The recent arbovirus disease epidemic in Brazil

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Abstract
The Oropouche Orthobunyavirus (OROV; a bunyavirus) has an urban maintenance cycle in the Northern and Midwestern regions of Brazil and is transmitted human-to-human by the midge Culicoides paraensis. It has been associated with outbreaks of acute febrile illness, including some cases of meningitis. MAYV and OROV outbreaks have been recently reported in Manaus City. The majority of human cases of illness associated with these 3 arboviruses likely remain undiagnosed. In the last 3 decades, new arbovirus types have been introduced to Brazil. Dengue virus (DENV; a flavivirus) serotypes 1, 2, 3, and 4 were introduced between 1986 and 2007, mostly from Caribbean countries but in at least one case from Asia. The number of DENV outbreaks has been increasing due to the alternating predominance of the different serotypes that have been spreading across the country. During these outbreaks, approximately 10 million cases of acute febrile illness have been reported. These include dozens of thousands of patients suffering from toxic shock syndrome, meningitis, or other severe forms of the disease, resulting in thousands of deaths. The West Nile virus (WNV; another flavivirus) has likely been introduced to Brazil from North America in the past decade. West Nile virus, which is transmitted from birds to humans by Culex mosquitoes, has caused many infections in horses. The first human case of meningoencephalitis associated with WNV was reported in Northeastern Brazil (State of Piauí) in 2014. In the past 2 years, the introduction of 2 genotypes of the Chikungunya virus (CHIKV; an alphavirus), likely from the Caribbean and Asia, to different regions of the country has significantly worsened the situation. Chikungunya virus has rapidly spread through the Northern (State of Amapá), Northeastern (State of Bahia), Midwestern, and Southeastern (City of São Paulo) regions of Brazil, and outbreaks are predicted to increase in the next years. In 2015, the Zika virus (ZIKV; a flavivirus) was introduced to Brazil, likely from Asia, producing outbreaks of acute febrile illness in Northeastern Brazil (State of Bahia) and spreading to other Brazilian regions. ZIKV is transmitted to humans by Aedes spp. mosquitoes. It has recently been suggested that the virus can also be transmitted through sexual contact. Considering the recent increase in the introduction of new arbovirus types to Brazil, the question why Brazil has been experiencing this recent epidemic arises. We hypothesize that it is likely the result of a combination of factors. Infected migratory birds can travel from North to South America and thereby introduce WNV to Brazil where many Culex mosquito species, which are known to transmit the virus, are found.

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