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Pathogenesis
Virology
HPV is a double-stranded DNA virus that belongs to the
Papovaviridae family. Genital types have specific tropism
(affinity) for genital skin and mucosa.
Infection is identified by the detection of HPV DNA or
capsid protein.
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Genital HPV types are generally characterized in
terms of their oncogenic potential.
- Low-risk types
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Associated
with genital warts and benign or low-grade
cervical cell changes (mild Pap test
abnormalities).
- Most visible genital warts are caused by HPV
types 6 and 11.
- Recurrent respiratory papillomatosis, a rare
condition, is usually associated with HPV types
6 and 11.
- High-risk types
- Associated
with low-grade cervical cell changes, high-grade
cervical cell changes that are precursors to
cancer (moderate to severe Pap test
abnormalities), and, in rare cases, anogenital
(i.e., cervix, vulva, anus, and penis) cancers.
- HPV types 16 and 18 account for more than half
of HPV types found in anogenital cancers.
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Most women infected with high-risk HPV types
have normal Pap test results and never develop
precancerous (high-grade) cervical cell changes
or cervical cancer.
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Patho genesis
HPV infection stimulates cellular proliferation in
stratified squamous epithelial cells. Affected cells display
a broad spectrum of changes ranging from benign
hyperplasia
to dysplasia to invasive
carcinoma.
Natural History of HPV
Most infections are transient, asymptomatic, or
subclinical, and have no clinical consequences in
immunocompetent individuals. The
incubation period is
unclear; it is probably three weeks to months for genital
warts and several months to years for cervical cellular
abnormalities.
The median duration of new cervical infections (measured by
detection of HPV DNA) is 8 months but varies by HPV type.
Persistent infection is infection that is not cleared
by the immune system and is characterized by persistently
detectable HPV DNA. Factors associated with persistent
infection include older age, high-risk HPV types, and
immunodeficiency. Most women with persistent HPV infection
do not develop cervical cancer precursors or cervical cancer.
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HPV infection that persists is the most important
risk factor for precancerous (high-grade) cervical cell
changes and cervical cancer.
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