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Hantavirosis are emerging diseases in the Americas. Although considered rare in children, among the five cases diagnosed in Brazil, one was in this age group. To know the serum-prevalence of hantavirosis in the pediatric group (schoolchildren) of low social economic level in Salvador, Bahia State, and to associate demographic, socio-economic and environmental factors to the serologic results, a standard questionnaire was applied and blood samples were collected from 379 students of two public schools. Sera were tested by indirect Immunofluorescent Antibody (IFA) IgG for Hantaan Virus (HTN) and Immunoenzymatic test (ELISA) for Sin Nombre viruses. Ages varied from five to seventeen years with a mean age of 10.2 years. The proportion of sera positive to HTN virus was 13.2%, and there were no positive antibodies to SN virus. The frequency of positivity was higher in the older group, similar among sexes and racial groups, and there was no association with the exposure to urban rodents. The antibodies anti-HTN serum-prevalence in low social economic level school children is high and confirm the circulation of hantaviruses in Salvador-Bahia, Brazil; the nonobservation of antibodies anti-SN indicates that the species are other than Sin Nombre Virus.

The results of serological investigation on Hantavírus antibodies carried out between February 1986 and August 1990 in human populations of the States of São Paulo and Paraná, Brazil, which had close contact with urban rats or wild rodents and others small mammals are described. OBJECTIVE--To identify the human infection caused by Hantavíruses, which are the etiological agents of Hemorrhagic fever with renal syndrome. METHODS--Sera from 1063 persons were tested by enzyme immunoassay (ELISA) to Hantaan, Seoul and Puumala antigens. Plaque reduction neutralization test to the same antigens and indirect immunofluorescent test to Hantaan antigen were performed in the positive sera. RESULTS--Antibodies to Hantaan, Seoul or Puumala viruses were detected in 32 persons by enzyme immunoassay (ELISA) and immunofluorescent test. Plaque reduction neutralization test performed in these 32 sera were positive in 5 (3 for Puumala and 2 for Seoul viruses). One serum reacted with high titer to Seoul virus in all tests. It was from a male resident in the rural area of Ribeira Valley, State of São Paulo, where he was born and has always lived. He had only travelled inside the State of São Paulo. CONCLUSION--There are serological evidences of Hantavírus infections in residents of the rural areas of the Amparo Island, Paranaguá Bay, State of Paraná and the Ribeira Valley, State of São Paulo; in employees of the port of Paranaguá, State of Paraná and in patients of the Emílio Ribas Hospital, São Paulo, State of São Paulo, who had a presumptive diagnosis of leptospirosis.

St. Louis encephalitis (SLE) virus was isolated from a 21-year-old female hospitalized on 4 October 1978 in Belém, Brazil. Symptomatology on admission included fever, chills, severe headache, abdominal pain, myalgia, arthralgia and jaundice. SLE virus was isolated from her blood drawn on the 8th day of illness and subsequent seroconversion was documented. Serological tests showed the isolate to be closely related to the Belém prototype of SLE virus but distinct from other flaviviruses tested. The patient was discharged without sequelae after 16 days of hospitalization. Epidemiological investigations where the patient worked and lived revealed no evidence of extensive transmission of SLE virus.

Epidemiological investigations of an outbreak of Mayaro (MAY) virus which occurred inthe rural village of Belterra, Pará, Brazil are reported. Human cases were first recorded in December 1977 and continued through June 1978. Approximately 20% of the more than 4,000 persons resident in Belterra were infected, and a very high proportion of those infected suffered overt clinical illness. Cases were identified in all areas of Belterra and among all age groups; however, the greatest number of cases was seen among those who resided in close proximity to the forests. Yellow fever (YF) virus was also active in Belterra concurrently with the MAY virus outbreak. Six human cases of YF were identified, of which five were fatal. The YF outbreak ended following YF vaccination of the human population.

Results in entomological and vertebrate host investigations made during dual outbreaks of Mayaro (MAY) and yellow fever (YF) viruses in Belterra, Pará, Brazil in 1978 are reported. Over 9,000 insects representing 26 species were assayed in 396 pools for the presence of arboviruses. Pools of Haemagogus janthinomys Dyar yielded the only isolates of either MAY or YF virus. The minimum field infection rate for nine isolates of MAY virus from Hg. janthinomys was 1:82, and for two isolates of YF virus was 1:368. Analysis of collection data showed Hg. janthinomys to be attracted to man as a blood source and present in all habitats sampled, although most abundant in the forest canopy. Twelve hundred bird sera and 584 mammal sera were tested by hemagglutination-inhibition (HI) tests for antibody to MAY virus. Highest MAY antibody prevalence rates were found among marmosets (Calithrix argentata, 32 positive of 119 tested, 27%). Mayaro virus was also isolated from the blood of a sylvan marmoset captured at the peak of the MAY virus outbreak. Experimental infection of marmosets with MAY virus confirmed that a substantial viremia follows infection with this virus. Marmosets were also found with HI antibody to YF virus (5/119, 4%). The results presented indicate that Hg. janthinomys was the principal vector of both MAY and YF viruses and that marmosets were the main amplifying hosts for MAY virus, and perhaps for YF virus as well.

A serosurvey of domestic rats was conducted in several South American cities between September 1982 and March 1983 for evidence of hantavirus infection. Antibody-positive rats were found in Belem, São Paulo and Recife-Olinda, Brazil and in Buenos Aires, Argentina, with the highest antibody prevalence rate detected in Belem (30 positive of 54 tested, 56%). A virus isolated from tissues of a Rattus norvegicus captured in Belem, was shown to be antigenically similar to Girard Point viruses isolated from domestic rats captured in the United States and clearly distinct from prototype Hantaan virus, causative agent of Korean hemorrhagic fever in Asia. This represents the first isolation of a virus of the genus Hantavirus from South America and supports previous observations that indicate a widespread distribution of urban rat-associated hantaviruses. The abundance of domestic rats and their regionally high antibody rates suggest that risk of human hantavirus infection in some locations of South America may be significant.

An outbreak of human illness caused by Mayaro (MAY) virus occurred in Belterra, Pará, Brazil in the first half of 1978. A total of 55 cases were confirmed, 43 by virus isolation and serology, and 12 by serology alone. The disease in Belterra presented as a distinct clinical syndrome characterized by fever, arthralgia and exanthema. No fatalities could be attributed to MAY virus infection. Arthralgia, accompanied by joint edema in 20% of cases, was a very prominent sign which caused temporary incapacity in many patients. Arthralgia was present in virtually all confirmed cases and persisted in some for at least 2 months, although with decreasing severity. Rash was present in two-thirds of the cases, and was either maculopapular or micropapular. The incidence of rash was higher in children than in adults. Contrary to arthralgia, which started with the onset of clinical illness, rash usually appeared on the 5th day and faded within 3-4 days. Fever, chills, headache, myalgia, lymph-adenopathy and other minor clinical manifestations were also recorded, and generally persisted for from 2-5 days. Leucopenia was a constant finding in all cases. Mild albuminuria was seen in four of 25 patients, and slight thrombocytopenia was seen in 10 of 20 cases. The fact that viremia levels higher tha 5.0 log10/1.0 ml of blood were recorded in 10 patients rises the possibility that man may have be an amplifying host in the MAY virus cycle. The MAY virus illness, as seen in Belterra, has clinical features similar to those observed in persons infected with chikungunya virus.