Contribution to laboratory diagnosis of mumps and parainfluenza.

Specific IgM and IgG antibodies to mumps virus (MV) were detected in sera of mumps-patients by ELISA in agreement with the results obtained by indirect immunofluorescence (IF). Of given sera 37.5% contained IgM reacting in indirect ELISA also with the antigens of parainfluenza virus (PiV) T3. In all patients with respiratory illness over 2 years of age, the significant increase of antibodies to PiV in haemagglutination inhibition (HI) test was in good correlation with serum IgM and IgG antibody levels to PiV T3 determined by ELISA; but, in addition, 30.7% of these sera cross-reacted with MV antigens. The cross-reactions were eliminated by using MV-nucleocapsid antigen in indirect ELISA, or in direct ELISA using the peroxidase-labelled whole virion antigen. In some children under two years of age a discrepancy was observed between the significant increase of serum antibodies in HI and the inability to detect specific IgM antibodies by means of ELISA in their sera. The low-avidity antibodies appearing after primary PiV infection were probably washed off during the ELISA procedure.