Applications of remote sensing to the identification of the habitats of parasites and disease vectors

Distribution of Phlebotomus argentipes Annandale & Brunetti, 1908 in the Anuradhapura district, North Central Sri Lanka

Background & objectives

Phlebotomus argentipes Annandale & Brunetti, 1908 (Diptera: Psychodidae) is the main vector responsible for the transmission of Leishmania donovani (Laveran & Mesnil, 1903) Ross, 1903 in the subcontinent of India. It is the potential vector of cutaneous leishmaniasis in Sri Lanka. The present study determined ecological factors that influence the abundance of P. argentipes in areas with high disease prevalence in the Anuradhapura district, North Central Sri Lanka.

Methods

CDC light traps and yellow sticky traps were used for sampling, and abundance was recorded throughout 12 months with selected environmental parameters namely, relative humidity, wind speed, and temperature. The relationships between the abundance of P. argentipes with mean temperature, % relative humidity, and wind speed were tested with regression analysis. The temporal distribution of the vector population was tested with a time series analysis.

Results

The study identified the most preferable microhabitats of P. argentipes: shrubs, unclear areas, gardening areas, wet soil areas with leaf litter, and termite hills. The results indicated that the abundance of P. argentipes was highly dependent on mean temperature (P = 0.00, R2 = 68%), and a high number of P. argentipes was recorded for a low mean temperature range of 24.7-27.3°C. Furthermore, the abundance of P. argentipes exhibited an increasing trend with high humidity levels of 72-88% (P = 0.00, R2 = 91.6%).

Interpretation & conclusion

These findings may help predict the temporal variation of the potential vector population with studied ecological parameters and contribute to a successful vector management strategy with thorough knowledge of the behavioral pattern of P. argentipes.

Ecology and natural infection of phlebotomine sand flies in different ecotopes and environments in the municipality of Pains, Minas Gerais, Brazil

Phlebotomines (Diptera: Psychodidae) are vectors of protozoa of the genus Leishmania and distributed throughout Brazil, formerly restricted to rural areas, have expanded including to periurban and urban regions, been recorded in different habitats. This study aimed to understand the dynamics of sand flies in different ecotopes in the municipality of Pains. Sand flies were captured during thirty samplings using HP light traps installed in seven different ecotopes for two consecutive nights, once a month, from August 2018 to July 2019. A total of 1,352 sand flies were captured, representing 24 species belong to ten genera. Evandromyia edwardsi was the most abundant species, followed by Evandromyia lenti and Micropygomyia quinquefer. Leishmania DNA was detected in seven female sand flies in four ecotopes, for an infection rate of 0.9%. Sand flies were collected in all seven ecotopes, although forest (23.04%), cave (20.88%) and pasture (17.75%) had higher abundance and richness. Similarity was found among ecotopes, indicating that they are all important for the maintenance of the sand fly community. Spatial analysis indicated high densities of sand flies in areas with natural characteristics. All ecotopes in the municipality were evidenced to have an adequate and harmonious epidemiological profile for the transmission and expansion of leishmaniasis throughout the territory. Because of the increasing environmental changes and deforestation in the municipality, the risk of generating ecological imbalance and increased cases of leishmaniasis is imminent, which highlights the importance of developing preventive and control strategies.

Rapid identification of shallow inundation for mosquito disease mitigation using drone-derived multispectral imagery

Mosquito breeding habitat identification often relies on slow, labour-intensive and expensive ground surveys. With advances in remote sensing and autonomous flight technologies, we endeavoured to accelerate this detection by assessing the effectiveness of a drone multispectral imaging system to determine areas of shallow inundation in an intertidal saltmarsh in South Australia. Through laboratory experiments, we characterised Near-Infrared (NIR) reflectance responses to water depth and vegetation cover, and established a reflectance threshold for mapping water sufficiently deep for potential mosquito breeding. We then applied this threshold to field-acquired drone imagery and used simultaneous in-situ observations to assess its mapping accuracy. A NIR reflectance threshold of 0.2 combined with a vegetation mask derived from Normalised Difference Vegetation Index (NDVI) resulted in a mapping accuracy of 80.3% with a Cohen's Kappa of 0.5, with confusion between vegetation and shallow water depths (< 10 cm) appearing to be major causes of error. This high degree of mapping accuracy was achieved with affordable drone equipment, and commercially available sensors and Geographic Information Systems (GIS) software, demonstrating the efficiency of such an approach to identify shallow inundation likely to be suitable for mosquito breeding.

Applications of Space Technologies to Global Health: Scoping Review

Background

Space technology has an impact on many domains of activity on earth, including in the field of global health. With the recent adoption of the United Nations’ Sustainable Development Goals that highlight the need for strengthening partnerships in different domains, it is useful to better characterize the relationship between space technology and global health.

Objective

The aim of this study was to identify the applications of space technologies to global health, the key stakeholders in the field, as well as gaps and challenges.

Methods

We used a scoping review methodology, including a literature review and the involvement of stakeholders, via a brief self-administered, open-response questionnaire. A distinct search on several search engines was conducted for each of the four key technological domains that were previously identified by the UN Office for Outer Space Affairs’ Expert Group on Space and Global Health (Domain A: remote sensing; Domain B: global navigation satellite systems; Domain C: satellite communication; and Domain D: human space flight). Themes in which space technologies are of benefit to global health were extracted. Key stakeholders, as well as gaps, challenges, and perspectives were identified.

Results

A total of 222 sources were included for Domain A, 82 sources for Domain B, 144 sources for Domain C, and 31 sources for Domain D. A total of 3 questionnaires out of 16 sent were answered. Global navigation satellite systems and geographic information systems are used for the study and forecasting of communicable and noncommunicable diseases; satellite communication and global navigation satellite systems for disaster response; satellite communication for telemedicine and tele-education; and global navigation satellite systems for autonomy improvement, access to health care, as well as for safe and efficient transportation. Various health research and technologies developed for inhabited space flights have been adapted for terrestrial use.

Conclusions

Although numerous examples of space technology applications to global health exist, improved awareness, training, and collaboration of the research community is needed.

Uso e cobertura do solo e prevalência de leishmaniose visceral canina em Teresina, Piauí, Brasil: uma abordagem utilizando sensoriamento remoto orbital

Resumo: Este estudo examina a associação entre uso e cobertura do solo e a ocorrência de leishmaniose visceral (LV) canina. Estudo caso-controle em que casos foram residências com cães soropositivos para LV canina e controles, as residências com cães soronegativos. Utilizaram-se imagens de sensoriamento remoto (CBERS: 2/CCD e 2B/HRC) para descrever o uso e cobertura do solo em quadrículas de 625m2 na região do estudo. A chance da LV canina foi duas vezes maior em domicílios localizados em quadrículas com área ≤ 25m2 coberta por estruturas residenciais com pouca vegetação em comparação com aquelas em que essa cobertura alcançou ≥ 600m2. Domicílios localizados em quadrículas com até metade da área coberta por estruturas residenciais com muita vegetação tiveram chances 65% menores de LV canina em comparação com aquelas situadas em áreas quase totalmente cobertas por essa característica. Como a infecção canina costuma preceder a ocorrência de casos humanos, a identificação de características de uso e cobertura do solo associadas à LV canina pode contribuir para a delimitação de áreas de risco para LV humana.

Spatial relations among environmental factors and phlebotomine sand fly populations (Diptera: Psychodidae) in central and southern Morocco

Phlebotomine sand flies (Diptera: Psychodidae, Phlebotominae) are of considerable public health importance because of their ability to transmit several human parasites, mainly as vectors of Leishmania spp. Over the past decade, the epidemiological situation of cutaneous leishmaniasis (CL) has significantly increased with its geographic expansion to previously free areas and the emergence of overlapping foci of cutaneous leishmaniasis and visceral leishmaniasis (VL) in several provinces of Morocco. A total of 15,313 specimens was collected during this entomological survey. The genera Phlebotomus (57.38%) and Sergentomyia (42.62%) were identified. Sergentomyia minuta (22.01%) was the most prevalent species, followed by S. fallax (18.21%), Phlebotomus perniciosus (14.35%), P. papatasi (14.06%), P. sergenti (12.85%), P. longicuspis (10.74%), P. ariasi (2.68%), S. dreyfussi (1.53%), P. alexandri (1.31%), P. bergeroti (1.14%), S. christophersi (0.62%), S. africana (0.25%), P. chabaudi (0.14%), P. chadlii (0.05%), and P. kazeruni (0.04%). We aimed to determine current distribution of leishmaniases vectors, their ecological characteristics, and the significance of the predominant species at any bioclimate stage, altitude range, and soil texture in terms of the risk of leishmaniasis transmission.

[Object-oriented remote sensing image classification in epidemiological studies of visceral leishmaniasis in urban areas]

This study explored the use of object-oriented classification of remote sensing imagery in epidemiological studies of visceral leishmaniasis (VL) in urban areas. To obtain temperature and environmental information, an object-oriented classification approach was applied to Landsat 5 TM scenes from the city of Teresina, Piauí State, Brazil. For 1993-1996, VL incidence rates correlated positively with census tracts covered by dense vegetation, grass/pasture, and bare soil and negatively with areas covered by water and densely populated areas. In 2001-2006, positive correlations were found with dense vegetation, grass/pasture, bare soil, and densely populated areas and negative correlations with occupied urban areas with some vegetation. Land surface temperature correlated negatively with VL incidence in both periods. Object-oriented classification can be useful to characterize landscape features associated with VL in urban areas and to help identify risk areas in order to prioritize interventions.

Re-examining environmental correlates of Plasmodium falciparum malaria endemicity: a data-intensive variable selection approach

Background

Malaria risk maps play an increasingly important role in disease control planning, implementation, and evaluation. The construction of these maps using modern geospatial techniques relies on covariate grids: continuous surfaces quantifying environmental factors that partially explain spatial heterogeneity in malaria endemicity. Although crucial, past variable selection processes for this purpose have often been subjective and ad-hoc, with many covariates used in modeling with little quantitative justification.

Methods

This research consists of an extensive covariate construction and selection process for predicting Plasmodium falciparum parasite rates (PfPR) in Africa for years 2000-2012. First, a literature review was conducted to establish a comprehensive list of covariates used for malaria mapping. Second, a library of covariate data was assembled to reflect this list, a process that included the construction of multiple, temporally dynamic datasets. Third, the resulting set of covariates was leveraged to create more than 50 million possible covariate terms via factorial combinations of different spatial and temporal aggregations, transformations, and pairwise interactions. Fourth, the expanded set of covariates was reduced via successive selection criteria to yield a robust covariate subset that was assessed using an out-of-sample validation approach.

Results

The final covariate subset included predominately dynamic covariates and it substantially out-performed earlier sets used by the Malaria Atlas Project (MAP) for creating global malaria risk maps, with the pseudo-R² value for the out-of-sample validation increasing from 0.43 to 0.52. Dynamic covariates improved the model, with 17 of the 20 new covariates consisting of monthly or annual products, but the selected covariates were typically interaction terms that included both dynamic and synoptic datasets. Thus the interplay between normal (i.e., long-term averages) and immediate conditions may be key for characterizing environmental controls on parasite rate.

Conclusions

This analysis represents the first effort to systematically audit covariate utility for malaria mapping and then derive an objective, empirically based set of environmental covariates for modeling PfPR. The new covariates produce more reliable representations of malaria risk patterns and how they are changing through time, and these covariates will be used to characterize spatially and temporally varying environmental conditions affecting PfPR within a geostatistical-modeling framework, thus building upon previous research by MAP that produced global malaria maps for 2007 and 2010.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-015-0574-x) contains supplementary material, which is available to authorized users.

From predicting mosquito habitat to malaria seasons using remotely sensed data: practice, problems and perspectives

Remote sensing techniques are becoming increasingly important for identifying mosquito habitats, investigating malaria epidemiology and assisting malaria control. Here, Simon Hay, Bob Snow and David Rogers review the development of these techniques, from aerial photographic identification of mosquito larval habitats on the local scale through to the space-based survey of malaria risk over continental areas using increasingly sophisticated airborne and satellite-sensor technology. They indicate that previous constraints to uptake are becoming less relevant and suggest how future delays in the use of remotely sensed data in malaria control might be avoided.

Climate, niche, ticks, and models: what they are and how we should interpret them

Ticks spend most of their life cycle in the environment, and all tick life cycle stages are dependent on a complex combination of climate variables. Furthermore, host availability and vegetation significantly modulate the dynamics of tick populations. Tick recruitment is dependent on successful reproduction, which in turn requires sufficient adult tick densities, available blood meal sources, and egg survival. Though many animals can serve as hosts, there are several determinants of host suitability. For example, host availability in time and space is an important determinant of tick bionomics. Shelter and protection from environmental extremes are critical to tick survival. Questing and diapausing ticks are vulnerable to extremes of temperature and humidity. There are concerns about how predicted climate change may alter several critical features of host-parasite relationships of ticks, the potential for invasion of new areas or alteration of patterns of pathogen transmission in particular. However, modeling approaches that relate known occurrences of tick species to climate (and/or landscape) features and predict geographic occurrences are not completely fulfilling our needs to understand how the "tick panorama" can change as a consequence of these climate trends. This is a short review about the concept of ecological niche as applied to ticks, as well as some raised concerns about its evaluation and strict definition, and its usefulness to map geographical suitability for ticks. Comments about how climate, hosts, and landscape configuration are briefly discussed regarding its applicability to tick mapping and with reference about their impact on tick abundance. I will further comment on already published observations about observed changes in the geographical range of ticks in parts of Europe.

Seroprevalence of malaria in inhabitants of the urban zone of Antananarivo, Madagascar

Background

Antananarivo, the capital of Madagascar, is located at an altitude of over 1,200 m. The environment at this altitude is not particularly favourable to malaria transmission, but malaria nonetheless remains a major public health problem. The aim of this study was to evaluate exposure to malaria in the urban population of Antananarivo, by measuring the specific seroprevalence of Plasmodium falciparum.

Methods

Serological studies specific for P. falciparum were carried out with an indirect fluorescent antibody test (IFAT). In a representative population of Antananarivo, 1,059 healthy volunteers were interviewed and serum samples were taken.

Results

The seroprevalence of IgG+IgA+IgM was 56.1% and that of IgM was 5.9%. The major risk factor associated with a positive IgG+IgA+IgM IFAT was travel outside Antananarivo, whether in the central highlands or on the coast. The abundance of rice fields in certain urban districts was not associated with a higher seroprevalence.

Conclusion

Malaria transmission levels are low in Antananarivo, but seroprevalence is high. Humans come into contact with the parasite primarily when travelling outside the city. Further studies are required to identify indigenous risk factors and intra-city variations more clearly.

GIS tools for tick and tick-borne disease occurrence

Geographic information systems (GIS), their fundamental components and technologies are described. GIS is a computer-based system enabling the storage, integration, query, display and analysis of data using information on data location. Further, remote sensing (RS) methods and their application in landscape characterization are described. Landscape pattern analysis, combined with statistical analysis, allows the determination of landscape predictors of disease risk. This makes RS/GIS a powerful set of tools for disease surveillance, enabling the prediction of potential disease outbreaks and targeting intervention programs. The 'pre-GIS era' is briefly described including the early mapping of tick distribution, analyses and the display of biogeographical and medical data. The theory of natural focality of diseases (NFD) is explained and its significance in tick-borne diseases (TBD) research is discussed. Many problems of tick ecology and TBD epidemiology and epizootology have been addressed by means of GIS and examples of these studies are presented and discussed.

[Use of remote sensing to study the influence of environmental changes on malaria distribution in the Brazilian Amazon]

Construction of the Tucuruí hydroelectric dam in Southeast Pará State, Brazil, in 1981, caused enormous environmental changes, deforestation, and human migration to the region. This study focuses on the influence of these changes and the appearance of malaria in the municipality of Jacundá, Pará, using remote sensing and geographic information systems. The variables used to construct maps were distances from roads, farming areas, rivers, the dam, streams, and the urban area. This study confirmed the elevation of malaria to the epidemic level since the construction of the Tucuruí dam. The study suggests that a seasonal pattern of malaria incidence is associated with the flooding season and exposure of workers during harvest. Malaria cases were related to the form of land occupation, especially in more densely populated areas.

[Spacial modeling of cutaneous leishmaniasis risk zones]

OBJECTIVE

To spatially delimit cutaneous leishmaniasis (CL) human contact risk zones (CoRZ) using remote sensing and geoprocessing techniques.

METHODS

A total of 27 CL cases reported from 1992 to 1997 in the municipality Itapira, Brazil, were studied. The influence of some important environmental variables related to CL such as altitude and vegetation density measured by normalized difference vegetation index (NDVI) images were analyzed for each CoRZ.

RESULTS

The results showed that about 50% of the dwellings where CL cases were reported were located less than 200 meters from the limits of forest remnant area; more than 70% of the total area of the CoRZ, for each criterion, were in altitudes lower than 750 meters; and about 50% of the CoRZ, for each criterion, were located in a very dense green area (NDVI ranging from 0.45 to 1.00).

CONCLUSIONS

The study shows there may be three transmission modes in the study area: intra-forest, extra-forest (in this setting, transmission might be influenced by the vegetation density surrounding forest remnants); or domiciliary.

Remote sensing as a tool to survey endemic diseases in Brazil

The objective of this study, based on a systematic literature review, is to present the characteristics and potentialities of remote sensing as a useful environmental surveillance tool for applied research in the control of endemics in Brazil. Onboard satellite sensors allow for monitoring the territory, furnishing spatial and temporal information on various scales and regions in the electromagnetic spectrum. Based on the literature review on the application of this technology to the study of endemics and the identification of the potential of new sensors with better spectral, spatial, and temporal resolutions, this study highlights perspectives for the use of remote sensing in the study of important endemics for Brazil.

[Chagas Disease Control Program in the State of São Paulo: persistence of high triatomine infestation rates in some localities during the 1990s]

The purpose of our investigation was to analyze the persistence, in the State of São Paulo, of domiciliary units highly infested with Chagas disease triatomine vectors. Comprehensive epidemiologic information collected from 1990 to 1999 in the State of S o Paulo was retrieved from database files. Consistently high infestation rates were found in 43 localities distributed among 21 municipalities in the Ara atuba region. Captures produced predominantly peridomiciliary Triatoma sordida specimens, mostly adult females and fifth-instar nymphs, 94.6% of which containing ingesta negative for human blood. The houses, mostly inhabited (87.4%), were located near the residual woodland savanna in 64.3% of the localities. Poultry coops were found in association with 97.6% of all domiciliary units. Interestingly, in all the houses with persistent infestation, the inhabitants paid no evident attention to hygiene Lack of timely infestation control associated with the biological characteristics of the reduviid species involved, along with the conditions prevailing around the dwellings, favor the repeated invasion and consequent maintenance of colonization by triatomines.

Forecasting habitat suitability for ticks and prevention of tick-borne diseases

Climate and vegetation are the major factors affecting the distribution of ticks. Consequently, spatial distributions can be analysed by statistical methods that look for correlations between abiotic factors and known data about tick presence/absence. Remote sensing features can be obtained from a wide database of sensors with different characteristics, then applied to the problem of mapping prediction of tick distribution. Some studies had demonstrated that the use of these abiotic variables from satellite imagery has biological significance, therefore statistical accuracy of these distribution models can be interpreted under an ecological framework. Furthermore, models can be linked to these predictive maps, enabling the forecast of spatial and temporal dynamics of ticks, looking for seasonal patterns of activity and accurate use of acaricide treatments.

Application of geographic information systems and remote sensing to schistosomiasis control in China

Progress in China on developing prediction models using remote sensing, geographic information systems and climate data with historical infection prevalence and malacology databases is reviewed. Special reference is made to the effects of the Yangtze river Three Gorges dam project on environmental changes that may impact changes in the spatial and temporal distribution and abundance of Schistosoma japonicum in China, and the future success of disease control programs.

Linking remote sensing, land cover and disease

Land cover is a critical variable in epidemiology and can be characterized remotely. A framework is used to describe both the links between land cover and radiation recorded in a remotely sensed image, and the links between land cover and the disease carried by vectors. The framework is then used to explore the issues involved when moving from remotely sensed imagery to land cover and then to vector density/disease risk. This exploration highlights the role of land cover; the need to develop a sound knowledge of each link in the predictive sequence; the problematic mismatch between the spatial units of the remotely sensed and epidemiological data and the challenges and opportunities posed by adding a temporal mismatch between the remotely sensed and epidemiological data. The paper concludes with a call for both greater understanding of the physical components of the proposed framework and the utilization of optimized statistical tools as prerequisites to progress in this field.

Spatial statistics and geographical information systems in epidemiology and public health

This chapter surveys the principles behind spatial statistics and geographic information systems (GIS), and their application to epidemiology and public health. Like the other introductory chapters, it is aimed mainly to facilitate understanding in the chapters specific to certain diseases that follow, and to provide a short introduction to the field. A brief overview of spatial statistics and GIS is provided in the introduction. The sections that follow explore the ways in which we can map the distribution of disease, ways in which we can look for spatial patterns in the distribution of disease, and ways in which we can apply spatial statistics and GIS to the problem of identifying the causal factors of observed patterns. In the last section I discuss some of the ways in which these techniques have been applied to assist decision making for disease intervention, and conclude by discussing future developments in the field, and some of the issues surrounding the integration of spatial statistics and GIS.

Education, outreach and the future of remote sensing in human health

The human health community has been slow to adopt remote sensing technology for research, surveillance, or control activities. This chapter presents a brief history of the National Aeronautics and Space Administration's experiences in the use of remotely sensed data for health applications, and explores some of the obstacles, both real and perceived, that have slowed the transfer of this technology to the health community. These obstacles include the lack of awareness, which must be overcome through outreach and proper training in remote sensing, and inadequate spatial, spectral and temporal data resolutions, which are being addressed as new sensor systems are launched and currently overlooked (and underutilized) sensors are newly discovered by the health community. A basic training outline is presented, along with general considerations for selecting training candidates. The chapter concludes with a brief discussion of some current and future sensors that show promise for health applications.

Assessing infestation risk by vectors. Spatial and temporal distribution of African ticks at the scale of a landscape

Control of major livestock diseases in the tropics, such as theileriosis or trypanosomosis, is still largely based on the control of their vectors. Understanding the distribution of vectors, such as ticks and tsetse flies, is needed in order to improve the efficiency and economical viability of control operations. Technical improvements such as remote sensing and global information systems have allowed valuable improvements for the prediction of large-scale vector distribution (continental to national), but trying to make these predictions at the scale of a landscape is facing other challenges. At this scale, an analysis of host/vector interactions with an evolutionary point of view is useful. A study was undertaken on a mixed game/cattle ranch in Zimbabwe during which we monitored variations in the abundance and spatial distribution of the immature free stages of Rhipicephalus appendiculatus/R. zambeziensis and R. e. evertsi, two major groups of tick species in Southern Africa. We found two contrasting distributions in relation to contact between tick larvae. The ungulate-host R. e. evertsi appeared to be unpredictable, whereas R. appendiculatus/R. zambeziensis were predictable in time and space, but associated with key-resources for ungulates (water and forage resources). The consequences of such distributions are discussed in terms of vector control.

Remote sensing and geographic information systems: charting Sin Nombre virus infections in deer mice

We tested environmental data from remote sensing and geographic information system maps as indicators of Sin Nombre virus (SNV) infections in deer mouse (Peromyscus maniculatus) populations in the Walker River Basin, Nevada and California. We determined by serologic testing the presence of SNV infections in deer mice from 144 field sites. We used remote sensing and geographic information systems data to characterize the vegetation type and density, elevation, slope, and hydrologic features of each site. The data retroactively predicted infection status of deer mice with up to 80% accuracy. If models of SNV temporal dynamics can be integrated with baseline spatial models, human risk for infection may be assessed with reasonable accuracy.

Earth observation, geographic information systems and Plasmodium falciparum malaria in sub-Saharan Africa

This review highlights the progress and current status of remote sensing (RS) and geographical information systems (GIS) as currently applied to the problem of Plasmodium falciparum malaria in sub-Saharan Africa (SSA). The burden of P. falciparum malaria in SSA is first summarized and then contrasted with the paucity of accurate and recent information on the nature and extent of the disease. This provides perspective on both the global importance of the pathogen and the potential for contribution of RS and GIS techniques. The ecology of P. falciparum malaria and its major anopheline vectors in SSA in then outlined, to provide the epidemiological background for considering disease transmission processes and their environmental correlates. Because RS and GIS are recent techniques in epidemiology, all mosquito-borne diseases are considered in this review in order to convey the range of ideas, insights and innovation provided. To conclude, the impact of these initial studies is assessed and suggestions provided on how these advances could be best used for malaria control in an appropriate and sustainable manner, with key areas for future research highlighted.

Population dynamics of Aedes albifasciatus (Diptera: Culicidae) south of Mar Chiquita Lake, central Argentina

Spatial and temporal changes in the abundance of adult female Aedes (Ochlerotatus) albifasciatus (Macquart) were studied using CDC miniature light traps at 7 sites along an 80-km transect parallel to the southern shore of Mar Chiquita Lake (central Argentina) during the rainy seasons between 1994 and 1997. Abundance was greatest and most variable at sites near larval habitats. Rainfall and an index combining rainfall and temperature predicted adult female abundance near larval habitats 7-15 d in advance. The spatial distribution of population abundance seemed to be influenced strongly by local factors, because temporal change at sampling sites located >10 km apart was asynchronous.

Epidemiological uses of a population model for the tick Rhipicephalus appendiculatus

The spatial and temporal risk of tick-borne disease depends fundamentally on the distribution, abundance and seasonal dynamics of the vector ticks. The latter factor exerts a major quantitative influence on the transmission dynamics of tick-borne parasites. The population model for Rhipicephalus appendiculatus applies throughout the range of this tick in eastern Africa, and predicts all three fundamental risk factors on the basis of the local temperature and rainfall conditions. Satellite imagery can provide more detailed, real-time measures of environmental conditions over extensive areas than climatic data. There is preliminary evidence to suggest that the population model could be driven by satellite-derived surrogates of its climatic predictors, thus providing wide-scale predictive risk maps of theileriosis.

Geostatistics and remote sensing using NOAA-AVHRR satellite imagery as predictive tools in tick distribution and habitat suitability estimations for Boophilus microplus (Acari: Ixodidae) in South America. National Oceanographic and Atmosphere Administration-Advanced Very High Resolution Radiometer

Remote sensing based on NOAA (National Oceanographic and Atmosphere Administration) satellite imagery was used, together with geostatistics (cokriging) to model the correlation between the temperature and vegetation variables and the distribution of the cattle tick, Boophilus microplus (Canestrini), in the Neotropical region. The results were used to map the B. microplus habitat suitability on a continental scale. A database of B. microplus capture localities was used, which was tabulated with the AVHRR (Advanced Very High Resolution Radiometer) images from the NOAA satellite series. They were obtained at 10 days intervals between 1983 and 1994, with an 8 km resolution. A cokriging system was generated to extrapolate the results. The data for habitat suitability obtained through two vegetation and four temperature variables were strongly correlated with the known distribution of B. microplus (sensitivity 0.91; specificity 0.88) and provide a good estimation of the tick habitat suitability. This model could be used as a guide to the correct interpretation of the distribution limits of B. microplus. It can be also used to prepare eradication campaigns or to make predictions about the effects of global change on the distribution of the parasite.

[Satellite remote sensing as a tool for the analysis of the occurrence of American cutaneous leishmaniasis in an urban area of southeastern Brazil]

INTRODUCTION

The occurrence of American cutaneous leishmaniasis in the region of the Paraiba valley and the Northern shore of the State of S. Paulo, Brazil, is studied by remote sensing satellite imagery and maps of the region.

METHOD

The places where infections might have occurred were plotted on a false color composition made up of Landsat TM-3, 4 and 5 band images, the relevant vegetation (shrubs and trees) has been identified and correlations were sought for those areas seen as areas of risk for the disease and the environmental characteristics and their changes. The maps made it possible to add to the composite image the creeks and the contours of the tops of the large number of hills found in that region.

RESULTS

An area is characterized which may prove to be a macro-habitat for vectors, reservoirs and etiological agents. The search for changes in the landscape and the evaluation of meteorological data has not yielded any possible additional risk factor.

CONCLUSIONS

There is full correlation among the areas considered to present risk of infection and the presence of creeks and relevant vegetation (shrubs and trees).

A organização espacial condiciona as relações entre ambiente e saúde: o exemplo da exposição ao mercúrio em uma fábrica de lâmpadas fluorescentes

O espaço tem sido utilizado nas análises que relacionam o ambiente com a saúde, ora como simples plano geométrico para a disposição de dados epidemiológicos, ora como uma aproximação para a diferenciação de condições sociais, ou mesmo como uma circunstância de fatores espaciais que induzem risco. Neste trabalho são descritas as três principais abordagens espaciais em saúde e suas limitações. O uso do geoprocessamento na área de saúde tem sido facilitado pelo amplo acesso a bases de dados epidemiológicos e pela disponibilização de ferramentas cartográficas e estatísticas computadorizadas. O uso desta ferramenta pressupõe, no entanto, modelos de explicação do processo saúde/doença, que são baseados em variáveis espaciais como a distância, vizinhança, e o interrelacionamento com dados de caracterização do lugar. O exemplo de uma fábrica de lâmpadas fluorescentes permite compreender o espaço como mediador de relações sociais. A localização e atividade dos trabalhadores na fábrica condicionam os riscos a que estes estarão submetidos. Através da análise espacial de indicadores de emissão, contaminação e exposição ao mercúrio, foi possível identificar áreas e atividades de risco aos trabalhadores. Estes fatores, por sua vez, estão intrinsecamente ligados à organização interna e externa da produção.

[Occurrence of American cutaneous leishmaniasis by remote sensing satellite imagery in an urban area of Southeastern Brazil]

The areas in which american cutaneous leishmaniasis was reported in 1993 and 1994 for the region around the town of Lagoinha, S. Paulo, Brazil (Lat 23 degrees 05' S; Long 45 degrees 11w) were plotted on a TM-LANDSAT image. The false color composition of bands 3, 4 and 5 made it possible to identify the relevant vegetation (shrubs and trees) within the boundaries of those areas and in their proximity, where they were found at a distance of not more than about 250 meters from the perimeter of each area. The use of means capable of presenting a larger view of a geographical area made the advantages of remote satellite sensing as a tool for the study of this endemic disease clear.

Remotely sensed surrogates of meteorological data for the study of the distribution and abundance of arthropod vectors of disease

This paper gives an overview of how certain meteorological data used in studies of the population dynamics of arthropod vectors of disease may be predicted using remotely sensed, satellite data. Details are given of the stages of processing necessary to convert digital data arising from satellite sensors into ecologically meaningful information. Potential sources of error in these processing steps are also highlighted. Relationships between ground-measured meteorological variables (saturation deficit, ground temperature and rainfall) and data from both the National Oceanic and Atmospheric Administration's, polar-orbiting, meteorological satellites and the geostationary, Meteosat satellite are defined and examples detailed for Africa. Finally, the current status of existing satellite platforms and future satellite missions are reviewed and potential data availability discussed. How such satellite-based predictions have proved valuable in understanding the distribution of tsetse fly species in Côte d'Ivoire and Burkina Faso will be the subject of a future review.

Climate, satellite imagery and the seasonal abundance of the tick Rhipicephalus appendiculatus in southern Africa: a new perspective

Recent predictive models for the distribution of the African tick Rhipicephalus appendiculatus Neumann, based on the computer packages CLIMEX and BIOCLIM and data derived from meteorological satellites, and for the seasonal dynamics of the same tick using the computer simulation models ECFXPERT and T3HOST, all have their limitations. Statistical analysis of the relationships between the seasonal abundance of all three life stages of this tick and climatic and satellite-derived data from five sites in southern Africa, taken from the literature, supports a new perspective that it is the timing of the questing activity of the desiccation-vulnerable larvae that determines the pattern of the tick's seasonal dynamics. The timing of the activity of nymphs and adults is determined by temperature-dependent development rates plus the delaying phenomenon of photoperiod-sensitive diapause, the timing and duration of which have evolved to achieve maximum generation survival by ensuring the occurrence of eggs and larvae during periods of optimal climatic conditions. The most important environmental factor appears to be night-time minimum temperature, determining condensation and saturation deficit and thus the tick's ability to replenish moisture lost during the daytime and so to survive while questing for hosts. It is the larvae whose numbers are correlated most closely with these factors, consistent with earlier experimental results showing larvae to be most susceptible to desiccating conditions. There is a statistical linkage between larval tick numbers and satellite imagery, arising from the correlation between larval numbers and minimum temperature and saturation deficit conditions, and in turn the relationship between these climatic conditions and the subsequent vegetational changes monitored by the satellites. Moisture availability to larvae is likely to be the critical factor throughout the geographical range of R. appendiculatus, but the precise combination of climatic conditions that optimize moisture availability and questing tick survival can be expected to vary geographically. The relationships between ticks, temperatures and satellite data in parts of equatorial Africa have yet to be established. These correlative patterns highlight both the critical life stage and environmental factors when trying to understand temporal, and ultimately spatial, variations in tick abundance.

Geographic models and control of cattle liver flukes in the Southern USA

John Malone and Stanley Zukowski describe climate forecast and soil hydrology-based geographic information system models of snail habitat extent that provide an environmental context for site-specific mathematical models of fascioliasis. These have potential for the development of broad-scale control models that include a cost-benefit analysis component.

Use of LANDSAT MSS imagery and soil type in a geographic information system to assess site-specific risk of fascioliasis on Red River Basin farms in Louisiana

A geographic information system (GIS) was constructed in an ERDAS environment using maps of soil types from the USDA Soil Conservation Service, LANDSAT satellite multispectral scanner data (MSS), boundaries for 25 study farms, and slope and hydrologic features shown in a two-quadrangle (USGS, 7.5') area in the Red River Basin near Alexandria, Louisiana. Fecal sedimentation examinations were done in the fall of 1989, spring of 1990, and fall and winter of 1990-1991 on 10-16 random samples per herd. Fecal egg shedding rates for F. hepatica ranged from 10-100% prevalence and 0.3-21.7 eggs per two grams of feces (EP2G). For Paramphistomum spp., a rumen fluke also transmitted by F. bulimoides but not affected by flukicides, egg shedding rates ranged from 10-91% prevalence and 0.1-42.8 EP2G. Soil types present ranged from sandy loams to hydric, occasionally flooded clays. Herd Paramphistomum spp. egg shedding rates increased with the proportion of hydric clays present, adjusted for slope and major hydrologic features. F. hepatica infection intensity followed a similar trend, but were complicated by differing treatment practices. Results suggest that earth observation satellite data and soil maps can be used, with an existing climate forecast based on the Thornthwaite water budget, to develop a second generation model that accounts for both regional climate variation and site-specific differences in fascioliasis risk based on soils prone to snail habitat.