Human papillomavirus: morphology, reproduction, and sexual transmission

Human papillomavirus (HPV) is a virus that causes warts. HPV is one of the most common sexually transmitted diseases (STDs). It belongs to the Papovaviridae family. HPV is a small oncogenic DNA virus, which infects epithelial cells of skin and mucous membranes. The epithelial surfaces include all areas covered by skin and/or mucous membranes of the mouth, genital and anus (the area that poop comes out of). A definitive diagnosis of HPV infection depends on the detection of nucleic acids (DNA or RNA) or proteins.

Morphology

HPV is a relatively small, non-enveloped virus, and 55 nm in diameter. It has an icosahedral capsid composed of 72 capsomers, which contain at least two capsid proteins, L1 and L2. Each capsomer is a pentamer of the major capsid protein, L1. Each virion capsid contains several copies (about 12 per virion) of the minor capsid protein, L2. The virus is said to somewhat resemble a golf ball when viewed by electron microscopy.

How does HPV reproduce?

All cells in the abnormal tissues (such as warts) caused by HPV contain the DNA of HPV. DNA is a chain of many connected genes. Genes are tiny structures that contain coded instructions for how proteins should be constructed and how certain bodily characteristics should develop. Genes are contained in structures called chromosomes.

The genes of most viruses will not become activated until an infected type of cell (known as a keratinocyte) leaves the bottom section of the epidermis. The epidermis is the top layer of the skin that does not contain blood vessels. The reproduction of keratinocytes in the bottom section of the epidermis is what is thought to lead to the development of abnormal tissue areas.

Production of HPV occurs in the epithelium, where the cells are discarded off into the environment. More specifically, when the discarded cells degenerate, the virus is released. Epithelium is a group of cells that occur in one or more layers, which cover the entire surface of the body and line most of the hollow structures in it.

The HPV virus only multiplies in the nucleus (central structure) of affected cells. As a result, the nuclei of affected cells have a very abnormal appearance under the microscope. An example of such an abnormality is koilocytosis. Koilocytosis refers to the presence of squamous cells that often have two nuclei and small holes near the nuclei. The presence of koiliocytosis is characteristic of the human papillomavirus (HPV) infection.

How is it transmitted?

About 33% of HPV types can be passed on from person to person, through sexual contact. Sexual activity is most commonly associated with higher risk for anogenital and/or mucosal types of HPV. During sexual intercourse or after minor scraping of the skin, the epithelium can become disturbed, allowing HPV to come through and cause an infection.

Some studies have estimated that most sexually active people are exposed to at least one or more types of HPV. All forms of sexual intercourse, including anal and oral sex are all capable of spreading HPV. Even foreplay can lead to the spreading of HPV and cause warts to develop on the hands or in the mouth. The virus passes through skin contact with an infected person, such as touching an infected wart.

Having sex at an early age (especially age 16 or younger) or having many sexual partners leads to an increased chance of getting HPV. One does not need to have many sexual partners to come in touch with the virus since it is so common. Having sex with a partner that has or has had many sexual partners increases the chance of getting HPV. Someone is most likely to pass on HPV after he/she first gets the virus.

It is more common for HPV to be spread through sexual intercourse in women who have visible warts. In fact, about 66% of people who have sexual contact with a person with genital warts will develop HPV. This usually happens within three months of contact with the genital warts.

It is also true that about half of people that have HPV never develop genital warts. HPV can be passed on from people who do not have warts or who have had warts in the past. This indicates that the virus is passed on through body fluids, such as fluids in the cervix or semen. Semen is a fluid that is discharged from a male's penis in order to reproduce with a female. If a person or his/her partner has a history of genital warts, sexually transmitted diseases, cervical cancer, penis cancer, or abnormal Pap smears, it increases the chance of getting HPV.

Just one episode of unprotected sexual activity with a person that has HPV carries a 60% risk of being infected with this virus. Women with another type of sexually transmitted virus known as HIV (human immunodeficiency virus) who also have HPV have a 40% greater risk of developing severe abnormalities in the cells of the cervix compared to women with HPV that do not have HIV. People with HIV and lowered body defenses are more likely to develop HPV. People with lowered body defenses are especially likely to be infected with HPV if they have skin cancer.

Sexual contact is not the only way to spread HPV. For example, if someone with HPV, related warts on the bottom of the feet walks barefoot, he/she can spread this virus. This is because HPV can survive for months in cold temperatures without a host (organism to live in or on). When another person walks on the area of the floor that the barefoot person walked, he/she can get infected with the virus on the floor.

Symptoms of HPV

HPV may exist without any apparent symptoms. However it may display some signs of its presence in most people. People with compromised immunity tend to develop symptoms quicker and with greater intensity. It may take between 3 weeks and 2 months from the time of infection, for symptoms to appear, though in some individuals, no symptoms may develop for an indefinite period. The common symptom of HPV is the presence of warts in the genital area and inside the anus. The warts can be felt by passing a finger over the affected skin. The infection may coalesce into larger eruptions and acquire one of a set of characteristic forms. They may also be pigmented and display color. There are 5 common kinds of warts. The first kind has the appearance of a set of small cauliflowers put together. The second kind of warts has smooth surfaces with dome like shape. The warts may group to form a plaque, which is the third kind of wart. The fourth kind is flat and may have a distinct color. Warts in the mucous membrane tend to be white and constitute the fifth kind. A patient may have more than one kind of wart. The infection may increase to the extent that it causes itching and may bleed as well. The warts may become cancerous, though such progression of the disease is rare.

How is HPV infections detected?

Testing sample of cervical cells is an effective way to identify high-risk types of HPV that may be present. This test, which looks for viral DNA is performed by collecting cells from the cervix and then sending them to a laboratory for analysis. The test can detect high-risk types of HPV even before there are any conclusive visible changes to the cervical cells.

How is HPV treated?

HPV cannot be cured, but the warts can be treated. Although warts may go away on their own, the viruses can remain. If warts do not go away or if they recur, they may need treatment. The type of treatment depends on where the warts are on your body. Warts can be treated with medication applied to the area or surgery to remove them.

If you have a lot of warts, or very large ones, your doctor may recommend that they be removed with surgery. Although all these treatments destroy the warts, the virus may still be in nearby tissue. It can produce new growths weeks or even months after the old ones are gone. You may then need more treatment.

How can HPV be prevented?

The only way to prevent contracting HPV is to avoid the virus altogether. The chances of contracting HPV can be reduced by not having sex or by using spermicides (substances that kill sperm). Sperm is the male sex cell that joins with the female egg to produce offspring.

Reducing or avoiding risky sexual activity (such as reducing the number of sex partners) can decrease the chance of developing HPV. Having sex with condoms made of latex or polyurethane may decrease the risk of developing conditions related to HPV, such as genital warts and cervical cancer. Latex and polyurethane are two substances that help make flexible materials.

Condoms do not offer full protection from HPV because the virus may be found on parts of the body that is not protected by the condom, such as the anus. However, they may reduce the risk of getting HPV when used correctly and consistently. Condom use has also been associated with decreased risk for diseases related to HPV, such as cervical cancer.

Doctors recommend that people avoid having contact with partners that have genital warts, until the warts are treated. This can decrease the chance of getting HPV. It is important to mention that going to a doctor for regular check-up can easily prevent cervical cancer, which is one of the possible results of HPV infection.