From the Guidelines
After 2 weeks of clinical symptoms of Epstein-Barr virus (EBV) infection, IgG antibodies would typically be low or still rising, as the immune system takes time to switch from producing IgM to IgG antibodies. The immune response to EBV infection involves an initial increase in IgM antibodies, which can be detected early in the infection, followed by a switch to IgG production as the infection progresses 1. According to the guidelines by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM), heterophile antibodies, which are a type of IgM antibody, usually become detectable between the sixth and tenth day following symptom onset and increase through the second or third week of the illness 1. The presence of VCA IgM (with or without VCA IgG) antibodies in the absence of antibodies to EBNA indicates recent primary infection with EBV, and it is not until later, typically more than 6 weeks after symptom onset, that EBNA antibodies, which are IgG, become detectable 1. Therefore, at 2 weeks after symptom onset, the IgG response may still be in its early stages, and IgG levels may not have reached their peak. Key points to consider in the diagnosis of EBV infection include:
- The timing of symptom onset and the type of antibodies present
- The distinction between acute and past infections based on IgM and IgG levels
- The use of additional laboratory tests, such as EBV antibody testing for IgG and IgM to viral capsid antigen (VCA) and Epstein-Barr nuclear antigen (EBNA), to confirm the diagnosis 1.
From the Research
EBV Infection and IgG Levels
- Epstein-Barr virus (EBV) has a long incubation period, typically lasting around six weeks 2.
- During this incubation period, the virus replicates in the oral cavity and disseminates to the blood, where it can be detected at low levels about 3 weeks before symptoms appear 3.
- The immune response to EBV infection involves the expansion of natural killer cells and the decrease of plasmacytoid dendritic cells, but these changes occur after symptom onset 3.
- The measurement of EBV-IgG anti-VCA avidity can aid in the early and reliable diagnosis of primary EBV infection, as low-avidity IgG anti-VCA is indicative of recent infection 4.
IgG Levels After 2 Weeks of Clinical Symptoms
- After 2 weeks of clinical symptoms, IgG levels are likely to be high, as the immune response to EBV infection is characterized by the production of IgG antibodies against the viral capsid antigen (VCA) and Epstein-Barr nuclear antigen (EBNA-1) 4.
- The avidity of IgG anti-VCA antibodies, which measures the strength of binding between the antibody and the antigen, increases over time after infection, with mean avidity rising from 54% at 6 weeks to 82% by 28 weeks after the onset of symptoms 4.
- Therefore, after 2 weeks of clinical symptoms, IgG levels are expected to be high, but the avidity of IgG anti-VCA antibodies may still be relatively low, indicating recent infection 4.