ARBOVIRUS TITER VARIATION IN FIELD-COLLECTED MOSQUITOS

Patterns in the distribution of titers in arbovirus-positive mosquito pools were examined. Virus isolation records from the Division of Vect or-Borne Infectious Diseases, Centers for Disease Control and Preventi on, from 1974 through 1993 were used to estimate virus titers in field -collected pools. Pools were classified as either low titer (less than or equal to 3.0 log(10) plaque-forming units [PFU]/ml) or high titer (>3.0 log(10) PFU/ml). The proportion of virus-positive pools that had high titers varied among the different domestic arboviruses, within v iruses among field sites and years, and within viruses among mosquito species tested. Alphaviruses produced a greater proportion of pools wi th high titers than did the flaviviruses. Variation in the proportion of pools with high titers among sites and years suggested variation in mosquito and/or virus strains. Variation in the proportion of pools w ith high titers among mosquito species indicated species-specific diff erences in vectorial capacity. The results show that information about the titer of virus in mosquito pools can complement other parameters, such as the minimum infection rate, currently used in mosquito-based arbovirus surveillance programs.