Where does Human papillomavirus come from and How are HPV infections prevented?

Warts, the kind that appear on the skin, often of older children, are common and benign.

There are various treatments that can get rid of them, but most of them go away by themselves after a year or two. Yet there are many viruses, probably 60 or more, that cause warts, and the warts these viruses cause are not all alike. Some of them have consequences that are not benign.

Human papillomavirus (HPV) is transmitted during sexual contact. This is the virus that causes genital warts, although a person can be infected with HPV and have no symptoms.

At any one time, 20 million Americans are infected with HPV, and the disease is quite contagious, there are 5.5 million new infections every year. There are 30 different types of HPV that can infect the genitals. Some cause warts, others don’t, and most of these infections clear up by themselves, although reactivation is always possible.

There are treatments for the warts, including some that can be done by the patient such as using podofilox and imiquimod, which are creams or gels that can be applied directly to the warts. A health care professional can also apply the topical preparations podophyllin resin, trichloroacetic acid (TCA), or bichloroacetic acid (BCA). Injecting interferon directly into the warts can also be effective. A doctor can perform cryotherapy (freezing) or surgical removal. But the types of HPV that don’t cause warts are more common.

When these latter infections are persistent, there is no effective treatment, and they can lead to cervical, penile, and anal cancer. Persistent infection of the cervix with certain of these viruses is the chief risk factor for cervical malignancies, there are four of them that account for 80 percent of cervical cancer. Although researchers are now working on it, there is still no vaccine to prevent HPV.

Sexually transmitted HPV is very common among reproductive age Americans. Estimates are that 75 percent of that population has been infected at one time or another, and that currently 15 percent of Americans between 15 and 45 have HPV. In a study of female college students, 43 percent became infected during the three-year period of the study. Among women under 25, studies show prevalence rates of between 28 and 46 percent.

Most HPV infections don’t have any symptoms, and there isn’t any way to tell if you have it by a physical exam or even by an examination of a sample of cells under a microscope. Some types of HPV cause abnormal Pap smear results, but the most reliable way of finding out if you are infected is through a test that reveals the presence of HPV DNA.

The most common serious consequence of HPV infection is cervical cancer. Most types of the virus don’t lead to cancer, but more than 90 percent of cervical cancers are preceded by some form of HPV infection. This doesn’t mean that HPV is the cause of cervical cancer, many other factors are involved, including the number of sex partners, age at first intercourse, other infectious agents besides HPV, cigarette smoking, certain dietary deficiencies, and immunosuppression. But HPV infection is certainly one of the most powerful risk factors, and preventing HPV infection would surely lower the number of cases of cervical cancer.

The best method for detecting cervical cancer at its earliest possible stage is an annual Pap smear and pelvic examination for all women who are or who have been sexually active or who have reached age 18. After a woman has had three or more consecutive satisfactory normal annual examinations, the Pap test may be performed less frequently at the discretion of her physician.

HPV infection also puts you at greater risk for anal cancer, a relatively rare malignancy but one with an increasing incidence. Over the past 25 years there has been a substantial increase in anal cancer among men who have sex with men, and a somewhat smaller increase among women. Although anal Pap smears are not widely used for this purpose, they may be as sensitive a detector of anal cancer as they are of cervical cancer, and there is reason to believe that screening for anal cancer among susceptible populations may be worth the effort. There is no test for penile cancer, it can only be found by biopsy of a suspicious lesion found on physical examination.

Prevention of HPV infection is fraught with problems. The spread of HPV is a function of three factors: how easily the virus can be transmitted, the duration of the infection once you have it, and the number of new partners an infected person has.

Condoms probably don’t benefit either men or women because HPV can involve the external genital skin and not just the mucosal linings of the reproductive tract. There is some evidence that certain microbicides may be effective in inactivating HPV, but this is still uncertain and there is currently none approved for use. There is no pill or shot for HPV as there is for syphilis and gonorrhea. The treatment of genital warts reduces viral DNA and mRNA in subsequent biopsies, but nearby clinically normal skin or mucosa often contain HPV, which may explain why people get reinfected.

What should you know if you are infected? You should know that there is a high prevalence of the infection among sexually active adults, that the infection is contagious through sexual activity, and that it can be persistent for an indefinite amount of time after treatment. You should know that condoms don’t help prevent transmission, but that their use for the prevention of other STDs is still important.

Because HPV is so common among sexually active people and because the duration of infectiousness is unknown, the value of disclosing a past infection to a sexual partner is unclear. Still, frank discussion of past STDs is almost always a good idea.