Studies of arboviruses in Southwestern Venezuela: I. Isolations of Venezuelan and Eastern Equine Encephalitis viruses from sentinel hamsters in the Catatumbo region.

The purpose of this report is to describe isolations of Venezuelan (VEE) and Eastern (EEE) Equine Encephalitis virus made in the lowland moist tropical forest of the Catatumbo region on the southwestern part of the State of Zulia, Venezuela. We have isolated four strains of EEEV from sentinel hamsters exposed at Caño Mocho and Madre Vieja sites in 1973 and 1974, and three strains of EEEV in Hacienda (Hda.) Las Nubes in 1975. Both viruses were recovered during silent interepidemic periods and we believe these viruses are maintained in this region in sylvatic conditions. The recovered virus strains were detected within 24 to 48 hours, both in SMB and Vero Cell monolayer cultures and the sentinel hamsters yielded virus infectivities up to 10(4) PFU ml. Our VEEV isolate (IVIC PAn 23645-47), recovered during the silent interepizodemic period had an elution profile on the hydroxylapatite column corresponding to that of a I-D (VEEV-3880) or a I-E (VEEV-63A216) 'enzootic' subtype. However, considering other in vitro criteria (KHI; HA pH 5.8-6.0; small plaque size in Vero monolayers with suitable overlay media), this later and other previous isolates had some very distinct properties of the 'epizootic' strains. Thus, the evidence suggests that in Venezuela the VEEV cycle in nature is maintained either by the so called 'enzootic' and/or 'epizootic' virus types, or the virus population of the isolates have particular in vitro properties which do not correlate to the virulence markers in vivo. We consider this important question must be further clarified, and in addition, the isolation of three strains of EEEV are reported; this is the first report of the presence of this virus in Venezuela. Although the EEEV isolates may be of the South American type, they must be considered as potentially dangerous in the case of outbreaks.