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Background: Yellow Fever (YF) is a viral hemorrhagic disease transmitted by aedes mosquito species. Approximately, 200,000 cases and 30,000 deaths occur worldwide every year. In Ethiopia, the last outbreak was reported in 1966 with 2200 cases and 450 deaths. A number of cases with deaths from unknown febrile illness reported from South Ari district starting from November 2012. This investigation was conducted to identify the causative agent, source of the outbreak and recommend appropriate interventions., Methods: Medical records were reviewed and Patients and clinicians involved in managing the case were interviewed. Descriptive data analysis was done by time, person and place. Serum samples were collected for serological analysis it was done using Enzyme-linked Immunosorbent Assay for initial screening and confirmatory tests were done using Plaque Reduction and Neutralization Test. Breteau and container indices were used for the entomological investigation to determine the risk of epidemic., Results: A total of 141 Suspected YF cases with 43 deaths (CFR = 30.5%) were reported from November 2012 to October 2013 from South Omo Zone. All age groups were affected (mean 27.5, Range 1-75 Years). Of the total cases, 85.1% cases had jaundice and 56.7% cases had fever. Seven of the 21 samples were IgM positive for YF virus. Aedes bromeliae and Aedes aegypti were identified as responsible vectors of YF in affected area. The Breteau indices of Arkisha and Aykamer Kebeles were 44.4% and 33.3%, whereas the container indices were 12.9% and 22.2%, respectively., Conclusion: The investigation revealed that YF outbreak was reemerged after 50 years in Ethiopia. Vaccination should be given for the affected and neighboring districts and Case based surveillance should be initiated to detect every case.

The fact that yellow fever (YF) has never occurred in Asia remains an "unsolved mystery" in global health. Most countries in Asia with high Aedes aegypti mosquito density are considered "receptive" for YF transmission. Recently, health officials in Sri Lanka issued a public health alert on the potential spread of YF from a migrant group from West Africa. We performed an extensive review of literature pertaining to the risk of YF in Sri Lanka/South Asian region to understand the probability of actual risk and assist health authorities to form evidence informed public health policies/practices. Published data from epidemiological, historical, biological, molecular, and mathematical models were harnessed to assess the risk of YF in Asia. Using this data we examine a number of theories proposed to explain lack of YF in Asia. Considering the evidence available, we conclude that the probable risk of local transmission of YF is extremely low in Sri Lanka and for other South Asian countries despite a high Aedes aegypti density and associated dengue burden. This does not however exclude the future possibility of transmission in Asia, especially considering the rapid influx travelers from endemic areas, as we report, arriving in Sri Lanka.

Yellow fever is an unpredictable disease of increasing epidemic threat in East Africa. Aedes (Stegomyia) aegypti has never been implicated as a vector in this region and recent outbreaks have involved a newly emerging virus genotype (East African). To better understand the increasing epidemic risk of yellow fever in East Africa, this study is the first to investigate the vector competence for an emerging East African virus genotype in Kenyan A. aegypti sensu latu (s.l) and A. (Stegomyia) simpsoni s.l. mosquito species. Using first filial generation mosquitoes and a low passage yellow fever virus, this study demonstrated that although A. aegypti s.l. is a competent vector, A. simpsoni s.l. is likely a more efficient vector., (Copyright © 2012 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved.)

To address concerns that a flavivirus vaccine/wild-type recombinant virus might have a high mosquito infectivity phenotype, the yellow fever virus (YFV) 17D backbone of the ChimeriVax-dengue 4 virus was replaced with the corresponding gene sequences of the virulent YFV Asibi strain. Field-collected and laboratory-colonized Aedes aegypti mosquitoes were fed on blood containing each of the viruses under investigation and held for 14 days after infection. Infection and dissemination rates were based on antigen detection in titrated body or head triturates. Our data indicate that, even in the highly unlikely event of recombination or substantial backbone reversion, virulent sequences do not enhance the transmissibility of ChimeriVax viruses. In light of the low-level viremias that have been observed after vaccination in human volunteers coupled with low mosquito infectivity, it is predicted that the risk of mosquito infection and transmission of ChimeriVax vaccine recombinant/revertant viruses in nature is minimal.

The yellow fever virus has been isolated from a pool of Aedes africanus caught on men in a region situated between forest and savannah near Touba, in the Ivory Coast. This isolation, occurring at an interepidemic period, proves for the first time in West Africa, the part played by this mosquito in the transmission of the yellow fever virus.