Herpes is a chronic viral infection with no current cure or vaccine. Once infected an individual carries the herpes virus for life.
There are two types of herpes simplex virus - type 1 (HSV-1) and type 2 (HSV-2) - but they are extremely difficult to differentiate between. HSV-1 tends to be acquired during childhood and is most frequently associated with oro-facial lesions, while HSV-2 is generally considered to be a sexually transmitted infection. However this division is not invariable and in recent years an increase in genital HSV-1 has been seen, for instance in the UK. Nevertheless it is recognised that HSV-2 gives rise to a more serious genital infection in which ulceration is both more severe and is more frequently symptomatic.
Type 2 Herpes simplex virus (HSV-2) is a major cause of genital ulcer disease worldwide. Seroprevalance surveys have suggested that as many as 15% of the adult population in Europe are infected and, respectively, 22% in North America and 50% in Africa. Additionally, the incidence of HSV-2 is increasing in many populations around the world.The infection is characterised by symptomatic periods in between periods of latency.
Viral shedding from the vaginal tract can give rise to neonatal infection. This can range from mild disease to a fatal disseminated infection but overall the risk of neurological complications in the neonate is very high. A major concern is the role of genital HSV-2 infection in facilitating HIV transmission. The two infections appear to exacerbate each other; genital ulceration in an HIV negative individual increases the risk of acquiring HIV but it also appears to increase the infectivity of individuals who are HIV positive. This association with HSV-2 and HIV infections is leading several research groups to design intervention studies with the aim of reducing the HIV incidence in developing countries.
Problems of current diagnostic tests
Virological methods can be used to detect and distinguish infections but a major drawback is that virus may not be detected in between episodes of disease. A simple blood test to detect antibodies to HSV-2 has until recently not been available, simply because HSV-1 and HSV-2 are antigenically so similar. Simple serological assays using whole virus cannot distinguish between the HSV types and as HSV-1 infections are far more common, the predictive power of these tests is negligible.
The Kalon Biological HSV2 IgG ELISA
More refined techniques, such as Western Blotting and blocking assays, are available in specialised laboratories. The publication of the sequence of glycoprotein G (gG) a glycoprotein in HSV where there are large differences between type 1 and type 2 meant that simple type specific assays became a practical proposition. The use of purified, native type 2 glycoprotein G (gG2) may not completely overcome the problems of cross reactivity as the shorter gG1 is homologous with gG2 over much of its length. For this reason, the Kalon Biological HSV2 IgG test employs a unique recombinant modified gG2 giving the assay a high sensitivity and specificity.
The Kalon Biological HSV2 IgG ELISA has all the expected convenience and safety features including in-well dilutions and colour coded reagents. With three 30 minute incubations, results can be read within 2 hours. But what results to expect?
- When tested against the Centers for Disease Control (CDC), Atlanta HSV/CMV serum panel the Kalon kit showed a sensitivity of 97% and a specificity of 100%.
- In a study of 299 sera collected in a UK genito-urinary medicine clinic, the Kalon test was found to have a relative sensitivity of 96.4% and relative specificity of 99.1% compared with an HSV-2 specific monoclonal blocking assay.
- In another study, the Kalon Biological HSV2 IgG ELISA was compared to Western Blot and another commercially available ELISA on culture confirmed cases of HSV-2. The sensitivity in cases of recurrent HSV-2 was 100% and the specificity in cases of recurrent HSV-1 was 100%, significantly better than the other ELISA compared. However the time taken to detect seroconversion after a first HSV-2 episode was longer, with a median time of 4 to 5 months after onset of symptoms.
- The test has also been compared to other commercially available kits for its ability to accurately detect HSV-2 antibodies in a large study of sera from Kenya, Zambia, Benin and Cameroon in sub-Saharan Africa. The study found the Kalon Biological HSV2 IgG ELISA to have the best performance with a relative sensitivity 92.3% and a relative specificity of 97.7%. These results indicate that the Kalon Biological HSV2 IgG ELISA is the kit of choice for research studies where there is a need to detect antibodies to HSV-2, for example HIV intervention studies.
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Click here for a list of references regarding the Kalon HSV2 IgG ELISA kit.
The Kalon Biological HSV2 IgG ELISA is offered for research use only. The product has not been cleared for use in the USA by the FDA, and it does not currently bear a CE mark for use as a diagnostic device in the European Union.