People in general tend to lump sexually transmitted infections together under one category; as illnesses which affect the sexual organs.

But, aside from the fact that STIs can present symptoms elsewhere on the body, the type of organism causing these infections can vary too.

In some cases they are caused by a bacteria, in others a viral strain, in some a fungus, and in other cases a parasite.

And, as you might expect, the treatment for STIs can vary according to their cause, just as they can for non-sexual illnesses. Different types of infection respond to different types of treatment; and while some can be cured, others cannot, and must be managed instead.

So what are the differences between these sub-categories of sexual diseases, and what are the medication options available for them?


  • Chlamydia
  • Gonorrhoea
  • Syphilis
  • Bacterial Vaginosis


  • Herpes
  • Genital Warts
  • HIV
  • Hepatitis


  • Trichomonas Vaginalis
  • Pubic Lice
  • Scabies


  • Candidiasis


Infections of this kind include syphilis, chlamydia and gonorrhoea.

In such illnesses, a bacteria will establish a presence in the body and spread by replicating its own DNA.

As these infections spread, symptoms may develop, which might include discharge and urinary pain. Other symptoms may vary depending on the gender of the person affected, but it is common for bacterial STIs to present no symptoms.

Left untreated, it is possible for harmful complications to develop; particularly in the case of syphilis.

But bacterial STIs are curable.

A course of treatment will usually consist of a one-off dose or short course of antibiotic medicine.

The way these treatments work is to stall the growth of the infection-causing bacteria. Once the bacteria is weakened, the immune system is better able to fight off what remains of it. Symptoms will then clear up.

Depending on the type of antibiotic, which might be given as an oral tablet, an injection, or a combination of both, these medications do this in a variety of ways.


Chlamydia is the most common STI here in the UK, with almost 140,000 15-24 year old cases diagnosed by the NHS in 2013.

This type of infection is normally treated with azithromycin, a macrolide antibiotic which attacks the chlamydia trachomatis bacteria. It works by preventing a process called ‘protein synthesis’. This is the action by which the bacteria generates a protein, which allows it to replicate its own cells and multiply.


The recommended treatment for gonorrhoea has in fact changed numerous times over the course of the last 30 years.

The first line treatment at present in the UK is Azithromycin (given as a tablet) and Ceftriaxone (given as an injection). These antibiotic treatments work in a similar way, by inhibiting the growth of the neisseria gonorrhoeae bacteria.

Ceftriaxone is a type of medicine called a cephalosporin, which disrupts these bacterial cell walls and weakens them, increasing their susceptibility to the immune system.

In the 1970s, antibiotic resistant strains of gonorrhoea began to emerge in the US, and have become more common since. This is why a combination of drugs is often used, to eliminate the risk of the infection persisting after treatment.


Later stage cases of syphilis can be life-threatening and will always require hospital admission and monitoring. But when the infection is in its initial phase, medication may be issued in the form of antibiotics.

The current first-line treatment is benzathine benzylpenicillin, given as an injection. The drug works by preventing protein synthesis, stopping the treponema pallidum bacteria from reproducing itself, and rendering it susceptible to the body’s defences.

This illness is still largely sensitive to penicillin, but macrolide-resistant strains have become known; most notably in a 2009 study conducted in China, undertaken in the midst of a resurgence of the condition in that country.

Bacterial Vaginosis

Bacterial vaginosis is not strictly categorised as an STI, even though it is often mistaken for one, because it can develop in cases where sexual intercourse has not taken place.

Research into the condition has indicated that there is seldom a need for male partners of female cases to be tested.

Getting the infection treated, however, remains important.

The go-to drug for most cases is metronidazole, which is also available under the brand name Flagyl.

Its function is to penetrate the cells of the gardnerella vaginalis bacteria, and interfere with their DNA structure. Once again, this weakens the bacteria and the body is better equipped to fight it off.


How are viral STIs different from bacterial infections?

They can’t always be cured with medication.

In such cases, antiviral products are used to force the infection into dormancy, and limit the risk of a reactivation; antibiotics will usually have little or no effect in the treatment of viruses.

Symptoms caused by these viruses can vary, and may not just affect the sexual organs.

What type of treatment the infection requires will usually depend on its nature and severity: certain instances may necessitate hospitalisation; others a course of prescription medication; and some may be cleared naturally by the immune system.


In the UK, the most common viral STI is herpes.

A recent report by Health Protection England put the number of new diagnoses of genital herpes at a yearly figure of around 30,000.

There are two main strains of herpes: HSV-1 and HSV-2.

The former is more commonly associated with oral blistering, or cold sores; whereas the latter is more often the cause of genital cases. Medication for this group of infections is issued in the form of aciclovir, famciclovir or valaciclovir.

While the action of these treatments is not the same as that of antibiotics, their strategy is comparable. The herpes virus requires an enzyme, DNA polymerase, in order to generate copies of its own cells and spread.

Aciclovir and similar variations work by penetrating these cells and restricting the activity of this enzyme, so that the virus stops growing.

Granted, this will not rid the body of the virus in the same way antibiotics will with bacteria, but it will send the infection into remission.

The medication is applied again if (or when) the virus reactivates. If used at an early enough stage, before symptoms have had a chance to develop, the above treatments can be very useful at preventing an outbreak.

Genital Warts

The viral strain responsible for genital warts is the human papillomavirus, or HPV.

Numerous strains exist, and can cause different symptoms. Genital warts are often the result of the 6 and 11 strains.

A cure is not currently available for the virus itself, but there are medicines which can treat the effects, including genital warts. Once again, these are issued in the form of antiviral drugs.

Condyline and Warticon are topical solutions which contain podophyllotoxin.

This substance enters the wart cells and interferes with the function of topoisomerase II, an enzyme which these cells use to maintain their DNA structure. As a result, the cells begin to decrease in number, healthy skin cells replace them, and symptoms disappear.

One other option for genital warts is the treatment imiquimod, which works slightly differently.

Rather than attacking the warts cells itself, it enhances the function of the immune system, by encouraging it to release more of the chemicals known as cytokines, which fight wart cells.

These treatments were shown in one study undertaken in 2011 to have a very similar rate of success in eradicating genital warts: 72% in the case of podophyllotoxin and 75% in the case of imiquimod.

For more severe cases of warts, such as those clusters which have a surface area of more than 4cm2, surgical removal may be required. This may involve laser or electrosurgery, cutting off (excision) or freezing the warts (cryotherapy).


The human immunodeficiency virus, more commonly known as HIV, is considered the most life-threatening of all STIs, due to its ability to develop into AIDS, a condition which renders the immune system ineffective.

Some treatments have been developed since the virus became so prominent in the UK in the 1980s, and even though it is still not curable, antiretroviral drugs can be adept at keeping the illness under control, and prevent it from progressing.

Known as ARVs, these drugs are often issued in combination, as HIV possesses the capacity to adjust and become resistant to one type. In the majority of cases, these will need to be taken every day, for the rest of a person’s life.

Protease inhibitors work by blocking the function of protease, an enzyme which, once again, viral cells utilise in order to copy themselves and spread. Nevirapine, which is a type of drug called a non-nucleoside reverse transcriptase inhibitor, works in a similar way, but tackles the function of a different enzyme which the virus needs to grow.

For those who have had unprotected sex with someone who is infected, but have not yet developed the illness, an emergency programme of medication is available which can prevent HIV, called post-exposure prophylaxis.

Referred to as PEP, this is also given in the form of antiretroviral drugs, but must be taken within 72 hours of suspected transmission to be effective. It should also be noted that this does not provide a guarantee against the development of HIV.

In one study involving 702 patients, one per cent of participants who took PEP to prevent the onset of HIV still developed the virus.


This term is actually the name given to liver inflammation, and can occur for a number of reasons, many of which have nothing to do with sex.

Some strains of viral hepatitis, however, can be transmitted through sexual intercourse. Hepatitis B and C both have the potential to cause liver failure, but how the body deals with them is quite different.

It is more likely that someone with hepatitis B will be able to fight off the infection on their own in a matter of months. Others may develop a more chronic case, and have to take antiviral treatment over a long period of time to keep symptoms at bay.

Someone with hepatitis C isn’t as likely to get rid of the condition naturally, and treatment for such cases will be required, again in the form of antiviral medicine.

Peginterferon alfa-2a is an example of one such drug. It is issued as a once-weekly injection which helps the immune system to prevent the virus from developing in instances of hepatitis B.

In the case of hepatitis C, it is frequently given as a twice weekly injection and works to completely clear the virus in over 80% of cases. The treatment functions by enhancing the effects of immune system, and helping it to combat viral cells.

A doctor may choose to issue a combined treatment programme, containing an oral tablet such as ribavirin in addition to an injection, to increase the likelihood of stopping the infection. This is usually taken twice daily.

Like other antivirals, it works to prevent the function of enzymes which the virus needs to reproduce itself, thus providing a dual approach to stopping viral cell development.

If injections have been insufficient in relieving hepatitis B, Tenofovir and Entecavir are examples of antiviral oral tablets which a doctor may suggest. These are also DNA polymerase inhibitors.


Simply put, a parasite is an organism which feeds on the nutrients of its host. In the case of STIs, these can manifest on either the outside or the inside of the body, and result in a variety of symptoms.

Treatment is usually short term, and highly effective in wiping out the infection.

For internal parasites, an antibiotic may be used; whereas for external cases, a cream or lotion will sufficiently eradicate the infection in the majority of cases.

Trichomonas Vaginalis

A protozoal infection, the parasite which causes the condition trichomoniasis is often abbreviated to ‘TV’. It is found in the urinary tract and causes vaginitis and urethritis in women and men respectively, and is the most common STI of this kind.

In terms of both its symptoms, and its treatment, TV is very similar to the bacterial infection, BV.

The condition is treated with the antibiotic metronidazole.

This interferes with the production by the parasite of nucleic acid, which it requires to adequately preserve its DNA structure. And in the same way as it would with a bacterial infection, the drug enables the immune system to fight off the protozoan cells.

Pubic Lice

Referred to more commonly as ‘crabs’ due to their appearance, these tiny lice reside in the pubic hair of an infected individual and can cause itching and inflammation.

They are transferred through close physical contact, such as through sex, but can also be spread via shared items such as bed linen and towels.

To treat the condition, a doctor will often suggest a special insecticide lotion or shampoo. After the initial administration, it is usually applied again after a period of three to seven days.


This illness is caused by Sarcoptes scabiei, which are small mites that burrow into the skin and lay eggs.

Their presence causes the immune system to react, and a rash will often appear in the affected region.

Once again, close physical contact through sex, or shared household items such as those listed above, are the primary means of transmission for this infection.

Medication for the condition may be issued is the form of a topical cream or lotion. This is typically applied twice, with a one-week gap between doses.


While they are not considered STIs because they have a broad range of causes, including the use of antibiotics and contraceptives, some fungal infections can be transmitted through sexual intercourse.


Referred to more commonly as thrush, is characterised by an abundance of one particular type of yeast in the vagina.

Candida albicans, which is a type of fungus that usually lives harmlessly on the body, can cause infection when present in higher numbers than other types.

To help get levels of fungus back to normal, doctors will typically issue an antifungal medication.

Treatments like Diflucan and Gyno-Daktarin work by interrupting the outer layers of cell membranes. In doing so, they create holes in the fungal cell walls, and the contents of the cell are then susceptible to leaking out, and the cells decrease in number.

The Importance of Testing and Treatment

If there’s one lesson to be taken from the above, it’s that STIs can manifest in varying forms, and there is no one treatment type which can tackle them all. Some aren’t easily solved with a course of antibiotics, and may require lifelong maintenance measures.

This prospect, along with the risk of spreading STIs to others, is why practising safe sex is so important.

Page last reviewed:  22/06/2020