HPIVs belong to the Paramyxoviridae family. They are enveloped RNA viruses. There are four types (1 through 4) and two subtypes (4a and 4b) of HPIVs. The clinical and epidemiological features for each HPIV type can sometimes vary. In the United States, infections associated with HPIV-1 usually peak every other year.
https://www.cdc.gov/parainfluenza/hcp/clinical-overview/index.html