Laboratory diagnosis of viral infections :Serology

This approach is currently the most widely used. Typically during acute primary infection, virus specific IgM Abs appear in serum between 5-10 days after initiation of infection, reach peak concentration at 2-4 weeks, and then decline to undetectable level at 2-4 months, although they may last considerably longer in some infections. In the course of persistent infections, IgM Ab is usually negative, although they can reappear during episodes of reactivation of virus. Thus, detecting IgM to a given virus, with or without the corresponding IgG, even in a single serum sample obtained during the acute phase of illness, denotes current or very recent primary infection or reactivation of persistent infection by that virus. By contrast, the presence of virus specific IgG but not IgM signifies past infection.