Serological diagnosis of parainfluenza virus infections by enzyme immunoassay with special emphasis on purity of viral antigens.

Enzyme immunoassay (EIA) for parainfluenza virus type 1, 2, and 3 antibodies was compared with the complement fixation test (CF) as a diagnostic method in 180 patients with respiratory symptoms. The CF test detected rises in parainfluenza virus antibodies in 30 cases, whereas EIA detected 47 rises. Patients with antibody rises in parainfluenza or mumps virus antibodies were studied for cross-reactions by CF, hemagglutination inhibition (HAI), and EIA using purified viral envelope glycoprotein and nucleocapsid preparations. All methods showed marked cross-reactivity between parainfluenza virus type 1 and 3 antibodies. Mumps virus infection often raised heterologous antibodies even against purified viral antigens. Rabbit antisera produced against viral envelope glycoproteins showed heterologous antibody responses between parainfluenza 1 and 3 antibodies and between parainfluenza 1 and mumps antibodies by HAI, EIA, and immunoprecipitation. The cross-reactive antibodies were usually directed against both of the envelope glycoproteins, HN and F proteins, of the viruses.