Urban Transmission Research Articles

Evaluation of Potential West Nile Virus Vectors in Volgograd Region, Russia, 2003 (Diptera: Culicidae): Species Composition, Bloodmeal Host Utilization, and Virus Infection Rates of Mosquitoes

Potential West Nile virus (family Flaviviridae, genus Flavivirus, WNV) vectors were assessed during 2003 at indoor and outdoor collection sites in urban Volgograd, Russia, and in three nearby towns and surrounding rural areas. In total, 9,182 female mosquitoes comprising 13 species in six genera were collected. Relative abundance and bloodmeal host utilization differed temporarily and spatially. During June and July in Volgograd, Aedes vexans (Meigen) (85.4%) and Culex p. pipiens L. (7.6%) were the two most abundant species collected indoors, whereas during August, Cx. p. pipiens was the dominant species, accounting for 87.9% of specimens collected. Two WNV-positive mosquito pools were detected in August: one pool was composed of Cx. p. pipiens and the other pool of Culex modestus Ficalbi. Anopheles messeae Falleroni, Aedes caspius (Pallas), Ae. vexans, Cx. modestus, and Cx. p. pipiens used both humans and birds as bloodmeal sources. In urban areas, 20.4% of the Cx. p. pipiens fed on humans, 58.1% fed on chickens, and six specimens were positive for both chicken and human blood. Culex p. pipiens collected from flooded basements were predominantly autogenous (91.7%), whereas adult females resting in buildings with dry basements were composed of 67.5% anautogenous and 32.5% autogenous specimens. Our data suggest that the primary WNV vectors in the Volgograd region were Cx. p. pipiens and Cx. modestus and that intense transmission of WNV to humans in urban areas during the epidemic of 1999 may have been facilitated by the abundance and concentration of anautogenous Cx. p. pipiens in multistory buildings. The role of autogenous Cx. p. pipiens in urban transmission remains unresolved.

Urban lymphatic filariasis in central Nigeria

Wuchereria bancrofti and the other mosquito-borne parasites that cause human lymphatic filariasis (LF) infect over 120 million people world-wide. Global efforts are underway to stop transmission of the parasites, using annual, single-dose mass drug administrations (MDA) to all at-risk populations. Although most MDA to date have been in rural settings, they are also recommended in urban areas of transmission. It remains unclear whether there is significant urban transmission in West Africa, however, and the need for urban MDA in this region therefore remains a matter of debate.Clinic-based surveillance, for the clinical manifestations of LF, has now been used to identify areas of urban transmission of W. bancrofti in Jos, the major urban population centre of Plateau state, Nigeria. The eight clinics investigated were all located in slum areas, close to vector breeding sites, and were therefore considered to serve at-risk populations. Over a 1-month period, selected providers in these clinics sought hydrocele, lymphoedema, elephantiasis, or acute adenolymphangitis among the patients seeking treatment. The consenting patients who were suspected clinical cases of LF, and a cohort of patients suspected to be cases of onchocerciasis, were tested for W. bancrofti antigenaemia. All the patients were asked a series of questions in an attempt to determine if those found antigenaemic could only have been infected in an urban area. During the study, 30 suspected clinical cases of LF were detected and 18 of these (including two patients who were found to be antigenaemic) lived in urban areas. Of the 98 patients with exclusively urban exposure who were tested for filarial antigenaemia, six (6.1%) were found antigenaemic. Clinic-based surveillance appears to be a useful tool for determining if there is W. bancrofti transmission in an urban setting.

Development of a single-phase 30 m HTS power cable

HTS power transmission cables appear to be the replacement and retrofitting of underground cables in urban areas and HTS power transmission cable offers a number of technical and economic merits compared to the normal conductor cable system. A 30 m long, single-phase 22.9 kV class HTS power transmission cable system has been developed by Korea Electrotechnology Research Institute (KERI), LS Cable Ltd., and Korea Institute of Machinery and Materials (KIMM), which is one of the 21st century frontier project in Korea since 2001. The HTS power cable has been developed, cooled down and tested to obtain realistic thermal and electrical data on HTS power cable system. The evaluation results clarified such good performance of HTS cable that DC critical current of the HTS cable was 3.6 kA and AC loss was 0.98 W/m at 1260 Arms and shield current was 1000 Arms. These results proved the basic properties for 22.9 kV HTS power cable. As a next step, we have been developing a 30 m, three-phase 22.9 kV, 50 MV A HTS power cable system and long term evaluation is in progress now.

Transmission System for ISDB-T/sub SB/ (Digital Terrestrial Sound Broadcasting)

In the Integrated Services Digital Broadcasting-Terrestrial Sound Broadcasting (ISDB-T/sub SB/)transmission system, a narrow-band orthogonal frequency division multiplexing with one or three segment(s) is adopted. It is robust against multipath interferences in urban radio wave transmission. In addition, it is capable of mobile reception because of time interleaving. A bandwidth of 432 kHz for one segment is narrow enough in order to allocate channels flexibly, and the connected transmission scheme, which allows multiple segment with no guard band, is a highly efficient usage of the frequency resource. The ISDB-T/sub SB/ system is consistent with ISDB-T, hence it enables a common receiver for partial reception of ISDB-T, digital television broadcasting. In this paper, the ISDB-T/sub SB/ system,especially the differences from the ISDB-T system, is introduced,and the current status of the ISBD-TSB digital terrestrial sound broadcasting service is shown.

Lymphatic filariasis in Ghana: establishing the potential for an urban cycle of transmission

Lymphatic filariasis is a significant public health and economic problem in many tropical and sub-tropical regions. Unplanned urbanization leading to a lack of proper sanitary conditions has resulted in an increase in the urban-based transmission of a number of vector-borne diseases, including lymphatic filariasis. It has been well established that lymphatic filariasis is endemic in rural areas of Ghana. The goal of this study was to determine if there is a potential of establishing urban transmission cycles in Ghana's major cities. We clinically and immunologically assessed 625 individuals from the three major urban areas (Bawku, Bolgatanga and Secondi/Takoradi), finding that the prevalence of infection with Wuchereria bancrofti ranged from 0 to 12.5%. The results of a polymerase chain reaction based analysis of mosquitoes collected from these areas suggested that there is a low but detectable prevalence of mosquitoes infected with W. bancrofti. We conclude that there may be a potential for an established urban transmission of lymphatic filariasis in Ghana.

INTEGRATED URBAN MALARIA CONTROL: A CASE STUDY IN DAR ES SALAAM, TANZANIA

The rapid growth of cities in sub-Saharan Africa, much of it driven by rural-urban migration, is associated with complex transformations of these ecosystems and an intricate set of challenges for malaria control. Urban malaria transmission is substantially less intense and much more focal than in rural and peri-urban settings. However, the danger of epidemics is higher and the presence of substantial non-immune populations places people of all ages at comparable levels of risk. The limited number of breeding sites in urban centers suggests that prevention strategies based on vector control, with emphasis on environmental management, should be a central feature of urban malaria control programs. We focus on malaria in the city of Dar es Salaam, Tanzania. Following a brief review of the 100-year history of malaria control in this urban center, we describe and evaluate a control program that operated from 1988 to 1996 as a consequence of a bilateral agreement between the governments of Tanzania and Japan. We present an innovative urban malaria risk mapping methodology based on high-resolution aerial photography with ground-based validation. This strategy clarifies that remote sensing technology at a level of resolution of one meter is essential if this kind of information is to play a role in guiding the detailed specification of intervention strategies for urban malaria control. The Tanzania-Japan multiple-intervention malaria control program, adaptively implemented over time, is described and evaluated with implications for urban malaria control in sub-Saharan Africa more generally.

The burden of Leishmania chagasi infection during an urban outbreak of visceral leishmaniasis in Brazil

First noted in the city of Teresina in 1981, the last decades have witnessed a remarkable increase in urban transmission of American visceral leishmaniasis (VL) in many Brazilian cities. Teresina, the site of this study, has faced two large outbreaks of VL. The first occurred from 1981–1985 when almost 1000 new cases were reported. The second started in the 1990s, and between 1993 and 1996 more than 1200 new cases were detected. This report describes the prevalence of infection with Leishmania chagasi in Teresina at the end of the second outbreak and gives estimates of the number of people who became infected during the epidemic. Between June 1995 and May 1996, 200 households were chosen at random from a list of addresses covering about 93% of Teresina's urban households. In each household, one person over the age of 1 year was screened for Leishmania antibodies and skin-tested. Nearly 50% of persons had a positive leishmanin reaction, but only 13.9% had detectable antibodies to L. chagasi. While prevalence estimates based on the leishmanin skin-test increased with age ( P<0.001), those based on serological tests showed a lesser, and non significant, variation with age ( P=0.31). Using a geometric growth equation, and assuming that the annual distribution of clinical cases may serve as an approximation to what would have been the distribution of infections by year, we estimated that over 320 000 persons were infected during the epidemic. Little is known about the epidemiology of VL in urban areas, where social networks, population density, and relationships of housing with the natural environment are more varied and complex than in the rural scene. In those areas, control interventions have failed to eliminate transmission of the parasite and prevent new epidemics. Further epidemiological studies of VL in urban areas might be needed to inform control actions.

Oral susceptibility to yellow fever virus of Aedes aegypti from Brazil.

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.

Urban malaria transmission in Mutare City; an unlikely phenomenon.

With an average altitude of 1,113 m above sea level and a mean maximum temperature of 28.6 degrees C, malaria transmission is possible in Mutare. Against transmission is the regular occurrence of ground frost. We reviewed epidemiological data and undertook a survey for the Anopheles vector. The Anopheles survey used standard techniques for sampling larvae and adult mosquitoes. Species identification was done by the polymerase chain reaction (PCR) technique. A random sample of blood slides was examined at the Blair Laboratory. Patient residence was determined from the outpatient register. Daily maximum and minimum temperatures monitored from the Mutare Fire Station, were obtained from the Meteorology Office in Harare. Mutare city and suburbs. There was no evidence of rising temperatures in Mutare. Only non-vector Anopheles mosquitoes were identified (An. quadriannulatus and An. pretoriensis). One slide positive case had gametocytes present. Mapping generally showed no clustering, but there were two possible transmission foci. Temperatures are high enough, but winter lows (< 18 degrees C) do not support malaria transmission in Mutare. The Anopheles survey did not find the vector. Two suggestive clusters were mapped. While present data do not support ongoing malaria transmission within Mutare, in the past, An. gambiae, An. fenestus and An. pretoriensis were recorded. Careful monitoring will be needed.

A study of the urban malaria transmission problem in Khartoum

A study of malaria prevalence and transmission was carried out in Khartoum, the capital of Sudan. The sentinel sites were El manshia, an urban area on the Blue Nile and Ed dekheinat, a lower-income peri-urban area bordering the White Nile. Anopheles arabiensis, the only malaria vector encountered, was present throughout the year although vector density varied seasonally. Plasmodium falciparum was the only species found in El manshia. In Ed dekheinat P. falciparum, Plasmodium ovale and Plasmodium vivax constituted 84.9, 8.2 and 6.9% of the cases, respectively. Plasmodium ovale appears to have recently spread into Khartoum since it has not previously been reported there. We conclude that focal transmission of malaria in the districts bordering both Niles has become established and that the reservoir of human infections has increased in recent years leading to increased risk of malaria epidemics, particularly in the aftermath of seasonal flooding.

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.

Urbanisation of yellow fever in Santa Cr uz, Bolivia

Reinvasion by Aedes aegypti of cities in the Americas poses a threat of urbanisation of yellow fever. After detection of yellow-fever infection in a resident of the city of Santa Cruz, Bolivia, in December, 1997, we investigated all subsequent suspected cases. We introduced active surveillance of yellow fever in the Santa Cruz area. Hospitals and selected urban and rural health centres reported all suspected cases. Patients were serologically screened for yellow fever, dengue, hepatitis A and B, and leptospirosis. We collected clinical and epidemiological information from patients' records and through interviews. We also carried out a population-based serosurvey in the neighbourhood of one case. Between December, 1997, and June, 1998, symptomatic yellow-fever infection was confirmed in six residents of Santa Cruz, five of whom died. Five lived in the southern sector of the city. Two had not left the city during the incubation period, and one had visited only an area in which sylvatic transmission was deemed impossible. Of the 281 people covered in the serosurvey 16 (6%) were positive for IgM antibody to yellow fever. Among five people for whom this result could not be explained by recent vaccination, there were two pairs of neighbours. Urban transmission of yellow fever in Santa Cruz was limited in space and time. Low yellow-fever immunisation coverage and high infestation with A. aegypti in the city, and the existence of endemic areas in the region present a risk for future urban outbreaks. We recommend immediate large-scale immunisation of the urban population, as well as tightened surveillance and appropriate vector control.

Vector competence of Aedes notoscriptus (Diptera: Culicidae) for Ross River virus in Queensland, Australia.

Aedes notoscriptus (Skuse) mosquitoes colonized from Brisbane, Queensland, Australia, were fed on blood containing Ross River (RR) virus isolated from Brisbane, Queensland, Australia. This colony was highly susceptible to infection, ID50 = 10(3.2) CCID50 per mosquito, with titers in infected mosquitoes peaking 9 d after infection. Transmission occurred between days 9 and 14, with a maximum rate of 13% between days 12 and 14 after infection. Considering the peridomestic abundance and human blood feeding habit of Ae. notoscriptus, positive transmission of RR virus indicates the need to consider this species more seriously in the context of urban RR transmission.

Urban schistosomiasis in Itamaracá Island, Pernambuco, Brazil: epidemiological factors involved in the recent endemic process.

Schistosomiasis has been considered as a rural endemic disease. In the State of Pernambuco, migratory human movements from endemic areas to urban ones with precarious sanitary and environmental conditions, is being pointed out as responsible for expansion and transmission of schistosomiasis (CS Barbosa et al. 1996 Rev Saude Publica 14: 693-700). The possibility that schistosomiasis mansoni could reach urban populations of high socio/economic background levels have been negleg. In 1991, four autochthonous cases from accidental exposure were detected near the Fort Orange beach, in Itamaraca Island, Pernambuco (JF Goncalves et al. 1992 Cad Saude Publica 7: 424-425). All cases occured in individuals from medium/high classes, that were in vacation in the island. After the detection of these accidental cases our major objective was to search for factors involved in schistosomiasis transmission in this area: a condominium composed by 560 houses of vacationists or tourists, built upon a destroyed mangrove ecosystem. An epidemiological quantitative study was conducted through demographic, sanitary, parasitological, social/economic and malacological surveys. Information about previous morbidity were also provided by the individuals that were temporary visitors in the area. The malacology survey identified 19 breading sites of Biomphalaria glabrata and 27 capture stations were set up. Snails were collected and examined each month during a year. The results show sazonal variation in mollusc populational density, associated with infection rates. The concentration of snails in water collections during the period from September to December 1997 were the highest observed, with infection rates of 18.2% (CS Barbosa et al. 1998 unpublished data). So, it is possible to imagine the potencial environmental risk of infection for human population in summer vacation on this beach. In the coproscopical survey, fecal samples of 349 vacationists and 91 local inhabitants were collected. Among vacationists, 10 cases of Schistosoma mansoni infection were detected (Table I). Moreover, 12 additional confirmed and autochthonous cases of schistosomiasis, in the last three years, were detected by refered morbidity survey (Table II). The prevalence of infection among local residents (fisherman and civil construction laborers) was 41.8%. Either, vacationist and local residents showed very few eggs of S. mansoni, indicating low levels of exposure. However, vacationists showed clinical acute forms, with characteristic exacerbated symptoms. The autochthony of cases was confirmed by personal interviews. We can conclude that the urban transmission of schistosomiasis in Itamaraca Island have dis-

Antibodies to Bartonella Species in Inner-city Intravenous Drug Users in Baltimore, Md

Bartonella quintana has recently been associated with homeless alcoholic men. Both B quintana and Bartonella henselae have been shown to be opportunistic pathogens of people with acquired immunodeficiency syndrome. The reservoirs and modes of transmission of these infections are incompletely known. To examine serum samples that were taken from inner-city intravenous (IV) drug users for antibodies to Bartonella organisms to determine whether there is an urban transmission cycle for Bartonella species and to examine the demographic and behavioral characteristics of IV drug users to identify possible risk factors for infection with any of these agents. A serologic survey was conducted, using a convenience sample of serum specimens collected during a study of IV drug use and human immunodeficiency virus infection among 630 inner-city residents in Baltimore, Md. A detailed questionnaire was administered at the initial collection of serum, and additional serum collections and questionnaire updates were made at 6-month intervals. The most recent available serum sample was tested for Bartonella antibody titer by using the indirect immunofluorescent antibody test with 3 antigens: Bartonella elizabethae, B henselae, and B quintana. Univariate and multivariate analyses of selected potential demographic and behavioral risk factors were conducted. Antibodies to Bartonella were highly prevalent in this group; more than 37% of all samples reacted with at least 1 antigen. Overall seroprevalence of antibodies to B elizabethae, B henselae, and B quintana was 33%, 11%, and 10%, respectively. Current IV drug use, frequency of injection, and seronegative human immunodeficiency virus status were significantly associated with Bartonella antibody presence, but these associations varied by analysis. There was a significant inverse association of antibody prevalence to B henselae and B quintana by using CD4+ cell counts among human immunodeficiency virus-seropositive individuals. Intravenous drug users have an elevated prevalence of antibodies to Bartonella organisms and may be at significant risk of becoming infected. Current IV drug use, high frequency of injection, and seronegative human immunodeficiency virus status are significant risk factors for an increased prevalence of Bartonella antibodies. The current natural histories of Bartonella species are rapidly changing, and mechanisms of transmission remain unknown.

Leishmaniasis in the Porto Ferreira district

Since 1981, the incidence of leishmaniasis is increasing in the district of Porto Ferreira, due to favorable environmental conditions for phlebotomini breeding. The data were collected from the Epidemiological Investigation Card and also through interviews with local inhabitants cases. Until the first semester of 1993, forty cases had been recorded and they basically occurred in an area we called critical. The epidemiological features of the disease in the country are different from those listed in literature by the observation that women working at home were more affected, which characterizes an autoctone, domiciliar and urban transmission. The sequence of assistance of patients has also been evaluated, identifying some questions concerning the time elapsed from the first symptoms to the specific treatment. Actions of epidemic-sanitary control were proposed in order to conter the incidence the disease in the district.

Development of the urban and rural transmission networks in Russia

The paper describes the main characteristics of the transmission networks that are used in the urban and rural areas. Existing principles of the urban and rural transmission networks' creation are given. The subscriber transmission network is considered. The St. Petersburg transmission network is analyzed as an example of an urban transmission facility. Aspects related to commercial network creation are briefly discussed. >

Vector incrimination and effects of antimalarial drugs on malaria transmission and control in the Amazon basin of Brazil.

World ecosystems differ significantly and a multidisciplinary malaria control approach must be adjusted to meet these requirements. These include a comprehensive understanding of the malaria vectors, their behavior, seasonal distribution and abundance, susceptibility to insecticides (physiological and behavioral), methods to reduce the numbers of human gametocyte carriers through effective health care systems and antimalarial drug treatment, urban malaria transmission versus rural or forest malaria transmission, and the impact of vaccine development. Many malaria vectors are members of species complexes and individual relationships to malaria transmission, seasonal distribution, biting behavior, etc. is poorly understood. Additionally, malaria patients are not examined for circulating gametocytes and both falciparum and vivax malaria patients may be highly infective to mosquitoes after treatment with currently used antimalarial drugs. Studies on the physiological and behavioral effects of DDT and other insecticides are inconclusive and need to be evaluated.

The error performance of CD900-like cellular mobile radio systems

The symbol error performance of CD900-like digital cellular mobile radio systems over narrowband and urban wideband transmission channels was investigated. The basic performance is presented for Gaussian, flat-fading Rayleigh, and log-normal channels in the presence of selection and ratio combining space diversity schemes. For wideband channels having more than one resolvable fading path, a CD900-like system without diversity reception suffers from large residual symbol error probabilities P/sub R/( approximately=10/sup -1/). The introduction of adaptive correlation diversity (ACD) mitigates the effects of multipath, yielding a P/sub R/ of 6*10/sup -5/. Although this P/sub R/ value is relatively low, the probability of symbol error (P/sub e/) versus signal-to-noise ratio (SNR) is significantly poorer than for the Gaussian channel. By combining the ACD scheme with space diversity, the P/sub R/ is eliminated by P/sub e/>10/sup -5/, and the channel SNR is within 5 dB of the Gaussian channel performance when P/sub e/ is 10/sup -10/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Cutaneous leishmaniasis in Niger

This is the first report of cutaneous leishmaniasis in Niger subsequent to the initial finding in 1911 and the report of a second case in 1943. The clinical, histopathological, and epidemiological features of 64 parasitologically confirmed cases are described. Lesions were mostly multiple, situated on exposed areas of skin, but rarely on the face. Two clinical forms were predominant: ulcero-crusted and humid-ulcerous. Nodular lymphangitis was not uncommon. Patients were mostly from rural areas, but urban transmission did occur. The majority of lesions appeared during the June-October rainy season. All features appeared to be similar to those of this disease in other countries in the sahelian endemic zone.