Titer Distribution Analysis of Chikungunya Virus in Aedes Albopictus (Diptera: Culicidae)

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Abstract
The growth of chikungunya virus was compared in strains of Aedes albopictus from Oahu, Hawaii, and Hyogo, Japan, after feeding on a blood-virus mixture with a titer of ca. 105 PFU per mosquito. Determination of virus quantities in individual Oahu mosquitoes indicated rapid virus multiplication and appearance of high-titered mosquitoes mainly in the early phase of infection, followed by separation into the unsusceptible (<101 PFU), moderately susceptible (103 − 104 PFU), and highly susceptible (106 − 107 PFU) groups 14 days after feeding. In contrast, only 2 of 58 Hyogo mosquitoes at day 14 showed virus titers over 104 PFU. A trimodal pattern of titer distribution was consistently observed at day 14 in Oahu mosquitoes, but not when these mosquitoes were maintained for 21 or 28 days. Despite a similar course of digestion and excretion for blood ingested by Oahu and Hyogo mosquitoes, the Hyogo strain was fundamentally different in virus retention. In this strain the infection rate decreased to 40–50% at day 2 and remained unchanged up to day 14, while all Oahu mosquitoes retained the virus up to day 7 and ca. 30% of the sample became uninfected between days 7 and 14.