A gel-precipitin test for the diagnosis of varicella.

Varicella may be difficult to distinguish clinically from smallpox. Because of this difficulty, much anxiety has occurred when cases of chickenpox are misdiagnosed as smallpox in areas where smallpox is not endemic. Surveillance of smallpox has also been complicated in areas where eradication programmes are in progress. A gel-diffusion test has been developed that can detect varicella-zoster (V-Z) antigen in vesicular fluid. This simple test, which can be performed in the field, identified V-Z antigen in vesicular fluid in all 14 cases of varicella or zoster that were tested. No reactions were observed with vaccinia precipitin antigen. The production of V-Z precipitin antigen in tissue culture provided a positive control that yielded lines of identity with vesicle fluid. This material was also used to screen human sera for suitable antisera for the test.