Molecular Epidemiological Study of Mumps Epidemics of 2015 in Okinawa, Japan

Area of Science:

• Virology
• Epidemiology
• Molecular Biology

Background:

• Okinawa Prefecture historically experiences mumps epidemics every 4-5 years without laboratory confirmation.
• A significant mumps outbreak began in Okinawa in October 2014.

Purpose of the Study:

• To conduct laboratory diagnoses and molecular epidemiology of mumps in Okinawa.
• To identify the genotypes and lineages of mumps viruses circulating during the 2015 epidemic.

Main Methods:

• Collected clinical samples from 31 patients across four Okinawan areas (Hokubu, Nanbu, Miyako, Yaeyama) between July and December 2015.
• Performed virus isolation and reverse transcription-polymerase chain reaction (RT-PCR).
• Conducted phylogenetic analyses to classify viral isolates.

Main Results:

• Positive detection rates for mumps virus were 52% (virus isolation) and 87% (RT-PCR).
• All isolates belonged to genotype G, predominantly subgenotypes Ge (55.6%) and Gw (40.7%), recently prominent in Japan.
• A novel lineage, similar to a 2014 Hong Kong isolate, was detected in Japan for the first time.
• Ge viruses were found on the main island and Yaeyama Islands; Gw isolates were mainly detected in the Miyako Islands, indicating separate geographic distributions.

Conclusions:

• The 2015 Okinawa mumps epidemic was primarily caused by Ge and Gw mumps viruses.
• These two major lineages appear to have spread independently within distinct regions of Okinawa.
• This study provides the first molecular epidemiological data on mumps outbreaks in Okinawa Prefecture.