Herpes Simplex virus infections are caused by two distinct antigenic types; HSV-1 and HSV-2 (1). Both HSV types are common human pathogens. HSV-1 is usually associated with infections in the oropharyngeal area and eyes while HSV-2 causes most genital and neonatal infections (1,2). However, the tissue specificity is not absolute (3). HSV-2 can be isolated occasionally from the oropharyngeal area, and 5% to 10% of primary genital infections may be caused by HSV-1(1,4).
HSV infections are classified as either first time or recurrent. Following a first time infection, a latent infection is established in sensory neurons and recurrent infection results from reactivation of the latent infection (2). Recurrent infections tend to be less severe and of shorter duration than the first time infection (1). HSV infections are usually localized to the initial site of infection. However, serious localized or disseminated disease may occur in persons who are immunologically impaired. Such persons include newborn infants, and patients on immunosuppressive therapy such as transplant recipients and cancer patients (1,2).
HSV infections are transmitted by virus containing secretions through close personal contact. HSV infections, both primary and recurrent are often subclinical and asymptomatic. Shedding of the virus is the most important factor contributing to the spread of the virus (2). From 75% to 90% of persons of lower socioeconomic status acquire HSV antibodies by the end of the first decade of life (5,7). In persons of higher socioeconomic status, 30% to 40% become seropositive by the middle of the second decade (5).
Primary HSV-1 infections of the oral mucosa usually occur in children of less than 5 years of age (2). Most infections are asymptomatic. Symptomatic infections are characterized by gingivostomatitis associated with fever, malaise and tender swollen cervical lymph nodes (2). Numerous small vesicles develop on the oral mucosa, become ulcerated and heal within about two weeks. The most common form of recurrent HSV-1 is herpes labialis in which vesicles appear on the lips, nostrils or skin around the mouth (1,2). Symptoms of genital HSV infections are multiple ulcerative lesions accompanied by pain, fever, dysuria and lymphadenopathy (6).
The most severe complication of genital HSV infection is neonatal disease (2). Unlike cytomegalovirus, HSV rarely crosses the placenta to infect the fetus in utero(1). HSV is transmitted from the mother to the neonate at the time of delivery (1). Infants acquire the infection by passage through an infected birth canal or if membranes have been ruptured for more than six hours (6). Of mothers with an active primary infection, the risk of transmission to infants is as high as 40% (5). About 69-80% of infants who develop neonatal herpes are born to women who are asymptomatic of genital HSV infection at the time of birth (5).
Infants infected with HSV appear normal at birth but almost invariably develop symptoms during the newborn period (1,5). Neonatal HSV infection may remain localized or become disseminated (1,5). Localized infection may involve one or a combination of sites. These are skin, eyes, mouth or central nervous system. Disseminated infection is manifested by pneumonitis, hepatitis, disseminated intravascular coagulopathy and encephalitis (1,5). Of the infants with neonatal HSV, about one half will die if not treated, and about one half of the surviving infants will develop severe neurological or ocular sequelae (3).
Serological procedures may be useful for diagnosis of primary HSV infections, and for determining evidence of past infection with HSV. Diagnosis of primary infection is based on demonstration of seroconversion or a significant rise in titer between paired acute and convalescent sera (2,4). Serological procedures are less useful for diagnosis of recurrent HSV infection since recurrent infections are often not reflected by a change in antibody levels (2,4). Also, among persons with a first time HSV-2 infection who experienced a previous childhood HSV-1 infection, little or no increase in HSV-2 type specific antibodies may be produced (2,4).
A number of serologic procedures have been developed to detect antibodies to HSV. These include complement fixation, indirect immunofluorescent antibody, plaque neutralization, and ELISA (2,4,6). The ELISA procedure was first described by Engvall and Perlman, and has subsequently been applied to the detection of a wide variety of different antigens and antibodies (10-12). When compared to other serologic tests, ELISA may be a very specific, sensitive and reliable method for detection of antibodies to HSV (6,13,14). The ELISA procedure allows an objective determination of antibody status to be made on a single dilution of the test specimen and is suitable for screening large numbers of patient samples. High affinity IgG antibodies to HSV, if present in a sample, may interfere with the detection of IgM specific antibody (15,20). High affinity IgG antibody may preferentially bind to HSV antigen leading to false negative IgM results (15). Also, rheumatoid factor, if present along with antigen specific IgG may bind to the IgG causing false positive IgM results (16). Both of the above problems can be eliminated by removing IgG from the sample before testing for IgM (17-20). Several different methods of separating IgG have been used. These include gel filtration (17), absorption with protein A (18), ion exchange chromatography (19), and precipitation of IgG with anti-human IgG serum (20).