Efficacy and durability of a recombinant subunit West Nile vaccine candidate in protecting hamsters from West Nile encephalitis.

The efficacy of a new recombinant subunit West Nile virus (WNV) vaccine candidate was determined in a hamster model of meningoencephalitis. Groups of hamsters were immunized subcutaneously with a WNV recombinant envelope protein (80E) with or without WNV non-structural protein 1 (NS1) mixed with adjuvant or adjuvant alone. At 2 weeks, 6 months, and 12 months after two immunizations at 4 week intervals with the respective immunogens, groups of animals were challenged via the intraperitoneal route with a virulent strain of WNV. The two recombinant antigen preparations gave similar results; hamsters in both groups had a strong antibody response following immunization, and none of the animals became ill or developed detectable viremia after challenge with WNV at 2 weeks or 6 months post-booster vaccination. In contrast, mortality among the control animals at 2 weeks post-booster challenge was 73%, and at 6 months post-booster, the mortality was 53% among the control animals. When challenged 12 months after the booster vaccination, a low level viremia was detected in some of the vaccinated hamsters, and one hamster became sick, but recovered. In contrast, all of the control animals that received adjuvant only developed a viremia, and the mortality rate was 77%. These results with the recombinant subunit WNV vaccine are very encouraging and warrant further animal studies to evaluate its potential use to protect humans against WNV disease.

Comparaçäo de dois testes de neutralizaçäo, utilizados no diagnóstico sorológico do vesiculovírus Piry / Comparison of two neutralization test for the use in the Piry serologic vesiculovirus diagnose

Realizou-se inquérito sorológico para pesquisar anticorpos neutralizantes contra o vesiculovírus Piry, na cidade de Catolândia, Bahia, Brasil. Duas técnicas de vírus-neutralizaçäo foram comparadas em cultura das células C6/36, com revelaçäo pelo método imunoenzimático (TN-C6/36) e em camundongos recém-nascidos (TN-camundongos), que é considerada a prova maior. Em 204 soros, dos 1.274 colhidos, a concordância das duas técnicas foi de 98,7 por cento (K=0,9853). Com este resultado do TN-C6/36, que também é mais exeqüível, decidiu-se desenvolver o estudo soro-epidemiológico do vesiculovírus Piry, em Catolândia, baseado nesta nova técnica

New entomological and virological data on the vectors of sylvatic fever in Brazil

The present report focuses on recent ecoepidemiological data on yellow fever, obtained recently in two very distinct ecoepidemiological contexts: the Barcarena (PA) area, situated in the dense Amazonian rain forest, and the Campo Grande (MS) region, situated in the cerrado with gallery forest in central Brazil. In the first region, one strain was isolated from a pool of 6 Haemagogus janthinomys. In the other region, 2,480 anthropophilous mosquitoes were collected, of which near 40 per cent were potential YF vectors. These species, classified by decreasing relative abundance, were: Aedes scapularis, Sabethes chloropterus, Hg.janthinomys, Hg. leucocelaenus, Hg. spegazinii, and Sa. soperi. Four strains of YF virus were isolated from Hg. janthinomys, one from Sa. cheoropterus (first report for South America) and one from Sa. soperi (first report). The minimal infection rates varied among the three localities of collection but were all high, compared with previous data. The mean daily survival rate was O.9635 for the populations of Hg. janthinomys, allowing extrapolation of the value of the infection rate when people were infected most recently. It was deduced that the epizootics were intense and more or less concomitant in the three areas. The main problem that remained to be solved concerns the mode(s) of reintroduction or survival of YF virus in each of the two regions under study.

A comparative study of yellow fever in Africa and South America

In order to look for an ecoepidemiological model of sylvatic yellow fever (YF) transmission in South America, differences from and similarities to available African YF data are considered. Strains from both areas, representing various topotypes, are distinct serologically, genetically and biochemically. In Africa, all vector mosquitoes are Aedes species, some related to the forest cycle and others responsible for the transmission in dryer areas. In South America, and particularly in Brazil, the main vector is Haemagogus janthinomys. Hg. albomaculatus has been incriminated in human peridomestic transmission in Central Amazonia. In the two continents, monkeys are the only regular vertebrate hosts of YF but the indigenous neotropical monkeys, show higher mortality rates. The South American and African vectors are diurnal and crespuscular/nocturnal in habit, respectively. The urban vector (Ae. aegypti) has the same habits in both continents, but its competence in transmitting the virus is very variable, and no urban epidemic has been notified in South America since the 4Os. A general ecoepidemiological model was elaborated to explain the maintenance and circulation of YF virus in West and Central Africa, which are related to the phytoclimatical regions. Because no such hypothesis has yet been presented in the case of YF in South America, we tested this with the available data from Brazil. All occurrences (of which 386 were lab-confirmed) were distributed in five phytogeographical zones: dense rain forest (l89), open rain forest (30), savannah with gallery forest (l47), ecotones (lO) and decidual seasonal forest (7). For each of these zones mean intervals between years with occurrences of YF were estimated. They were all found to be lower than 3 years, and lower than 5 years when standard deviation was added. Despite the close values obtained for the means, the distribution of the years as a function of number of occurrences of YF showed two groups: a) gallery forest and dense forest and b) open forest and ecotones. However, more data are necessary to enable the study of such variations which are thought to be related to ecological differences in YF transmission.

Study of two different enzyme immunoassays for the detection of Mayaro virus antibodies

This paper presents the evaluation of an enzyme immunoassay in which Mayaro virus-infected cultured cells ara used as antigen (EIA-ICC) and an IgM antibody capture ELISA (MAC-ELISA) for Mayaro serologic diagnosis using 114 human sera obtained during a Mayaro outbreak occurred in Bolivia, in 1987. Results were compared with those obtained by haemagglutination-inhibition test (HAI). MAC-ELISA was the most sensitive technique for anti-Mayaro IgM detection. MAC-ELISA was twice sensitive as IgM EIA-ICC. The data shows that MAC-ELISA is a practical and valid technique for diagnosis of recent mayaro infection. IgG-ICC showed hight sensitivity and high specificity compared to HAI. The combination of anti-Mayaro IgG and IgM EIA-ICC results presented the highest sensitivity of the study. Anti-Mayaro IgG and IgM simultaneous detection by ELISA-ICC can be used for recent infection diagnosis (in spite of a less sensitive IgM detection than by MAC-ELISA), for surveillance and sero-epidemiologic studies, and for studies of IgG and IgM responses to Mayaro infection