Experimental Infection and Intracage Transmission of Venezuelan Equine Encephalitis Virus (Subtype IB) among Cotton Rats, Sigmodon Hispidus (Say and Ord)

Ann T. HowardDepartment of Clinical Pathology, Mount Sinai Hospital of Cleveland, Cleveland, Ohio 44106

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Experimental infection and intracage transmission studies were conducted in cotton rats (Sigmodon hispidus) with a Texas epizootic strain (Three Rivers) of Venezuelan equine encephalitis (VEE) virus, subtype IB. Twenty cotton rats, inoculated subcutaneously with 3.8 log10 SMicLD50, became viremic and shed VEE virus in their throat and urine specimens for up to 8 days after inoculation. Nine of the 20 died between days 3 and 10. Deaths were associated temporally with cardiac puncture and with the presence of virus in brain, heart, liver, spleen, and kidney specimens harvested as late as 24 hours after death. Two of the inoculated rats were pregnant females which aborted by day 5; a third inoculated rat had a litter, 4 days old at the time of inoculation, which was dead by day 3. Neutralization, hemagglutination-inhibition, and complement fixation antibodies appeared on days 5, 6, and 10, respectively. Contact transmission was demonstrated by virus isolations from blood or throat specimens in 8 of 20 uninoculated cagemates. Two of the 8 survived infection and developed antibodies to levels comparable to those of the inoculated rats. The high virus levels detected in the cotton rats indicates their potential as amplifying hosts during an epizootic. The successful transmission by contact of an epizootic strain demonstrates the existence of at least one extra-arthropod mechanism for VEE viral maintenance.