The invention concerns a reagent for diagnosing an infection caused by a
virus, characterized in that it comprises essentially a mixture consisting
of (1) an immunodominant fragment of a protein of said virus comprising
not more than 60 aminoacids, preferably between 20 and 30 aminoacids and
(2) a mixture (called mixotope) of convergent combining peptides, derived
from said immunodominant fragment, which peptides are obtained by total or
partial artificial degeneration of said immunodominant fragment by
systematic or partial replacement of each aminoacid by another according
to an appropriate substitution matrix. The invention concerns a reagent
for detecting and monitoring infections caused by the Epstein-Barr virus
of EBV, which is, in particular, the causal agent of infectious
mononucleose and its applications for detecting an EBV infection at any
stage of the infection (primo-infection, healthy carriers and induced
tumors). Said diagnosis reagent comprises essentially a mixture consisting
of (1) a C-terminal fragment of the protein VCAp18 SEQ ID n.sup.o 1 of the
Epstein-Barr virus (EBV) comprising not more than 60 aminoacids,
preferably between 20 and 30 aminoacids, and (2) a mixture of convergent
combining peptides, derived from said C-terminal fragment.
