Actividad del virus de la encefalitis equina venezolana en el norte de Colombia, abril y mayo de 1983 / Venezuelan equine encephalitis virus activity in northern Colombia during April and May 1983

Venezuelan equine encephaltis (VEE) virus was isolated from sentinel hamsters exposed in the Rio de Oro region of Colombia, in the Lake Maracaibo drainage área near the border with Venezuela, in 1983-13 years after the first strain was isolated from the region near Tibu. Hydroxylapatite elution profiles of three isolates from the Rio de Oro region were typical of enzootic strains. Relative abundance data and past isolations suggest that culex (Melanoconion) pedroi is a probable enxootic vector at this focus. The virus was no isolated from forests near Santa Marta and Magangue in the Rio Magdalena drainage área in 1983-9 and 16 years, respectively, after the last previous isolations in those áreas. However, equine animals 2 to 10 years of age and humans 25 to 67 years of age living near the Magangue field study área were positive for VEE virus-specific neutralizing antibodies

Vector competence of Culex (Melanoconion) taeniopus for allopatric and epizootic Venezuelan equine encephalomyelitis viruses.

The vector competence of Culex (Melanoconion) taeniopus was examined in the laboratory for "enzootic" allopatric and "epizootic" strains of Venezuelan equine encephalomyelitis viruses of hemagglutination inhibition subtypes I, II, III, and IV. Following bloodmeals from viremic hamsters, and extrinsic incubation of 20-22 days, mosquitoes were allowed to refeed for transmission attempts. Infection rates never exceeded 50% with oral doses of less than 10(4) chick embryo cell culture plaque forming units (CECPFU), and approached 100% only after ingestion of greater than or equal to 10(5.5) PFU. Transmission was achieved for some "epizootic" subtype IABC and "enzootic" subtype ID strains after bloodmeals containing greater than or equal to 10(3.4) CECPFU; subtypes II, III, and IV were never transmitted despite oral doses up to 10(5.0) CECPFU. These data contrast sharply with those reported previously for sympatric "enzootic" subtype IE Middle American Venezuelan encephalitis viruses.

Laboratory vector competence of Culex (Melanoconion) cedecei for sympatric and allopatric Venezuelan equine encephalomyelitis viruses.

Laboratory vector competence of Culex (Melanoconion) cedecei was examined for Venezuelan equine encephalomyelitis (VEE) viruses. Colonized adult female mosquitoes originating from a southern Florida population were given bloodmeals from viremic hamsters circulating various titers of 3 hemagglutination inhibition (HI) subtypes of VEE viruses. Following extrinsic incubation of about 3 weeks, mosquitoes were allowed to refeed on uninfected hamsters for transmission trials. Cx. cedecei was highly efficient in becoming infected with and transmitting its sympatric, HI subtype II "Everglades" virus. With bloodmeal titers of 10(0.9) chick embryo cell culture (CEC) plaque forming units (PFU), the infection rate was 9% and transmission occurred following extrinsic incubation. Infection rates were greater than or equal to 80% with oral doses of greater than or equal to 10(1.8), and all infected mosquitoes were capable of transmission following incubation. Cx. cedecei was also highly sensitive to infection with allopatric HI subtype IE Middle American VEE virus isolates. Infection rates were greater than or equal to 50% with bloodmeal titers undetectable by CEC assay. Rates were 100% with oral doses of greater than or equal to 10(0.8) CECPFU. Transmission rates were 100% in all experiments. Similar results were obtained with HI subtype IAB "epizootic" VEE virus isolates from the 1969 Middle American outbreak. Infection rates were 100% with oral doses of greater than or equal to 10(1.2), and transmission rates were 100% after extrinsic incubation. Comparisons with laboratory vector competence of the Middle American enzootic VEE virus vector, Culex (Melanoconion) taeniopus, are discussed.

Actividad del virus de la encefalitis equina venezolana en el norte de Colombia, abril y mayo de 1983 / Venezuelan equine encephalitis virus activity in northern Colombia during April and May 1983

Venezuelan equine encephaltis (VEE) virus was isolated from sentinel hamsters exposed in the Rio de Oro region of Colombia, in the Lake Maracaibo drainage area near the border with Venezuela, in 1983-13 years after the first strain was isolated from the region near Tibu. Hydroxylapatite elution profiles of three isolates from the Rio de Oro region were typical of enzootic strains. Relative abundance data and past isolations suggest that culex (Melanoconion) pedroi is a probable enxootic vector at this focus. The virus was no isolated from forests near Santa Marta and Magangue in the Rio Magdalena drainage area in 1983-9 and 16 years, respectively, after the last previous isolations in those areas. However, equine animals 2 to 10 years of age and humans 25 to 67 years of age living near the Magangue field study area were positive for VEE virus-specific neutralizing antibodies