Here we describe a new genome of a rare Bruconha orthobunyavirus, isolated in 2011 at Brazilian Atlantic Forest biome. In 1961, Adolfo Lutz Institute began a program that aimed to investigate arbovirus diversity and epidemiology in São Paulo State, when several arboviruses, including new Bunyavirales, were discovered and characterized. Boraceia virus, a member of the Anopheles B group, was isolated from a pool of Anopheles cruzii at Serra do Mar, a forest area near São Paulo city, in 1962 , and later from Phoniomyia pilicauda . This virus was considered as the causative agent of an infectious illness among residents in Salesópolis, distant 100 Km away from São Paulo city, the capital of the State . Strains of Bertioga virus (Guama group) and Anhembi virus (Bunyamera group) were isolated from sentinel mice, and Phoniomyia pilicauda, Trichoprosopon pailidiventer, and from a spiny rat (Proechimys iheringi) . BRCV was isolated from Culex sacchettae mosquitoes in Cananéia city, located in the south coast of São Paulo State, on February, April and November, 1976. Almost 4 decades later, we describe a new isolate of BRCV from Iguape county. This new isolate was obtained 60Km from the original one, showing that it may be dispersed through this region. We also found that nucleotide differences varied from 1.5%, 5.3% and 5% (L, M and S segments respectively) from the 1976 prototype.
Reassortant events have shaped the evolution of several segmented viruses, including that of Group C orthobunyaviruses [5, 11], and it was proposed that BRCV obtained its S segment from CARV . On the other hand, Caraparu and Itaqui viruses had nearly identical L and S segments, but different M segments. Interestingly, within group C, Span321532 had the highest S segment (N protein) similarity with Itaqui virus (82.9%), while M and L with different Caraparu strains, one isolated in Bolivia in 2008, and the other in Peru, in 2006, respectively. It is important to note that other Caraparu isolates were obtaine from the Brazilian Amazon basin, at the North region, Peru, and also in São Paulo state, from Culex mosquitoes, humans and non-human primates . However, BRCV was never isolated outside Atlantic Forest, although intensive programs for virus discovery have been performed during the last decades in Brazil. These differences corroborates with previous studies which demonstrates that the S and M segments have different evolutionary histories . However, isolate Span321532 had no evidence of reassortants within other Orthobunyavirus belonging to group C.
Only one human case that was caused by Caraparus virus (or a close-related virus) was described at Vale do Ribeira, when a 28 year old male biologist that worked with entomological investigation presented a mild febrile disease, and fully recovered . As this virus is quite similar to BRCV, it is likely that it may cause an undiagnosed illness at the region. For instance, several orthobunyaviruses have recently emerged in different parts of the world, causing disease in human or animal diseases, with many associated with CNS disease, such as Jamestown Canyon virus (JCV), a mosquito-borne orthobunyavirus that causes an acute febrile illness, meningitis, or meningoencephalitis .
Interestingly, despite arbovirus high mutation rates and the great diversity of pathogenic orthobunyavirus at Vale do Ribeira, outbreaks caused by this genus were never reported in the southeastern region of Brazil. In fact, the circulation of several arbovirus are often related with climate, habitat, presence of vectors and animal density and movement. A possible explanation regarding the low disease incidence at Vale do Ribeira is the conservation of the biome, where one may observe a dilution effect . This region harbors several conservation units since the 1980’s, with lower deforestation of Atlantic Forest remnants when compared to other Brazilian biomes, which may decrease the risk of human infection. More, BRCV apparently is restricted to Atlantic Forest biome, where only two genomes were obtained until now within a 35 years interval, with high similarities and lack of reassortant events. Increasing virus active surveillance in order to obtain more sequences of Bunyavirales would generate improvements on information regarding viral genetics and evolution, shedding light in this question. More, given the high biodiversity in Vale do Ribeira, these studies would allow us to better known sylvatic hosts and vectors. Although it is known that Group C Orthobunyavirus circulate among rodents, marsupials and eventually humans in São Paulo State, epidemiological aspects regarding BRCV are scarce. More, in order to understand the patterns of other arbovirus circulation in the human population at Vale do Ribeira, it is urged to perform differential diagnosis for Dengue, Zika and Chikungunya viruses during the acute phase, when one can perform direct methods for viral detection.