Historical, epidemiological and ecological aspects of arboviruses in Argentina: Togaviridae, Alphavirus

This is a review of the arboviruses in Argentina belonging to families Flaviridae, Bunyaviridae and Rhabdoviridae. Of the many viruses belonging to these families, the flavivirus St. Louis encephalitis (SLE), has been most intensively studied. SLE virus strains have been recovered from three sources: 2 strains from humans with an undifferentiated, febrile disease; 6 from mosquitoes; and 2 from rodents. The viruses recovered from rodents are attenuated and those from mosquitoes are virulent based on a neuroinvasiveness test in mice; the degree of virulence of the mosquito strains remain to be analyzed. Serological surveys indicate a wide distribution and endemicity of SLE virus in the temperate and subtropical areas (central and northern Argentina), but no data are available from the andean region or from the South. The virulent SLE virus strains appear to be transmitted between Culex (Cx.)spp. from which they were isolated, and wild birds, based on antobody prevalence. A urban cycle may involve Cx. quinquefasciatus (source of a viral isolate and a competent experimental vector) and abundant birds (house sparrows, doves, and/or chickens), chickens are experimentally competent host species. Despite similarities in the ecology of SLE between Argentina and North America, urban outbreaks of SLE have not been recognized. Possible explanations for this discrepancy include virus strain differences in virulenc, ecologic factors determining the rate of virus transmission, and the lack of disease recognition and specific laboratory diagnosis of human meningoencephalitis. The transmission cycle of attenuated SLE virus strains isolated from rodentshas not been studied. Ilheus virus has isolated only once from a human being. The available serological data are difficult to interpret due to cross-reactivity with other flaviviruses, and the ecologyand medical importance of this agent remain uncertain. Dengue has not been recognized in Argentina since 1916, although is vector, Aedes aegypti, was not erradicated until 1963. Dengue was previously present in coastal localities of Chaco. Corrientes and Misiones Provinces. Within the last few years, Argentina was reinfested by Ae. aegypti. Although no human cases have vet been reported, outbreaks of dengue in bordering countries (Brazil, Paraguay, Bolivia) since 1986, cleary signal that the country in once againat risk of importantion ans spread of the virus

Use of immunoglobulin M antibody capture enzyme-linked immunosorbent assay in the surveillance of Rocio encephalitis

In 1975-1976 an extensive epidemic of Rocio encephalitis occurred in the South region of the Sao Paulo State, Brazil. Since June 1976 no serological confirmation of this diagnosis has been made. Sera from 90 patients clinically suspected of having contracted Rocio encephalitis between July 1976 and December 1982, were tested with an immunoglobulin M (IgM) antibody capture enzyme immunoassay (MAC ELISA). Only one serum sample was available for each of these patients. Four presumptive cases of Rocio encephalitis were identified. Three of these sera had been collected in August and September of 1976. The fourth one, from a boy one year of age who died from the disease, was collected in April 1980. These results indicate that Rocio virus was circulating in the human population causing severe disease, at least until 1980. MAC ELISA is useful for surveillance of Rocio encephalitis in an area where the collection of paired sera samples is very difficult.