Urban Yellow Fever Research Articles

Serologic survey for yellow fever and other arboviruses among inhabitants of Rio Branco, Brazil, before and three months after receiving the yellow fever 17D vaccine

During a yellow fever vaccination campaign among residents of Rio Branco (Acre State), the frequency of HI antibodies to the most prevalent arboviruses in the Amazon region and to yellow fever virus was determined before and three months after immunization with YF 17D vaccine. From 390 inhabitants included in the first phase of serologic survey (August 1999), only 190 provided a second serum sample, after the use of 17D vaccine (January 2000). Among first phase samples, the frequency of HI antibodies was: 17D (27.2%); Ilheus (5.9%); Mayaro (5.4%); Caraparu (4.9%); Dengue-2 (4.1%); Oropouche (2.3%); and Dengue-1 (0.3%). In the second study phase, the serologic conversion to YF reached 89.7% among previously negative persons. Serologic conversions were also observed to Ilheus (6.2%); Dengue-3 (3.2%); Mayaro (1.1%); and Oropouche (1.1%) viruses. In conclusion, considering the high YF antibody rate after vaccination, the risk of urban yellow fever seems insignificant, although the lower prevalence of HI antibodies to dengue viruses, is of concern and inhabitants are under high risk of dengue outbreaks, especially to DEN-3 recently introduced in Brazil, as was observed in 2000 and 2001 with DEN-1 and DEN-2.

Aedes aegypti in Brazil: genetically differentiated populations with high susceptibility to dengue and yellow fever viruses

Aedes aegypti was eliminated from Brazil in 1955, but re-infested the country in the 1970s. Dengue outbreaks have occurred since 1981 and became endemic in several cities in Brazil after 1986. Urban yellow fever has not occurred since 1942, and only jungle yellow fever cases have been reported. A population genetic analysis using isoenzyme variation combined with an evaluation of susceptibility to both yellow fever and dengue 2 viruses was conducted among 23 A. aegypti samples from 13 Brazilian states. We demonstrated that experimental infection rates of A. aegypti for both dengue and yellow fever viruses (YFV) are high and heterogeneous, and samples collected in the endemic and transition areas of sylvatic yellow fever were highly susceptible to yellow fever virus. Boa Vista, a border city between Brazil and Venezuela, and Rio de Janeiro in the Southeast region are considered as the most important entry points for dengue dissemination. Considering the high densities of A. aegypti, and its high susceptibility to dengue and yellow fever viruses, the risk of dengue epidemics and yellow fever urbanization in Brazil is more real than ever.

Dengue and the risk of urban yellow fever reintroduction in São Paulo State, Brazil.

To propose a mathematical method for the estimation of the Basic Reproduction Number, R0, of urban yellow fever in a dengue-infested area. 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. 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. Currently there is a great number of non-vaccinated people living in Aedes aegypti infested area in the state of São Paulo.

Brazilian Flavivirus phylogeny based on NS5.

In this work, a comprehensive phylogenetic study based on 600 base pair nucleotide and on putative 200 amino acid sequences of NS5 was carried out in order to establish genetic relationships among 15 strains of 10 Brazilian flaviviruses: Bussuquara, Cacipacore, dengue type 1, 2 and 4, Iguape, Ilheus, Rocio, Saint Louis encephalitis (SLE), and yellow fever. Phylogenetic trees were created by neighbor-joining and maximum parsimony methods. These trees showed Brazilian flaviviruses grouped into three main branches: yellow fever branch, dengue branch subdivided in types 1, 2 and 4 branches, and Japanese encephalitis virus (JEV) complex branch including SLE virus strains, Cacipacore, Iguape, Rocio, Ilheus and Bussuquara. Viruses transmitted by Aedes mosquitoes, such as dengue and urban yellow fever, that are also the only Flavivirus causing hemorrhagic fevers in Brazil, were grouped in the same cluster. Encephalitis associated viruses, transmitted by Culex mosquitoes such as JEV complex branch including SLE virus strains, Cacipacore, Iguape, Rocio, Ilheus and Bussuquara were also grouped in the same clade.

Vector competence of Brazilian Aedes aegypti and Ae. albopictus for a Brazilian yellow fever virus isolate

Because the potential urban yellow fever (YF) mosquito vectors Aedes aegypti and Ae. albopictus are at historical highs in Brazil, both in terms of density and geographical range, we assessed the risk of an urban YF epidemic in Brazil. We evaluated and confirmed in a laboratory setting the vector competence of Brazilian Ae. aegypti for a currently circulating strain of YF virus, and investigated the potential for Brazilian Ae. albopictus to transmit YF.

The risk of yellow fever in a dengue-infested area

Yellow fever and dengue are viral infections that in urban centres are transmitted by the same arthropod vector, a mosquito of the genus Aedes. In order to estimate the risk of an epidemic of urban yellow fever in a dengue-infested area we calculated the threshold in the basic reproduction number, R 0, of dengue, above which any single sylvatic yellow fever-infected individual will trigger an urban yellow fever epidemic. Specifically, we analysed the relationship between the extrinsic incubation period and the duration of viraemia, from which it is possible to define the R 0 for dengue that would also suggest an outbreak potential for yellow fever. We also calculated the critical proportion of people to vaccinate against yellow fever in order to prevent an epidemic in a dengue-endemic area. The theory proposed is illustrated by the case of São Paulo State in southern Brazil, where dengue is endemic and the risk of urban yellow fever is already imminent.

Yellow fever.

With the infestation by Aedes aegypti, urban yellow fever might already exist. This did not occur because of either the lacking of a sufficient contact between the diseased individual and the A. aegypti or perhaps because this, after sixty years without transmitting the virus, needs an adaptation phase to infecting again.

Facing up to re-emergence of urban yellow fe ver

Transmitted from person to person by Aedes aegypti, urban yellow fever was eliminated in the first half of this century, with the eradication of its mosquito vector from most of South America. However, reinfestation began in the 1970s is now almost complete, and vector control is considerably more difficult now than before. The threat of urban yellow fever is greatest in towns such as Santa Cruz, Bolivia, near the forest, but improved transport links increase the likelihood of spread by viremic people to nonendemic areas. Van der Stuyft et al. have reported the first instance of urban transmission of yellow fever in the Americas in 44 years. Since residents of the densely populated cities and much visited areas in coastal South America have never been vaccinated, an outbreak there would facilitate widespread dissemination of the disease, even to other continents. While urban yellow fever is a significant threat, carrying a case-fatality rate of about 20%, the constrained dynamics of transmission, early recognition of the striking clinical presentation, and efforts to control the infection should limit the impact of the disease. Laboratory-based surveillance, together with the prevention and control strategies outlined by van der Stuyft et al. are the key defensive measures against the future threat of urban epidemics.

Estratégias de Comunicação frente ao Desafio do Aedes Aegyptino Brasil

O presente artigo desenvolve uma análise das diferentes dimensões e especificidades dos processos de planejamento e desenho de estratégias de comunicação no combate ao Aedes aegyptino Brasil. A reflexão se organiza em torno do problema do combate aos criadouros do vetor da Dengue e da Febre Amarela Urbana e é atravessada por uma perspectiva conflitual da comunicação, que a situa no campo dos processos de disputa de sentidosnas sociedades contemporâneas.

Yellow fever: ecology, epidemiology, and role in the collapse of the Classic lowland Maya civilization.

Mystery has long surrounded the collapse of the Classic lowland Mayan civilization of the Peten region in Guatemala. Recent population reconstructions derived from archaeological evidence from the central lowlands show population declines from urban levels of between 2.5 and 3.5 million to around 536,000 in the two hundred year interval between 800 A.D. and 1000 A.D., the period known as the Classic Maya Collapse. A steady, but lesser rate of population decline continued until the time of European contact. When knowledge of the ecology and epidemiology of yellow fever and its known mosquito vectors are compared with what is known of the ecological conditions of lowland Guatemala as modified by the Classic Maya, provocative similarities are observed. When infection and mortality patterns of more recent urban yellow fever epidemics are used as models for a possible series of Classic Maya epidemics, a correlation is noted between the modeled rate of population decline for a series of epidemics, and population decline figures reconstructed from archaeological evidence.

Urban yellow fever epidemic in western Nigeria, 1987

A large epidemic of urban yellow fever occurred in April and May 1987 in Oyo State, western Nigeria. The principal vector was Aedes aegypti, breeding in domestic water containers. The 1987 outbreak followed an epidemic of sylvatic yellow fever in eastern Nigeria the previous year, and probably resulted from introduction of the virus by viraemic travellers. The outbreak in Oyo State ended in early July, by which time 805 cases and 416 deaths had been officially notified. However, surveys of 3 villages in the epicentre, a region with over 4 million inhabitants, indicated an infection rate of approximately 20%, a clinical attack rate of 2·9% and a mortality rate of 0·6%, suggesting that the true incidence of cases and deaths far exceeded the official reports. Yellow fever virus was isolated from persons with fully developed yellow fever as well as mild febrile illness. One virus isolate was made from blood of an individual with mild illness, who had received 17D vaccine 5 d earlier; monoclonal antibody analysis showed that the isolate was a wild-type virus. Larval indices of Ae. aegypti were very high; however, low vector competence of the Ae aegypti population may have provided a constraint on spread of the epidemic. In late 1987 a third epidemic appeared in Niger State, northern Nigeria, with 644 reported cases and 149 deaths. The vector(s) involved is (are) unknown.

Dengue fever

Dengue fever, also known as breakbone fever, is a mosquito-borne, virus disease characterized by fever, headache, myalgia, and arthralgia, and often an exanthem. Epidemics of dengue-like illness have been recognized for more than 200 years and were common in Asia, along the Atlantic and Gulf coasts of the United States, and the Caribbean until the first half of this century. 1,2 During World War II, thousands of soldiers contracted dengue fever in the Pacific and Asia. 3 A more severe clinical form of dengue infection, dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), was first recognized in the Philippines in 1954 and subsequently spread throughout Southeast Asia. 4,5 DHF/DSS is currently a major cause of morbidity and, without appropriate treatment, mortality in children in tropical Asia and is occurring with increasing frequency in the Western Hemisphere. 6 The etiologic agents of dengue fever are four serologically related RNA viruses, dengue 1,2,3 and 4, that belong the the family Flaviviridae. This virus group also includes yellow fever, St. Louis encephalitis, and Japanese encephalitis viruses. The principal mosquito vector of dengue and urban yellow fever is Aedes aegypti. This species breeds in water that has collected in natural and artificial containers around human habitations. Diminished mosquito control efforts in the Western Hemisphere over the past two decades have resulted in increased distribution of this mosquito vector in the region. Ae. aegypti is found throughout the southeastern United States. Another important mosquito vecter of dengue, Aedes albopictus, has recently become established in this country through the importation of tires from Asia. 7 Dengue fever currently occurs in tropical and subtropical zones in the Caribbean, Mexico, central and South America, Africa, Asia, and the Pacific. Cases of dengue-like illness in travelers returning to the United States from these areas are reported each year. 8 In 1986, 33 serologically confirmed cases were reported from 10 states and the District of Columbia. 9 In areas where potential mosquito vectors of dengue are present, introduction of the virus may result in secondary transmission. Indigenous transmission of dengue was documented in Texas during 1986 for the second time in 6 years. 9

Malaria studies and control in Brazil.

In the greater part of Brazil's extensive territory climatic conditions are propitious for the establishment of endemic malaria, which has been causing pain and death among the country's inhabitants for generations. In Brazil the epidemiology of malaria has presented some peculiar aspects: besides being transmitted in most areas by anophelines breeding in groundwater collections, its dissemination in a restricted but economically important zone was entirely due to mosquitoes breeding in water accumulated in plants of the family Bromeliaceae. It is the so called “bromeliad malaria.” To the native vector species, the alien Anopheles gambiae, introduced to the country, added a new problem. Considerable efforts have been made by Brazilians and foreigners to understand malaria epidemiology and control its transmission. Among the foreigners one immediately thinks of Fred Lowe Soper. Following his contribution to the elimination of Aedes aegypti and urban yellow fever in Brazil, Soper was one of those most directly responsible for the eradication of An. gambiae from this part of the world.

Factors influencing the development of Plasmodium gallinaceum in Aedes fluviatilis.

Aedes fluviatilis is susceptible to infection by Plasmodium gallinaceum and is a convenient insect host for the malaria parasite in countries where Aedees aegypti cannot be maintained in laboratories. In South America, for instance, the rearing of A. aegypti the main vector of urban yellow fever, is not advaisable because of the potential health hazard it represents. Our results of the comparative studies carried out between the sporogonic cycle produced with two lines of P. gallinaceum parasites into A. fuviatilis were as follows. As proved for A. aegypti, mosquito infection rates were variable when A. fluviatilis blood-fed on chicks infected with and old syringe-passaged strain of P. gallinaceum. Oocysts developed in 41% of those mosquitos and the mean peak of oocyst production was 56 per stomach. Salivary gland infections developed in about 6% of the mosquitos. The course of sporogony was unrelated to the size of the inoculum administered to chicks or to the route by which the birds were infected. The development of infected salivary glands was unrelated to oocyst production. Sporogony of P. gallinaceum was more uniform when mosquitos blood-fed on chicks infected with a sporozoite-passaged strain. Oocysts developed in about 50% of those mosquitoes and the mean peak of oocyst production was 138 per stomach, with some individuals having as many as 600-800 oocysts. Infected salivary glands developed in a mean of 27% of the mosquitos but, in some batches, was a high as 50%. Patterns of salivary gland parasitism were similar to those of oocyst production. The course of sporogony of P. gallinaceum in A. fluviatilis is analized in relation to degree of parasitemia and gametocytemia in the vertebrate host.

Febre amarela ll - Estudo histopatológico do fígado

Ao curso de um surto epizoótico de febre amarela acontecido no ano de 1973 nas regiões norte e centro-oeste do Brasil, foram feitos exames histopatológicos de material de fígado de casos suspeitos, retirados por viscerotomia e necropsias. Foram diagnosticados 57 casos positivos. Os exames histopatológicos demonstraram que não existe diferença da doença entre os casos da África e da América do Sul. O diagnóstico histopatológico continua baseado no fígado, na lesão de Councilman, na hiperplasia e hipertrofia das células de Kupfer, nas inclusões nucleares de Magarino Torres, no sinal de Eudoro Villela nos casos de longa duração. Não houve diferença histológica entre os casos descritos nas epidemias de F.A. urbana e os surtos epidêmicos e enzoóticos de F.A. silvestre nos últimos 43 anos.

Febre amarela. I - Aspectos cíclicos e epidemiológicos

Relata-se um resumo epidemiológico do surto epizoótico de febre amarela ocorrido no ano de 1973. São postas em evidência a sua incidência, a distribuição por idades, a distribuição por sexo e a distribuição geográfica. Em seguida, são apresentados os resultados obtidos pela revisão dos casos de febre amarela, que vêm sendo estudados, recolhidos e arquivados na Coleção do Serviço de Viscerotomia da Seção de Histopatologia da Febre Amarela do Instituto Oswaldo Cruz, desde 1931. O trabalho está documentado com tabelas e gráficos que registram os dados acima indicados. Os autores ressaltam os seguintes pontos: 1) A Febre amarela, urbana e silvestre, apresenta quadros epidemiológicos inteiramente diferentes; 2) A incidência da febre amarela silvestre ocorre principalmente no sexo masculino, de acordo com os dados estatisticamente significativos; 3) A idade mais atingida pela forma silvestre é a entre 20 e 30 anos; 4) A febre amarela silvestre continua em áreas enzoóticas, ao longo dos cursos d'água; 5) Parece existir uma relação entre as condições climáticas e a incidência da febre amarela; 6) Os surtos de febre amarela ocorrem aproximadamente de 7 em 7 anos; 7) É do máximo valor o programa de vacinação e o serviço de viscerotomia da SUCAM.

1964 progress report of the Aedes aegypti eradication program.

Summary The Aedes aegypti eradication program was activated in FY 1964, and by the end of June was operational in southern Florida, southern Texas, Puerto Rico, and the American Virgin Islands. It is planned to have full-scale operations underway in all of the nine infested states in the southeastern United States and also in the State of Hawaii by 1967. This program meets U. S. commitments to participate with other member nations of the PAHO in eradicating the Ae. aegypti species from the Western Hemisphere as a permanent solution for the prevention of urban yellow fever. During the latter half of 1964, substantial progress was made in reducing infestations by means of insecticides and source reduction measures in all operational areas. These limited operations have shown the strengths and weaknesses in the eradication methods employed and will thus provide valuable guidance in developing more effective and efficient operations in the future.

The elimination of urban yellow fever in the Americas through the eradication of Aedes aegypti.

THE CONCEPT of a disease having I individuality and being eradicable came as a logical development fairly soon after Pasteur had eradicated germs in a bottle and had begun the identification of specific bacteria as the causative agents of individual diseases. The prePasteur definition of eradicate, in Webster's Dictionary of 1864, cites the usage ; as, to eradicate disease. This refers to disease in the individual patient and not to a disease as a specific entity. The present generation of health workers is witnessing the validation of this usage, still cited in the Webster International Dictionary, 1961, with reference to the eradication of disease, as a specific separate entity. Examples of the initial enthusiasm for disease eradication include: The Bureau of Animal Industry's eradication of bovine pleuropneumonia in the United States in the last decade of the 19th century. Chapin's much quoted statement, in 1888, regarding the eradicability of tuberculosis; Ronald Ross's work in the early 1900's on the mathematical theory of malaria eradication; William C. Gorgas's declaration in 1909 that yellow fever could be eradicated; and, in the same year, the founding of the Rockefeller Sanitary Commission for the Eradication of Hookworm Disease in the United States. The creation of the Rockefeller Foundation, in 1913, was followed by many overseas campaigns for the eradication of hookworm disease and, in 1915, by the beginning of an effort to eradicate yellow fever from the world. Hookworm disease was peculiarly difficult to eradicate and failed to disappear rapidly from any of the countries where so-called eradication programs were executed. Yellow fever disappeared from the statistics of many countries but its continued existence was dramatically proclaimed to the world when Brazil's capital, Rio de Janeiro, became reinfected in 1928. About this time, severe criticism was leveled at the Rockefeller Foundation for having foisted eradication programs -which could not be executed-on the health authorities of many countries. Eradication programs and even uni-

Mosquitoes and Yellow Fever in the Sudan

Dr. J. Lewis, of the Stack Medical Research Laboratories, has discussed the relationship of mosquitoes and yellow fever in the Sudan (Bull. Ent. Res., 3, pt. 4; 1947). It appears that most of the southern half of the Sudan is a yellow fever area in the sense that people immune to the disease have been found in many parts of that territory. The chance of the disease spreading to parts hitherto free is liable to be increased by such outbreaks as the great Nuba Mountains epidemic of 1941. It is noteworthy that several towns in the Sudan lie on important air, rail and water routes leading to countries free from yellow fever. Some 140 species of mosquitoes are known from the Sudan, and, of these, twelve kinds are known to be capable of transmitting the yellow fever virus, while several other kinds are suspected in this connexion. Two further species are able to retain this virus throughout life without apparently possessing the ability to transmit the disease by their blood-sucking habits. The object of the present paper is to record information on the occurrence and distribution of mosquitoes in the Sudan. The Anophelines are only briefly considered because they are unlikely to transmit yellow fever. Among the Culicines that affect man and frequent human habitations, Aedes taylori is believed to be one of the chief vectors in the case of the Nuba Mountains epidemic. As regards Aedes cegypti, it appears that mosquito control measures have had the effect of rendering urban yellow fever epidemics, carried by this species, virtually impossible, and the disease has been exterminated from Khartoum. The relation of Tceniorhynchus africanus to the disease is of special interest owing to its wide range and abundance in the Sudan. While there is no evidence that this species can act as a vector, it seems likely that it can act in this way in limited epidemics about the Upper Nile area. The author concludes by discussing the measures of mosquito control in the Sudan, which greatly restrict the possibilities of the spread of yellow fever. At the same time it is evident that the control of a rural epidemic would be difficult to achieve.

The Distribution of Yellow Fever in Colombia in Recent Years 1

Summary Before the anti-stegomyia campaigns in Havana, Panama and Guayaquil, epidemics of yellow fever were not uncommon in the towns and cities of Colombia along the coast and in the Magdalena valley. Following the last known outbreak in a coastal town, which occurred in Buenaventura in 1920, the country appeared to be entirely free of the disease until the unexplained appearance of urban yellow fever in Bucaramanga in 1923. After six quiet years, the disease broke out unexpectedly again in Socorro in 1929. Immunity surveys carried out by the newly discovered mouse protection test in 1931 and 1932 gave evidence that yellow fever might be endemic in some rural areas of Boyaca and Santander. As a result of a systematic study which was begun in Colombia in 1934, cases of jungle yellow fever have been found each year since in zones comprised of the departments of Antioquia, Boyaca, Caldas, Cundinamarca, Santander and Tolima, and the Intendencia del Meta. The results of an extensive immunity survey during this period confirm this distribution of yellow fever and make it appear probable that the disease has existed in recent years in other widely separated parts of the country such as the Atrato valley and the Colombian Amazon drainage. With the exception of a very small epidemic in Buenavista, Caldas, in 1937, no incidence of yellow fever transmitted by Aedes aegypti has been observed in Colombia since 1929.