Overview

Sexually transmitted infections (STIs) are originally developed by sexual contact affecting sexually active individuals in a range between 50% to 70%, STIs have high mortality and morbidity rates compared to other infections. Human papillomaviruses (HPVs) are one of the oldest viruses characterised with high diversity in terms of genotype and biological properties, currently, there are about 225 types categorised into 5 groups, the largest groups are Alphapapillomaviruses (α), Betapapillomaviruses (ß), and Gammapapillomaviruses (γ), a subgroup of 15 of the α-types is of high risk as it can cause invasive carcinomas. HPVs are double-stranded DNA viruses without envelope and resistant to acid, heat, and ether.^1,3

Persistent HPV infection accounts for more than 5 % of all cancers related to infection worldwide. Following the infection within 1 to 2 years, approximately 90% of the HPV viruses clear or become dormant. Statistical studies demonstrate that most of the women who were infected with the high-risk HPV serotype were diagnosed with cervical cancer after 3 to 5 years, knowing that HPV causes non-persistent acute infections in the majority.²

HPV Classification

Latest epidemiological classification

According to the International Agency for Research on Cancer (IARC), HPV was divided based on their oncogenicity into the following.¹

• Group 1: carcinogenic to humans, in other words, it has the potential to cause cancer in humans.
• Group 2A: carcinogenic to humans.
• Group 2B: possibly carcinogenic to humans.
• Group 3: not classified to be carcinogenic to humans.

Tropism classifications

HPVs were categorised into two broad groups: 

• Cutaneous HPV: is the main form responsible for common or vulgar warts. In other words, cutaneous HPV causes skin lesions characterised by white-greyish or brown flat or raised bumps, particularly in the hands and feet. The genotypes that are warts-related include 1, 2, 3, 4, and 7. However, cutaneous HPV genotypes 5, 8, 9, 12, 14, 15, 17, 19, 20, 47, and 49 are associated with rare conditions of chronic evolution characterised by familiar dermatosis of several papular and macular elements, this condition known as epidermodysplasia Lewandowsky-Lutz verruciform. It usually appears during childhood, however, within 20-30 years of onset a neoplastic transformation can take place causing squamous cell carcinomas. 
• Mucosal HPV: it includes genotype 6 and genotype 11, they are responsible for the infection in the female and male genitalia, the perianal area, the urethra, and the anus. Mucosal HPV serotypes cause benign mucous lesions that are distinguished specifically by sharp and flat warts.

Transmission route

It occurs via three ways of contact:¹

• Direct contact: this includes oral sexual contact through saliva-saliva or sexual intercourse through genital mucous membranes. Oral sexual contact is one of the most frequent ways of transmission of HPV.
• Indirect contact: due to the use of contaminated medical equipment, linen, or utensils. 
• Vertical maternal-fetal transmission: occurs during childbirth or postnatal. 

HPV infection and carcinogenesis

HPV viruses can be persistent and carcinogenic, this depends on the high-risk HPV serotypes and the omitted viral genes in the host. HPV infection occurs when HPV integrates the viral deoxyribonucleic acid (DNA) into the host cells, omitting the early and late HPV genes E2, E4, E5, L1, and L2. However, the two early viral proteins E6 and E7 are of oncogenic properties, particularly in the high-risk HPV forms, thus, they have the potential to cause cancer. These viruses invade the cervical epithelial cells and use the host machinery to express the oncogenic proteins E6 and E7 resulting in the disruption of the host protein p53 and then retinoblastoma protein (RB). Moreover, the high-risk HPVs (HR-HPVs) can remain in human keratinocytes and maintain chronic status, knowing that these viruses have a very specific type of antigen marking tumour cells. Therefore, the integration of the viral DNA is the major step that leads to cancer, for example, induction of cervical cancer, so persistent HPV is not a sufficient factor to cause cancer. Interestingly, this could be a great pathway to reach antitumor therapeutic goals in the future.  

Oral signs and symptoms

Subclinical infection: acts as a reservoir for transmission of infection in a normal mucosa. 

Squamous papilloma: linked to HPV 6 and 11, it is the most common manifestation of oral HPV infection found on the nonkeratinised mucosa which are soft palate and lingual belly or keratinised which includes the hard palate. It is identified as an exophytic neoformation with a cauliflower surface.

Verruca vulgaris: it is related to HPV 2 and 4, a rare condition in the oral mucosa that infects mainly children. It is located at the level of keratinised mucosa (adherent gingiva, lingual dorsum), self limited resolving in less than 2 years.

Condyloma acuminata: it involves HPV 2, 6, and 11, and it is characterised by a wider base than papillomas and warts and a more pinkish colour. Moreover, it is highly contiguous linked to genital warts, localised on non keratinised mucosa (soft palate, lingual belly).

Squamous cell carcinoma: It is associated in particular with HPV 16, it plays an important role in the pathogenesis of oropharyngeal cancer (cancer of the back of the mouth). There is a whole literature which demonstrates a relationship between sexual behaviours and the incidence of oropharyngeal cancer. However, lately there is a hypothesis that shows a different pattern in regards to the recent oral cavity cancers caused by HPV and that of classic tumours of the oral cavity which is linked to known risk factors as alcohol and smoking.

Diagnostic methods

Molecular diagnosis of HPV

The molecular techniques are the optimal choice to detect HPV DNA because of the complicated cultivation process of HPV in cultures. The diagnostic techniques and genotyping of HPV were classified into the following:²

Nucleic acid detection-based methods: these methods rely on the use of polymerase chain reaction (PCR) to amplify, detect, and type the HPV DNA via using specific primers to amplify the viral capsid L1 gene. The used PCR techniques are the following:

Conventional PCR-based methods: it acts by amplifying the PCR product via using specific probes (labelled DNA nucleotides) that target a type-specific DNA sequence or apply a restriction enzyme to determine the specific DNA sequence in the sample related to a serotype of HPV. 

The PCR following by hybridization–based methods: it could be a traditional PCR technique which is performed on the slide of intact paraffin-embedded tissue followed by hybridization with certain DNA probes, or a PCR method followed by using colorimetric hybridization to specific on microplates.

The real-time PCR-based HPV genotyping-based methods: this method is the most reliable method in terms of sensitivity and accuracy in detecting HPV-DNA and genotyping. This technique is based on using fluorescent probes along with PCR primers. Thus, this method can be used to quantify the viral genome.

HPV E6/E7 mRNA-based Screening Assays: this method is performed through the amplification of the viral oncoproteins E6/E7 messenger ribonucleic acid (m-RNA). In order to amplify the viral m-RNA  instead of viral DNA, the reverse-transcriptase-PCR is the ideal method to be used followed by real-time PCR (quantitative PCR method).

Immune-biochemical-based methods

Enzyme-linked immunosorbent assay (ELISA): it uses specific oligonucleotides probes in microplates and the hybridization is highlighted through a colorimetric reaction. 

HPV neutralisation assay: this assay is characterised by its high reproducibility and used as a gold standard to determine the evaluation of the protective ability of antibodies that are produced by HPVs vaccines during the experimental studies. 

Treatment and future therapeutic studies

There are no specific therapeutics to treat HPVs, as it is sometimes a self limiting infection. However, some scientists believe that HPV can’t be eliminated completely after recovery and still would be a chance for the presence of undetectable levels of HPV. The current available used vaccines are gardasil (quadrivalent vaccine for HPV 6, 11, 16, 18), cervarix (bivalent vaccine for HPV 1, 18), and nonavalent vaccine for HPV 6, 11, 16, 18, 31, 33, 45, 52 and 58. Moreover, these vaccines can act against certain oncogenic HPV serotypes which are between 2 and 7, also they prove their efficiency to reduce the incidence of the disease in the long-term. Interestingly, some studies proved that HPV vaccination is an effective program in cancer prevention.

Furthermore, some researchers have shown that current vaccines will not be effective for preventing all HPV types responsible for causing cancers. Additionally, Japanese scientists in 2019 reported the detection of rare unusual symptoms after HPV vaccination in a significant number of girls in adolescent age, they were complaining of a psychiatric illness in the absence of clinical findings or laboratory tests. Thus, the recommendation of vaccination was withdrawn by the Japanese Ministry of Public Health. However, at present the vaccination program is implemented in many countries as Argentina, Australia, Belgium, United Kingdom, Canada, USA, Italy, Ireland, Spain, France, Germany, Greece and others. 

There are currently several forms of vaccines assessed in the preclinical and clinical trials : cell-based vaccines, nucleic acid, protein or peptide, and live vector. The monovalent anti-HPV 16 vaccine has not been released yet.^1,2

Summary

Human papillomaviruses are one of the oldest existing viruses of high diversity transmitted through oral sexual contact, sexual intercourse, contaminated medical equipment, and infected mother to foetus. 

HPVs are classified according to their genotypes, oncogenicity, and biological properties.

HPV viruses can be persistent and carcinogenic, this depends on the presence of  the two early viral proteins E6 and E7 which are of oncogenic properties, particularly in the high risk HPV forms, they have the ability to cause cancer through omitting their DNA into the host. 

Diagnostic methods are divided between polymerase chain reaction (PCR)  based methods which are of different types and serological methods particularly ELISA. 

There is no specific treatment for HPV, sometimes it could be self limiting. However, there are 3 currently used vaccines to prevent HPV and some are being investigated through preclinical and clinical trials.