HIV - 'human immunodeficiency virus'
UK data for 2014 reveals that there were 6,151 new cases of HIV. Of these, 55% of cases occured in men who have sex with men (MSM).
The Health Protection Agency estimates that currently there are over 103,000 people in the UK who are HIV-positive, but around a quarter of them do not know that they have the virus.
Some of those who are HIV-positive will go on to develop AIDS and its complications.
AIDS is a potentially fatal disease.
HIV invades and destroys the immune system, which protects the body from infection. This means that a person who carries the HIV virus is prone to many different illnesses and may die from diseases that are harmless to healthy people.
In some countries, particularly those located in Sub-Saharan Africa, the HIV rates are very high. For instance, in the Republic of South Africa it's estimated that about 11 per cent of the population is HIV-positive.
Genital warts (HPV)
At the present time, UK clinics see about 100,000 new cases of genital warts a year. Many other people develop warts, but they are not seen at clinics.
Warts, or condylomata acuminata, are caused by the human papilloma virus (HPV).
Many months can pass from the time of infection to the actual development of warts, so it may be very difficult to determine who you got them from.
In women, HPV can lead to microscopic changes in the cervix and to the development of cervical cancer.
HPV is now thought to be associated with various other cancers, including carcinoma of the anus and possibly of the throat and adjoining regions.
Public Health England reports a 76% increase in the number of cases of syphilis in the UK since 2012.
If left untreated, syphilis is a dangerous and life-threatening disease. It's caused by a corkscrew-shaped germ called Treponema pallidum.
It's passed on by intercourse or by almost any other form of sexual interaction.
The first symptom appears between 9 and 90 days after exposure to the germ that causes it. A small lump develops at the infection site, and this soon breaks down to form a painless ulcer called a chancre.
Later, there is a secondary stage (characterised by fever, rashes and throat ulcers), and eventually a tertiary stage in which the bacteria attack the brain, spinal cord and other organs, which can be very serious, leading to stoke, paralysis, blindness and even death.
Trichomonas Vaginalis (TV)
Trichomonas vaginalis (often known as 'TV') is a protozoan 'bug' that affects the vagina.
It causes a green or yellowish, bubbly vaginal discharge and intense vulval soreness. It also produces a 'fishy' smell.
However, some women have no symptoms at all, and men rarely do.
For unknown reasons, the incidence of 'TV' in the UK has declined sharply in recent years, though it is reported as still being common in the USA. Only about 6,000 cases were diagnosed in UK clinics last year. In addition, a substantial number were treated by GPs.
Bacterial Vaginosis (BV)
The diagnosis of bacterial vaginosis (BV) has become common during the last 10 years, with about 97,000 women per year being seen in GUM clinics, and an unknown number being treated elsewhere.
BV is a common cause of vaginal discharge. The discharge is usually whitish or greyish or sometimes yellowish, and tends to have an off-putting ‘fishy’ odour.
Unlike the discharges caused by thrush or trichomonas, it’s not usually associated with soreness, discomfort or itching.
It's uncertain if BV is transmitted sexually, especially as there's no equivalent condition in males.