Human papillomavirus (HPV) - MegaMicro

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Human papillomavirus (HPV)

Microbiology > Virology > DNA viruses
Structure:   
• A member of the Family Papillomaviridae, HPV is a small, nonenveloped virus with an icosahedral capsid containing a double-stranded DNA circular genome.
• HPV infects only humans, with over 200 genotypes identified, including 40 genotypes that preferentially infect the anogenital mucosa.

Epidemiology:
• The most common sexually transmitted disease worldwide, with approximately 14 million new infections  reported each year in the USA.
• HPV is present in nearly 100% of all cervical cancers, with HPV-16 and HPV-18 in 70% of them.  HPV-6 and HPV-11 are low risk genotypes for cervical cancer, but may cause condyloma acuminatum (anogenital warts), oral and laryngeal papillomas.
• 10% of women infected with high risk HPV genotypes will develop precancerous lesions.
• Transmission is by direct contact: (1) through small breaks in the skin or mucous membranes, (2) sexual intercourse, (3) while an infant is passing through an infected birth canal.  Asymptomatic shedding may promote transmission.

Pathobiology:
• The replication of the virus is integrally linked to epithelial cell differentiation.  The virus infects the basal stem cell via specific cellular receptors.  Upon desquamation of this short-lived cell, new virions are released for the next round of infection.
• The risk for persistence and progression to cancer varies by HPV genotype and host factors,  many which are poorly understood.

Disease manifestations:
• Most HPV infections are transient and asymptomatic.
• Different HPV genotypes have a propensity to infect different body sites and are thus associated with different diseases.
• Clinical syndromes include: skin warts (generally hands and feet), condyloma acuminate (anogenital warts), benign oral, laryngeal or conjunctival papillomas, cervical cancer and other anogenital and oral cancers.

Laboratory Diagnosis:
• PAP smear screening: cytological changes in cervical squamous epithelial cells (koilocytosis) associated with HPV infection.
• Molecular detection of HPV in cervical swabs or oropharyngeal tissue.
• HPV does not grow in culture and serology is only used in research settings.

Differential Diagnosis:

Treatment:
• Warts usually spontaneously regress, but this may take months to years.
• If removal is required, methods such as surgical cryotherapy, electrocautery or chemical means (podophyllin) are used.
• Cancerous lesions may involve surgery, chemotherapy and/or radiation.

Prevention and Control:
• Prevent exposure to infected tissue by safe sexual practices (for example, the use of condoms).
• Vaccination of individuals prior to sexual activity.  Three HPV vaccines are licensed in the USA, however, only the 9-valent vaccine (Gardasil 9, Merck) is being distributed as of 2016.  The vaccine is composed of virus-like particles prepared from recombinant L1 capsid protein prepared from the targeted HPV genotypes.

Related concepts
Papovaviruses, papilloma virus, anogenital warts, cervical cancer, oropharyngeal cancer


 
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