Sexually Transmitted Infections


Sexually Transmitted Infections (STIs), formerly called venereal diseases, infections that are spread by sexual contact. These can be infections of the skin around the genitals (external genitalia), spread by skin-to-skin contact; infections of the internal reproductive tract such as the male urethra (the tube through which urine passes out of the bladder), prostate, or testicles, or female urethra or vagina; or infections of the uterus, spread by unprotected penetrative sexual intercourse. Other STIs transmitted by unprotected sexual contact can infect the entire body (systemic infections) such as human immunodeficiency virus (HIV) and hepatitis B. Safer sex, by using a condom, is the best way of preventing transmission of STIs during sexual intercourse.

The term “sexually transmitted disease” has previously been commonly used to cover this subject, but today it is considered too restrictive, as some such diseases can also be transmitted by non-sexual means.

Many STIs, particularly Chlamydia, have no symptoms at all, and many people who are found to have STIs had no previous symptoms or signs that they had an infection. Some STIs can cause an abnormal discharge from the vagina or urethra. These include Chlamydia, gonorrhoea, Trichomonas, and non-specific urethritis (NSU).

STIs such as genital herpes, syphilis, chancroid, lymphogranuloma venereum, and Donovanosis (Granuloma inguinale) cause ulcers on the genitals.

Genital warts are caused by the human papillomavirus (HPV). There are several different types of this virus. Warts that appear on the skin of the genitals are called Condyloma acuminate and are diagnosed by being able to feel and see warts, and are similar to those that occur on other parts of the skin. A different type of HPV can infect the cervix. This is only seen in a Pap test or Pap smear, or by a procedure that looks for this on the cervix (colposcopy), and it is connected with cervical intraepithelial neoplasia and cervical cancer. Other lesions with a wart-like appearance can be caused by molluscum contagiosum.

There are some infections of the female reproductive tract that are not sexually transmitted, but can result in vaginal itchiness or soreness and vaginal discharge, such as candida and bacterial vaginosis.

Scabies (Sarcoptes scabiei) can be spread by sexual contact, although household spread is also common. This infection causes an itchy skin rash in the external genitalia, or other areas of the skin, particularly fingers, wrists, and elbows.

Crab lice are caused by a bloodsucking louse named Pthirus pubis, which may be found on any hairy area of the body but most frequently in pubic hair. Lice are transmitted by close body contact. It results in itchiness in the area, and the lice and eggs (nits) can often be seen, as well as a black powder (the louse faeces).

Syphilis is caused by the bacteria Treponema pallidum, and causes painless genital ulceration in the primary phase. In the secondary phase, syphilis can infect any system in the body including the skin, lymphatic system, and the brain.Some STIs can spread to internal reproductive organs such as the uterus, Fallopian tubes, prostate, and testes. In women this is called pelvic inflammatory disease and is often caused by Chlamydia or gonorrhoea infections spreading to the internal reproductive organs, where it may cause infertility.

Urinary tract infections can often lead to a burning sensation on passing urine, and the frequent need to do so. In women this is very rarely due to STIs. However, in men these symptoms can be indicative of an STI, particularly if associated with a urethral discharge.

Transmission of all these diseases occurs only by intimate contact with an infected person, because all of the causative organisms die quickly if removed from the human body. Although the usual area of contact is the genitals, anal and oral sex also lead to cases of anal and oral infections. A few of these diseases, notably chancroid and scabies, can be spread by the infected person from one area of skin to another by the hands; scabies, lice, genital herpes, and vaginitis caused by Trichomonas and monilia may also be acquired by other than sexual contact. Gonorrhoea, syphilis, and chlamydial infections can also be transmitted from a pregnant woman to her infant, either in the womb or during birth. Such congenital infections can be quite severe.


The global trend of STIs has changed over time. Whereas syphilis and gonorrhoea were both epidemic at one time, widespread use of penicillin brought syphilis under moderate control. Attention then turned to control of gonorrhoea, at which time syphilis again began to increase in frequency. Genital herpes, NSU, and Chlamydia increased in the 1970s and early 1980s.

In the United Kingdom and the United States sexually active people under 25 years and people with multiple sexual partners are at the highest risk of contracting STIs, and genital warts and Chlamydia are the most common infections. Penicillin has been an effective drug against syphilis and gonorrhoea, but many gonorrhoeal organisms are now resistant to this agent. Spectinomycin is effective in these instances. Tetracyclines are used to treat lymphogranuloma venereum, granuloma inguinale, and chlamydial urethritis. The antiviral drug aciclovir is proving useful in treating recurrent genital herpes. Salicylic acid, or cryotherapy (freezing), is used to treat genital warts.

Other than sexual abstinence, the use of condoms is the principal means of preventing many STIs. Sexual contact should be deferred until any infections have been treated. The spread of STIs can be alleviated by locating individuals who have had sexual contact with the infected person and determining whether they also need treatment. Usually this is done through genital urinary medicine clinics, where the majority of STIs are reported. Locating all sexual contacts, however, can be difficult and by no means are all cases reported.

Sexually Transmitted Infections
Contributed By:
Marie Stopes Internationa