User:Mvolz/Efficacy of condoms at preventing STIs

Condoms are effective at preventing sexually transmitted infections and are one of the most important public health interventions available for preventing the spread of disease. However, efficacy varies depending on the STI; condoms are most effective at preventing HIV and Hepatitis B, and less effective at preventing transmission of other STDs. Condoms are most effective at preventing transmission of diseases that are spread through bodily fluids only (e.g. blood, semen) and are significantly less effective at preventing diseases that are transmitted in other ways (i.e. via skin contact). There is some concern that the public health messages around condom usage has given the public the incorrect idea that condoms are effective at preventing all sexually transmitted infections.

Viruses present in semen
Both the HIV virus and the Hepatitis B virus are present in blood and semen (a serum-derived bodily fluid) but are unable to infect or penetrate the skin. They are able to penetrate mucous membranes, however, even this creates a moderate barrier. Transmission is much higher when there are small tears in the mucous membranes, which are commonly introduced during sex. Viral loads are much lower in vaginal secretions and the anal cavity than are present in semen.

Transmission from the insertive partner (viral particles coming from the semen) to the receptive partner is prevented when semen is prevented from entering the vagina, anus, or mouth. Condoms are highly effective at preventing contact of the semen with the internal mucousal membranes.

Transmission from the receptive partner (viral particles coming from the vagina or anus) to the insertive partner is primarily from the entrance of viral particles through the urinary meatus. If a condom is worn, the condom provides a highly effective barrier over the urinary meatus that prevents the entrance of vaginal secretions or anal secretions into the urinary meatus.

HIV
HIV is the virus that causes AIDS (acquired immunodeficiency syndrome.) AIDS is a significant contributor to morality and morbidity worldwide. There is no vaccine for HIV available, and thus preventing transmission of the disease is essential. Although treatment and PrEP (pre-exposure prophylaxis) reduces the probability of transmission significantly, modelling suggests that these alone are unable to stop the epidemic, and the use of condoms remains essential.

Hepatitis B Virus
Hepatitis B virus is a virus that causes a large proportion of hepatitis causes worldwide and is a significant contributor to mortality and morbidity worldwide. (It is unrelated to the Hepatitis A and C viruses, which are not sexually transmitted). A highly effective vaccine for Hepatitis B is available and it expected that this, in addition condom use, will continue to lower prevalence.

Viral warts and skin lesions
Genital warts and lesions are caused by a variety of viruses, including many subtypes of HPV, Herpes (both HSV-1 and HSV-2), and other forms of wart-causing viruses such as molluscum contagiosum (water warts). Condoms range from being somewhat effective to not at all or unknown effectiveness. This is due to mode of transmission. Unlike with virus like HIV and Hepatitis where skin provides an effective barrier to infection, these viruses are adapted to infecting the skin cells themselves. Thus the infectious surface is typically anywhere there are warts or lesions, and the vulnerable surface includes any skin, including the pubis mons. The condom covers only the skin on the penis, leaving the pubis mons in penetrative partner vulnerable to infection. In the receptive partner, the exterior of the anus and surface area of the pubis mons and the labia majora are vulnerable to infection.

Water warts
Water warts, caused by the virus MCV-1, MCV-2, MCV-3, or MCV-4, is a very mild skin infection more commonly known as a childhood disease. In adults, it is transmitted almost exclusively sexually. Warts typically occur on the pubis mons. They have a fairly long duration, and may be unsightly, or leave scarring, particularly if removed. Whilst conventional wisdom suggests they are only infectious when visible, and therefore visual inspection is effective against transmission, there is some evidence that transmission may occur from asymptomatic individuals. Because the disease is mild, it is of more limited public health interest, and consequently not well studied.

Diseases transmitted by contact between infected muscousal membranes
While condoms are most effective at preventing contact between semen and mucousal membranes, and least effective at preventing contact between the skin of the pubis mon, condoms do offer good protection against diseases which primarily infect mucous membranes. In the insertive partner, the infection is primarily of the urethra. In the receptive partner, infection occurs in the walls of the rectum, vagina, cervix, and throat.