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An outbreak of Yellow fever virus (YF) occurred in Maranhao State in 1993 (Barra do Corda, Esperantinopolis and Mirador) and 1994 (Pastos Bons), where several cases were reported. In 1993 a total of 932 people were examined for YF distributed as follows : 32 from Barra do Corda, 26 from Esperantinopolis and 874 from Mirador. From these, 70 cases were YF confirmed serologically (IgM capture MAC ELISA), histophathologically and/or by virus isolation. Another 4 cases diagnosed clinically and epidemiologically, brought the total to 74 (Barra do Corda : 5, Esperantinopolis : 7, and Mirador : 62). The age of the patients ranged from 2 to 71 years old (mean : 24) : 32 (43.2%) were female and 42 (56.8%) male and the total lethality-rate was 17.5% (13/74). In Mirador (17,565 inhabitants), where an intensive survey was carried out, the incidence was 3.5 per 1,000 people, but in the rural YF risk area (14,659 inhabitants) the incidence was 4.2, and the mortality 16.1% (10/62). A total of 45.2% (28/62) asymptomatic infections were registered. In 1994, a total of 49 serum samples were obtained from Pastos Bons. Of these, 16 cases, 8 females and 8 males, were YF confirmed as follows : 2 by virus isolation, 2 by seroconversion and 12 by serology. On the other hand, no fatal cases were reported in Pastos Bons. In 1993, 936 potential YF vectors were captured in Mirador and a single strain was isolated from a pool of #Haemagogus janthinomys$ (infection rate (IR) : 0.16%). In 1994, 16 strains were isolated from 1,318 #Hg. janthinomys$ (IR : 1.34%) and one #Sabethes chloropterus$ (IR : 1.67%). Our results suggest that this was the most extensive outbreak of YF in the last 20 years in Brazil. (Résumé d'auteur)

The main aspects of the clinical manifestations and epidemiological data regarding human arboviruses in the Brazilian Amazon region are reviewed. Thirty-six arboviruses and other viruses of vertebrates have been associated with human disease among over 200 isolates made in Brazil. Five of them are important in public health and are involved in epidemics, they are the Dengue (DEN), Mayaro (MAY), Oropouche (ORO), Rocio (ROC) and Yellow Fever (YF) viruses. ORO and DEN are associated with epidemics of human disease in urban areas, while MAY, ROC and YF have been responsible for epidemics in rural areas. Usually, ORO causes a febrile disease, sometimes accompanied by aseptic meningitis. MAY and DEN are associated with febrile disease and rash, while YF produces a hemorrhagic fever and ROC is an agent responsible for encephalitis. Thirty-one other arboviruses are involved in rare and sporadic cases of febrile illness. All arboviruses (with the exception of DEN and arenaviruses) are maintained by a slyvatic cycle in the forest, where several species of hematophagous insects act as vectors and wild vertebrates are involved as hosts. DEN has a cycle in which the #Aedes aegypti$ mosquitoes are the vectors and man the vertebrate host. Arenaviruses are transmitted directly to man by rodents. With the exception of the five viruses associated with epidemics which are of great economical and social impact, and may be responsible for deaths, (e.g. of DEN,; ROC and YF), the exact involvement of these viruses as systematic agents of human disease is unknown. Further studies are needed to clarify aspects of their epidemiology. Arenaviruses are directly transmitted to man by way of the excreta of infected rodents which are the reservoir-hosts of these viruses. Appropriate safety measures should be adopted when handling these viruses as they can be transmitted via the respiratory tract (droplet infection). (Résumé d'auteur)

Yellow fever virus transmission was very active in Maranhao State in Brazil in 1993 and 1994. An investigation was carried out to evaluate the magnitude of the epidemic. In 1993, a total of 932 people was examined for yellow fever from Maranhao : 70 were positive serologically, histopathologically, and/or by virus isolation, and another four cases were diagnosed clinically and epidemiogically. In Mirador (17,565 inhabitants), the incidence was 3.5 per 1,000 people (case fatality rate [number of deaths/number of cases diagnosed] = 16.4%), while in a rural yellow fever risk area (14,659 inhabitants), the incidence was 4.2 and the case-fatality rate was 16,1% (10 of 62). A total of 45.2% (28 of 62) asymptomatic infections were registrered. In 1994, 49 serum samples were obtained and 16 cases were confirmed (two by virus isolation, two by seroconversion, and 12 by serology). No fatal cases were reported. In 1993, 936 potential yellow fever vectors were captured in Mirador and a single strain was isolated from a pool of #Haemagogus janthinomys$ (infection rate = 0.16%). In 1994, 16 strains were isolated from 1,318 #Hg. janthinomys$ (infection rate = 1.34%) and one #Sabethes chloropterus$ (infection rate = 1.67%). Our results suggest that this was the most extensive outbreak of yellow fever in the last 20 years in Brazil. It is also clear that the lack of vaccination was the principal reason for the epidemic, which occurred between April and June, during the rainy season, a period in which the mosquito population in the forest increases. (Résumé d'auteur)

L'histoire de la dengue au Brésil est survolée depuis les premières relations d'épidémies au XIXème siècle jusqu'aux grands épisodes de la dernière décennie. Les sérotypes DEN-1 et DEN-4 ont été isolés pour la première fois au Brésil en 1982, au cours d'une épidémie à Boa Vista, Roraima. En 1986, le virus DEN-1 fut le responsable d'épidémies à Rio de Janeiro et dans le Nordeste du Brésil. A partir de 1990, le virus DEN-2 était présent également dans l'intérieur du pays en Amazonie. A Rio de Janeiro (1990-1991) et dans l'Etat du Ceara (1994) où les deux sérotypes DEN-1 et DEN-2 circulaient en même temps, plusieurs cas de DHF/DSS ont été signalés. Environ 500000 cas de dengue ont été notifiés de 1982 à 1994. #Aedes aegypti$ est le seul vecteur urbain à partir duquel 4 souches de DEN-4, 7 souches de DEN-1 et 16 souches de DEN-2 ont été isolées. La transmission transovarienne ne semble pas avoir lieu chez cette espèce au Brésil. (Résumé d'auteur)

Les épidémies de fièvre jaune (FJ) urbaine ont disparu au Brésil depuis environ 50 ans, mais un cycle sylvatique du virus amaril persiste et des cas de FJ, plus ou moins nombreux selon les années, sont signalés dans de nombreux Etats. #Aedes aegypti$, après avoir été éradiqué du pays en 1956, est réapparu en 1967, temporairement, puis en 1976-1977, cette fois-ci définitivement. Il est vecteur de la fièvre jaune mais également de la dengue, dont la première manifestation épidémique a eu lieu en 1982. Depuis, la dengue est devenue endémique dans de nombreuses régions. Un second vecteur de #Flavivirus$, #Aedes albopictus$, existe depuis une dizaine d'années, dans plusieurs Etats, dont celui de Sao Paulo. L'analyse des cas de fièvre jaune entre 1972 et 1994 a permis de déterminer les zones épidémiologique d'endémicité et d'épiendémicité. Dans la première, le virus amaril circule à "bas bruit" chez les singes et les cas d'émergence humaine sont assez rares. Dans la seconde zone, on assiste de manière plus ou moins cyclique à des épizooties et à l'apparition de cas humains qui, s'ils sont nombreux, forment alors des épidémies dites "selvatiques" tant qu'#Aedes aegypti$ n'entre pas en jeu. Partant de la région amazonienne, le virus circule le long des galeries forestières des affluents de l'Amazone, du nord vers le sud. Actuellement, les épidémies de dengue apparaissent dans pratiquement tout le pays et reflètent la répartition géographique d'#Aedes aegypti$. Depuis peu, il est présent dans la région de Carajas, située au sud de l'Etat du Para, région considérée comme à l'origine des plus importantes épidémies de fièvre jaune. #Aedes albopictus$, quant à lui, est en train d'agrandir son aire de répartition aux zones péri-urbaines. L'écologie de ce vecteur potentiel, qui semble posséder un grand pouvoir d'adaptation, le place en position intermédiaire. (Résumé d'auteur)