Infection by Human papillomavirus (HPV)

Author: Dr. Tímea Tisza

Source: HIPPOCRATES Family medicine and occupational health

Summary

Genital infection by Human papillomavirus (HPV) is currently the most frequently occuring sexually transmitted disease of viral origin. The author provides an overview of the current problems of genital HPV infection based on more than 15 years’ worth of published data. The pubilcation includes detailed discussion of the latent, subclinical and clinical symptoms of the infection in terms of frequency, the mode of transmission, and infection of the sexual partner. Diagnostic tests and the most frequently utilized or recommended treatment schemes are described. The author also discusses data related to the connection between HPV and intraepithelial neoplasias, as well as other diseases of unknown etiology.

Introduction

The significance of the genital infection by human papillomavirus is based on two basic facts.

First, this is the most frequently occurring viral STD of our day, and secondly, based on convincing epidemiological and cellular biological evidence, it is practically accepted that certain types of the virus function as etiological factors in the development of cervical cancer.

The pathogen

Approximately 100 different types of the human papillomavirus, which belongs to the papovaviridae family, are known, of which 50 have been identified in genital lesions. The virus cannot be cultured, the individual types can be identified by the differences in the nucleotides in the double-stranded circular DNA contained by the virus¹, the number depending on the order in which the individual type was identified. Papillomaviruses are essentially species-specific, therefore HPV infects only humans². The productive cycle of HPV is based on the differentiation of the infected epithelial cell, which is the reason it multiplies only in keratinocytes²³. Infection involves the basal cells, the proliferation of which results in the development of verrucae and condyloma. Every cell of the growth contains HPV DNA, but only the early genes are expressed in the lower layers of the epithelium The expression of the later genes, the synthesis of the capsid proteins of the virus and the virus particles takes place in the differentiated , keratinized layer of the epithelium. Viral particles are present in large numbers in e.g., warts on the soles of the feet, while they exist in minimal numbers in genital condyloma. Normal cellular differentiation is gradually lost in cervical intraepithelial neoplasia (CIN) and cervical carcinoma, after which capsid proteins and viral parts are no longer synthesized. Only the transforming E6 and E7 viral proteins continue to be expressed in invasive carcinoma. HPV infection is localized, there is no lytic phase, nor is there viremia, which may be the reasons why the immune response to HPV infection is neither marked nor persistent 4,5.

The frequency and mode of infection

Condyloma acuminatum (genital warts) appears in 1%of sexually active adults, with the highest rate of occurrence in the 19-22 year age group of women, and 22-26 year age group of men.

If the frequency of HPV infection is measured on the basis of cytological smears or HPV DNA tests, instead of by clinical symptoms, epidemiological data of significantly higher proportions can be observed. In combining results of various tests carried out on healthy young men, the HPV infection rate is in the range of 5.8-31% (8,9,10). In follow-up studies, the HPV virus was detected in only 6% of the infected in two serially taken samples (11), which supports the well-known tendency for spontaneous remission.

In women, the frequency of occurrence is significantly related to age – 20-25% in the 20-24 year age group, 1-2% (12) above 35 years of age – and the number of sexual partners (13). Test results of sexually inactive women support the hypothesis that HPV is primarily spread through sexual contact, since no positive results or only rarely were positive results found in this population. (14,15,16,17). In 50-70% of cases, observable symptoms were present on the penises of male partners of women in whom cervical changes were present (18,19,20,21,22,23,24). Although the clinical manifestations are identical in some of the cases, it is not rare for the male partner to be infected by a different type of virus, or by the same virus of a different phylum (25).

Infection occurs primarily through sexual contact, although other paths of infection are also possible. The infection can be spread via infected articles or from the mother to the newborn during birth, which can resul in larnygeal papillomatosis (usually appearing at 2-3 years of age) or the developmet of genitoanal lesions in children(26). Infection from mother to child is primarily the prenatal or perinatal transmission of types 6,11,16 and 18 of HPV. Infrequently, genital condylomatosis is observed in children, caused by autoinoculation by types 1 or 2, which otherwise cause verruca vulgaris (common warts).

Anogenital condylomatosis in children can also be the result of sexual abuse; however, the significance of this is difficult to estimate, since the relevant published data (28) has significant variance (4-91%).

The symptoms of the viral infection and the problems of clinical diagnosis

Infection by HPV does not necessarily mean that clinical symptoms are present; the infection may be latent, subclinical or clinical.

The latent infection can only be proven using HPV DNA testing as clinical symptoms are not observable, nor does the histological examination signal the presence of the virus in many cases. In subclinical infection, symptoms are not visible to the naked eye, but the histological picture is typical (see below). In clinical infection, various, well-known pathological forms may appear in the genitoanal region. The classical picture of condyloma accuminatum (genital warts) is the presence of skin-colored growths of varying number and size on the genitalia, anus, perineum, inguinal fossa, pudendum. Flat condyloma are somewhat less frequent, grow less exophytically, tend to have papular exteriors and a less explicit wart-like characteristic of their surface, while multiple, mainly pigmented, papular lesions can be observed in the case of bowenoid papulosis.

Unusual clinical manifestations make diagnosis difficult, in which case the acetic acid test can be helpful. Painting of the suspicious lesion with 5% acetic acid (29) causes the lesion to turn white. Subclinical changes can be demonstrated with the test, but the results should be critically assessed, as other lesions of inflammatory origin in the anogenital region may also test positive (18,30,32,32).

In addition to the use of acetic acid, changes in the cervix and penis can also be colposcopically examined (colposcopy, penoscopy), which is an important diagnostic step in the identification of preneoplastic and neoplastic lesoins (33). HPV-caused morphological changes examined by colposcopy and penoscopy may be typical (well-defined lesions with slightly raised edges, point-like capillaries), suspicious (without point-like capillaries), and atypical (undefined edges and without point-like capiallaries) (5). A biopsy specimen can also be more safely taken with the magnification of colposcopy, the extent of the affected area can also be more exactly judged in the course of local treatment.

Options for laboratory diagnosis

The establishment of a correct diagnosis requires specimen collection by swab or biopsy for the purpose of cytological, histological examination and/or HPV DNA testing.

Only a fraction of total cases can be identified through cytological examination – the reason being that cytomorphological changes develop in the virus-infected epithelium only in some cases, or are present in very discrete form (34). The two most typical deviations are the presence of koilocytes and dyskeratocytes. In koilocytes (balloon cells), an irregular, sharply defined, light halo is always visible around the cell nucleus. The nucleus appear to be positioned in the center of a large cavity (koilos = cavity). The cytoplasm of dyskeratocytes is smaller than the superficial cell and exhibits keratinization. The nuclei are larger, more hyperchromic, and the structure of the chromatin is difficult to recognize.

In addition to the criteria of histological diagnosis – hyperplasia, acanthosis, hyper/para/dyskeratosis – the presence of koilocytes is pathognostic (35). Although the diagnostic value of histologic examination is highly valued by some authors and disputed by others, the reigning view is that histopathologic signs of HPV infection cannot be considered to be of diagnostic value; as with all infectious disease, the “gold standard” can only be the demonstration of the pathogen (36).

Laboratory techniques for HPV DNA diagnosis, depending on whether the DNA in the specimen was multiplied or not before testing, can be either “non-amplified” or “amplified” techniques. Among the non-amplified procedures, the classic Southern blot, dot blot, in situ hybridization and filter in situ hybridization have not become widely used in routine diagnosis due to various methodological problems (37,38).

Hybridization in solution (hybrid capture test)(39) and the amplification technique, the polymerase chain reaction (PCR) is currently used worldwide for routine diagnosis.

The hypbrid capture method is suitable for determining the presence of “low risk” or “high oncogenic risk” viral groups (group A or B) in the tested specimen, while PCR is capable of identifying the specific type of virus contained in the specimen. This provides an opportunity to judge the efficacy of treatment or to substantiate the persistence of the virus (the probability of malignant transformation increases with the persistence of particular oncogenic viruses). In addition, the „amplification” technique – which multiplies the DNA in the specimen and detects the multiplied nucleic acid – makes for a significantly more sensitive detection of the virus than do the “non-amplification” techniques.

Therapeutic options

Currently available therapies cannot cure human papillomavirus infections. The goal of the treatment is to eliminate the lesions caused by the infection, for which numerous methods are used: locally applied cytostatic agents (podofillin, podofillotoxin, 5-fluoouracil, bleomycin), various forms of surgical or other instrumental intervention (cryotherapy, diathermic coagulation, carbon dioxide laser treatment, surgical removal) and non-specific immune stimulation (locally: interferon, imiquidmod; systemic: interferon, inosiplex, levamisol).

Based on data from the literature and our own experience, there is no significant difference in the effectiveness of these methods and, unfortunately, the occurrence of relapse remains high in connection with each of the methods (41,42).

The treatment is more successful with less extensive condylomas, which have been present for less than one year. Most specialists agree that relapses are usually due to a reactivation of the subclinical infection and not from reinfection by the infected partner. Various publications mention urethral reservoirs in men and endocervical reservoirs in women (43,44).

Without treatment, a condyloma can spontaneously disappear, stagnate or grow. In placebo-controlled studies, untreated condylomas disappeared spontaneously in 20-30%of patients within 3 months.

Choice of therapy depends on anatomic location, the size and extensiveness of the lesions, cost of treatment, effectiveness, and the risk of side effects.

Carbon dioxide laser treatment and surgical intervention is recommended in the case of extensive lesions, which are refractory to other treatments. Interferon treatment is very costly, side effects are frequent and it is not more effective than other treatments. Data regarding non-specific immune stimulation with inosin panobex is inconsistent (45, 46).

Creams containing 5-fluorouracil (pyrimidine antagonist, which blocks RNA/DNA synthesis) are also useful (47). Painful ulcerations may occur as a side effect. The creams may also be used prophylactically, to prevent recurrence following removal of the condylomas with other methods (48,49).

Recommended therapeutic schemes

(Based on the recommendation of the Centers for Disease Control)

For condyloma on the external genitalia-perianal region:

1. Cryotherapy – not particularly costly, does not require anesthetic, no scarring with proper usage; requires special instrumentation, moderate pain following treatment. Effectiveness: 63-88%, rate of recurrence: 21-39%

2. 0.5% podofilox solution – can be self-administered, twice daily for 3 days, followed by 4 days of non-treatment. Treatment cycle should be repeated no more than 4 times. The treated territory should not be larger than 10 cm² and the total dose should not exceed 0.5 ml/die. Embryotoxic, contraindicated for pregnant patients! Not particularly costly, simple to use, safe. Pure compound, does not break down, does not have to be washed off. Mild or moderate irritation may result. The more keratinized lesions may not react as readily as those located on a moist surface. Can only be used in locations which the patient can physically reach. Effectiveness: 45-88%, rate of recurrence: 33-60%.

3. Podophyllin 10.25% solution – Podophyllin is the alcoholic extract of the aPodophyllum emodi and the Podophyllum peltatum plants, and has been used since 1944 for the treatment of condyloma acuminatum (50). The biologically most active component is podofillitoxin, which exerts its antimitotic effect in the metaphase of cellular division, thereby casuing necrotization of the condyloma (51).

A few reports exist of severe, systemic side effects, related to the neurotoxicity of the remedy (weakness, polyneuritis, paralyticus ileus, coma, death) (52).

Must be repeated weekly. If the lesion does not react after 6 treatments, another treatment should be subsituted. The maximum dose per occasion is the same as for podofillotoxin. Embryotoxic, contraindicated in pregnancy! Inexpensive, easy to use. Local irritative dermatitis is frequent, therefore it is recommended that the treatments be carried out by the physician, not the patient. Must be washed off after several hours. Keratinized lesions react less readily than those located on the moist mucous membranes. Effectiveness: 32-79%, rate of recurrence: 27-65%.

4. trichloroacetic acid 80-90% – Should be applied only on the condyloma, non-reactive acid must be neutralised using talcum or sodium bicarbonate. Weekly repetitions required. If the lesion does not react after 6 treatments, another treatment should be substituted. Very little data available. Effectiveness: 81%, rate of recurrence: 36%

5. electrocauterization – Contraindicated for patients with pacemakers and with lesions close to the anal sphincter. Effectiveness: 94%, rate of recurrence: 22%. Requires local anesthesia.

Considerations and recommendations for special localizations and patient groups:

Cervical condyloma: dysplasia must be ruled out in every case before beginning a treatment. Cryotherapy may be appropriate for the treatment of lesions of CIN (53) and gravid (54) patients.

Intravaginal condyloma: 1. cryotherapy (contact treatment in the vagina is contraindicated due to risk of perforation and fistulization) 2. TCA 3. podophyllin on territory not larger than 2 cm² per treatment occasion. Extra care required to avoid systemic side effects (absorption!).

Condylomas of the meatus urethrae: 1. cryotherapy 2. podophyllin for 1-2 hour period

Perianal condylomas: 1. cryotherapy 2. TCA 3. surgical intervention. Proctologist should carry out treatment in the event of involvement of the rectal mucosa.

Mouth: 1. cryotherapy 2. electrocauterization 3. surgical removal

Anogenital condylomatosis of gravid patients: cesarean section recommended if the condyloma represents an obstacle in the birth canal, or if excessive bleeding is expected during delivery.

HIV-positive patients: The effectiveness of the usual therapies is lower, the recurrence rate is higher than for other patients. Recall that human papillomavirus infection which is extensive, therapy-resistant, and appears at an unusual age can be considered to be diagnostic in the case of undiagnosed HIV-status, and can have prognostic value for known HIV-status.

Advising the patient, prevention of further spread of the infection

The examination and treatment of the patient’s sexual partner is recommended. The patient with exophytic anogenital condyloma acuminatum must understand that the illness is contagious. The majority of partners are likely to be subclinically infected, even if there are no visible lesions. Screening tests are currently not available. Even after the condyloma is removed, the patient cannot be considered cured of the infection, since the virus may be present in the surrounding, healthy-looking tissue, just as visibly symptom-free individuals may be carriers of the virus. The use of condoms can prevent further spread of the infection to the non-infected partner, as well as to new partners. It is not clear whether or not the patient with condyloma acuminatum is more infectious than individuals with latent or subclinical infections.

Oncogenesis

Cervical carncinoma was already considered to be a sexually transmitted disease more than 40 years ago (56); writings from as early as 1842 state that the disease occurs extremely rarely in sexually inactive women (57). Numerous risk factors associated with sexual behavior were assumed in connection with the development of cervical carcinoma, among which were age at first sexual intercourse, the total number of sexual partners, and various genital infections, such as infection by Chlamydia trachomatis, cytomegalovirus, herpes simplex virus. Additional risk factors were identified in connection with epidemiological analysis, such as smoking, multiple childbirths, use of oral contraceptives, dietary habits and lower socioeconomic status. The factors related to sexual behavior are also known risk factors for the acquisition of HPV infection.

The idea that HPV plays an important role in carcinogenesis emerged more than 10 years ago (58). The genomes of the “high risk” viral group were demonstrated in virually 100% of tumor specimens. (59, 60, 61, 62).

The cumulative HPV prevalence exhibits a growing tendency in line with the degree of dysplasia; using PCR, the virus was detected in mild dysplasias with a frequency of 71%, and in 100% of in situ carcinomas(60).

Since both the vulva and the cervix are exposed to the same external influences, including HPV infection, the question of whether HPV infection has a role in the development of vulva carcinoma also arose. Data taken from the relevant literature indicates that HPV DNA was found in 0-80% of vulva carcinoma samples, 52% on average (63). Vulva carcinomas can be categorized into three types: keratinized flat epithelium, papilloma and basaloid carcinoma (64). The first type is the most common, appearing mainly in older women and is rarely seen together with VIN III. The latter two types occur typically in younger patients, with dysplasia in the surrounding tissue occurring in 78% of cases and lesions which are HPV-positive in 75% of cases (64).

Although the primarily oncogenetic HPV genome has been demonstrated in penis carcinoma 65,66,67), the etiological role of the infection has not been duly established, i.e., the identification of HPV is much lower in penis carcinoma, than in severe PIN (68). A fact which may support the sexual transmission of the disease is that there is a significantly high number of women who succumbed to cervical carcinoma among the wives of patients with penis carcinoma (69,70).

Some publications support the possible role of HPV infection in the development of anal flat epithelial cancer. 55% of patients with anal carcinoma were found to be seropositive with respect to HPV 16 capsid, as compared to 4% for the control group (71). Examination of in situ hybridization of anal carcinoma tissue revealed that the HPV genome was found in 34% of the samples, mostly types 16 and 18 (72).

HPV DNA has been demonstrated very rarely in cases of oropharyngeal flat epithelial cancer, but its pathogenic role has not been clarified (73,74,75).

However, a correlation has been made in the case of oral koilocytotic dysplasia, where an occurrence of 80% has been registered using ISH (76).

Virtually no correlations have been found thus far in examinations of esophageal flat epithelial cancer (77,78), bladde rcarcinoma (79) and prostate carcinoma (80).

The etiologic role of HPV infection has been considered in certain benign illnesses of unknown etiology (balanitis plasmocellularis Zoon (81), vulvaris vestibulitis (82), prostate hyperplasia (83)), but this has not been corroborated.

(Bibliography available from the author)