A study of the environmental determinants of malaria and schistosomiasis in the Philippines using Remote Sensing and Geographic Information Systems.

Malaria and schistosomiasis are two water-related parasitic diseases affecting millions of people worldwide particularly tropical and subtropical countries. In the Philippines, malaria is found in 72 out of 78 provinces while schistosomiasis is endemic in 24 provinces. The Anopheles mosquito and the Oncomelania snail involved in the transmission of these diseases depend on certain environmental determinants that support mosquito and snail populations. This study, done for the first time in the Philippines, successfully showed how Remote Sensing (RS) and Geographical Information Systems (GIS) can be effectively used in showing how these environmental factors affect the spatial distribution of these two diseases. The study sites, i.e. the municipalities of Asuncion and Kapalong, are known endemic sites for both malaria and schistosomiasis. Georeferenced data enabled visualization of prevalence data in relation to physical maps thus facilitating assessment of disease situation in the two municipalities. RS and GIS data proved that other factors aside from climate influence the epidemiology of the diseases in the two sites. Topography and slope as main physical factors influence the vegetation cover, land use and soil type prevailing in particular areas. In addition, water sources especially irrigation networks differed in various places in the study sites in turn affecting the magnitude and distribution of malaria and schistosomiasis. Significant correlations found between the diseases and the environmental variables formed the basis for development of models to predict the disease prevalence in the two municipalities. Proximity to snail breeding sites and irrigation networks and the highly agricultural nature of the barangays were identified as the most common factors that define the high prevalence areas for schistosomiasis confirming the fact that conditions that support the snail populations will in turn favor the presence of the disease. For malaria, the predictive models included temperature, humidity, soil type, predominance of reproduction brush, presence of cultivated areas, distance from deep wells and distance from conventional water source which are in turn influenced by the factor of elevation.

A global network for the control of snail-borne disease using satellite surveillance and geographic information systems.

At a team residency sponsored by the Rockefeller Foundation in Bellagio, Italy, 10-14 April 2000 an organizational plan was conceived to create a global network of collaborating health workers and earth scientists dedicated to the development of computer-based models that can be used for improved control programs for schistosomiasis and other snail-borne diseases of medical and veterinary importance. The models will be assembled using GIS methods, global climate model data, sensor data from earth observing satellites, disease prevalence data, the distribution and abundance of snail hosts, and digital maps of key environmental factors that affect development and propagation of snail-borne disease agents. A work plan was developed for research collaboration and data sharing, recruitment of new contributing researchers, and means of access of other medical scientists and national control program managers to GIS models that may be used for more effective control of snail-borne disease. Agreement was reached on the use of compatible GIS formats, software, methods and data resources, including the definition of a 'minimum medical database' to enable seamless incorporation of results from each regional GIS project into a global model. The collaboration plan calls for linking a 'central resource group' at the World Health Organization, the Food and Agriculture Organization, Louisiana State University and the Danish Bilharziasis Laboratory with regional GIS networks to be initiated in Eastern Africa, Southern Africa, West Africa, Latin America and Southern Asia. An Internet site, www.gnosisGIS.org, (GIS Network On Snail-borne Infections with special reference to Schistosomiasis), has been initiated to allow interaction of team members as a 'virtual research group'. When completed, the site will point users to a toolbox of common resources resident on computers at member organizations, provide assistance on routine use of GIS health maps in selected national disease control programs and provide a forum for development of GIS models to predict the health impacts of water development projects and climate variation.

Vector-borne parasitic diseases: new trends in data collection and risk assessment.

Climates and topography effectively restrict vector-borne infections to certain geographical areas, a clear illustration of how strongly the spatial distributions of these diseases rely on environmental factors. This is hardly a new revelation, but just a few years back, without the support of computer-assisted collection and handling of data, we were far less able to grasp the full picture. Fortunately climate data collection by Remote Sensing (RS) by earth-observing satellites, a technology particularly well suited to pinpointing constraining endemic factors, has not only become affordable but also reached a high degree of sophistication. Meanwhile, geographical information systems (GIS) and global positioning systems (GPS) permit spatial information of great accuracy as well as digitalization of collected data on the spot enabling visualization of the data in relation to physical maps and facilitating comparisons of the results of longitudinal investigations. Adoption of these technologies at the national level promotes intersectoral collaboration and promises improved planning and management in the control of endemic diseases. Applications in areas such as malaria, onchocerciasis, lymphatic filariasis, trypanosomiasis and schistosomiasis are briefly reviewed. Reports in the fields of the former two diseases dominate the literature, while information is lagging with regard to the others. The need for a broadening of the GIS approach is emphasized with the aim of rejuvenating the dynamic aspect of epidemiological studies.

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.

Schistosomiasis vaccine development: progress and prospects

The undisputed worldwide success of chemotherapy notwithstanding, schistosomiasis continues to defy control efforts in as much rapid reinfection demands repeated treatment, sometimes as often as once a year. There is thus a need for a complementary tool with effect for the longer term, notably a vaccine. International efforts in this direction have been ongoing for several decades but, until the recombinant DNA techniques were introduced, antigen production remained an unsurmountable bottleneck. Although animal experiments have been highly productive and are still much needed, they probably do not reflect the human situation adequately and real progress can not be expected until more is known about human immune responses to schistosome infection. It is well-known that irradiated cercariae consistently produce high levels of protection in experimental animals but, for various reasons, this proof of principle cannot be directly exploited. Research has instead been focussed on the identification and testing of specific schistosome antigens. This work has been successful and is already at the stage where clinical trials are called for. Preliminary results from coordenates in vitro laboratory and field epidemiological studies regarding the protective potential of several antigens support the initiation of such trials. A series of meetings, organized earlier this year in Cairo, Egypt, reviewed recent progress, selected suitable vaccine candidates and made firm recommendations for future action including pledging support for large-scale production according to good manufacturing practice (GMP) and Phase I trials. Scientists at the American Centers for Diseases Control and Prevention (CDC) have drawn up a detailed research plan. The major financial suppport will come from USAID, Cairo, which has established a scientific advisory group of Egyptian scientists and representatives from current and previous international donors such as WHO, NIAID, the European Union and the Edna McConnel Clark Foundation.

Schistosomiasis vaccine development: progress and prospects.

The undisputed, worldwide success of chemotherapy notwithstanding, schistosomiasis continues to defy control efforts in as much rapid reinfection demands repeated treatment, sometimes as often as once a year. There is thus a need for a complementary tool with effect for the longer term, notably a vaccine. International efforts in this direction have been ongoing for several decades but, until the recombinant DNA techniques were introduced, antigen production remained an insurmountable bottleneck. Although animal experiments have been highly productive and are still much needed, they probably do not reflect the human situation adequately and real progress can not be expected until more is known about human immune responses to schistosome infection. It is well-known that irradiated cercariae consistently produce high levels of protection in experimental animals but, for various reasons, this proof of principle cannot be directly exploited. Research has instead been focussed on the identification and testing of specific schistosome antigens. This work has been quite successful and is already at the stage where clinical trials are called for. Preliminary results from coordinated in vitro laboratory and field epidemiological studies regarding the protective potential of several antigens support the initiation of such trials. A series of meetings, organized earlier this year in Cairo, Egypt, reviewed recent progress, selected suitable vaccine candidates and made firm recommendations for future action including pledging support for large-scale production according to good manufacturing practice (GMP) and Phase I trials. Scientists at the American Centers for Disease Control and Prevention (CDC) have drawn up a detailed research plan. The major financial support will come from USAID, Cairo, which has established a scientific advisory group of Egyptian scientists and representatives from current and previous international donors such as WHO, NIAID, the European Union and the Edna McConnell Clark Foundation.

Schistosomiasis vaccine:research to development.

In this article, Robert Bergquist and Dan Colley deal with the consolidated, international efforts to generate a schistosomiasis vaccine; in particular, they summarize the deliberations of a series of meetings, held in Cairo, Egypt, 21-25 May 1997, with the aim of reviewing the current status of affairs in this respect in order to make recommendations for the future course of schistosomiasis vaccine development.

Schistosomiasis vaccine development: approaches and prospects

Mounting evidence for acquired immunity to schistosomiasis in humans supports the case for immunological intervention. On the other hand, rapid reinfection poses a threat to younger age groups due to the slow maturation of natural resistance. However, rational approaches, based on advances in immunology and molecular biology, have substantially increased the odds of producing an effective vaccine. Since the parasite cannot replicate in the human host and serious morbidity generally occurs only after a relatively long period of heavy worm burden, complete protection against infection is not essential. The chances of success would increase if more than one of the various host/parasite interphases were targeted, for example reducing morbidity through decreased worm loads as well as through suppression of egg production. Several promising schistosome antigens have now reached an advanced phase of development and are currently undergoing independent confirmatory testing according to a standardized protocol. A few molecules are being contemplated for scaled-up production but, so far, only one has reached the stage of industrial manufacture and safety testing. Since schistosomiasis cannot realistically be controlled by a single approach, vaccination is envisaged to be implemented in conjunction with other means of control, notably chemotherapy.

Schistosomiasis vaccine development: approaches and prospects.

Mounting evidence for acquired immunity to schistosomiasis in humans supports the case for immunological intervention. On the other hand, rapid reinfection poses a threat to younger age groups due to the slow maturation of natural resistance. However, rational approaches, based on advances in immunology and molecular biology, have substantially increased the odds of producing an effective vaccine. Since the parasite cannot replicate in the human host and serious morbidity generally occurs only after a relatively long period of heavy worm burden, complete protection against infection is not essential. The chances of success would increase if more than one of the various host/parasite interphases were targeted, for example reducing morbidity through decreased worm loads as well as through suppression of egg production. Several promising schistosome antigens have now reached an advanced phase of development and are currently undergoing independent confirmatory testing according to a standardized protocol. A few molecules are being contemplated for scaled-up production but, so far, only one has reached the stage of industrial manufacture and safety testing. Since schistosomiasis cannot realistically be controlled by a single approach, vaccination is envisaged to be implemented in conjunction with other means of control, notably chemotherapy.

Schistosomiasis research funding: the TDR (Special Programme for Research and Training in Tropical Diseases) contribution.

In spite of the recent decline in financial support on the part of some major donors, the overall international support for schistosomiasis research in current US dollars has been holding steady. However, when adjusted for inflation, a clear decline-during the last decade appears and only in a few countries has this decline been balanced by increased national or bilateral funding. The prevailing level of support for schistosomiasis research is barely sufficient to maintain established laboratories and researchers, and highlights the need to attract young investigators. The important goal of bringing a new generation of scientists into the field of schistosomiasis can only be achieved by a considerable long-term increase in funding, both at the national and the international levels. A break-through in current research emphasizing improved techniques for control is needed to encourage donors and governments to improve the situation.

Present aspects of immunodiagnosis of schistosomiasis.

Facilitated and improved by advances in molecular biology, techniques for the immunodiagnosis of schistosomiasis, including assays based on the detection of antigens circulating in the serum and/or excreted in the urine, have now reached the stage of multi-centre trials. There is a need to complement parasitological techniques as some national programmes are becoming increasingly successful in establishing control of the disease and the classical approach frequently fails to reveal low-intensity infection. Epidemiological survey teams in some areas have tentatively started to use serology and their experience indicates that antibody detection suffices in eradicated or controlled areas with low expected prevalence but that detection of circulating antigens is needed for assessment of the incidence of infection or reinfection in areas recently brought under control. Before reagents and procedures can be recommended for routine use of national control programmes, the assays must be standardized with sera from clinically well-characterized patients in geographically defined regions, hence emphasizing the need for a reference serum bank. Implementation of serological testing, carried out by national public health laboratories using standardized testing systems, would permit valid comparisons between different areas providing support for decisions regarding national health policies.

Present aspects of immunodiagnosis of schistosomiasis

Facilitated and improved by advances in molecular biology, techniques for the immunodiagnosis of schistosomiasis, including assays based on the detection of antigens circulating in the serum and/or excreted in the urine, have now reached the stage of multi-centre trials. There is a need to complement parasitological techniques as some national programmes are becoming increasingly succesful in establishng control of the disease and the classical approach frequently fails to reveal low-intensity infection. Epidemiological survey teams in some areas have tentatively started to use serology and their experience indicates that antibody detection suffies in eradicated or controlled areas with low expected prevalence but that detection of circulating antigens is needed for assessment of the incidence of infection or reinfection in areas recently brought under control. Before reagents and procedures can be recommended for routine use of national control programmes, the assays must be standardized with sera from clinically well-characterized patients in geographically defined regions, hence emphasizing the need for a reference serum bank. Implementation of serological testing, carried out by nationsl public health laboratories using standardized testing systems, would permit valid comparisons between different areas providing support for decisions regarding national health polices

Schistosomiasis research funding: the TDR contribution

In spite of the recent decline in financial support on the part of some major donors, the overall international support for schistosomiasis research in current US dollars has been holding steady. However, when adjusted for inflation, a clear decline during the last decade appears and only in a few countries has this decline been balanced by increased national or bilateral funding. The prevailing level of support for schistosomiasis research is barely sufficient to maintain estabilished laboratories and researchers, and highlights the need to attract young investigators. The important goal of brunging a new generation of scientists into the field of schistosomiaisis can only be achieved by a considerable long-term increase in funding, both at the national and the international levels. A break-through in current research emphasizing improved techniques for control is needed to encourage donors and governments to improve the situation

Application of an indirect carbon immunoassay (CIA) for the rapid diagnosis of antibody to Toxoplasma gondii in sheep.

Carbon immunoassay (CIA), a novel indirect rapid test for Toxoplasma antibody in sheep, was compared with indirect fluorescent antibody assay (IFA). CIA relies on the adherence of carbon particles of India-ink to rabbit immunoglobulin G.l Carbon labelled anti-sheep rabbit IgG was used for the detection of sheep antibody when attached to tachyzoites of Toxoplasma gondii. The result was read in an ordinary light microscope and there was a clearcut difference between negative and positive reactions. Out of a total of 97 sheep sera tested, 15 sera were negative in both tests and 12 were negative in CIA but showed low positive titres in IFA. The remaining 70 sera were positive in both tests but the titres were usually about 3 dilution steps lower when investigated with CIA as compared to IFA.

A novel simple immunoassay for rapid detection of human IgG antibodies to Toxoplasma gondii.

The carbon immunoassay (CIA) is a direct serological test relying on a specific reaction between the carbon particles of India ink and rabbit immunoglobulin G. On addition of the India ink reagent, particulate antigens may be visualized in the light microscope after rabbit antibodies have reacted with them. Serum, India ink reagent and antigen may be mixed together in a single step and the result read within 5 min. The applicability of CIA can be expanded to include human sera by pretreatment of India ink with staphylococcal protein A. Sera from 50 suspected toxoplasmosis patients were examined by immunofluorescence (IF), the dye test of Sabin-Feldman (SF) and CIA. There was good correlation between results by the CIA and IF. Sera with low SF titres were usually negative by IF and negative or weakly positive by CIA. With sera positive by all 3 tests, CIA and IF gave similar titres, but SF titres were generally higher. CIA provides a simple inexpensive and rapid laboratory test for diagnosis of toxoplasmosis.