|Herpes Simplex Virus 2 - IgG/IgM Immunoblot|
Immunoblot for the detection of IgG- or IgM-antibodies against Herpes Simplex Virus Type 2 in serum
SUMMARY AND EXPLANATION OF THE TEST
The herpes viridae comprise a large group of DNA viruses found in many species. 6 of them have been isolated in humans. 2 of these, herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2), are very similar to each other. They have 50% homology in the genom, and the virions have many similar antigenic determinants.Both viruses can cause ano-genital as well as oral, facial and pharyngeal infections, although HSV-1 is isolated more often from the latter three locations and HSV-2 is isolated more often from ano-genital region.
The infection with HSV-2 is sexually transmittted. The incubation period of a primary herpes genitalis is 3 – 7 days. The first symptoms are mostly itching, redness and genital pain after which the vesicles appear on various parts on the genitalia. This is often accompanied by severe pain, oedema, vaginal/urethral discharge, dysuria, urethritis and cystitis or cervicitis. The inguinal lymph nodes may be swollen, and often there are general symptoms such as slackness, fever, headaches, muscular pain and dysuria. After about 2 days, the vesicles burst and ulcers develop which form crusts and heal after 10 - 21 days.
Although most genital herpes simplex virus infections are caused by HSV-2, nearly 20% are caused by HSV-1. The severity and duration of primary genital HSV-1 or HSV-2 infections do not differ. However, the recurrence rate of HSV-1 genital herpes is much lower compared to the recurrence rate of HSV-2 genital herpes. Furthermore, the symptoms of a reactivated HSV-1 genital herpes are beyond the clinical horizon in most cases. In contrast, the HSV-2 recurrence on the average 4 times in the first 12 months after primary infection and in every case there are clinical manifestations, although less severe than the first infection. So a treatment of a HSV-1 genital herpes with Acyclovir or Zovirax, for example, seems not to be reasonable, but for HSV-2 genital herpes it is, of course. Therefore a differentiation of both viruses, serologically or by typing in an antigen detection system, seems to be useful.
There is a high risk for neonates to be infected with HSV during delivery, when the infant passes through an infected birth canal. In the 86 % of all Herpes neonatalis HSV-2 was isolated from the neonate. Postnatal infection can occur, but this is in most cases HSV-1 with a far better prognosis. Neonatal herpes infections can be divided into 3 categories according to severity:
The local infection has the best prognosis. The course is rarely lethal, but without therapy 75 % of these infections would progress to disseminated infections. The mortality of disseminated infection (80 %) and CNS encephalitis (50 %) is very high and the survivors of the encephalitis often have neurological damage like psycho-motoric retardation, microcephaly, hydranencephaly, spasticity, blindness or learning difficulties. In view of the high mortality and the severe complications of neonatal herpes infection, one should be extremely vigilant in identifying women at risk. All pregnant women positive for HSV-2 antibodies should be examined with special care for signs of active disease before giving birth.
HSV-2 IgG/IgM Immunoblot
Analysis of band pattern and interpretation of the results
Cut off - Standard setting: IgM - 10 %, IgG - 20 %
The following antigens can be identified by this immunoblot:
The glycoprotein gpG2 is the one and only highly specific marker for an HSV-2 infection. Antibody titer rises after 7 - 14 days after onset of infection. Cross reactivity are not described so far. Therefore if antibodies against gpG2 can be detected, it is a proof of a contact or recent infection (IgM positive) with HSV-2.
Antibodies against these proteins are early markers of a HSV infection. They are not specific for HSV-2, but cross-react to HSV-1. Therefore these antibodies can confirm a positive IgM result but not differentiate between a HSV-1 and a HSV-2 infection. These antibodies are cross-reactive and are the first immunoresponse to both HSV-1 and HSV-2 infections.
Further interpretation criteria
A true positive HSV-2 result can be reported if the specific gpG2 (92 kDa) band is labeled.
IgM-antibodies against the 40 kDd 65 kDa are the earliest response after onset of infection. They can be observed after 3 - 7 days. The corresponding IgG antibodies rise 10 days. Unfortunately the antibodies allow no differentiation between both Herpes simplex viruses. Antibodies against gpG2 are produced after 7 - 14 days. If these antibodies are missing in the first sample, a second should be drawn some days later for a sure differentiation.
The IgG and IgM results for HSV-2 are positive if the highly specific gpG2 band is clearly marked. The IgM and IgA response is usually weaker and the weaker bands here must also be taken into consideration.
Further assistance in interpretation:
IgM antibodies against 40 kD and 65 kD are produced approximately between the 3rd and 7th day of the infection, IgG antibodies against 40 kD and 65 kD rise after about the 7th- 10th day. These antibodies are only proof of an infection with Herpes. The antibodies against the highly molecular Glycoprotein G 2 92 kDa (gpG2)are not produced until after the 7th – 14th day, and only then is it possible to differentiate between the two Herpes types.
LIMITATIONS OF USE
A correlation between band pattern and intensity and the severity of disease is not possible. A negative result does not preclude the possibility of a recent infection. If clinical signs can be found, an IgM test is recommended. If both tests are negative an additional sample should be taken after 6 to 8 days from this patient to exclude a delayed antibody response.