Oral susceptibility to yellow fever virus of Aedes aegypti from Brazil.
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The oral susceptibility to yellow fever virus was evaluated in 23 Aedes aegypti samples from Brazil. Six Ae. aegypti samples from Africa, America and Asia were also tested for comparison. Mosquito samples from Asia showed the highest infection rates. Infection rates for the Brazilian Ae. aegypti reached 48.6%, but were under 13% in 60% of sample tested. We concluded that although the low infection rates estimated for some Brazilian mosquito samples may not favor the establishment of urban cycle of yellow fever in some parts of the country, the founding of Ae. aegypti of noteworthy susceptibility to the virus in cities located in endemic and transition areas of sylvatic yellow fever, do pose a threat of the re-emergence of the urban transmission of the disease in Brazil. (+info)
Breeding structure of Aedes aegypti populations in Mexico varies by region.
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A population genetic analysis of Aedes aegypti was conducted among 38 collections from throughout coastal regions of Mexico. Multiple collections were made within 5 cities to examine local patterns of gene flow. Single-strand conformation polymorphism analysis was used to screen for variation in a 387-bp region of the Nicotinamide Adenine Dinucleotide Dehydrogenase subunit 4 mitochondrial gene (ND4) and 25 haplotypes were detected. Northeastern Mexico collections were genetically differentiated from and had lower genetic diversity than Yucatan and Pacific coastal collections. Yucatan and Pacific collections were genetically homogeneous. Regression analysis of geographic distances and F(ST) values indicated that collections were genetically isolated by distance in the Pacific and the Yucatan, but not among collections in the northeast. Free gene flow occurred among all collections within 130 km of one another in the northeast and within 180 km in the Yucatan. F(ST) values were never large among Pacific collections, suggesting extensive gene flow along the Pacific coast. (+info)
Comparative safety and immunogenicity of two yellow fever 17D vaccines (ARILVAX and YF-VAX) in a phase III multicenter, double-blind clinical trial.
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Yellow fever (YF) is a significant health problem in South America and Africa. Travelers to these areas require immunization. The United States, infested with Aedes aegypti mosquitoes, is at risk of introduction of this disease. There is only a single U.S. manufacturer of YF 17D vaccine, and supplies may be insufficient in an emergency. A randomized, double-blind outpatient study was conducted in 1,440 healthy individuals, half of whom received the U.S. vaccine (YF-VAX) and half the vaccine manufactured in the United Kingdom (ARILVAX). A randomly selected subset of approximately 310 individuals in each treatment group was tested for YF neutralizing antibodies 30 days after vaccination. The primary efficacy endpoint was the proportion of individuals who developed a log neutralization index (LNI) of 0.7 or higher. Seroconversion occurred in 98.6% of individuals in the ARILVAX group and 99.3% of those in the YF-VAX group. Statistically, ARILVAX was equivalent to YF-VAX (P = .001). Both vaccines elicited mean antibody responses well above the minimal level (LNI 0.7) protective against wild-type YF virus. The mean LNI in the YF-VAX group was higher (2.21) than in the ARILVAX group (2.06; P = .010) possibly because of the higher dose contained in YF-VAX. Male gender, Caucasian race, and smoking were associated with higher antibody responses. Both vaccines were well tolerated. Overall, the treatment groups were comparable with respect to safety except that individuals in the ARILVAX group experienced significantly less edema, inflammation, and pain at the injection site than those in the YF-VAX group. No serious adverse events were attributable to either vaccine. YF-VAX participants (71.9%) experienced one or more nonserious adverse events than ARILVAX individuals (65.3%; P = .008). The difference was due to a higher rate of injection site reactions in the YF-VAX group. Mild systemic reactions (headache, myalgia, malaise, asthenia) occurred in roughly 10% to 30% of participants during the first few days after vaccination, with no significant difference across treatment groups. Adverse events were less frequent in individuals with preexisting immunity to YF, indicating a relationship to virus replication. (+info)
A Belgian traveler who acquired yellow fever in the Gambia.
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A 47-year-old Belgian woman acquired yellow fever during a 1-week vacation in The Gambia; she had never been vaccinated against yellow fever. She died of massive gastrointestinal bleeding 7 days after the onset of the first symptoms. This dramatic case demonstrates that it is important for persons to be vaccinated against yellow fever before they travel to countries where yellow fever is endemic, even if the country, like The Gambia, does not require travelers to be vaccinated. (+info)
Yellow fever vaccine. Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2002.
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This report updates CDC's recommendations for using yellow fever vaccine (CDC. Yellow Fever Vaccine: Recommendations of the Advisory Committee on Immunizations Practices: MMWR 1990;39[No. RR-6]1-6). The 2002 recommendations include new or updated information regarding 1) reports of yellow fever vaccine-associated viscerotropic disease (previously reported as febrile multiple organ system failure); 2) use ofyellow fever vaccine for pregnant women and persons infected with human immunodeficiency virus (HIV); and 3) concurrent use of yellow fever vaccine with other vaccines. A link to this report and other information related to yellow fever can be accessed at the website for Travelers' Health, Division of Global Migration and Quarantine, National Center for Infectious Diseases, CDC, at http://www.cdc.gov/travel/index.htm, and through the website for the Division of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, CDC, at http://www.cdc.gov/ncidod/ dvbid/yellowfever/index.htm. (+info)
Alteration of clinical outcome and histopathology of yellow fever virus infection in a hamster model by previous infection with heterologous flaviviruses.
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Using a recently described hamster model of severe yellow fever (YF), we examined the hypothesis that prior infection with heterologous flaviviruses protects against severe or fatal YF. Hamsters were singly or sequentially infected with Japanese encephalitis, St. Louis encephalitis, West Nile, and/or dengue-1 viruses, and then challenged with a virulent strain of yellow fever virus (YFV). In contrast to control (naive) hamsters, many of which appeared clinically ill or died after YFV infection, the flavivirus-immune animals remained asymptomatic. The flavivirus-immune hamsters also had a reduced viremia and lower serum levels of alanine aminotransferase and total bilirubin, compared with naive hamsters, following YFV infection. Histologically, livers of animals in the flavivirus-immune and control groups showed comparable levels of multifocal necrapoptosis. However, steatosis was not observed in the flavivirus-immune animals, whereas naive hamsters developed extensive microvesicular steatosis in the liver following YFV infection. These findings suggest that hepatocytic steatosis is an adverse microscopic feature associated with severe disease in YFV infection. Our experimental results support earlier anecdotal reports that prior exposure of humans to heterologous flaviviruses reduces subsequent risk of fatal YFV infection. (+info)
Large genetic differentiation and low variation in vector competence for dengue and yellow fever viruses of Aedes albopictus from Brazil, the United States, and the Cayman Islands.
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We conducted a population genetic analysis of Aedes albopictus collected from 20 sites in Brazil, the United States (Florida, Georgia, and Illinois), and the Cayman Islands. Using isoenzyme analysis, we examined genetic diversity and patterns of gene flow. High genetic differentiation was found among Brazilian samples, and between them and North American samples. Regression analysis of genetic differentiation according to geographic distances indicated that Ae. albopictus samples from Florida were genetically isolated by distance. Infection rates with dengue and yellow fever viruses showed greater differences between two Brazilian samples than between the two North American samples or between a Brazilian sample and a North American sample. Introductions and establishments of new Ae. albopictus populations in the Americas are still in progress, shaping population genetic composition and potentially modifying both dengue and yellow fever transmission patterns. (+info)
Dengue and the risk of urban yellow fever reintroduction in Sao Paulo State, Brazil.
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OBJECTIVE: To propose a mathematical method for the estimation of the Basic Reproduction Number, R0, of urban yellow fever in a dengue-infested area. METHODS: The method is based on the assumption that, as the same vector (Aedes aegypti) causes both infections, all the quantities related to the mosquito, estimated from the initial phase of dengue epidemic, could be applied to yellow fever dynamics. It is demonstrated that R0 for yellow fever is, on average, 43% lower than that for dengue. This difference is due to the longer dengue viremia and its shorter extrinsic incubation period. RESULTS: In this study the analysis was expanded to the epidemiological situation of dengue in S o Paulo in the year 2001. The total number of dengue cases increased from 3,582 in 2000 to 51,348 in 2001. It was then calculated R0 for yellow fever for every city which have shown R0 of dengue greater than 1. It was also estimated the total number of unprotected people living in highly risky areas for urban yellow fever. CONCLUSIONS: Currently there is a great number of non-vaccinated people living in Aedes aegypti infested area in the state of Sao Paulo. (+info)