Jorge Boshell

Re-emergence of epidemic Venezuelan equine encephalomyelitis in South America

BACKGROUND Venezuelan equine encephalomyelitis (VEE) virus has caused periodic epidemics among human beings and equines in Latin America from the 1920s to the early 1970s. The first major outbreak since 1973 occurred in Venezuela and Colombia during 1995, and involved an estimated 75,000 to 100,000 people. We report an epidemiological and virological investigation of this epidemic. METHODS Virus isolates were made in cell culture from human serum, human throat swabs, and brain tissue from aborted and stillborn human fetuses, as well as from horse brain tissue and pooled mosquito collections. Human sera were also tested for VEE-specific antibodies. The serotypes of VEE isolates were identified by antigen assays, and viruses were characterised genetically by sequencing PCR products generated from the E3 and E2 genes. Phylogenetic analyses were done to determine evolutionary relations with respect to previous epidemic/epizootic and enzootic VEE virus isolates. Mosquito collections were made to identify possible vectors, and clinical findings were determined by direct observation of patients visiting hospitals and clinics in affected regions, and by inspecting patient records. Equine vaccination and vector control were used in an attempt to halt the spread of the outbreak. FINDINGS Most affected people had an acute, self-limited febrile illness of 3 to 4 days duration. However, convulsions were often seen in children, and abortions and fetal deaths occurred in pregnant women infected with VEE virus. Antigenic characterisation of 12 virus isolates spanning the temporal and spatial range of the outbreak indicated that all are VEE serotype IC. Phylogenetic analysis revealed that all of the 1995 viruses were closely related to serotype IC viruses isolated during a large VEE outbreak that occurred in the same regions of Colombia and Venezuela from 1962-1964. A 1983 mosquito isolate from north central Venezuela was also closely related to the 1995 isolates. INTERPRETATION This outbreak was remarkably similar to one that occurred in same regions of Venezuela and Colombia during 1962-1964. Symptoms of infected patients, estimated mortality rates, meteorological conditions preceding the epidemic, and seasonal patterns of transmission were all very similar to those reported in the previous outbreak. In addition, viruses isolated during 1995 were antigenically and genetically nearly identifical to those obtained during 1962-1964. These findings suggest that the epidemic resulted from the re-emergence of an epizootic serotype IC VEE virus. Identification of a similar virus isolate in mosquitoes in Venezuela in 1983, 10 years after epidemic/epizootic VEE activity ceased, raises the possibility of a serotype IC enzootic transmission cycle in northern Venezuela.

Natural enzootic vectors of Venezuelan equine encephalitis virus, Magdalena Valley, Colombia.

To characterize the transmission cycle of enzootic Venezuelan equine encephalitis virus (VEEV) strains believed to represent an epizootic progenitor, we identified natural vectors in a sylvatic focus in the middle Magdalena Valley of Colombia. Hamster-baited traps were placed into an active forest focus, and mosquitoes collected from each trap in which a hamster became infected were sorted by species and assayed for virus. In 18 cases, a single, initial, high-titered mosquito pool representing the vector species was identified. These vectors included Culex (Melanoconion) vomerifer (11 transmission events), Cx. (Mel.) pedroi (5 transmissions) and Cx. (Mel.) adamesi (2 transmissions). These results extend the number of proven enzootic VEEV vectors to 7, all of which are members of the Spissipes section of the subgenus Melanoconion. Our findings contrast with previous studies, which have indicated that a single species usually serves as the principal enzootic VEEV vector at a given location.

Venezuelan equine encephalitis virus infection of spiny rats.

Enzootic strains of Venezuelan equine encephalitis virus (VEEV) circulate in forested habitats of Mexico, Central, and South America, and spiny rats (Proechimys spp.) are believed to be the principal reservoir hosts in several foci. To better understand the host-pathogen interactions and resistance to disease characteristic of many reservoir hosts, we performed experimental infections of F1 progeny from Proechimys chrysaeolus collected at a Colombian enzootic VEEV focus using sympatric and allopatric virus strains. All animals became viremic with a mean peak titer of 3.3 log10 PFU/mL, and all seroconverted with antibody titers from 1:20 to 1:640, which persisted up to 15 months. No signs of disease were observed, including after intracerebral injections. The lack of detectable disease and limited histopathologic lesions in these animals contrast dramatically with the severe disease and histopathologic findings observed in other laboratory rodents and humans, and support their role as reservoir hosts with a long-term coevolutionary relationship to VEEV.

Hepatitis C virus seroprevalence in multi-transfused patients in Colombia

BACKGROUND Hepatitis C Virus (HCV) infection is a public health problem worldwide, with particular relevance in multi-transfused patients given that HCV is principally transmitted by exposure to infected blood. STUDY DESIGN Between February and September 2003 a cross-sectional study was carried out in four hospital centres in Bogotá and Medellin, Colombia, to determine the risk factors for HCV infection in 500 multi-transfused patients. RESULTS The study population was distributed in five groups: haemophilia, haemodyalsis, acute bleeding, ontological illnesses and sickle cell disease or thalassemia. Serum samples from patients were tested for HCV antibodies (Asxym, Abbott). An overall prevalence (9.0%; 95% confidence interval (CI): 6.4-11.6) (45/500) of HCV infection was found. Anti-HCV antibodies were detected in 32.2% of patients with haemophilia, 6.1% of patients undergoing haemodialysis, 7.1% of patients with sickle cell disease or thalassemia, 2.6% of patients with acute bleeding and 3.4% of patients with ontological or hematological diseases. The main risk factors associated with infection by HCV were: to be hemophilic (odds ratio, OR = 18.03; 95% Cl: 3.96-114.17), having received transfusions before 1995 (OR = 12.27; 95% Cl: 5.57-27.69), and having received more than 48 units of blood components (OR = 6.08; 95% CI: 3.06-12.1). In the multivariate analysis, only the year of transfusions (before 1995) remained significantly associated with risk of infection by HCV. CONCLUSIONS The data show a 3-fold reduction in the infection risk between 1993 and 1995, when the serological screening for HCV in blood donors was being introduced. A reduction greater than 90% was achieved by 1995 when the screening coverage reached 99%.

ESTABLISHMENT AND CHARACTERIZATION OF A CELL LINE FROM THE MOSQUITO ANOPHELES ALBIMANUS (DIPTERA : CULICIDAE)

A new cell line designated LSB-AA695BB, was established from embryos of the mosquito Anopheles albimanus. The primary culture was initiated in April, 1995, and the first passage was made 48 days later. Serial subcultures of the cells have been carried through 90 passage from Abril 1995 to February 1996. The cells were grown at 28 degrees C in MK/VP12 medium, supplemented with 20% fetal bovine serum: the pH tolerance ranged between 6.8 to 7.0. The cells have also been adapted to MM/VP12 medium under the same pH, temperature and serum concentration. The majority of the cells were a fibroblast-type. Isozyme characterization showed a pattern similar to that of An. albimanus pupae and adults but distinct from Ae. taeniorhynchus and Ae. albopictus (C6/36) mosquito cell lines. The culture was shown to be free of mycoplasma, bacteria and fungi. Microsporidia contamination of transovarial transmission was controlled with 6.0 micrograms/ml of albendazole.

Initiation of primary cell cultures from embryos of the mosquitoes Anopheles albimanus and Aedes taeniorhynchus (Diptera: Culicidae)

Primary cell cultures were obtained from eggs of Anopheles albimanus and Aedes taeniorhynchus mosquitoes, vectors of human malaria and of Venezuelan equine encephalitis virus, respectively. The cellular growth of the An. albimanus cells began four weeks after explanting the embryonic tissues in MK/VP12 medium, supplemented with 15% fetal bovine serum. The culture showed heterogeneous cellular morphology. With regard to the Ae. taeniorhynchus culture, growth occurred three weeks after initiating the culture in MM/VP12 medium. The majority of cells were small and round. Karyotypes were examined in the latter species.