Human papillomavirus or HPV


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much more. Try it free today! Human papillomaviruses, or HPV for short,
are a group of non-enveloped DNA viruses that specifically infect human epithelial cells. There are over 100 different types of HPVs
which can be categorized by the epithelial cells they prefer to infect; like cutaneous
epithelial cells of the skin, especially the face, hands and feet; and epithelial cells
of mucous membranes, especially the respiratory tract including the pharynx, and nasal and
oral cavities; and anal and genital regions. Some types can cause benign tumors, called
papillomas or warts; and some can lead to carcinomas, or cancer of the epithelial cells. HPV may have contributed to both actor Michael
Douglas’s throat cancer diagnosis, and former first lady of Argentina, Eva Perón’s fatal
cervical cancer. Epithelial cells line the outer surfaces of
organs and blood vessels and separate the interior of the body from the external world. They primarily serve as a protective barrier
to invasion by pathogenic bacteria, fungi, parasites and viruses; and to water loss. In locations like the skin, anus, genitals,
and respiratory tract, they can be stratified, having more than one layer of epithelial cells. At the base, the layer closest to the interior
of the body, these cells are less mature, rounded stem cells, also called basal cells. Basal cells divide and replenish all the cells
found in the epithelium. As the basal cells divide and mature, they
move toward the outermost layer, flattening out and becoming more squamous shaped in appearance. Once they reach the top layer, these mature,
flat cells are exfoliated, or shed, from the epithelium. Now, typically basal cells are well protected
under all those layers. But if there are abrasions or cuts in the
epithelium, HPV can gain access to and infect the basal cells. Once that happens, HPV can replicate with
or without being incorporated into the basal cell’s DNA through the activities of two
particular viral genes called E6 and E7. The proteins of these genes cause dysregulation
of tightly-scheduled replication of the epithelial cells by altering the p53 and retinoblastoma
protein (pRB) tumor suppressor pathways that typically prevent unregulated growth of the
epithelial cells. In this way, HPV causes uncontrolled replication
of the epithelial cells, forming warts, and disrupts the normal structure of the epithelium,
forming lesions. In some types of HPV infections, a squamous
epithelial cell can become a koilocyte, or a cells with an irregular shape, enlarged
and dark staining nucleus, and a clear area around the nucleus that’s called a perinuclear
halo. These cells are typical of precancerous lesions
that can transform into carcinomas when the abnormal epithelial cells break through the
basement membrane of the epithelium and invade other tissues. The cause of an HPV infection is contact with
infected epithelial cells. Some activities can increase the risk of exposure,
like having multiple or new infected sexual partners, or delivering a baby through an
infected birth canal. And infections are more likely if a person
is already immunocompromised. Transformation to carcinomas is dependent
on HPV type and aided by other cofactors like tobacco use, immunosuppression, and radiation. Now, many HPV infections are asymptomatic,
but when symptoms are present, they can vary by HPV type. So, symptoms of nongenital cutaneous infections
can involve some kind of benign wart. Common skin warts of the hands or nails are
typically painless, dome-shaped projections that give the skin a rough appearance. Plantar warts on the soles of the feet can
be painful, and scaly. Flat warts of the face and extremities, particularly
in the pediatric population, are often painless, small, smooth, and flat-topped but numerous. Filiform warts of the face, particularly the
eyelids and lips, have long projections that appear thread- or finger-like. And in rare cases, where there is an underlying
genetic disorder called epidermodysplasia verruciformis, a chronic cutaneous infection
can start out as flat warts and transform into skin cancer. Infections of mucous membranes like the upper
respiratory tract, can cause respiratory papillomatosis and can lead to voice changes and high-pitched
breath sounds, particular if the larynx is infected. Anal and genital infections (like the female
vulva, cervix and vagina; and male penis and scrotum), can involve numerous warts called
condylomata acuminata. They tend to be skin-colored and can range
in size, but have a cauliflower-like look to their surface. Though they are typically painless, they can
cause itching, burning, local pain, or bleeding. Now, HPV types 6 and 11 are responsible for
the majority of laryngeal papillomatosis and genital warts and are considered low-risk
HPVs because they don’t tend to progress beyond warts. But high-risk HPV types like types 16 and
18 have a high risk of transforming into cancers of the cervix, vagina, vulva, penis, anus,
or upper respiratory tract over one or two decades. Warts are used to diagnosis HPV, particularly
in cutaneous infections. Infections of mucous membranes may require
additional interventions to visualize epithelial cells. An endoscopy, a tube with a camera at the
end, may be needed if an infection of the upper respiratory tract is suspected; and
regular pap or acetic acid tests of the cervix after 21 years old are recommended even if
symptoms are sub-clinical. But a definitive diagnosis of HPV can not
be made without molecular testing of biopsied cells for viral DNA or RNA. So treatments often center around removal
of warts and precancerous lesions with salicylic acid products, liquid nitrogen cryotherapy,
or laser or surgical removal. In cases of frequent re-occurrences, immune
modifiers may be used to help boost the immune system to remove the infection on its own. Most HPV infections can resolve on their own
over time, particularly with low-risk types and in younger people. But really, prophylaxis against infection,
is the best course. But limiting contact with potentially infected
persons; or receiving the HPV vaccine before first exposure to an infection source can
also be protective against several strains, including high-risk types 16 and 18. Condom use should also be considered a measure
of prevention. So, to recap: Human papillomavirus is a DNA
virus spread through contact that infects human epithelial cells of the skin and mucous
membranes. Symptoms can range from warts, to precancerous
lesions and carcinomas. Definitive diagnosis can be made molecularly
and treatment can range from allowing the immune system to clear the infection, to mechanical
or chemical removal of infected cells.

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