Covid 19 crisis has taught us a lot of new things including understanding the unpredictable behaviour of the viruses!
Not many know that viruses besides acute infections such as influenza or this SARS COV 2 also cause life threatening cancers.
It was American Pathologist Francis Payton Rous who introduced the concept of tumour producing viruses for which he earned Nobel Prize in 1966.
Cancer of the Cervix (lower part or neck of the Uterus) is the second most common cancer in women after Breast cancer and is caused by Human Papilloma Virus ( HPV) . Unfortunately India has the dubious distinction to carry the highest number of patients and resultant huge deaths due to cervical cancer in the world . It is estimated that infective agents including viruses are responsible for almost 20 % of all cancers of which one fourth are due to HPV infection which is a sexually transmitted disease. Early age of sexual debut , multiple sexual partners ,poor sexual hygiene ,poverty and immunosuppressed states - all predispose to this cancer and HPV related other diseases. Every year around one lak women die in India of this imminently preventable cancer as per the available data with the WHO . This Human Papilloma virus (HPV)is a DNA virus which is also responsible for genital warts and cancers of Vagina , vulva ,penis , Anus ,mouth and throat region .
The credit to find out the cause of this virus induced cancer goes to a German physician and virologist Dr HERALD ZUR HAUSEN for which he was awarded the Nobel prize in 2008 for physiology or medicine.
In 1960s few seriously took viruses as the causative agent of cancer though Dr Hausen while working as intern in gynaecology wards came across many cases of cervical cancer resulting into painful deaths which brought his attention towards this dangerous disease .Dr Hausen hypothesised that cells if transformed by a virus into a tumour ( cancer) the viral DNA should be present in such tumours .Presence of Ebstein Bar virus DNA in Burkitts’ lymphoma and Nasopharyngeal carcinoma by in situ hybridisation technique supported his viral hypothesis . He looked for the presence of Human Papilloma Viral DNA in cervical cancer tissues and it’s related precursor ,the Genital Warts . Dr Herald Zur Hausen ‘s theory was soon supported by Drs Meisels and Fortin who found koilocytotic atypical cells in virus infected cervical tissues as manifestation of HPV induced cellular changes as precursor to full blown cancer of cervix. With the advent of electron microscopy more specific evidences came suggesting HPV as the cause of genital wart -condylomata and cancer. His team found that HPV subtypes HPV 16 and HPV 18 DNA were present in 82% of invasive cervical cancer tissues. HPV 6,11, 42 subtypes to the contrary were associated with non cancerous lesions. HPV virus infects first the keratinocytes of Basal layer of skin and then spreads to involve the superficial layers first at the most meta plastic zone of squamous-Columnar junction of uterine Cervix . it was also found that 90% of cells recover naturally in almost two to three years time and that only 10% cells continue to carry the viral DNA and very slowly progress towards cancerous changes in ten to twenty years time . As many as 50 to 80% of sexually active population remain HPV infected during their life time almost without any symptom. It was also established that two viral Onco genes E6 and E7 were responsible for the maintenance of tumour state.
PAP smear , HPV DNA test besides colposcopy and tissue biopsy are routine investigative methods for diagnosis of cervical cancer .
Dr Herald Zur Hausen ‘s assertion that only a limited number of HPV subtypes are the causative agents led to the availability of VLPs ( Virus Like Particles) as vaccines which prevented the infections in dogs and rabbits . Since 2018 two types of vaccines are available in India containing two ,four or nine subtypes of HPV DNA with the trade name Gardasil ( Merck) and Cevarix (GSK) . The more modern type with nine subtypes , has greater efficiency but is far too costly. These vaccines should be given two to three times intramuscularly much early in the life soon after menarche,preferably at 11 to 14 years of age and upto the age of 26 years . American CDC recommends even males to take the vaccine for more effective control of HPV spread.
Most western countries have taken the advantage of this vaccine and it has reduced sharply the incidence of all HPV associated cancers and diseases .
Developing world including India has to understand it’s value and seriously adopt this vaccine as part of regular immunisation practice which they have not done so far.
(Author is former Professor and Head of Medicine, RIMS, Ranchi)