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Vector-borne disease problems in rapid urbanization: new approaches to vector control.

Owing to population growth, poor levels of hygiene, and increasing urban poverty, the urban environment in many developing countries is rapidly deteriorating. Densely packed housing in shanty towns or slums and inadequate drinking-water supplies, garbage collection services, and surface-water drainage systems combine to create favourable habitats for the proliferation of vectors and reservoirs of communicable diseases. As a consequence, vector-borne diseases such as malaria, lymphatic filariasis and dengue are becoming major public health problems associated with rapid urbanization in many tropical countries. The problems in controlling these diseases and eliminating vectors and pests can be resolved by decision-makers and urban planners by moving away from the concept of "blanket" applications of pesticides towards integrated approaches. Sound environmental management practices and community education and participation form the mainstay of some of the most outstanding successes in this area. On the basis of these examples, it is argued that the municipal authorities need to apply a flexible methodology, which must be based on the possibilities of mobilizing community resources, with minimal reliance on routine pesticidal spraying. In this way, vector control becomes a by-product of human development in the city environment. This is now a true challenge.

Animals

Discriminant analysis: a method of identifying foci of vector-borne diseases.

Identification of foci of vector-borne diseases does not require knowledge of exact abundances of vectors and pathogens; rather, a focus is defined by the presence, or some minimal level of abundance, of a vector and pathogen. Stepwise discriminant analysis (DA) was applied to data on free-ranging adult wood ticks (the vector) and to data on isolations of Colorado tick fever virus from small mammals. Trap stations were grouped on the basis of relative abundance of wood ticks for one set of analyses and on the presence or absence of virus for another set of analyses. Additional data consisted of easily measured environmental variables. It is concluded that DA provides a useful tool for analysis of ecosystem structure and an effective means of identifying foci of infection.

Animals

Some applications of bloodmeal identifications in relation to the epidemiology of vector-borne tropical diseases.

No attempt has been made to give a complete review of the value of bloodmeal identifications of haematophagous arthropods in relation to the epidemiology of disease but rather to choose certain topics of current interest. A brief review of the current techniques for bloodmeal identification is given with particular reference to recent studies on mosquitoes and sandflies using the haemagglutination inhibition test. New data on mixed feeding by Anopheles gambiae (a mixture of species B and C) collected in Ethiopia confirm the earlier work with A. sacharovi that interrupted feeding is important. Details of current attempts to measure the cryptic portion of multiple meals using blood-typing techniques are given. Information collected on the feeding patterns of Culex univittatus group and Mansonia uniformis from Kenya demonstrates that caution must be shown in interpreting blood meal analyses since sampling techniques as well as several other factors can affect the results. A recent survey of sandflies in West Bengal suggest that a dangerous situation now exists and an outbreak of visceral leishmaniasis could occur.

Aged

rRNA gene organization in the Lyme disease spirochete, Borrelia burgdorferi.

Lyme disease is the most common vector-borne disease in the United States. The causative agent is the spirochete Borrelia burgdorferi. The copy number and organization of the genes encoding the rRNAs of this organism were determined. There is a single gene for 16S rRNA and two copies each of the 23S rRNA and 5S rRNA genes. All of the genes are located within a chromosomal fragment of approximately 9.5 to 10.0 kb. The 23S and 5S rRNA genes are tandemly duplicated in the order 23S-5S-23S-5S and are apparently not linked to the 16S rRNA gene, which is situated over 2 kb upstream from the 23S-5S duplication. The individual copies of the 23S-5S duplication are separated by a 182-bp spacer. Within each 23S-5S unit, an identical 22-bp spacer separates the 23S and 5S rRNA sequences from each other. The genome organization of the 23S-5S gene cluster in a number of different B. burgdorferi isolates obtained at a number of different geographical locations, as well as in several other species of Borrelia, was investigated. All isolates of B. burgdorferi tested displayed the tandem duplication, whereas the closely related species B. hermsii, B. anserina, and B. turicatae all contained a single copy of each of the genes. In addition, different geographical isolates of B. burgdorferi can be differentiated on the basis of a restriction fragment length polymorphism associated with the 23S-5S gene cluster. This polymorphism can be a useful tool for the determination of genetic relatedness between different isolates of B. burgdorferi.

Base Sequence

Vesicular erythema migrans.

BACKGROUND: Lyme disease is the most common vector-borne disease in the United States. The characteristic rash, erythema migrans, is an early sign of the disease. Clinical criteria remain the "gold standard" for diagnosis at this stage of illness. OBSERVATIONS: Five (8%) of 65 patients with erythema migrans seen in a Lyme disease diagnostic center in Westchester County, New York, had a lesion with vesicles. Borrelia burgdorferi was cultured from two of five. In one case the positive culture came from a swab of the blister fluid. CONCLUSIONS: Recognition of erythema migrans and its variants is important, since early treatment of Lyme disease may prevent late complications. Vesicular erythema migrans should be added to the differential diagnosis of inflammatory vesicular rashes in the appropriate clinical setting.

Adolescent

Epidemiology, clinical features, and diagnosis of Lyme disease.

Lyme disease is the most common vector-borne disease in the United States. Epidemiologic research has contributed to a better understanding of the factors involved in the geographic spread and increased incidence of the disease. Clinical features of Lyme disease, including skin, joint, cardiac, and neurologic involvement, are discussed here, along with recent studies that better characterize these clinical manifestations and more clearly define their immunopathogenesis. The diagnosis of Lyme disease is based on the clinical presentation. Laboratory testing may be helpful but has significant limitations, which we discuss in our review.

Humans

Aedes aegypti in Puerto Rico: environmental determinants of larval abundance and relation to dengue virus transmission.

In order to understand adquately the dynamics of vector-borne disease, one must understand how and why vector populations change over time. We describe a long-term, cooperative study of seasonal fluctuation in populations of the Aedes aegypti mosquito in Puerto Rico. During each month of the first 3 years of the project, A. aegypti was found breeding in all five communities studied. Mosquito density was positively correlated with rainfall, the relationship being more marked in the dry, south-coastal part of the island. Discarded tires and animal watering pans were the two most common larval breeding sites. In general, houses in Puerto Rico harbor more potential A. aegypti breeding sites than those in other tropical locations, probably because Puerto Rico is relatively more affluent.

Aedes

Identifying genomic surveillance gaps in Africa for the global public health response to West Nile virus: a systematic review.

West Nile virus (WNV) is a priority pathogen that poses a high risk for public health emergencies of global concern. Although WNV is endemic to Africa, only few (n=63) whole genomic sequences are available from the continent. In this Review, we examined the status of the molecular testing and genomic sequencing of WNV across Africa and mapped its global spatiotemporal spread. WNV has been detected in 39 African countries, the Canary Islands, and Réunion Island. Although publications, including those with molecular data, originated from 24 of these countries, genomic sequences were available from only 16 countries. Our analysis identified regions with detected viral circulation but without molecular surveillance. The current literature has substantial knowledge gaps in terms of the disease burden, molecular epidemiology, and distribution of WNV in Africa. Addressing these gaps requires an integrated One Health surveillance approach, which is challenging to establish. We propose three key surveillance needs that could improve the current understanding of the WNV disease burden in Africa, to strengthen the global public health response to this vector-borne disease.

West Nile Fever

Genomic profiling of digestion related enzymes in Anopheles aquasalis a major coastal neotropical malaria vector.

Digestive genes are fundamental for the development and survival of mosquitoes and can serve as a target for the development of strategies for mosquito control or vector-borne disease prevention. Genes related to digestion were identified in the genome of the neotropical malaria vector Anopheles aquasalis by similarity. We used reciprocal BLAST with annotated digestion proteins for Anopheles gambiae. Orthology and evolutionary analyses were performed using MEGA with a bootstrapped phylogenetic tree constructed by the neighbor-joining method, and copy number variation was measured by the standard deviation of the average copy number in each gene family. We identified 241 genes related to digestion in An. aquasalis: 56 genes related to carbohydrate digestion, 51 genes for lipid digestion, and 134 genes for protein digestion. Phylogenetic relationships with other anophelines show that An. aquasalis genes are closely related to those of neotropical mosquitoes Anopheles darlingi and Anopheles albimanus. Orthologous gene clusters are conserved in important families of all four species. Some of these conserved genes are of interest for studies on controlling mosquito vectors, such as larvicidal toxin receptor genes, alpha-amylase, alpha-glucosidase, and maltase; important target genes for transmission-blocking vaccines, such as aminopeptidase N1 and carboxypeptidase B; and the major intestinal serine proteases, such as trypsins and chymotrypsins, which can positively or negatively affect Plasmodium development in the midgut. These data provide a better understanding of digestion-related genes in American anopheline mosquitoes and may support further fundamental and applied studies aimed at malaria control.

Animals

Scalable, open-access and multidisciplinary data integration pipeline for climate-sensitive diseases.

Climate-sensitive infectious diseases pose an important challenge for human, animal and environmental health and it has been estimated that over half of known human pathogenic diseases can be aggravated by climate change. While climatic and weather conditions are important drivers of transmission of vector-borne diseases, socio-economic, behavioural, and land-use factors as well as the interactions among them impact transmission dynamics. Analysis of drivers of climate-sensitive diseases require rapid integration of interdisciplinary data to be jointly analysed with epidemiological (including genomic and clinical) data. Current tools for the integration of multiple data sources are often limited to one data type or rely on proprietary data and software. To address this gap, we develop a scalable and open-access pipeline for the integration of multiple spatio-temporal datasets that requires only the declaration of the country and temporal range and resolution of the study. The tool is locally deployable and can easily be integrated into existing climate-disease-modelling applications. We demonstrate the utility of the tool for dengue modelling in Vietnam where epidemiological data are legally required to remain local. We include a pipeline for bias correction of climate data to enhance their quality for downstream modelling tasks. The Dengue Advanced Readiness Tools-Pipeline empowers users by simplifying complex download, correction, and aggregation steps, fostering data-driven discovery of relationships between infectious diseases and their drivers in space and time, and enhancing reproducibility in research. Additional modules and datasets can be added to the existing ones to make the pipeline extendable to use cases other than the ones presented here.

automated workflows

Detection of human antibodies against Plasmodium falciparum antigens in blood meals of anopheline mosquitoes.

Human IgG antibodies against Plasmodium falciparum asexual stages, gametocytes and sporozoites were detected by indirect fluorescent antibody (IFA) techniques in the blood meals of Anopheles gambiae s.l. from a malaria-endemic area of western Kenya. Field-collected mosquitoes, which had been stored dry for over 2 years, were screened first for human IgG by ELISA. In 141 blood meal samples from human-fed mosquitoes, the prevalence of stage-specific antibodies was 87.9% for asexual-stage parasites, 78.0% for gametocytes, and 87.9% for sporozoites. There were no differences in the prevalence of stage-specific antibodies for mosquitoes collected from 2 sites, before and after the long rainy season of 1988. The detection of specific human antibodies in mosquito blood meals by IFA, or by more efficient methods, may provide alternative approaches for large-scale, epidemiologic studies of malaria and other vector-borne diseases.

Animals

The predisposing and protective factors against dengue virus transmission by mosquito vector.

An outbreak of dengue fever occurred in Taiwan between 1987 and 1988. The highest attack rate among adults was estimated at 5.6% in the city of Kao-hsiung. A case-control study was carried out to determine the risks of contracting dengue infection and to identify protective factors against the infection. One hundred dengue patients of the authors' hospital who were diagnosed by virologic or serologic tests constituted the case group. Each dengue patient was matched to a control patient of the same age and sex who had been diagnosed as suffering from a non-vector-borne disease on the same day as the dengue patient. Of the household protective measures against dengue infection prior to the occurrence of illness, the adjusted odds ratio, estimated by stratified analysis, was lower for people who lived in screened houses (odds ratio = 0.58, 95% confidence interval 0.36-0.92) as compared with inhabitants of unscreened houses. The odds ratio was as low as 0.18 (95% confidence interval 0.06-0.56) for people whose homes were fully screened with door screens opening outwardly. Patients who lived near markets and/or open sewers or ditches were running a risk of dengue infection 1.8 (95% confidence interval 1.3-2.4) times higher than those who lived elsewhere. To control dengue outbreaks, the authors recommend that special attention should be devoted to the reduction of outdoor vector sources. Full screening, especially outwardly opening screen doors, seems to be an individual's best protection against dengue fever.

Adolescent

Parasitic arthropods of sympatric meadow voles and white-footed mice at Fort Detrick, Maryland.

Twelve species of parasitic arthropods (one sucking louse, two fleas, one tick, and eight mites) were recovered from 51 meadow voles, Microtus pennsylvanicus (Ord); whereas nine species (one sucking louse, one bot, three fleas, one tick, and three mites) were collected from 48 white-footed mice, Peromyscus leucopus (Rafinesque), live-trapped on the grounds of Fort Detrick, Frederick County, MD., during 1990 and 1991. The most commonly collected arthropods from M. pennsylvanicus were the fur mite, Listrophorus mexicanus Fain (approximately 2,720 specimens); the tropical rat mite, Ornithonyssus bacoti (Hirst) (987); the laelapid mites, Laelaps kochi Oudemans (733) and Androlaelaps fahrenholzi (Berlese (322); the sucking louse, Hoplopleura acanthopus (Burmeister) (121); the tick, Dermacentor variabilis (Say) (47); and the chigger mite, Neotrombicula whartoni (Ewing) (45). Arthropod densities were lower on P. leucopus, from which the most frequently recorded species were the sucking louse, Hoplopleura hesperomydis (Osborn) (98 specimens); the fleas, Epitedia wenmanni (Rothschild) (85) and Orchopeas leucopus (Baker) (61); and the mite, A. fahrenholzi (83). Although six species of arthropods parasitized both species of rodents, only two of these, A. fahrenholzi and D. variabilis, were relatively common on both hosts. Therefore, although the habitats of both host species partially overlap, their associated parasitic arthropods remain principally host specific. The potential significance of these findings with respect to vector-borne disease transmission is discussed.

Animals

Host selection patterns of some Pakistan mosquitoes.

The host selection patterns of 18 species of Pakistan mosquitoes are described, emphasizing the presumed malaria vectors, Anopheles culicifacies, An. fluviatilis, and An. stephensi, and the probable vectors of West Nile virus, Culex pipiens fatigans and Cx. tritaeniorhynchus. All species tested, with the exception of Cx, p. fatigans, were considered to be essentially zoophilic. Few human feeds were recorded for An. annularis (0.7%), An. culicifacies (0.5%), An. fluviatilis (1.1%), An. nigerrimus (14.3%), and Cx. bitaeniorhynchus (2.8%), while Cx. p. fatigans (37.6%) commonly fed on man. No human positive feeds were recorded for An. stephensi. Temporal or spatial changes in host selection patterns were not discerned with the exception of Cx. p. fatigans, whose feeding patterns varied opportunistically with host availability. Cx. p. fatigans females collected from houses fed more commonly on man than those resting in cattle sheds or in agricultural fields. Cx. p. fatigans resting in cattle sheds during winter fed mostly on birds and bovids, changing to man and bovids during the spring and then to man and birds during summer. The relationships between these results and vector-borne disease transmission in Pakistan are discussed.

Animals

Impact of control measures on malaria transmission and general mortality.

This paper is an attempt to relate modifications observed in general and infant mortality rates with the dynamic changes in transmission induced by malaria control measures. The observations indicated relationships between the efficacy of control and a decrease in mortality. The daily parasitological inoculation rate was reduced from 0.00958 infective bites per individual before treatment to 0.00037 after treatment (a decrease of 96%). In two years, general mortality decreased from 23.9 to 13.5 deaths per 1000 population and infant mortality decreased from 157 to 93 per 1000 live births. This indirect benefit of malaria control deserves attention in a wider assessment of measures directed against vector-borne diseases.

Adult

Adopting the primary health care approach in malaria control in Malaysia: lessons in community participation.

The Primary Health Care approach in Malaysia was first tried out in Sarawak, East Malaysia in 1982. In 1984, the Vector Borne Disease Control Program, Kelantan decided to adopt the Primary Health Care approach as an additional strategy in its effort to control malaria in the state, which then experienced an increase in malaria cases. Much effort was directed at creating the awareness and stimulating the interest of health staff and communities to adopt the strategy. Kelantan was made the model state. The paper gives an outline of the process involved and some characteristics of PHC workers. A study was carried out among health workers, community members and health staff on their knowledge and involvement in PHC in three states, including Kelantan. In view of the overall success of this approach, and the weaknesses which have been identified possible solutions have been suggested and should be acted upon.

Communicable Disease Control

Field study of the relationship between skin-sensitizing antibody production in the cottontail rabbit, Sylvilagus floridanus, and infestation by the rabbit tick, Haemaphysalis leporispalustris (Acri: Ixodidae).

The resistance of cottontail rabbits to tick feeding appears correlated with the rabbits' development of skin-sensitizing antibodies. Resistance appeared to be greatest in adult rabbits which had been repeatedly infested with ticks. Rabbits with little exposure to ticks, usually the young cottontails, showed little or no skin-sensitizing antibody present in their blood and usually had relatively high tick loads when compared with adult rabbits. Models used to interpret the data show promise as tools for predicting tick population fluctuations and, perhaps, incidence of vector borne disease outbreaks. The existence of resistance to tick attachment has important implications for the host-parasite relationship. The research lends support to the hypothesis that the resistance may function as a homeostatic regulatory mechanism capable of maintaining the size of the tick population in equilibrium with the size of the rabbit population. In this way, host resistance may be advantageous to the parasite as well as to the host.

Animals