Structural Analysis
We have summarised below the useful morphological comparisons between HPV and MCV in Table 1.
Table 1 Structural comparisons between human papillomavirus and Merkel cell polyomavirus
Both MCV (family Polyomaviridae) and HPV (family Papillomaviridae) were classified within the family Papovaviridae (now obsolete) because of their structural similarities. Both viruses consist of a double-stranded (ds) DNA core, surrounded by non-enveloped capsid.
The MCV icosahedral capsid is formed of 72 capsomeres, each consisting of 5 VP1 proteins associating with a VP2 and a VP3 protein. The DS-DNS genome is approximately 5.4 kb in length.
The HPV icosahedral capsid is also formed of 72 capsomeres, which consist of 5 L1 proteins encasing an L2 core each. The DS-DNA genome is approximately 8 kb in length.
It is clear that HPV and MCV are structurally very similar. EM images of both viruses are essentially identical.
Aerosolization of Viruses in Laser or Diathermy Smoke
Although published data on MCV in electrocautery or laser smoke are not available, numerous published studies looking at HPV (a virus very similar in structure and size) in exactly this situation, are available. A previous study for HPV DNA detection in electrocautery smoke yielded positive identification of intact HPV virions, and demonstrated infectivity of these virions [15].
Further, there are anecdotal reports of HPV transmission from patient to surgeon via laser smoke. In one case, a surgeon contracted laryngeal papillomatosis after treating anogenital condylomata by ablation with laser [11]. The 44-year-old surgeon stated categorically that there were no other (i.e. sexually transmitted) methods in which he could have contacted HPV types 6 and 11 apart from the operating theatre. In another case (published in German), a 28-year-old gynaecological theatre nurse who assisted in laser ablation of anogenital condylomata developed laryngeal papillomatosis [1]. Her case was thoroughly investigated by a prestigious virology institute in Germany and hers was deemed to be a case of occupational disease.
There has also been a study to isolate bovine papillomavirus (BPV) from laser smoke in controlled laboratory conditions, and the authors succeeded in demonstrating infectivity by inoculation of the extracted virions onto bovine skin and mucosa, with subsequent growth of papillomas [7].
Papillomaviridae and Polyomaviridae are structurally very similar and share very similar morphology, and therefore data from one suggest that it could possibly be extrapolated to the other.
Finally, there are now recent anecdotal reports of HPV + oropharyngeal carcinoma occurring in gynaecological surgeons who have performed thousands of cases of laser surgery. These two cases in surgeons appear to confirm that the risk of contracting HPV from laser smoke is a real one, and, what is more concerning, the transmission of high-risk HPV appears to be responsible for these cases of head and neck carcinoma [13]. One of us, (R.A.F.C.), a senior gynaecological surgeon, has been a proponent of smoke extraction for CO2 lasering of the cervix since the 1990s. Furthermore, the adoption of large loop diathermy excision of the transformation zone by UK gynaecological oncology centres as the main treatment modality (as part of a single see and treat strategy) for the cervical screening programme has been useful, as it generates much less smoke compared to the CO2 laser.
Limitations of Study and Learning Points
The available published literature on viruses in smoke is small, and the case reports of virus-associated tumours are few and anecdotal. There is no direct evidence in terms of long-term follow-up studies. However, despite the circumstantial evidence, there is now sufficient evidence to emphasise that all healthcare personnel should be taking all available safety precautions in their daily work in seeing and treating patients, as the consequences of developing a malignancy is potentially life-threatening. The learning points are summarised below:
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Human papillomavirus (HPV) and Merkel cell polyomavirus (MCV) are viruses that cause cancers of the skin and mucosae.
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These cancers appear to increasing steadily in frequency across the world.
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Healthcare personnel are exposed to smoke from laser or diathermy plumes when treating patients.
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Viable infectious viruses have been isolated from smoke.
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Case reports of both benign and malignant tumours occurring in healthcare personnel with no other risk factors have now been reported.