GEOGRAPHIC-DISTRIBUTION AND SEROLOGIC AND GENOMIC CHARACTERIZATION OFMORRO-BAY-VIRUS, A NEWLY RECOGNIZED BUNYAVIRUS

More than 75,000 immature mosquitoes in three genera were collected fr om coastal California, reared to the adult stage, and tested for virus by plaque assay in Vero cell cultures. Twenty-six strains of Morro Ba y (MB) virus, a newly recognized member of the California (GAL) serogr oup, were isolated from Aedes squamiger, a pestiferous salt marsh mosq uito species restricted to intertidal salt marshes in coastal Californ ia and Baja California. The geographic distribution of the isolates wa s 10 from San Luis Obispo County, one each from Santa Barbara and Oran ge Counties, and 14 from San Diego County. No virus isolations were ma de from 23,157 Ae. squamiger collected north of San Luis Obispo County (midpoint in the geographic range of this species in California). Thu s, MB virus infection in Ae. squamiger appears to be restricted to the southern range of this species in California. Serum dilution neutrali zation tests indicated that MB virus represents a novel subtype of the California encephalitis (CE) serotype within the CAL serogroup. Compa rative analyses of genomic sequence data from four geographically dist inct MB virus isolates indicated that the isolates are genetically sim ilar to each other and distinct from other CE serotype bunyaviruses. P hylogenetic analysis of nucleocapsid protein gene sequence data indica ted that MB virus represents a distinct lineage within the CE serotype and thus supports the serologic classification of MB virus as a disti nct CAL serogroup virus.