One mistake that people often make is just grouping all sexually transmitted infections into one same category, thinking about them as simply diseases which affect sexual organs and reproductive system. However, everything in that line of thought is just partially true. Not only can STIs spread to other parts of the body, but they are also caused by different types of microorganisms.

A significant portion of known STIs is caused by bacteria, while some others are caused by viruses. Other infections might be fungal in origin, while somewhat smaller number is caused by different types of microscopic parasites. In accordance with this, the prescribed treatment can also significantly vary, just as it’s the case with other, better-known health conditions.

In this article, we will explore the differences between these sub-categories of STIs while paying special attention to the methods of treatment and the most commonly prescribed medications.

What’s on this page?

What types of STIs are there?

The first task of this article will be to detail the different types of sexually transmitted diseases. The primary factor of categorization used here will be the root cause of the infection or, more specifically, the type of organism causing it. As we already mentioned the four primary types, here we will list the most common STIs in the UK for each category.

Bacterial STIs

Viral STIs

Fungal STIs

Parasitic STIs

  • Chlamydia
  • Gonorrhoea
  • Syphilis
  • Bacterial vaginosis
  • Herpes
  • Genital warts
  • HIV
  • Hepatitis
  • Candidiasis
  • Trichomonas Vaginalis
  • Pubic lice
  • Scabies

Bacterial STIs

Bacterial sexually transmitted infections are, as the name implies, health conditions that are transmitted through unprotected sex and are of bacterial origin. This class of conditions includes some of the most common STIs in the UK including chlamydia, gonorrhoea and syphilis. When bacterial infection occurs, certain strain of bacteria will establish a presence in the organism, spreading and replicating while strongly relying on body’s own resources in order to do so. As the infection spreads, different symptoms will begin to manifest, most commonly genital discharge and pain during urination. Other, more specific symptoms will usually strongly depend on the gender of the person affected, although it is very common for bacterial STI to be completely asymptomatic in a vast majority of cases.

If left untreated, these conditions will progress further beyond the early symptoms, eventually causing significant health complications. This is especially true for syphilis which develops through three distinct stages with the last one being marked by severe health complications and a potential for lethal outcome.

Bacterial STIs treatment

However, the positive side, if we could phrase it like that, when it comes to bacterial STI is that for most time, they are easily treatable with simple antibiotic treatment, either with a one-off dose or a short course. The treatments of this type usually work by curbing the growth of the infection-causing bacteria. Once the bacteria are weakened, the immune system can take over and fight off the remaining infection. When this happens, the symptoms too will begin to diminish.

Depending on the exact type of antibiotic the treatment might be administered as an oral tablet, an injection or a combination of both. The exact brand and type of antibiotic that will be prescribed will depend on numerous factors such as your medical history, severity and the nature of your condition as well as on the possibility of presence of other secondary infections.


Chlamydia is without doubt the single most common STI in the UK, with more than 200.000 new cases reported annually and up to 140.000 of those being registered in the age group 15-24. This very common condition is, luckily, very easily treated with Azithromycin, a macrolide antibiotic which works by inhibiting the process of protein synthesis in individual bacteria, thus stopping them from replicating and spreading.


Gonorrhoea, also colloquially called “the clap” is the second most common sexually transmitted disease in the UK. According to NHS, somewhere between 25.000 and 30.000 new cases get discovered every year at British GUM and STI clinics. It is classified as a bacterial STI since it is caused by a strain of bacteria called Neisseria gonorrhoeae. During the last 30 years, there was no consensus about the best option for the treatment of this condition, although today, a majority of medical experts agree that Azithromycin (in tablet form) and Ceftriaxone (in injection form) should be considered so-called ‘first-line treatment’.

Unlike already discussed Azithromycin, Ceftriaxone belongs to a class of pharmaceutical compounds called cephalosporin antibiotics. As such, it acts by weakening the structure of bacterial cell walls and membranes, making it easier for the immune system to penetrate and neutralize bacterial cells, thus eliminating the infection.

However, ever since 1970s, medical experts begun noticing the emergence of a new strain of gonorrhoea bacterium in the US. This new strain, known for causing so-called super gonorrhoea, developed significant resistance to conventional antibiotic treatment. This influenced modern gonorrhoea treatment where a combination of different types of antibiotics is used in order to ensure success of the treatment.


Syphilis is a bacterial STI caused by a strain of bacteria called Treponema pallidum. Once infected, a person can still miss the symptoms for weeks or even months, as syphilis can lay dormant for significant periods of time, sometimes as long as three months. In the early stages, the symptoms can also be very non-specific, so even when they do appear, one can easily miss them or mistake them for something else. Syphilis progresses through three distinct stages with the last of those being the most dangerous, marked by severe health complications and potentially lethal outcome if left untreated.

However, despite the seriousness and severity of this condition, syphilis can be treated with antibiotic medicines, just like any other bacterial STD. While it is certainly more beneficial to start the treatment early on in the first phase of the condition, it is still possible to eliminate infection even in the later stage. However, if other complications occur by that time, treating the infection will prevent further deterioration, but will not mitigate the damage that has already been done at that point.

The most commonly prescribed syphilis treatment today is benzathine benzylpenicillin in the form of an injection. Similarly to Azithromycin, this medicine too inhibits protein synthesis mechanism within the bacterial cells, thus stopping them from multiplying and making them an easy target for the body’s immune system.

As of now, syphilis is, in most cases, still defenceless against penicillin. However, a study conducted in China in 2009 underlines the fact that new macrolide-resistant strains of Treponema pallidum are emerging, making the prospects of syphilis treatment in the near future much more uncertain.

Bacterial vaginosis

The condition known as bacterial vaginosis (or BV for short) is commonly mistaken for a sexually transmitted infection, although it doesn’t really belong to that category as it can often develop because it is not transmitted nor caused by sexual intercourse. While being sexually active certainly is a risk factor, BV occurs when there’s an imbalance in the vaginal flora, or more precisely, when one strain of bacteria naturally present within the vagina becomes overpopulated due to different factors. For example, things as simple and trivial as using a new shampoo or shower gel can be enough to disrupt the balance and bring on the condition.

Despite the fact that it is not a “conventional” STI, bacterial vaginosis still should be timely treated. The most commonly prescribed treatment for BV is antibiotic medicine based on the active ingredient metronidazole. Within the UK, it is sold and advertised under the brand name Flagyl.

STIs caused by viruses

The question many may ask is how viral STIs are different from bacterial infections. There are numerous significant differences. Of course, the biggest of those is the fact that bacterial STI are caused by the presence of bacteria within the system, while viral ones are caused by viruses.

As such, they cannot always be successfully cured by medication, but proper treatment is still important as it can force the infection into dormancy, curbing the symptoms and limiting the risk of reactivation. It is important to note that the use of antibiotic will have little to no effect on viral infections.

Another important difference between viral and bacterial STIs is the fact that symptoms accompanying viral infections do not necessarily have to be limited to genitals and reproductive organs.

The type of treatment will usually be conditioned by the nature and severity of the condition – in some cases, prescription medication might be enough to send the virus into remission, while in others, hospitalization might be necessary.


The most common viral STI in the UK, herpes is diagnosed in 30.000 people each year. However, there are two more or less distinct types of herpes virus known as HSV-1 and HSV-2. The former is usually associated with oral blisters, more commonly known as cold sores, which is not an STI, while the latter is the type of the virus that causes genital cases and which is at the root of herpes that is classified as an STD.

Most commonly prescribed treatments include medicines such as acyclovir, famciclovir and valaciclovir. While they are very different from antibiotics in their mechanism of action, there are some parallels which can be drawn. Of course, viruses can’t be directly attacked in the way bacteria can, but they to require a specific enzyme (DNA polymerase) in order to spread through cells of the host. Medicines used for the treatment of herpes restrict the activity of this enzyme, making it much harder for virus to infect other healthy cells.

This will, unfortunately, not eliminate the infection from the body the way antibiotics can eliminate bacteria, but it will help keep the infection under control, sending the virus into remission. If there is an outbreak or reactivation of the infection, the same treatment will be used again until the infection diminishes.

Genital warts

Caused by the human papillomavirus, better known as HPV, genital warts exist in around 11 different strains and are relatively benign, although uncomfortable condition. Antiviral medicines based on the active ingredient podophyllotoxin such as Condyline and Warticon are commonly used for the treatment of genital warts. They work by interfering with the function of an enzyme called topoisomerase II which HPV uses to make host cells copy the virus RNA code. As a result, the infected cells will decrease in number, allowing healthy skin cells to replace them (and leading to the disappearance of symptoms).

Another option, somewhat less used is imiquimod – a pharmaceutical compound which doesn’t affect the virus or the affected cells, but instead acts on the immune system itself, enhancing its function and stimulating the release of cytokines, naturally synthesized compounds that will fight off infection and eliminate infected cells.

For those more severe cases where clusters of warts where surface area larger than 4cm2 is affected, surgical removal might be necessary. This can be achieved through use of laser, electro-surgery, cutting off or freezing the affected area.


The human immunodeficiency virus, also known by its abbreviation HIV, is probably the best-known life-threatening sexually transmitted disease, especially in its later phase called AIDS that makes the immune system of the person affected completely ineffective.

While work on the possible treatment for HIV has been in progress ever since the 1980s, there is still no way to completely cure this condition. On the other hand, antiretroviral drugs can be used with noticeable yet limited success for keeping the condition under control and prevent it from progressing.

These medicines also known as ARVs often issued in combination, similar to way antibiotics are used to treat super gonorrhoea. This is so because HIV can also adapt to certain medications becoming resistant to one type of treatment, either temporary or even long-term in some cases. Once the treatment is prescribed, it is usually used for the rest of a person’s life.

Aside from this conventional treatment, there is also a kind of preventive therapy called post-exposure prophylaxis. This approach will be recommended if you had sex with someone who is infected, but you still haven’t developed the condition. This preventive approach is maybe even unexpectedly effective as it does manage to prevent HIV in a majority of cases, provided the treatment is started very, very early after exposure.

Post-exposure prophylaxis (or PEP for short) incorporates specific antiretroviral drugs that must be administered within 72 hours of suspected transmission in order to successfully prevent the onset of the condition. However, even then, PEP is far from 100% effective.


Hepatitis is a viral infection that exists in several strains. Similar to herpes, not all of those strains are STIs – in fact, only hepatitis B and C can be transmitted through sexual intercourse. Both of these types of herpes virus have the capacity to cause serious liver injury (including potentially fatal liver failure), but they are quite different in the ways they affect the body and also in the ways organism reacts to these infections.

Hepatitis B is significantly more likely to be defeated by the body’s natural defences within just a couple of months. In some cases, it can develop into a chronic illness, but even that it can be very successfully managed with proper antiviral treatment.

Hepatitis C, on the other hand, will always require immediate treatment as it is not possible for the immune system to deal with the condition on its own. If hepatitis C is diagnosed, antiviral medicine will always be prescribed in order to prevent further complications. One of the most commonly prescribed medicines is Peginterferon alfa-2a in the form of a twice-weekly administered injection that helps the immune system to fight off the infection in up to 80% of recorded cases.

An alternative to this would be combined treatment program that relies on both oral tablet (such as ribavirin, for example) and injection treatment, to increase the chances of successful treatment.

Parasitic STIs

Parasitic STIs, as the name implies, are sexually transmitted infections that are caused by a parasite organism that feeds on the nutrients of its host organism. When it comes to STIs specifically, parasitic organisms can inhabit both inner and outer parts of the body, resulting in a number of different symptoms.

Internal parasites can usually be killed by the use of antibiotic medicines, while external cases will usually require a kind of a cream or lotion in order to eradicate the infection.

Trichomonas Vaginalis (TV)

Trichomonas vaginalis is a parasitic infection caused by the protozoa from the genus Trichomonas. This microscopic organism inhabits the urinary tract and it is the most common parasitic STI in the United Kingdom. In terms of both symptoms and treatments, TV is very similar to bacterial vaginosis. It is successfully treated with metronidazole-based medicines which will affect the ability of the microorganism to produce vital nucleic acids and keep its DNA intact.

Pubic lice (‘crabs’)

Pubic lice, commonly known as ‘crabs’ due to their appearance, are tiny lice that inhabit pubic hair causing localized itching and inflammation. While they are most commonly transmitted through close physical contact which most of the times occurs only during sex, they can also be spread via shared items such as bad linen and towels.

Common treatment of this condition usually incorporates the use of an insecticide lotion or a shampoo that is used for a period between three to seven days.


Scabies is a popular name for a condition caused by the insect Sarcoptes scabiei, belonging to the lice genus. These tiny insects inhabit the skin around the genitals where they burrow into the skin and lay eggs there. Once they are present, the immune system will notice it and will react, usually resulting with a rash in the affected region.

Just like in the case of ‘crabs’, scabies are also transmitted through sexual contact or shared household items. Medication usually involves cream or lotion that is applied in two courses, one week apart.

Fungal STIs

Fungal STIs are very specific and are much more similar to bacterial vaginosis than other mentioned STIs because they are, in fact, caused by a number of different factors which don’t have to include sexual contact at all – although sexual activity still remains an important risk factor. Use of certain contraceptives, antibiotics or even cosmetic products can contribute to the onset of the conditions that are often called fungal STIs.


Better known as thrush, candidiasis is characterised by the increased abundance of one particular type of yeast in the vagina called Candida albicans. This type of fungus lives naturally on and within the body, but can cause an infection when it becomes over-populated. This usually happens when an external factor changes the environment of the vagina, causing other microorganisms to die off, leaving space for candida to colonise.

Usual treatment of candidiasis involves antifungal medication such as Diflucan or Gyno-Daktarin which affect the outer layers of cell membranes of fungal species, creating holes in the cell walls, efficiently killing them.

The role of STI testing

If we would need to choose one thing that we would like you to remember from our article it is that STIs can manifest in many different forms and there is no single treatment that could be effective in absolutely any situations. Some of them, especially viral infections, might require life-long treatment and management.

Naturally, the best way to prevent the onset of any of these conditions is to practice safe sex. If you are sexually active and don’t have one long-term partner, going to regular STI tests is of uttermost importance. Discovering a condition early will play a crucial role in ensuring proper treatment and management.