Abstract: The existence of at least one solution and the existence of extreme solutions of periodic boundary value problems for first-order integro-differential equations of mixed type are studied,in the presence of generalized upper and lower solutions. The discussion is based on new comparison theorems and coincidence degree and monotone iterative methods.

Key words: generalized upper and lower solutions, coincidence degree, monotone iteration, integro-differential equation of mixed typeanti GCRV and anti STIV activity in various cultured fish cells. Inhibition of viral replication in cells was dependent