A simple biological marker to differentiate the types of Herpes Simplex Viruses in resource-limited settings.

Herpes simplex viruses (HSV) multiply readily on the chorioallantoic membrane (CAM) of embryonated hen's egg and produce easily visible foci or pocks on this membrane. In the present study, pocks produced by the two antigenic types of HSV (1 & 2) were compared to evaluate the effectiveness of typing HSV isolates by pock size on CAMs. A total of 57 HSV isolates from both non-genital and genital samples were typed by the pock size produced on the CAMs of fertile hen's eggs. Twenty two HSV isolates yielded visible pocks on CAM, of which 9 (40.9%) produced small pocks, while 13 (59.1%) produced large pocks. All pocks produced on CAM were confirmed by antigenic typing by the Direct Fluorescent Antibody (DFA) method. HSV isolates which produced small pocks were in complete (100%) concordance with HSV type-1, while those producing larger pocks were in full (100%) concordance with HSV type-2. Thus, the pock size on CAM of embryonated fertile hen's egg may be used as a simple and relatively inexpensive biological marker for the differentiation of HSV types 1 & 2.