First detection of Rio Negro Virus (alphavirus) in Córdoba, Argentina

PISANO, MB; RE, VIVIANA; DIAZ, A; FARIAS, A; VENEZUELA, F ; SPINSANTI, L; CONTIGIANI, M

Buenos Aires

Simposio; III Simposio Virologia Clínica y avances en vacunas.; 2010

CEMIC

Venezuelan Equine Encephalitis complex (VEE) (alphavirus, Togaviridae) has 6 antigenic subtypes, divided in two epidemiological groups: epidemic/epizootic viruses (IAB and IC), which cause outbreaks in Central America and Northern South America, involving humans and equines, with high morbidity and mortality rates; and enzootic subtypes (ID, IE, IF, II-VI), transmitted by mosquitoes in swamp habitats, which are generally avirulent in horses but capable of causing human disease. Most of infections are asymptomatic or mild, with symptoms similar to those of dengue or influenza (headache, chills, fever, myalgias, retroocular pain, nausea and vomiting), which last 3-5 days. Argentina, free of epizootic VEE, is the only country with circulation of Rio Negro Virus (RNV) (VEE subtype VI), associated with acute febrile illness in humans. Antibodies for subtypes I and VI have been detected in humans, and circulation of subtype IV in mosquitoes of Chaco and Tucumán provinces has been recently described. We investigated the presence of RNV in humans and mosquitoes of Córdoba city between November 2004 and May 2005. Mosquitoes were collected with CDC light traps with CO2, grouped by species and date and analyzed by RT-Nested PCR for alphavirus detection. Positive samples were sequenced. Human serum samples were processed by Neutralization assay (NT) for detection of antibodies against RNV. Positive samples were tittered. Fifty-two mosquito pools were analyzed; 1 resulted positive. Phylogenetic analysis revealed that it grouped with RNV, separated from the other Argentinean isolates. Detection of antibodies for RNV was done in 392 serum samples, resulting 1 positive, with titer of 1/320, indicating probable recent infection. Our results show that RNV circulated in Córdoba in 2005. This is the first report of its detection in our province. Molecular results have strong correlation with serology, demonstrating that circulation in mosquitoes and humans infections occurred during the same period. These findings show the expansion of RNV into new regions, probably due to climatic changes. The occurrence of clinical cases of febrile undifferentiated illness produced by these viruses must be taken into account for differential etiologic diagnosis of cases reported as probable dengue. Studies of longer and more variable genomic regions are needed as well as increase surveillance to get a better understanding of these viruses and their impact on public health.