Abstract
BackgroundYellow fever (YF) is a viral hemorrhagic fever, endemic in the tropical forests of Africa and Central and South America. The disease is transmitted by mosquitoes infected with the yellow fever virus (YFV). Ethiopia was affected by the largest YF outbreak since the vaccination era during 1960–1962. The recent YF outbreak occurred in 2013 in Southern part of the country. The current survey of was carried out to determine the YF seroprevalence so as to make recommendations from YF prevention and control in Ethiopia.MethodologyA multistage cluster design was utilized. Consequently, the country was divided into 5 ecological zones and two sampling towns were picked per zone randomly. A total of 1643 serum samples were collected from human participants. The serum samples were tested for IgG antibody against YFV using ELISA. Any serum sample testing positive by ELISA was confirmed by plaque reduction neutralization test (PRNT). In addition, differential testing was performed for other flaviviruses, namely dengue, Zika and West Nile viruses.ResultOf the total samples tested, 10 (0.61%) were confirmed to be IgG positive against YFV and confirmed with PRNT. Nine (0.5%) samples were antibody positive for dengue virus, 15(0.9%) forWest Nile virus and 7 (0.4%) for Zika virus by PRNT. Three out of the five ecological zones namely zones 1, 3 and 5 showed low levels (< 2%) of IgG positivity against YFV. A total of 41(2.5%) cases were confirmed to be positive for one of flaviviruses tested.ConclusionBased on the seroprevalence data, the level of YFV activity and the risk of a YF epidemic in Ethiopia are low. However additional factors that could impact the likelihood of such an epidemic occurring should be considered before making final recommendations for YF prevention and control in Ethiopia. Based on the results of the serosurvey and other YF epidemic risk factors considered, a preventive mass vaccination campaign is not recommended, however the introduction of YF vaccine in routine EPI is proposed nationwide, along with strong laboratory based YF surveillance.
Highlights
Yellow fever (YF) is a viral hemorrhagic fever, endemic in the tropical forests of Africa and Central and South America
There seems to be a decline in the prevalence of YF antibodies compared to previous studies which reported much higher YF seroprevalence rates, such as after the historic YF outbreaks in Ethiopia half a century ago
The low prevalence of Immunoglobulin G (IgG) antibodies implies that the proportion of Ethiopian population with protective antibodies against the virus is very low; or in other words, the majority of the population doesn’t have the protection against infection and this puts the population at risk of infection by yellow fever virus (YFV)
Summary
Yellow fever (YF) is a viral hemorrhagic fever, endemic in the tropical forests of Africa and Central and South America. An YF outbreak may not be detected because the clinical manifestation overlaps with the symptoms of other hemorrhagic fever, viral hepatitis, malaria, and leptospirosis, and this leads to misdiagnosis. In another scenario, yellow fever mild cases may remain undetected because the patients are often treated at home and do not seek care in a health facility. In general it is estimated that there are 200,000 YF cases annually and that 30, 000 deaths occur each year in 44 countries, almost all of them occur in sub-Saharan Africa [4]. A modeling study based on African data sources estimated the burden of YF during 2013 was 84,000–170,000 severe cases and 29,000– 60,000 deaths [5]
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