Human Papilloma virus : Magnitude of the problem
Becky Massaley (11 AM Micro) found our discussion about cancers caused by infectious agents (and therefore very potentially completely preventable by vaccination!) interesting. She found a recent report from the Morbidity Mortality Weekly Report on current epidemiology of HPV in the United States. Here is Becky’s summary:
Human papillomavirus (HPV) infection is the most common sexually transmitted disease (STD) in men and women in the United States. The viruses (HPVs) are prevalent and well-adjusted to their host. They are capable of insulating away from immune responses. HPV can be group according to the areas of the body where infection is found on external skin such as anal, genital area, and the oral mucosal. The mucus cutaneous HPV type can be further sub-divided into low risk (LR-HPV), mainly associated with benign warts. And high risk (HR-HPV) defined by their risk of progression or malignancy. The infections can cause abnormal tissue growth, and lesions, particularly in the immunocompromised person. Some HPV types only infect the genital area and may cause warts. Warts usually disappear spontaneously but occasionally may be resistant to treatment. Regrowth of lesions after treatment is frequently due to persistence of the virus in the skin surrounding the original wart. some may warts cause mild changes in cervical cells that do not turn into cancer, and some cause changes that may become cervical cancer or other types of cancer including penile cancer, anal and oropharyngeal (mouth and throat-cancers) if present for many years.
In adults, the disorder is considered a sexually transmitted infection, passed from person to person through intimate contact including vaginal sex, anal sex, and oral sex. The disease can also be transmitted vertically from mother to child, and during delivery. HPV infection is very common, although the majority of people have no symptoms (asymptomatic). Cervical cancer and other HPV related cancers are serious diseases that can be life threatening. The infection may cause the cells in the lining of the cervix, vulva and vagina, anus, penis, or throat to change from normal to precancerous lesions. If these lesions are not treated, they may turn cancerous. Among HPV related cancers, cervical cancer is the most common, with about 10,800 women getting cervical cancer each year in the US. Other cancers caused by HPV are less common, but oropharyngeal cancers (cancers of the throat, base of tongue and tonsils) are on the rise. According to the Centers for Disease Control, 8,400 people get oropharyngeal cancer each year. Some of these cases are related to tobacco or alcohol use, but it is thought that 72% of these cases are now HPV-related.
Recently, CDC conducted a studies which shows that about 14 million people are infected with HPV each year in United States. Another alarming concern is that the virus has about 150 types and 40 of these are transmitted sexually. I do learned from my microbiology class recently that proviruses are harmful and may remain later for a long period of time. Though they are latent, they are not safe for human body. Latent papillomaviruses are detectable only through the demonstration of HPV DNA in clinically and histologically normal skin and mucosa. Productive infections are associated with full viral gene expression and production of mature virus particles. While in persistent infection, normal cell function may dissolved and the events in the virus life cycle are disrupted. According to the study, the viruses that enter through the mucosa are considered high risk and may cause cancer. This includes genital skin, mouth, throat, mucus membrane, and also bodily fluids. Well I guess viruses are on the verge to take over human body and immune system. Base on the replication of the virus in its host, this might be a great concern for HPV epidemic and also pandemic (large geographical area or spread worldwide) in the future. CDC conducted a study which shows that the following cancers are related to human papilloma viruses, 66% of cervical cancers, 55% of vaginal cancers, 79% of anal cancers, and 62% of oropharyngeal cancers. The study also indicated that HPV vaccine (Gardasil) may prevent most cervical cancer in female, and anal cancer in both male and female if giving before expose to the virus. The vaccine may protects against 4 types of HPV (types 6, 11, 16, 18) that are linked to above condition. Although HPV is common among sexually active people, most are not infected with all four types that the vaccination may prevents. In clinical trials, individuals with current or past infections with one or more vaccine-related HPV types prior to vaccination were protected from disease caused by the remaining vaccine HPV types. The vaccine is expected to be long lasting.
|TABLE. Results of selected clinical trials* on human papillomavirus (HPV) vaccine efficacy against HPV vaccine-type precancers and anogenital warts — from the MMWR article|
|Cervical precancer||Bivalent and quadrivalent||Females||