Surveillance for Yellow Fever Virus in Non-Human Primates in Southern Brazil, 2001–2011: A Tool for Prioritizing Human Populations for Vaccination

Marco Antônio Barreto De Almeida ,Silvana L Gomes,Laura L Cruz,Brendan Flannery,Renate Mohrdieck,Edmilson Dos Santos,Marilina Bercini ,Alessandro Romano ,Mariana Aparecida Porto ,Alethea Fagundes Sperb ,Daltro Fernandes Da Fonseca ,Jáder Da Cruz Cardoso ,Zenaida Marion Alves Nunes ,Maria Teresa Schermann ,Fernando J C Faraco ,Tani Schilling Ranieri ,Zouraide Guerra Antunes Costa ,Kátia Campomar Vettorello ,Francisco Z Paz

doi:10.1371/journal.pntd.0002741

Abstract

In Brazil, epizootics among New World monkey species may indicate circulation of yellow fever (YF) virus and provide early warning of risk to humans. Between 1999 and 2001, the southern Brazilian state of Rio Grande do Sul initiated surveillance for epizootics of YF in non-human primates to inform vaccination of human populations. Following a YF outbreak, we analyzed epizootic surveillance data and assessed YF vaccine coverage, timeliness of implementation of vaccination in unvaccinated human populations. From October 2008 through June 2009, circulation of YF virus was confirmed in 67 municipalities in Rio Grande do Sul State; vaccination was recommended in 23 (34%) prior to the outbreak and in 16 (24%) within two weeks of first epizootic report. In 28 (42%) municipalities, vaccination began more than two weeks after first epizootic report. Eleven (52%) of 21 laboratory-confirmed human YF cases occurred in two municipalities with delayed vaccination. By 2010, municipalities with confirmed YF epizootics reported higher vaccine coverage than other municipalities that began vaccination. In unvaccinated human populations timely response to epizootic events is critical to prevent human yellow fever cases.

Highlights

Yellow fever (YF) is a disease caused by yellow fever virus (YFV), a member of the Flaviviridae family
Yellow fever epizootics are confirmed based on laboratory evidence of YFV infection in specimens collected from affected non-human primates or mosquitos
For rapid implementation of control measures, suspected YF epizootics are classified based on epidemiologic linkage, when four or more non-human primate deaths are identified in areas with evidence of YFV circulation, 10 or more dead animals are found in bordering areas or non-human primate die-offs occur in environments similar to those with evidence of YFV circulation

Summary

Introduction

Yellow fever (YF) is a disease caused by yellow fever virus (YFV), a member of the Flaviviridae family. Due to its varied clinical presentation and limited surveillance, yellow fever is underreported: annually, approximately 5,000 cases are reported to WHO (World Health Organization) from Africa and 300 cases from South America but true incidence is believed to be 10–50 fold higher [1]. While primate species in Africa rarely develop fatal disease following YFV infection [2], several species of New World monkeys in the Americas are susceptible to severe, fatal YF disease. In the Americas, deaths of susceptible non-human primates are sentinel events that may indicate presence of YFV in a specific geographic location or environment and surveillance for such events is an important tool to prevent human disease [3]. The goal of surveillance for deaths among non-human primates is to provide an early warning of risk of YFV transmission to humans, for rapid implementation of vaccination and prevention strategies. There have been few reports on how epizootic surveillance has been used to inform YF vaccination in human populations

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