Demographic profile of sylvatic yellow fever (SYF) in Brazil from 1973 to 2008 Fernando Portela Ca ˆ mara a, *, Luiz Max de Carvalho a and Ana Luisa Bacellar Gomes b a Sector for Infectious Diseases Epidemiology, Institute of Microbiology, Federal University of Rio de Janeiro (UFRJ), Health Sciences Center - Block I, University City - Funda ˜o Island, Rio de Janeiro - RJ - CEP: 21941-590, Brazil; b Instituto de Medicina Social, Universidade do Estado do Rio de Janeiro (UERJ), Rio de Janeiro, Brazil *Corresponding author: Tel: +55 21 2560-8344; Fax: +55 21 2560-8028; E-mail: portela@micro.ufrj.br Received 19 July 2012; revised 4 January 2013; accepted 7 January 2013 Background: Yellow fever is an acute, frequently fatal, febrile arbovirosis that in Brazil occurs only in the sylvatic form. Sylvatic yellow fever (SYF) appears in sporadic outbreaks over a large area of Brazil. In this paper, we analyze the demographic profile of 831 SYF cases that occurred between 1973 and 2008, to determine which segments of the exposed population are at greater risk. Methods: Data were statistically analyzed and were also geo-referenced in order to observe their spatial pattern. The basic reproductive number of infections, R 0, was estimated by the ratio between average life expectancy and the average age of the cases. Results: SYF cases showed a modal profile of young male adults, approximately 30 years of age, living in rural areas of the states of Para ´, Goia ´s, Maranha ˜o and Minas Gerais, who were unvaccinated or whose vaccination was out of date. The disease showed a high mortality rate (51%, 421/831) among the notified cases, with death occurring on around the seventh day of illness for most patients. The R 0 for SYF was estimated at approximately 2.4. Conclusion: The results of this study suggest that lack of vaccination coverage is a major risk factor for SYF, and that the groups most at risk are migrant laborers, farm workers and tourists. Keywords: Sylvatic yellow fever, Yellow fever vaccine, Demographic profile, Brazil Introduction Yellow fever is an acute infectious disease caused by an arbovirus of the family Flaviviridae, genus Flavivirus, transmitted by mos- quito vectors of the genera Aedes, Haemagogus and Sabethes. 1,2 Epidemiologically, yellow fever exists in two forms: sylvatic yellow fever (SYF), transmitted through a cycle that involves non-human primates and vectors of the genus Sabethes and Haemagogus; and urban yellow fever, in which the transmission cycle is adapted to urban ecology and involves the human host and Aedes aegypti mosquitoes. 3 In Brazil, only SYF has been detected in recent years. 4 Ca ˆmara and colleagues 5 detected a major 7-year cycle of human SYF in the Mid-West region of the country, where most cases occur, and a 14-year cycle in the North region, which has predominant Amazon (tropical rainfor- est) ecology and the country’s lowest population density. SYF is active in the rainforests of Africa and the Americas, oc- cupying much of the Brazilian territory and causing sporadic out- breaks in the Mid-West and South East regions of Brazil with recent increase in cases in the states of Para ´ (North region), Goia ´s (Mid-West), Maranha ˜o (North East) and Minas Gerais (South East). 4 The outbreaks are small in magnitude, with high mortality among the notified cases. 4 However, the total mortal- ity is unknown, because probably in most cases the illness evolves as a fever without complications and is not notified. In the past, the total mortality in urban outbreaks was low, with high rates occurring only in non-Brazilian Caucasian individuals (Ca ˆmara; in preparation). Yellow fever has an incubation period of 3–6 days after the bite of the infected mosquito vector and the symptoms at this stage of the illness (the infectious phase) are similar to those of dengue. Some patients recover spontan- eously after this phase but others, after a brief improvement, enter a toxemic phase; they experience a second peak of fever with serious hemorrhagic phenomena and visceral damage that are often fatal. The classical picture of yellow fever in humans includes severe hepatitis, jaundice, hematemesis (‘black vomit’), renal failure and sometimes encephalitis, on a background of mucocutaneous bleeding. Surveillance of human cases of SYF in Brazil relies on compul- sory notification (within 24 h) and case confirmation (within # Royal Society of Tropical Medicine and Hygiene 2013. All rights reserved. For Permissions, please email: journals.permissions@oup.com. ORIGINAL ARTICLE Trans R Soc Trop Med Hyg doi:10.1093/trstmh/trt014 1 of 4 by guest on March 5, 2013 http://trstmh.oxfordjournals.org/ Downloaded from