John B. Malone

World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) second edition of guidelines for evaluating the efficacy of anthelmintics in ruminants (bovine, ovine, caprine)

The first edition of the W.A.A.V.P. anthelmintic guidelines for ruminants was published in 1982. Since then improved parasitological procedures have been developed, new therapeutic and prophylactic products have appeared requiring different test methods, and registration authorities are requesting more detailed record keeping and data validation. This second edition addresses these developments and fulfills the original goal of publishing guidelines for high quality, scientifically valid testing standards for trials that would be accepted as proof of efficacy by registration authorities regardless of country of origin. This second edition includes updated guidance on standard parasitological procedures, dose titration, dose confirmation and clinical trials, and provides guidelines for evaluating products for efficacy against anthelmintic resistant parasites, persistence of activity and prophylactic activity. Tests for efficacy against nematodes, trematodes and cestodes are included.

A GEOGRAPHIC INFORMATION SYSTEM FORECAST MODEL FOR STRATEGIC CONTROL OF FASCIOLOSIS IN ETHIOPIA

A geographic information system (GIS) forecast model based on moisture and thermal regime was developed to assess the risk of Fasciola hepatica, a temperate species, and its tropical counterpart, Fasciola gigantica, in Ethiopia. Agroecological map zones and corresponding environmental features that control the distribution and abundance of the disease and its snail intermediate hosts were imported from the Food and Agriculture Organization (FAO) Crop Production System Zones (CPSZ) database on east Africa and used to construct a GIS using ATLAS GIS 3.0 software. Base temperatures of 10 degrees C and 16 degrees C were used for F. hepatica and F. gigantica, respectively, to calculate growing degree days in a previously developed climate forecast system that was modified to allow use of monthly climate data values. The model was validated by comparison of risk indices and environmental features to available survey data on fasciolosis. Monthly Fasciola risk indices of four climatic regions in Ethiopia were used to project infection transmission patterns under varying climatic conditions and strategic chemotherapeutic fasciolosis control schemes. Varying degrees of F. hepatica risk occurred in most parts of the country and distinct regional F. hepatica transmission patterns could be identified. In the humid west, cercariae-shedding was predicted to occur from May to October. In the south it occurred from April to May and September to October, depending on the annual abundance of rain. In the north-central and central regions, risk was highest during heavy summer rains and pasture contamination with metacercariae was predicted to occur during August-September, except in wet years, when it may start as early as July and extend up to October. At cooler sites above altitude of 2800 m, completion of an infection cycle may require more than a year. Fasciola gigantica risk was present in the western, southern and north-central regions of the country at altitudes of 1440-2560 m. However, a transmission cycle could be completed in a single year only at elevations below 1700 m. The greatest risk of F. gigantica infection was in the humid western region. Regional strategic chemotherapy schemes of two or three treatments per year were developed. Results suggest that the model can be extrapolated to all CPSZ in the country and adapted for use in control of other vector-borne diseases of economic and public health importance.

A geographic information system on the potential distribution and abundance of Fasciola hepatica and F-gigantica in east Africa based on Food and Agriculture Organization databases

An adaptation of a previously developed climate forecast computer model and digital agroecologic database resources available from FAO for developing countries were used to develop a geographic information system risk assessment model for fasciolosis in East Africa, a region where both F. hepatica and F. gigantica occur as a cause of major economic losses in livestock. Regional F. hepatica and F. gigantica forecast index maps were created. Results were compared to environmental data parameters, known life cycle micro-environment requirements and to available Fasciola prevalence survey data and distribution patterns reported in the literature for each species (F. hepatica above 1200 m elevation, F. gigantica below 1800 m, both at 1200-1800 m). The greatest risk, for both species, occurred in areas of extended high annual rainfall associated with high soil moisture and surplus water, with risk diminishing in areas of shorter wet season and/or lower temperatures. Arid areas were generally unsuitable (except where irrigation, water bodies or floods occur) due to soil moisture deficit and/or, in the case of F. hepatica, high average annual mean temperature >23 degrees C. Regions in the highlands of Ethiopia and Kenya were identified as unsuitable for F. gigantica due to inadequate thermal regime, below the 600 growing degree days required for completion of the life cycle in a single year. The combined forecast index (F. hepatica+F. gigantica) was significantly correlated to prevalence data available for 260 of the 1220 agroecologic crop production system zones (CPSZ) and to average monthly normalized difference vegetation index (NDVI) values derived from the advanced very high resolution radiometer (AVHRR) sensor on board the NOAA polar-orbiting satellites. For use in Fasciola control programs, results indicate that monthly forecast parameters, developed in a GIS with digital agroecologic zone databases and monthly climate databases, can be used to define the distribution range of the two Fasciola species, regional variations in intensity and seasonal transmission patterns at different sites. Results further indicate that many of the methods used for crop productivity models can also be used to define the potential distribution and abundance of parasites.

Satellite climatology and the environmental risk of Schistosoma mansoni in Ethiopia and east Africa

Annual and seasonal composite maps prepared from the normalized difference vegetation index (NDVI) and earth surface maximum temperature (T(max)) satellite data from the archives of the Global land 1-km program of the United States Geological Survey (USGS) were studied for. their potential value, using geographic information system (GIS) methods, as surrogates of climate data in the development of environmental risk models for schistosomiasis in Ethiopia. Annual, wet season and dry season models were developed and iteratively analyzed for relationships with Schistosoma mansoni distribution and infection prevalence rates. Model-predicted endemic area overlays that best fit the distribution of sites with over 5% prevalence corresponded to values of NDVI 125-145 and T(max) 20-33 degrees C in the annual composite map, NDVI 125-145 and T(max) 18-29 degrees C for the wet season map, and NDVI 125-140 and T(max) 22-37 degrees C for the dry season map. The model-predicted endemic area was similar to that of a prior model developed using an independent agroecologic zone data set from the United Nations Food and Agriculture Organization (FAO). Results were consistent with field and laboratory data on the preferences and limits of tolerance of the S. mansoni-Biomphalaria pfeifferi system. Results suggest that Global 1-km NDVI and T(max), when used together, can be used as surrogate climate data for development of GIS risk assessment models for schistosomiasis. The model developed for Ethiopia based on global 1-km satellite data was extrapolated to a broader area of East Africa. When used with FAO agroecologic zone climate data limits of <27 degrees C for average annual mean temperature and annual moisture deficits (annual rain-annual potential evapotranspiration) of <-1300 mm, the model accurately represented the regional distribution of the S. mansoni-B. pfeifferi system in the East Africa extrapolation area.

Geographic information systems and the distribution of Schistosoma mansoni in the Nile delta

New computer-based sensor technology and geographic methods have led to emerging interest in use of satellite environmental assessment tools for design of disease control programs, especially for those that are vector borne. The long-range goal of work reported here by John Malone and colleagues on behalf of this Egyptian Ministry of Health-USAID Schistosomiasis Research Project team (Box 1) is to utilize data from sensor systems on board earth-observing satellites to develop more-sensitive disease-prediction and -control models. If successful, methods developed may provide a potentially vital capability for use by disease control program managers, particularly in less-developed countries, where mapping resources are not well advanced. Longer term, broader basic questions on the interaction of environment and disease in anticipation of predicted global climate change may be addressed. These studies focused on the lower Nile river basin of Egypt. The specific objective was to link data on environmental requirements for propagation and transmission of schistosomiasis with parameters measurable from space.

Use of thermal and vegetation index data from earth observing satellites to evaluate the risk of schistosomiasis in Bahia, Brazil.

A geographic information system (GIS) was constructed using maps of regional agroclimatic features, vegetation indices and earth surface temperature data from environmental satellites, together with Schistosoma mansoni prevalence records from 270 municipalities including snail host distributions in Bahia, Brazil to study the spatial and temporal dynamics of infection and to identify environmental factors that influence the distribution of schistosomiasis. In an initial analysis, population density and duration (months) of the annual dry period were shown to be important determinants of disease. In cooperation with the National Institute of Spatial Research in Brazil (INPE), day and night imagery data covering the state of Bahia were selected at approximately bimonthly intervals in 1994 (six day-night pairs) from the data archives of the advanced very high resolution radiometer (AVHRR) sensor of the National Oceanic and Atmospheric Administration (NOAA)-11 satellite. A composite mosaic of these images was created to produce maps of: (1) average values between 0 and +1 of the normalized difference vegetation index (NDVI); and (2) average diurnal temperature differences (dT) on a scale of values between 0 and 15 degrees C. For each municipality, NDVI and dT were calculated for a 3x3 pixel (9 km(2) area) grid and analyzed for relationships to prevalence of schistosomiasis. Results showed a statistically significant relationship of prevalence to dT (rho=-0.218) and NDVI (rho=0.384) at the 95% level of confidence by the Spearman rank correlation coefficient. Results support use of NDVI, dT, dry period climatic stress factors and human population density for development of a GIS environmental risk assessment model for schistosomiasis in Brazil.

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.

A cross-sectional coprological survey of liver flukes in cattle and sheep from an area of the southern Italian Apennines

A cross-sectional coprological survey of liver flukes (Fasciola hepatica and Dicrocoelium dendriticum) was conducted on 81 bovine farms and 197 ovine farms with animals pasturing in an area (3971 km(2)) of the southern Italian Apennines. The farms were selected to be uniformly distributed throughout the study area using geographical information system (GIS) software. Between June 1999 and March 2000, faecal samples were collected from 975 cattle and 3940 sheep and examined using a modified McMaster technique. The results were subjected to statistical analysis and point distribution maps (PDMs) were drawn by GIS. Cattle of 9 of the 81 (11.1%) farms were positive for F. hepatica and of 43 (53.1%) for D. dendriticum. Sheep of 8 of the 197 (4.1%) farms were positive for F. hepatica and of 133 (67.5%) for D. dendriticum. Co-infection was found in cattle of 2 (2.5%) farms, and in sheep of 8 (4.1%) farms. The findings of the present survey show that D. dendriticum was the predominant liver fluke found in cattle and sheep with respect to egg count numbers for both farms and animals. In addition, the general trends of the PDMs show that D. dendriticum was widely and homogeneously spread throughout the study area, whereas F. hepatica was present only in a few concentrated zones of the study area that had both positive bovine and positive ovine farms.

Spatial epidemiology in zoonotic parasitic diseases: insights gained at the 1st International Symposium on Geospatial Health in Lijiang, China, 2007

The 1st International Symposium on Geospatial Health was convened in Lijiang, Yunnan province, Peoples Republic of China from 8 to 9 September, 2007. The objective was to review progress made with the application of spatial techniques on zoonotic parasitic diseases, particularly in Southeast Asia. The symposium featured 71 presentations covering soil-transmitted and water-borne helminth infections, as well as arthropod-borne diseases such as leishmaniasis, malaria and lymphatic filariasis. The work made public at this occasion is briefly summarized here to highlight the advances made and to put forth research priorities in this area. Approaches such as geographical information systems (GIS), global positioning systems (GPS) and remote sensing (RS), including spatial statistics, web-based GIS and map visualization of field investigations, figured prominently in the presentation.

Validation of a mapping and prediction model for human fasciolosis transmission in Andean very high altitude endemic areas using remote sensing data

The present paper aims to validate the usefulness of the Normalized Difference Vegetation Index (NDVI) obtained by satellite remote sensing for the development of local maps of risk and for prediction of human fasciolosis in the Northern Bolivian Altiplano. The endemic area, which is located at very high altitudes (3800-4100 m) between Lake Titicaca and the valley of the city of La Paz, presents the highest prevalences and intensities of fasciolosis known in humans. NDVI images of 1.1 km resolution from the Advanced Very High Resolution Radiometer (AVHRR) sensor on board the National Oceanic and Atmospheric Administration (NOAA) series of environmental satellites appear to provide adequate information for a study area such as that of the Northern Bolivian Altiplano. The predictive value of the remotely sensed map based on NDVI data appears to be better than that from forecast indices based only on climatic data. A close correspondence was observed between real ranges of human fasciolosis prevalence at 13 localities of known prevalence rates and the predicted ranges of fasciolosis prevalence using NDVI maps. However, results based on NDVI map data predicted zones as risk areas where, in fact, field studies have demonstrated the absence of lymnaeid populations during snail surveys, corroborated by the absence of the parasite in humans and livestock. NDVI data maps represent a useful data component in long-term efforts to develop a comprehensive geographical information system control program model that accurately fits real epidemiological and transmission situations of human fasciolosis in high altitude endemic areas in Andean countries.