Background The Amazon as a whole is the largest reservoir of arboviruses worldwide, while the Brazilian Amazon hosts the largest variety of arboviruses isolated to date. In this study, the results of an indirect sandwich IgG ELISA, standardized for 19 arbovirustypes circulating among horses in Brazilian Amazon, were compared to results of the hemagglutination inhibition test. A screening test assessed the conditional probability distribution and a Pearson linear correlation test determined the correlation strength among the absorbance values recorded for viruses from the same family.Findings Sensitivity varied between 40.85 and 100%; the specificity was low and ranged from 39.71 to 67.0%; and the accuracy varied between 41 and 65.2%. The test developed in this study yielded a large number of serological cross-reactions.Conclusions The test can be employed to detect IgG antibodies within one arbovirus family; however, the hemagglutination test or other more specific techniques, such as the serum neutralization test in mice or the plaque-reduction neutralization test, are essential complementary methods for positive cases.

Rocio virus (ROCV) is an encephalitic flavivirus endemic to Brazil. Experimental flavivirus infections have previously demonstrated a persistent infection and, in this study, we investigated the persistence of ROCV infection in golden hamsters (Mesocricetus auratus). The hamsters were infected intraperitoneally with 9.8 LD50/0.02 mL of ROCV and later anaesthetised and sacrificed at various time points over a 120-day period to collect of blood, urine and organ samples. The viral titres were quantified by real-time-polymerase chain reaction (qRT-PCR). The specimens were used to infect Vero cells and ROCV antigens in the cells were detected by immunefluorescence assay. The levels of antibodies were determined by the haemagglutination inhibition technique. A histopathological examination was performed on the tissues by staining with haematoxylin-eosin and detecting viral antigens by immunohistochemistry (IHC). ROCV induced a strong immune response and was pathogenic in hamsters through neuroinvasion. ROCV was recovered from Vero cells exposed to samples from the viscera, brain, blood, serum and urine and was detected by qRT-PCR in the brain, liver and blood for three months after infection. ROCV induced histopathological changes and the expression of viral antigens, which were detected by IHC in the liver, kidney, lung and brain up to four months after infection. These findings show that ROCV is pathogenic to golden hamsters and has the capacity to cause persistent infection in animals after intraperitoneal infection.

Em amostra da população da cidade de Rio Branco (Acre), foi pesquisada a freqüência de portadores de anticorpos contra os arbovírus, mais prevalentes na região amazônica, e o vírus vacinal da febre amarela, antes e após a imunização com a vacina 17D. Das 390 pessoas incluídas na primeira fase do estudo (agosto de 1999), somente 190 compareceram em janeiro de 2000, três meses após a aplicação da vacina 17D (outubro de 1999). Nas amostras da primeira fase, as freqüências de soropositivos (IH) para os vírus estudados foram: 17D (27,2%); Dengue-1 (0,3%); Dengue-2 (4,1%); Dengue-3 (0%); Dengue-4 (0%), entre outros 8 vírus. Nas amostras séricas de janeiro (2000), a soroconversão para o 17D foi de 89,7% (130/145) e 3,2% (6/190) passaram a ter anticorpos contra o sorotipo 3 (DEN-3). Em conclusão, por conta da elevada taxa de cobertura vacinal e de soroconversão há redução significativa do risco de urbanização do vírus da febre amarela na cidade de Rio Branco, apesar de não ser desprezível a possibilidade de uma nova epidemia de dengue, pelo DEN-3, a semelhança da registrada em 2000 e 2001 pelos sorotipos 1 e 2.

During a yellow fever vaccination campaign among residents of Rio Branco (Acre State), the frequency of HI antibodies to the most prevalent arboviruses in the Amazon region and to yellow fever virus was determined before and three months after immunization with YF 17D vaccine. From 390 inhabitants included in the first phase of serologic survey (August 1999), only 190 provided a second serum sample, after the use of 17D vaccine (January 2000). Among first phase samples, the frequency of HI antibodies was: 17D (27.2%); Ilheus (5.9%); Mayaro (5.4%); Caraparu (4.9%); Dengue-2 (4.1%); Oropouche (2.3%); and Dengue-1 (0.3%). In the second study phase, the serologic conversion to YF reached 89.7% among previously negative persons. Serologic conversions were also observed to Ilheus (6.2%); Dengue-3 (3.2%); Mayaro (1.1%); and Oropouche (1.1%) viruses. In conclusion, considering the high YF antibody rate after vaccination, the risk of urban yellow fever seems insignificant, although the lower prevalence of HI antibodies to dengue viruses, is of concern and inhabitants are under high risk of dengue outbreaks, especially to DEN-3 recently introduced in Brazil, as was observed in 2000 and 2001 with DEN-1 and DEN-2.

Visando investigar a possível patogenicidade do vírus isolado (GOI 4191) de um evento adverso fatal pela vacinação antiamarílica, realizou-se um ensaio experimental em Syrian hamsters (Mesocricetus auratus), usando-se a cepa vacinal 17DD como parâmetro. As amostras virais foram inoculadas por via intracerebral, intra-hepática e subcutânea. Nos soros foram determinados níveis de viremia, resposta imune e aminotransferases, e nas vísceras a presença de vírus, antígeno e lesões teciduais. Não se detectou viremia para as duas amostras, a resposta imune foi maior para GOI 4191, e as aminotransferases não apresentaram alterações compatíveis com danos hepáticos. Nos animais inoculados por via intracerebral o vírus foi recuperado somente a partir do cérebro, sendo o antígeno viral detectado, por imuno-histoquímica, no cérebro e fígado. Infiltrado inflamatório e corpúsculos acidófilos foram observados no fígado e lesões tipo encefalite viral no sistema nervoso central. Alterações histológicas e antígeno viral foram observados, também, no fígado dos animais infectados por via intra-hepática, e ausentes naqueles inoculados por via subcutânea. Os resultados foram similares para as duas amostras testadas, entretanto distintos daqueles relatados na literatura para cepas silvestres do vírus amarílico.

In order to investigate the pathogenicity of the virus strain GOI 4191 that was isolated from a fatal adverse event after yellow fever virus (YFV) vaccination, an experimental assay using hamsters (Mesocricetus auratus) as animal model and YFV 17DD vaccine strain as virus reference was accomplished. The two virus strains were inoculated by intracerebral, intrahepatic and subcutaneous routes. The levels of viremia, antibody response, and aminotransferases were determined in sera; while virus, antigen and histopathological changes were determined in the viscera. No viremia was detected for either strain following infection; the immune response was demonstrated to be more effective to strain GOI 4191; and no significant aminotransferase levels alterations were detected. Strain GOI 4191 was recovered only from the brain of animals inoculated by the IC route. Viral antigens were detected in liver and brain by immunohistochemical assay. Histothological changes in the viscera were characterized by inflammatory infiltrate, hepatocellular necrosis, and viral encephalitis. Histological alterations and detection of viral antigen were observed in the liver of animals inoculated by the intrahepatic route. These findings were similar for both strains used in the experiment; however, significant differences were observed from those results previously reported for wild type YFV strains.