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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)