Zika in Rio de Janeiro: Assessment of basic reproductive number and its comparison with dengue

Zika virus infection was declared a public health emergency of international concern in February 2016 in response to the outbreak in Brazil and its suspected link with congenital anomalies. In this study we use early notification data and disease natural history parameters to estimate the basic reproductive number R 0 . Our estimates of the basic reproductive number for Zika in Rio de Janeiro (R 0 =3.9, 95% CI: 3.1 -- 5.3) were higher than those obtained for dengue using data from two early epidemics in the city (year 2002: 2.5 [2.1 -- 3.1]; year 2012: 1.5 [1.4 -- 1.8]). Given the role of Aedes aegypti as an arbovirus vector, we also assessed the R 0 of Zika given entomological and epidemiological factors already reported for dengue transmission. Surprisingly, we find that Zika9s R 0 under a vectorial-only transmission model is lower than the basic reproductive number for dengue. These results suggest that either our current knowledge regarding the vectorial capacity of Aedes aegypti as a vector for Zika is incomplete or other modes of transmission are important players in sustaining this epidemic.