Describe the poxviruses, adenoviruses and papillomaviruses with their diseases. Add a note on smallpox eradication.

Poxviruses

• The largest and most complex viruses, visible by light microscopy as elementary bodies (Paschen bodies); brick-shaped with complex symmetry, a double-stranded DNA genome, and cytoplasmic replication — the only DNA viruses to do so, because they carry their own DNA-dependent RNA polymerase
• Highly resistant to drying, so scabs and clothing remained infectious for long periods

Adenoviruses

• Naked icosahedral viruses with double-stranded DNA and characteristic fibres projecting from the vertices, which carry the attachment protein and the haemagglutinin
• Being naked, they are resistant to drying, detergents and acid, so they survive on surfaces, in water and through the stomach
• Over 50 serotypes, with different serotypes causing different syndromes
• Diseases — respiratory (pharyngitis, pharyngoconjunctival fever from swimming pools, and acute respiratory disease in military recruits); ocular — epidemic keratoconjunctivitis, a highly contagious infection often spread in eye clinics by contaminated tonometers and hands; gastrointestinal — types 40 and 41 cause infantile diarrhoea, second only to rotavirus; haemorrhagic cystitis in children; and disseminated disease in the immunosuppressed
• Adenoviruses are widely used as vectors in gene therapy and in vaccines, including some COVID-19 vaccines

Papillomaviruses and Polyomaviruses

• Human papillomavirus (HPV) — naked icosahedral viruses with circular double-stranded DNA; over 200 types, infecting squamous epithelium and replicating only in differentiating keratinocytes, which is why the virus has never been grown in ordinary cell culture
• Low-risk types 6 and 11 cause genital warts (condyloma acuminatum) and recurrent respiratory papillomatosis in children born to infected mothers
• High-risk types 16 and 18 cause about 70% of cervical carcinoma, and also anal, vulval, vaginal, penile and oropharyngeal cancer. The oncoproteins E6 and E7 inactivate the tumour suppressors p53 and Rb respectively
• HPV is a necessary cause of cervical cancer — virtually every case contains high-risk viral DNA, which is an unusually strong causal relationship in oncology
• Prevention — the HPV vaccine (bivalent, quadrivalent and nonavalent recombinant L1 virus-like particle vaccines), most effective given to girls before sexual debut; and screening by cytology or HPV DNA testing, which is more sensitive and is replacing cytology
• Polyomaviruses — JC virus causes progressive multifocal leukoencephalopathy in the profoundly immunosuppressed, notably in AIDS and with natalizumab and rituximab; BK virus causes haemorrhagic cystitis and nephropathy in transplant recipients

Parvovirus and the Remaining DNA Virus Families

Applied Aspects

• Cervical cancer is the second commonest cancer in Indian women and is largely preventable; HPV vaccination and screening together could eliminate it, and India has begun introducing an indigenously developed vaccine
• Vaccinate before exposure; the vaccine is prophylactic and does not treat established infection or disease, so its value depends entirely on timing
• Screening remains necessary in vaccinated women, since the vaccine does not cover every oncogenic type
• Epidemic keratoconjunctivitis spreads in eye clinics; disinfect tonometers, wash hands between patients and use single-use drops, since outbreaks are frequently iatrogenic
• Smallpox eradication remains the template for surveillance-based elimination, and its lessons underlie the polio and measles programmes; laboratory stocks and the possibility of deliberate release keep it a biosecurity concern
• Molluscum contagiosum in an adult with widespread lesions should prompt HIV testing, since extensive or facial disease in adults suggests immunosuppression
• Adenovirus survives on surfaces and in swimming pools because it is naked, which is why outbreaks follow shared towels, inadequately chlorinated water and contaminated ophthalmic equipment
• HPV testing is replacing cytology for cervical screening because it is more sensitive and can be done on a self-collected sample, which matters greatly where access to gynaecological examination is limited
• Genital warts and cervical cancer are caused by different HPV types, so the presence of warts does not indicate cancer risk and their absence does not exclude it — a distinction patients find reassuring once explained
• Recurrent respiratory papillomatosis in a child is acquired from maternal genital warts at delivery, and is difficult to treat — another reason for vaccinating before childbearing age
• Consider PML in a patient on natalizumab or rituximab who develops progressive focal neurological signs; JC virus reactivation is a recognised and serious complication of these agents
• BK virus causes haemorrhagic cystitis and nephropathy after transplantation, and is monitored by viral load; the treatment is reduction of immunosuppression rather than an antiviral
• Mpox has emerged as an international concern, and the prominent lymphadenopathy that distinguishes it from smallpox is the clinical feature to look for
• Smallpox vaccination stopped in 1980, so most of the world's population is now susceptible — which is why laboratory stocks and the possibility of deliberate release remain a biosecurity concern
• Adenovirus vectors are used in modern vaccines, including some COVID-19 vaccines, and pre-existing immunity to the vector is one of the practical limitations of that platform
• Molluscum is self-limiting in healthy children and usually needs no treatment; destructive interventions in a young child are rarely justified
• India has introduced an indigenously developed HPV vaccine, which substantially reduces the cost barrier that has limited coverage until now
• Cervical screening should continue in vaccinated women, since the vaccine does not cover every oncogenic type and coverage of the population is incomplete
• Naked viruses need hypochlorite rather than alcohol, which governs outbreak control for adenovirus in eye clinics and for enteric viruses on wards
• Warts in a child are usually innocent and self-limiting, but anogenital warts warrant careful consideration of the mode of acquisition
• Vaccinating boys as well as girls reduces transmission and prevents anal and oropharyngeal cancer, and is increasingly recommended where resources permit
• Poxvirus lesions are resistant and remain infectious in scabs and bedding, which shaped the isolation practices used during smallpox eradication and applies again to mpox
• Eradication required no animal reservoir and no silent carriage; measuring a candidate disease against those criteria is how the feasibility of polio and measles elimination is judged