The human parainﬂuenza virus (HPIV) contains two viral glycoproteins in the viral envelope. Human parainﬂuenza viruses are closely related to the measles, mumps, and respi- ratory syncytial viruses. Human parainﬂuenza virus type 3 is the second leading cause of infant and childhood respira- tory disease (after RSV). Currently, no vaccine or antiviral is available. The human parainﬂuenza virus was ﬁrst discov- ered in the 1950s (Japan: Sendai virus). Since then, 4 types with numerous subtypes and subgroups/genotypes have been identiﬁed.
HPIV-3. Several approaches to vaccine development have been evaluated in recent years. Two separate live- attenuated vaccines have been under evaluation. The cold-passaged (cp) HPIV-3 vaccines are cold-adapted, temperature-sensitive prospects. In early studies, the cp-18 strain was not sufﬁciently attenuated for chil- dren, but the cp-45 strain showed more promising re- sults. When given intranasally to children, the vaccine candidate was immunogenic and safe (319). The anti- genically-related bovine parainﬂuenza-3 (BPIV-3) vac- cine has also been evaluated in early clinical trials (320,321). Results revealed that this vaccine is safe, immunogenic, and poorly transmittable. In addition, serum hemagglutination-inhibition antibody respons- es were increased with BPIV-3 when compared with those induced by cold-passaged HPIV-3. Trivalent sub- unit vaccines (322) as well as recombinant vaccines (323,324) are also under evaluation as potential parain- ﬂuenza vaccine candidates.
HPIV strains are seasonal. HPIV-1 and -2 usually cause respiratory outbreaks in the autumn. HPIV-3 may cause croup, but it may produce symptoms that mimic respiratory syncytial virus infection with bronchiolitis and pneumonia being common symp- toms. HPIV-3 is associated with spring outbreaks. HPIV-4 causes mild respiratory infections and is rarely observed. HPIV is very common and almost all children have had HPIV in at least one form by age 6 years. Children are most at risk, although bouts of HPIV are reported in foreign travelers. Hence, the elderly and other immunosuppressed in- dividuals are at risk.
Parainﬂuenza virus infections after hematopoietic stem cell transplantation occur in 7–8% of cases with 78% of these infections being community acquired. Three-fourths of these patients died from pneumonia within 180 days after pneumo- nia was diagnosed. Ribavirin and intravenous immunoglobu- lin were not effective treatments (325).