

According to this it was not introduced by sexual contact

[brianb]

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.

[brianb]

"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."
Sorry, I meant "rarely successful" in completely eliminating the disease or in humans' future susceptibility to harmful infection.
"Boosting the defence of the patient" and "promote her own healing" includes immunisation by weak or dead strain of the disease.

[Lievo]

We're told in school that the only way to catch an STD is to have intimate relations with someone who's already infected.
Maybe one should mention that this is just plain false. :rolleyes: