Enzootic transmission of yellow fever virus in Peru.
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The prevailing paradigm of yellow fever virus (YFV) ecology in South America is that of wandering epizootics. The virus is believed to move from place to place in epizootic waves involving monkeys and mosquitoes, rather than persistently circulating within particular locales. After a large outbreak of YFV illness in Peru in 1995, we used phylogenetic analyses of virus isolates to reexamine the hypothesis of virus movement. We sequenced a 670-nucleotide fragment of the prM/E gene region from 25 Peruvian YFV samples collected from 1977 to 1999, and delineated six clades representing the states (Departments) of Puno, Pasco, Junin, Ayacucho, San Martin/Huanuco, and Cusco. The concurrent appearance of at least four variants during the 1995 epidemic and the genetic stability of separate virus lineages over time indicate that Peruvian YFV is locally maintained and circulates continuously in discrete foci of enzootic transmission. (+info)
The yellow fever situation in Africa.
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WHILE THE TWENTIETH CENTURY HAS PRODUCED GREAT DEVELOPMENTS IN THE EPIDEMIOLOGY OF YELLOW FEVER AND IN TECHNIQUES FOR ITS CONTROL IN URBAN AREAS, THE ESSENTIAL METHOD OF CONTROL HAS NOT CHANGED: it is still the elimination of the urban vector, Aedes aegypti. The aim of those responsible for yellow fever control in Africa should be the eradication of this vector from all urban communities in the endemic area. In the case of sylvan yellow fever, complete control of the vectors is not yet possible, but mass immunization of the human population at risk is feasible. The solution of the yellow fever problem in Africa lies in the accomplishment of these two aims. (+info)
Isolation of the virus as a diagnostic procedure for yellow fever in West Africa.
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With modern organizations for mass vaccinations in operation, the diagnosis by serological tests of yellow fever is becoming increasingly difficult. The isolation of the virus from the circulating blood of the patient offers a reasonably reliable alternative method of diagnosis and has the advantage of giving a more rapid result.From a study of four epidemics in West Africa the chances of procuring a successful isolation are analysed according to the duration and severity of the illness. (+info)
Proved and potential vectors of yellow fever in South Africa.
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This paper, based on records obtained from the Entomology Department of the South African Institute for Medical Research, Johannesburg, gives a summary of the distribution, adult habits, and breeding-places of the proved and potential vectors of yellow fever in South Africa. (+info)
Immunizations for foreign travel.
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One of the most important aspects of preparing travelers for destinations throughout the world is providing them with immunizations. Before administering any vaccines, however, a careful health and immunization history and travel itinerary should be obtained in order to determine vaccine indications and contraindications. There are three categories of immunizations for foreign travel. The first category includes immunizations which are routinely recommended whether or not the individual is traveling. Many travelers are due for primary vaccination or boosting against tetanus-diphtheria, measles-mumps-rubella, pneumococcal pneumonia, and influenza, for example, and the pre-travel visit is an ideal time to administer these. The second category are immunizations which might be required by a country as a condition for entry; these are yellow fever and cholera. The final category contains immunizations which are recommended because there is a risk of acquiring a particular disease during travel. Typhoid fever, meningococcal disease, rabies, and hepatitis are some examples. Travelers who are pregnant or who are infected with the human immunodeficiency virus require special consideration. Provision of appropriate immunizations for foreign travel is an important aspect of preventing illness in travelers. (+info)
Identification of envelope protein epitopes that are important in the attenuation process of wild-type yellow fever virus.
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Monoclonal antibodies (MAbs) have been prepared against vaccine and wild-type strains of yellow fever (YF) virus, and envelope protein epitopes specific for vaccine (MAbs H5 and H6) and wild-type (MAbs S17, S18, S24, and S56) strains of YF virus have been identified. Wild-type YF virus FVV, Dakar 1279, and B4.1 were each given six passages in HeLa cells. FVV and B4.1 were attenuated for newborn mice following passage in HeLa cells, whereas Dakar 1279 was not. Examination of the envelope proteins of the viruses with 87 MAbs showed that attenuated viruses gained only the vaccine epitope recognized by MAb H5 and lost wild-type epitopes recognized by MAbs S17, S18, and S24 whereas the nonattenuated Dakar 1279 HeLa p6 virus did not gain the vaccine epitope, retained the wild-type epitopes, and showed no other physical epitope alterations. MAb neutralization-resistant (MAbr) escape variants generated by using wild-type-specific MAbs S18 and S24 were found to lose the epitopes recognized by MAbs S18 and S24 and to acquire the epitope recognized by vaccine-specific MAb H5. In addition, the MAbr variants became attenuated for mice. Thus, the data presented in this paper indicate that acquisition of vaccine epitopes and loss of wild-type epitopes on the envelope protein are directly involved in the attenuation process of YF virus and suggest that the envelope protein is one of the genes encoding determinants of YF virus pathogenicity. (+info)
Neutralizing and haemagglutination-inhibiting antibodies to yellow fever 17 years after vaccination with 17D vaccine.
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The duration of immunity conferred by yellow fever vaccine is as yet undetermined. In this study the neutralizing and haemagglutination-inhibiting antibodies to yellow fever were investigated in 108 persons living in Pouso Alegre, Brazil, where yellow fever has never been reported. These persons had been vaccinated with 17D yellow fever vaccine between 27 December 1940 and 5 February 1941, but not again; and their antibody pattern was compared with that of 78 controls who had never been vaccinated. In the vaccinated group the majority had neutralizing and haemagglutination-inhibiting antibodies present in the serum, whereas in the unvaccinated group antibodies were all but completely absent. Heterologous antibodies to other viruses of Casal's Group B were also found, and the significance of this finding is discussed. (+info)
Yellow fever vaccination in Malaya by subcutaneous injection and multiple puncture. Neutralizing antibody responses in persons with and without pre-existing antibody to related viruses.
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Because of the risk of introduction of yellow fever to South-East Asia, comparative studies were made of yellow fever vaccination in Malayans who had a high prevalence of antibody to related viruses and in volunteers without related antibody. The proportions of positive neutralizing antibody responses to subcutaneous vaccination with 17D vaccine were not significantly different between volunteers with and without heterologous antibody but the degree of antibody response was greater in those without. The ID(50) of 17D in both groups was about 5 mouse intracerebral LD(50). Multiple puncture vaccination with 17D gave a much lower response rate than subcutaneous vaccination in volunteers with heterologous antibody. In both groups subcutaneous doses of about 50 mouse intracerebral LD(50) gave larger antibody responses than higher doses. The neutralizing indices and analysis of results were calculated by a method based on the survival time of the mice. This method, which has advantages over that of Reed & Muench, is fully described in an annex to this paper. (+info)