Detecção do segmento S do vírus Oropouche em pacientes e em Culex quinquefasciatus em Mato Grosso, Brasil

Abstract

The genus Orthobunyavirus, family Bunyaviridae, contains medically importante arboviruses. These are involved in epidemics of febrile illness in tropical areas. In Brasil, Oropouche virus (OROV) is considered the most frequent arbovirus after dengue virus (DENV). The aim of this study was to investigate the circulation of orthobunyaviruses in Mato Grosso (MT). 529 serum samples collected between October, 2011 and July, 2012 of patients with acute febrile illness suspected of dengue for up to five days of symptom onset from MT and 387 pools of Cx. quinquefasciatus mosquitoes captured between January and April, 2013, were subjected to nested RT-PCR for the segment S of orthobunyaviruses belonging to Simbu serogroup. Positive samples were tested in at least two independent reactions and subjected to nucleotide sequencing for phylogenetic analysis. Positive samples were inoculated in vero cells. Among the 529 patients, five (0.94%) were positive for serogroup Simbu by nested RT-PCR and viral isolation. The virus was isolated from 3/8 pools. The OROV segment S was identified in five patients, four females, with 14-62 years-old. Two patients were co-infected with DENV-4. These patients are from Cuiabá (n=3), Várzea Grande (n=1) and Nova Mutum (n=1), all residents in urban areas, presenting fever, headache, retroorbital pain, myalgia, arthralgia, prostration and nausea. 8/387 pools of Cx. quinquefasciatus were positive for OROV segment S by nested-RT-PCR with a minimum infection rate (MIR) of 2.3 per 1,000 mosquitoes. The segment S nucleotide sequences presented 98% to 100% of homology with the same segment of OROV strains available in GenBank. Phylogenetic analysis indicate the human and mosquito samples belong to genotype Ia, similar to strains obtained in Pará from humans, sloths, Aedes (Ochlerotatus) serratus and Cx. quinquefasciatus. The genotype I is the most conserved among OROV genotypes. Cx. quinquefasciatus, the most abundant culicidae in Cuiabá, is considered a secondary vector for OROV in urban areas. Culicoides paraensis, the main vector for OROV in urban areas in the Amazon region, was not captured in the study. Serology for OROV was identified in humans in cities of Pará affected by the Cuiabá-Santarém highway and in primates in South Pantanal, corroborating for the findings in cities of MT geographically linked by the same highway. Sporadic infections by an orthobunyavirus from Simbu serogroup, possibly OROV, were identified in patients from MT, also eight Cx. quinquefasciatus pools from Cuiabá, indicating that has vectorial capacity and may be involved in the urban cycle of virus transmission in the state.