The virus family called herpesvirus includes several viruses that cause common infections in humans. Herpes simplex virus type 1 and herpes simplex virus type 2 are just two of these viruses. Although they are members of the same family and share some similarities, there are several differences between them, as well.
Epidemiology
People are infected with the herpes simplex virus type 1, or HSV-1, at an earlier age and more often, as compared to herpes simplex virus type 2. Over 90 percent of adults have antibodies to HSV-1 by the time they are 50 years old, writes Lawrence Corey, M.D., Chair of Medical Virology at the University of Washington in “Harrison’s Principles of Internal Medicine.” By comparison, 15 to 20 percent of American adults have antibodies to herpes simplex virus type 2, or HSV-2. In OB-GYN clinics, approximately 25 percent of women have HSV-2 antibodies, while 50 percent of people in STD clinics have this antibody.
Transmission
Someone who is infected with HSV-1 passes that infection through his saliva, or when someone touches his infected blisters. The first lesions will be on the face, writes Warren Levinson, M.D., Ph.D., in “Review of Medical Microbiology and Immunology.” HSV-1 then travels through a nerve. HSV-1 can also be transmitted to the genitals. HSV-2 is a sexually-transmitted disease. But newborn babies can contract this virus during birth, as they pass through the birth canal of an infected mother. The first lesions of HSV-2 are on the genitals. Similar to HSV-1, the virus will then travel through a nerve.
Diseases Caused by HSV-1
HSV-1 usually causes cold sores, gingivostomatitis, keratitis, keratoconjunctivitis and meningoencephalitis. Kenneth Kaye, M.D., Assistant Professor at Harvard Medical School writes about these diseases in “The Merck Manual for Healthcare Professionals” noting that gingivostomatitis is an inflammation of the gingiva, or gums, and other membranes in the mouth. Keratitis is the inflammation of the cornea, which is the clear area of the eye right in front of the pupil. Keratoconjunctivitis is the inflammation of the cornea and the conjunctiva. The conjunctiva is a membrane in the front part of the eye and inside the eyelid. An inflammation of the meninges membrane that covers the brain and of the brain itself is called meningoencephalitis.
Diseases Caused by HSV-2
HSV-2 is usually responsible for genital lesions, meningitis and infections of the newborn. Meningitis is the inflammation of the meninges membrane of the brain. As explained by Dr. Kaye in “The Merck Manual for Healthcare Professionals,” most babies contract herpes during the birth process and develop symptoms when they are only one to four weeks old. They may develop lesions just on their mouths, eyes and skin. But the virus can spread to their brain, lungs and liver.
Site of Latency
A herpes virus can become dormant after an infection, explains Dr. Levinson in “Review of Medical Microbiology and Immunology.” During the time that the virus is dormant, or latent, people do not have any symptoms. But if their immune system ever becomes suppressed, or there is some trigger like stress, the virus can become active again, causing the same symptoms as the initial infection. HSV-1 stays dormant in the nerve cell bodies of the trigeminal nerve in the face. HSV-2 will stay dormant in the nerve cell bodies of the lumbar or sacral nerves in the lower back.
References
- “Harrison’s Principles of Internal Medicine”; Anthony Fauci, M.D., Dennis Kasper, M.D., Dan Longo, M.D. et al.; 2008
- “Review of Medical Microbiology and Immunology,” Warren Levinson, M.D., Ph.D.; 2008
- The Merck Manual for Healthcare Professionals: Herpes Simplex Virus (HSV) Infections
