Diagnosis

Laboratory diagnosis of parainfluenza viruses can be performed by isolation and detection of the virus in cell culture, or detection of viral antigens directly within respiratory tract secretions using immunofluorescence (IFA), enzyme immunoassays (EIA), fluroimmunoassays or polymerase chain reaction (PCR). Also, analysis of specific IgG antibodies showing a subsequent rise in titer following infection (using paired serum specimens) can demonstrate an acute infection. However, individual parainfluenza virus types are known to cross-react making subtyping difficult. Hemagglutination inhibition tests (HIT), complement fixation (CF) and neutralization tests (NT) can be performed to differentiate the HPIV types by evaluating the specific IgM, IgG and IgA antibody titers.

During the acute phase of infection, two thirds of patients show a high serum titer of specific HPIV IgM antibodies which persist 2-11 weeks. In 70 – 80% of patients, an increase in specific IgG antibodies (at least fourfold within 10 days) is found during primary infection with HPIV-1, 2 or 3. New EIA assays rely on purified viral envelope glycoprotein and nucleocapsid preparations. In differential diagnosis, tests for other paramyxoviruses like mumps, pneumonia and simian virus type 5 must be performed due to possible cross-reactions.