HPV type 6

The human papillomavirus (HPV) is associated with a wide range of diseases, from skin warts to life-threatening cancers. HPV type 6 is a non-oncogenic virus, meaning it does not cause cancer.

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Structure HPV type 6

All types of human papillomavirus of the Papovaviridae family have the same structure, and HPV type 6 virions also exist in the form of an icosahedral capsid with a diameter of 52-55 nm, built from several dozen units of structural proteins L1 and L2 - self-organizing pentameric capsomeres.

The capsid, unprotected by a lipid membrane, contains a single circular DNA molecule of the viral genome, consisting of two strands or threads linked by proteins of the cell nucleus, called histones. The genome contains approximately eight open reading frames (ORFs), all of which are transcribed from a single strand of DNA.

HPV 6, like other papillomaviruses, is highly epitheliotropic, adapted to the host, and protected from the cell-mediated immune response. By expressing viral genes and replicating its DNA, it neutralizes immunocompetent cells of the epidermis (T cells, macrophages/monocytes, etc.) and penetrates into the keratinocytes of the stratified epithelium of the skin of the anogenital area and oral cavity. The life cycle of the virus, primarily its lytic phase, is associated with the differentiation of basal cells that ensure the proliferation of skin tissue cells.

For replication, HPV has proteins (E1-E7) that recognize its origin, regulate gene transcription and stimulate differentiating skin cells to repeatedly undergo the period of DNA doubling, that is, the S-phase of the cell cycle.

A feature of papillomavirus type 6, as a virus of low oncogenic risk, is the absence of aggressive inactivation of cellular tumor suppressor proteins p53 and pRb by its potentially oncogenic proteins E6 and E7, which do not lead to the launch of the program of malignant differentiation of skin cells and their mutation (which occurs in carcinogenic types of HPV).

In addition, this virus has a latent phase of the life cycle, when after the initial infection, the division of viruses ceases. At this stage, their genes can remain passive for a long time, located in the cytoplasm or nucleus of the host cells - in the form of individual structures of episomal DNA. However, the virus is able to reactivate the process of DNA replication without re-infecting a person.

How is HPV 6 transmitted? Most often, the virus is spread through skin contact between an infected and uninfected person - sexually.

Read also – Human papillomavirus: structure, life cycle, how it is transmitted, prevention

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Symptoms

HPV 6 infection can be overt, subclinical or latent. Its symptoms on the skin and mucous membranes – anywhere on the external genitalia, in the anal area and even in the mouth – are clinical manifestations of low-grade squamous intraepithelial lesions, which are diagnosed as condylomata acuminate or genital warts.

They appear on the skin of the vulva, vagina, cervix, groin, penis, scrotum or perianal area. They may appear as hyperkeratotic macules, plaques or papules of varying colours; they often appear as fleshy soft lesions, sometimes resembling miniature cauliflower. They are always contagious; in most cases they are painless, but they may cause discomfort and irritation with itching; they may increase in size, remain unchanged for years or spontaneously regress.

When the lesion becomes very large (5–10 cm) and extends into deeper tissues, it is called a giant condyloma of Buschke and Loewenstein. This benign lesion is most commonly found in men on the glans penis and foreskin, but can also be a perianal lesion in women.

For more information on HPV type 6 in men, see – Genital warts in men.

For more information on HPV type 6 in women, see the publication – Genital warts in women.

The activation of the HPV 6 DNA replication process and pregnancy are linked by a state of physiologically conditioned immunosuppression, which contributes to relapses, as well as accelerated reproduction and growth of genital warts. In most cases, they spontaneously regress after childbirth. All the details are in the material - Papillomas during pregnancy.

But their presence in pregnant women can lead to intranatal infection (during childbirth) and such a rare manifestation of HPV type 6 in a child as laryngeal papillomas or recurrent laryngeal papillomatosis, which makes breathing difficult and may be accompanied by coughing and problems with swallowing.

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Diagnostics

Methods such as electron microscopy, cell culture and some immunological methods used to diagnose viral infections are not suitable for detecting HPV.

To visualize subclinical genital HPV-associated lesions, an acetic acid test is performed: placing a gauze pad moistened with a 3-5% acetic acid solution on the affected area (for 10 minutes) makes invisible flat genital lesions visible (they turn white).

False positive results are common and may be due to focal parakeratosis in candidiasis, psoriasis or lichen planus.

Important diagnostic methods for HPV type 6 include biopsy and human papillomavirus testing.

Quantitative detection of HPV 6 can be performed by real-time polymerase chain reaction (qPCR) – kinetic monitoring of viral DNA amplification. Although this does not always allow identification of the specific virus type.

Also read – Human papillomavirus infection: detection of human papillomavirus.

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Treatment

Treatment of human papillomavirus should not be understood as drug therapy for persistent papillomavirus infection (there are simply no such drugs), but as treatment for visible warts.

According to experts, on average, in 56% of cases of squamous intraepithelial lesions of HPV 6, three years after their detection, spontaneous regression of formations is observed, which can recur at various intervals, especially against the background of weakened immunity.

External agents are used in treatment, in particular, Podophyllin solution, various ointments for papillomas. Surgical treatment is possible using cryo-, electro- and laser methods of removing genital warts.

Detailed information in the article - Review of effective methods of treatment of genital warts

There is no consensus among doctors regarding systemic immunotherapy for papillomavirus infection. For example, a combined immunostimulant drug Isoprinosine for HPV 6 (other trade names: Inosine Pranobex, Groprinosin, Gropivirin, Groprim, Neoprinosine, Dimepranol, Normomed, Inosiplex, Methisoprinol) can be prescribed as an additional therapy. Manufacturers equate immunomodulatory drugs with antiviral drugs, assuring their etiotropic action. Although among the components of Isoprinosine - inosine, 4-acetamidobenzoic acid and N-dimethylamino-2-propanol - none has a pharmacological effect on papillomaviruses. In addition, the latter ingredient is a precursor of psychotropic drugs.

Prevention HPV type 6

Experts estimate that a significant proportion of the general population is subclinically infected with one or more sexually transmitted HPV types.

Therefore, prevention includes protected sexual intercourse – the use of condoms, although it is only partially effective: warts can easily spread from areas not covered by a condom.

Vaccination will protect against HPV 6 - Vaccination against human papillomavirus with Gardasil vaccine 9).

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Forecast

Having genital warts is not associated with an increased risk of developing cancer in the future. However, the HPV virus cannot be eliminated: even after removing the warts, almost a third of patients experience recurrence of genital warts.

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