Herpesvirus infections
Herpesvirus infections are caused by a group of more than 130 known viruses, of which eight specifically infect humans. These viruses belong to the herpesvirus family, which is categorized into three subfamilies: Alphaherpesvirinae, Betaherpesvirinae, and Gammaherpesvirinae. Common infections result from HSV-1 and HSV-2, which cause oral and genital herpes, respectively, while varicella-zoster virus (VZV) leads to chickenpox and shingles. Herpesviruses are highly contagious and primarily spread through direct personal contact, including sharing saliva and skin contact.
Once infected, the virus remains dormant in the body and can reactivate under stress or other triggers, causing recurrent symptoms. Risk factors for contracting and reactivating herpesvirus infections include being immunocompromised, engaging in unprotected sex, and exposure to stressors such as illness or hormonal changes. Symptoms can vary widely, from cold sores and genital lesions to more severe conditions like congenital infections and certain cancers linked to viral reactivation.
While most herpesvirus infections cannot be cured, treatments are available to alleviate symptoms and manage outbreaks. Preventive measures, including antiviral medications and safe hygiene practices, are recommended to minimize transmission risks. Vaccines for specific herpesviruses, such as VZV, are routinely administered, while others are still under development. Understanding these infections is crucial for effective management and prevention strategies.
Herpesvirus infections
- ANATOMY OR SYSTEM AFFECTED: All
Definition
Herpesviruses are large, complex viruses composed of double-stranded DNA (deoxyribonucleic acid). More than 130 herpesviruses are known, but only eight infect humans. The human herpesvirus (HHV) family is divided into three subfamilies based on the duration of viral reproductive cycle, ability to grow in cell culture, and location of the latent virus in the body. Alphaherpesvirinae contains the simplexviruses (HSV-1 and HSV-2) and varicellovirus (VZV), which target epithelial cells, while Betaherpesvirinae includes cytomegalovirus (HCMV) and roseolovirus (HHV-6 and HHV-7), which target monocytes. Gammaherpesvirinae is composed of lymphocryptovirus (Epstein-Barr virus, or EBV) and Kaposi’s sarcoma-associated herpesvirus (HHV-8), which target lymphocytes.
Causes
Herpesvirus infections are highly contagious and spread by direct personal contact through sharing saliva or secretions or by contact with skin that is shedding the virus. After primary infection, the herpesvirus remains latent in the body in an inactive phase. However, under stressors, the virus enters a lytic cycle, whereby it replicates, travels to the skin surface, and reactivates the infection.
Risk Factors
Persons who are immunocompromised, such as those with human immunodeficiency virus (HIV) infection or cancer or those who have had an organ transplant, have the greatest risk for contracting herpesvirus infections. Unprotected sex increases transmission risk, too.
Predisposing factors for reactivation of a latent virus include colds or fevers, exposure to ultraviolet radiation, hormonal fluctuations, stress, and trauma. Some infections occur more frequently in the winter and spring seasons.
Young children are at greater risk for certain herpesvirus infections, such as cytomegalovirus (CMV) and chickenpox, while increasing age is associated with more severe symptoms when VZV is reactivated. Risk factors for vertical transmission of herpesviruses include primary infection within the pregnancy, prolonged rupture of the amniotic sac before delivery, and vaginal delivery.
Symptoms
An incubation period exists from initial herpesvirus contact to the appearance of clinical symptoms. Primary exposure may be asymptomatic or symptomatic.
Clinical findings associated with HSV-1 and, less commonly, HSV-2 include cold sores, otherwise known as fever blisters. These painful fluid-filled blisters occur on the mouth, lips, and nose and may be accompanied by swelling of the gums and lips. Recurrences typically occur in the same location.
Genital herpes are more common with an HSV-2 rather than an HSV-1 infection. Herpetic lesions appear as open sores or as red bumps on the genitalia, anus, thighs, or buttocks and may be associated with painful urination or abnormal discharge. Primary genital herpes takes longer to heal than recurrent outbreaks because of a lack of immune resistance.
HSV-2 is also the primary virus implicated with neonatal herpes, which may cause skin lesions and central nervous system abnormalities of the neonate when contracted through the vaginal birth canal. Neonatal herpes can be fatal in some cases because infants do not have fully developed immune systems. Early treatment is critical in children under four weeks old.
Primary VZV infection causes chickenpox and subsequently confers lifelong immunity to varicella. VZV reactivation results in herpes zoster, or shingles. Herpes zoster is characterized by a vesicular rash on the specific segment of the body where the varicella infection previously occurred and by pain that may persist for some time after the rash is treated. Fetal varicella syndrome occurs with primary maternal varicella exposure in the first and second trimester of pregnancy, causing mental retardation, seizures, and underdeveloped limbs.
Children and adults with CMV infection are often asymptomatic, but the virus causes the most common congenital infection in the United States. Severely affected newborns may have hearing loss, vision loss, mental retardation, cerebral palsy, seizures, and liver disease. Roseolovirus is often seen in children and causes roseola infantum, characterized by a fever and a faint pink rash that begins on the body trunk and spreads to the extremities. Symptoms generally spontaneously resolve, but seizures may occur during the febrile period.
Infants become susceptible to EBV when maternal antibody protection disappears following birth. Infected children may be asymptomatic or have mild flu-like symptoms, but infections in adulthood lead to mononucleosis, hepatitis, and encephalitis. Symptoms last for several months after initial onset. When reactivated, EBV increases the risk for cancers, including Hodgkin’s and Burkitt’s lymphoma.
HHV-8 has little consequence in a healthy person but manifests with flu-like symptoms. In an immunosuppressed person, a primary infection is more severe and possibly fatal. HHV-8 causes Kaposi’s sarcoma, an aggressive tumor and the most common malignancy found with acquired immunodeficiency syndrome. HHV-8 has also been implicated with diseases such as sarcoidosis and multiple myeloma.
Screening and Diagnosis
Often, laboratory tests are not needed to diagnose a herpesvirus infection, as symptoms are clinically recognizable. Serology and polymerase chain reaction studies are available to confirm many infections, although the tests are not always accurate or useful for treatment. Prenatal tests, such as amniocentesis, are diagnostic for cytomegalovirus and varicella, as they confer a risk to the pregnancy if vertically transmitted during pregnancy. Physical examinations are also performed in pregnancy and labor to detect active genital herpes outbreaks.
Treatment and Therapy
Treatment for most herpesvirus infections remains supportive because many infections spontaneously resolve. Topical creams, ointments, and lotions are available for pain, and acetaminophen can be taken to reduce fevers. Antiviral medications are prescribed for some but not all herpesviruses to shorten the duration of symptoms; these are most effective when taken at the first sign of illness. Steroids are controversial for mononucleosis from EBV as a means to reduce swelling of the throat and tonsils.
Prevention and Outcomes
Although people are most contagious during an active outbreak of herpesvirus, the virus is shed in saliva, feces, or skin after an infection has apparently resolved. Therefore, proper hygienic practices, such as frequent handwashing, sterilizing household items, and avoiding sharing toiletries, are all recommended. Safe sexual practices, such as abstinence or the use of condoms, are encouraged. Antiviral medications are also available to help prevent herpesvirus transmission between partners. These suppressive therapy medications include acyclovir, valacyclovir, or famciclovir.
Despite myriad recommendations, herpesvirus infections are lifelong and have no efficacious method of prevention or cure. The exception is the VZV vaccines that are routinely administered to children and immunocompetent adults. Other vaccines for CMV infections are in clinical trials.
Bibliography
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