Studies of Arboviruses in Southwestern Venezuela: I. Isolations of Venezuelan and Eastern Equine Encephalitis Viruses from Sentinel Hamsters in the Catatumbo Region

Abstract

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.

Virulence and viremia characteristics of 1992 epizootic subtype IC Venezuelan equine encephalitis viruses and closely related enzootic subtype ID strains.

“…This region includes many foci where enzootic subtype ID viruses circulate. 12,[39][40][41] Our demonstra-tion that these ID viruses fully protect horses against challenge with epizootic strain P676, known to be virulent for naïve horses, 7 supports the hypothesis that epizootics rarely involve regions of enzootic transmission because of natural enzootic equine immunization. Renewed vaccination following the 1992-1993 and 1995 outbreaks precludes the evaluation of natural equine immunity in the Trujillo region at the present time.…”

Ecological studies of enzootic Venezuelan equine encephalitis in north-central Venezuela, 1997-1998.

“…Surveillance in this region of Miranda State, assisted by satellite imagery, has not revealed the presence of any extensive, primary lowland tropical forests or swamps like those known to support continuous transmission of VEE viruses in other locations of South Ameri-ca. 15,[29][30][31][32][33][34] Studies are now underway to locate such a transmission cycle in Falcon State, where the 1995 outbreak began.…”

Genetic diversity and relationships among Venezuelan equine encephalitis virus field isolates from Colombia and Venezuela.

“…This area was originally covered by lowland tropical rainforest that has been converted into cacao (Theobroma cacao) plantations. 18 The other enzootic Venezuelan sites are tropical lowland forests in the Catatumbo region of western Venezuela 19,20 and near Sinamaica in the southern part of the Guajira Peninsula. 21 The 22 hamsters housed in modified Trinidad no.…”