Serious disease outbreaks caused by viruses transmitted by Aedes aegypti in Brazil.

Currently, a tragic combination of disease outbreaks caused by viruses transmitted by the mosquito Aedes aegypti occurs in Brazil. This African insect infests most of the urban areas of Brazil, as it is completely adapted to the urban conditions, and it is responsible for the transmission of viruses belonging to the genus Flavivirus, family Flaviviridae [dengue viruses (DENV 1-4) and Zika virus (ZIKV)], and genus Alphavirus, family Togaviridae [Chikungunya virus (CHIKV)]. Aedes aegypti has been introduced into Brazil many times during centuries. The arrival of yellow fever virus (YFV) and its vector, A.aegypti, in Brazil is most likely related to the slave trade and commodities trade, and it was brought by ships carrying infected individuals. YFV caused urban outbreaks in the XVII, XIX, and XX centuries, in the Brazilian coastal and coffee-farming areas. However, at some point, YFV jumped from the cycle involving humans-A. Aegypti to a sylvatic cycle involving Haemagogus mosquitoes of the forest canopy trees, and this virus is maintained as a primate zoonosis in the Amazon forest, Pantanal, and Central Plateau of Brazil. However, YFV causes epizootic outbreak waves through the river gallery forests, which leads to small outbreaks among humans in the highly populated regions of South and Southeast Regions of Brazil. Fortunately, YFV has not caused urban outbreaks to date, which are transmitted by A. aegypti, due to an efficient control of the virus, based on the excellent 17D vaccine. For safety reasons, and for the efficient protection of urban areas against YFV, 90% vaccination coverage should be achieved among the population(1). Dengue outbreaks have occurred in Brazil since XIX century, but during the last 30 years, four DENV serotypes have been introduced in the most populated areas of the country, DENV-1 in 1985, DENV-2 in 1990, DENV-3 in 2000, and DENV-4 in 2008. These viruses have spread and were probably reintroduced many times, producing subsequent large outbreaks that affect millions, cause severe disease in tens of thousands people, and lead to thousands of deaths. DENV serotype alterations increase the number of secondary infections and of the severe forms of disease. The circulation of DENV belonging to serotypes and genotypes associated with the severe forms of disease aggravates this situation further. DENV-1 has been the predominant serotype in 2016 outbreak. As a consequence of the endemic nature of this disease, this virus has caused severe forms of disease among children, leading to a large number of deaths(2). Two CHIKV genotypes were introduced in Brazil, most likely in 2013, from the Caribbean and Asia. In September 2014, an outbreak in Feira de Santana, Bahia, was the first documented outbreak of CHIKV. Asian genotype CHIKV spread through Northeast (Bahia), Midwest, and Southeast (São Paulo) Regions of Brazil(3). In 2015, 20662 suspected cases of Chikungunya fever were reported in the outbreaks that occurred in the States of Amazonas, Ceará, Goiás, Maranhão, Minas Gerais, Pará, Paraná, Pernambuco, Rio de Janeiro, Rio Grande do Sul, and São Paulo. Moreover, three fatal cases were reported, all in elderly (85, 83, and 75 years old) with chronic diseases. CHIKV infection is spreading even further, and in 2016 alone, 3,768 suspected cases of Chikungunya fever have been reported before February(4). CHIKV infection leads to a febrile illness affecting joints, and many patients show signs of acute arthritis. Ankles, wrists, and small joints of the hands are the most affected. However, larger joints, such as knees, shoulders, and spine, may also be involved. A bigger issue is that, as the studies in Asia showed, in more than 2% of individuals, these symptoms can become chronic. The joint disease is associated with the persistent presence of virus, which presents as viral osteomyelitis. The affected joints also show signs of inflammatory processes, and high levels of cytokines and chemokines are produced by synovial tissue cells. The presence of the virus and the accompanying inflammation can lead to the destruction of articular cartilage and bone(5). Large outbreaks of CHIKV may increase the number of individuals with chronic physical disabilities. Another Alphavirus, Mayaro virus (MAYV), is endemic in the Amazon and the Central Plateau of Brazil, leading to the outbreaks of acute febrile illness affecting joints(6). However, the circulation of this virus, which causes zoonotic disease of primates, is increasing. In the last three years, MAYV-caused Rev Soc Bras Med Trop 49(3):265-266, May-June, 2016 doi: 10.1590/0037-8682-0209-2016