Over 35,000 cases of Japanese encephalitis (JE) are reported worldwide each year. Culex tritaeniorhynchus is the primary vector of the JE virus, while wading birds are natural reservoirs and swine amplifying hosts. As part of a JE risk analysis, the ecological niche modeling programme, Maxent, was used to develop a predictive model for the distribution of Cx. tritaeniorhynchus in the Republic of Korea, using mosquito collection data, temperature, precipitation, elevation, land cover and the normalized difference vegetation index (NDVI). The resulting probability maps from the model were consistent with the known environmental limitations of the mosquito with low probabilities predicted for forest covered mountains. July minimum temperature and land cover were the most important variables in the model. Elevation, summer NDVI (July-September), precipitation in July, summer minimum temperature (May-August) and maximum temperature for fall and winter months also contributed to the model. Comparison of the Cx. tritaeniorhynchus model to the distribution of JE cases in the Republic of Korea from 2001 to 2009 showed that cases among a highly vaccinated Korean population were located in high-probability areas for Cx. tritaeniorhynchus. No recent JE cases were reported from the eastern coastline, where higher probabilities of mosquitoes were predicted, but where only small numbers of pigs are raised. The geographical distribution of reported JE cases corresponded closely with the predicted high-probability areas for Cx. tritaeniorhynchus, making the map a useful tool for health risk analysis that could be used for planning preventive public health measures.

Larval habitats of the main malaria vectors in Belize are associated with three distinctly different aquatic environments: marshes with sparse macrophytes and cyanobacterial mats (Anopheles albimanus), tall dense macrophyte marshes (An. vestitipennis), and floating detritus assemblages within freshwater rivers (An. darlingi). We assessed species-specific habitat suitability based upon nutrient characteristics using larval survival rates (SR) and wing lengths (WL) from floating habitat enclosures. Anopheles albimanus showed a high SR (81%) in all three habitats, while An. vestitipennis had a similarly high SR in its own habitat (82%) and An. darlingi's habitat (8 1 %). Anopheles darlingi only showed high SR (85%) in its own habitat. Both An. vestitipennis and An. darlingi showed very low SR in the An. albimanus habitat. There were no significant WL differences among field-caught, laboratory-reared, and experimental populations of An. vestitipennis and An. albimanus, with the exception of An. vestitipennis experimental populations and An. vestitipennis field populations placed in the An. albimanus habitat. Habitat quality indicators, particulate organic carbon (POC), dissolved organic carbon (DOC), and particulate organic nitrogen (PON), were consistently higher in An. vestitipennis habitats than in the habitats of the other two species. Correspondingly, An. vestitipennis adults were larger when measured both as dry mass and from WL. There were no differences in dry mass, lipids, or protein content among the same species reared at different locations. We compared SR and WL among mosquitoes from shaded and unshaded containers to test whether the high mortality rates for An. vestitipennis and An. darlingi in the An. albimanus habitat were due to intense sun exposure. There were no significant differences among developmental times, survivorship, or adult size for shaded versus sun-exposed populations. This indicates that other factors such as larval toxins, predator avoidance, interspecific species competition, etc. may be responsible for the higher mortality rates in those species not adapted to this particular habitat.

The recapture rates of wild-caught, unengorged Anopheles vestitipennis and Anopheles albimanus females were determined at 0, 400, and 800 m from a fixed release point in Belize, Central America. Three sampling trials, each consisting of two 12-hour collections, were performed at each distance during September-October 2003. A total of 1,621 An. vestitipennis and 1,326 An. albimanus were marked and released during the course of the study. The recapture rate of An. vestitipennis was greatest at 0 m (7.9%; 44/ 556) and declined from 3.0% (16/531) at 400 m to 0.2% (1/534) at 800 m. Anopheles albimanus females were recaptured only at the 0-m distance and in extremely low numbers (1.1%; 5/446). Biting patterns for the unmarked natural populations were similar to those previously described for Belize, and recaptures for both species occurred during these normal biting times. The overall recapture rates for An. vestitipennis (3.76%; 61/ 1,621) and An. albimanus (0.38%; 5/1,326) indicate that An. vestitipennis has a higher probability of being attracted to a human habitation.

The present study utilized an experimental hut to conduct human-baited landing collections for characterizing the all-night biting patterns and seasonal densities of adult Anopheles darlingi in the centrally located Cayo District of Belize, Central America. A total of 25 all-night collections (i.e., sunset to sunrise) were conducted from January 2002 to May 2003, capturing a total of 18,878 An. darlingi females. Anopheles darlingi exhibited a bimodal nightly biting pattern with one predominate peak occurring three h after sunset and a smaller peak occurring one h prior to sunrise. Biting females were collected throughout the night in higher densities indoors (9,611) than outside (9,267) the experimental hut (O:I=1.00:1.04). Seasonal adult collections show An. darlingi densities were highest during the transitional months between the end of the wet and beginning of the dry season (January) and the end of the dry season and beginning of the wet season (May). A total of 2,010 An. darlingi females was captured in 31 two-h, human-baited landing collections performed from January to October 2002. Anopheles darlingi monthly population densities were found to have no significant associations with high or low temperatures, precipitation, or river level. However, qualitative data examination indicates an inverse relationship between river level and An. darlingi adult collections suggesting a disturbance of larval habitats. All-night biting and seasonal distribution patterns for other anopheline species are also described. None of the adult specimens collected throughout the entire study tested positive for Plasmodium spp. infection using the VecTest rapid diagnostic kit.

Anthropogenic land use changes often alter natural patterns of disease transmission. The goal of this study was to determine whether phosphorus input from sugarcane, Saccharum officinarum L., cultivation in northern Belize could pose a significant environmental impact on malaria transmission by changing vegetation structure and composition of wetlands and associated larval habitats. Our primary focus was on the increased dominance of cattail, Typha domingensis Pers., a favored habitat for Anopheles vestitipennis Dyar & Knab. A land cover classification based on satellite imagery was used to select 20 marshes impacted by agricultural runoff and 20 marshes surrounded by forest (nonimpacted). A 100-m transect was established into each of the 40 marshes. Water, vegetation, and larval sampling were conducted at the 0-, 10-, 25-, 50-, and 100-m locations along the transect. Analyses of larval density data indicated that Anopheles albimanus Wiedemann was negatively correlated with percentage of cover of Typha (R2 = 0.39, P < 0.001) but positively correlated with sparse Eleocharis cellulosa Torr. (rush) cover (R2 = 0.19, P < 0.05) and presence of cyanobacterial mats (CBM) (R2 = 0.33, P < 0.0001). An. vestitipennis was found to be positively correlated with percentage of cover of Typha (R2 = 0.19, P < 0.001). Canonical correspondence analysis identified CBM and light as the variables associated with the presence of An. albimanuts larvae, Typha cover with An. vestitipennis larvae, and Eleocharis and absence of light with Anopheles crucians (Wiedemann). A positive correlation also existed between marshes adjacent to agricultural activities and presence of An. vestitipennis (R2 = 0.37, P < 0.05). These results indicate that marshes in proximity to agricultural fields are conducive for Typha growth, thereby providing habitat for the more efficient malaria vector

Previous studies in Belize have shown the preferred breeding habitats of the malaria vector Anopheles darlingi were floating detritus patches within riverine systems that were associated with overhanging bamboo. The present study focused on an experimental evaluation of overhanging bamboo in An. darlingi habitat selection using larval counts as an indicator of attractiveness. Four sets of 1-m2 floating screened enclosures were placed at a location with a documented presence of both larval and adult An. darlingi populations. Each enclosure set comprised a control (i.e., open water) and three other experimental treatments consisting of: 1) detritus, 2) detritus with overhanging bamboo, and 3) overhanging bamboo alone. Larvae were sampled from all treatments on Day 5, Day 11, and Day 17 post-setup. A total of 2,461 An. darlingi larvae were collected and identified from three trials conducted from March-May 2002. Of these, 1,997 larvae were sampled from detritus treatments, 256 from enclosures with bamboo and detritus, 139 from bamboo treatments, and 69 from control enclosures. The detritus treatment had a significantly higher average count of An. darlingi larvae than the other treatments (P<0.01), and no difference existed between the control treatment and the treatment containing overhanging bamboo alone (P=0.423). More importantly, enclosures containing the overhanging bamboo with detritus treatments did not have greater larval populations than the enclosures with only detritus. These data suggest that bamboo does not contribute to An. darlingi larval habitat attractiveness but may function as a barrier to surface water flow causing the lodging of debris, the preferred habitat, that will then attract gravid females for oviposition.

Mowing and burning of emergent vegetation were evaluated as potential management strategies for the control of the malaria vector, Anopheles vestitipennis, in northern Belize, Central America. The primary aim was reduction of tall dense macrophytes (dominated by Typha domingensis) as preferred larval habitat for An. vestitipennis. Nine experimental plots were established in a Typha marsh in Orange Walk District, Belize. Three plots were burned, three were treated by sub-aquatic mowing, and three were unaltered controls. After treatment, Typha height was most dramatically affected by the mow treatment. Plant heights at 21 and 95 days post-treatment reflected an 89% and 48% decrease, respectively, compared to pretreatment conditions. The Typha height in the burn plots was not as severely affected. Heights at 21 days post-treatment were 39% lower than those of pre-treatment vegetation, with a return to near pre-test heights by 95 days post-treatment. Both treatments resulted in a significant reduction in the number of An. vestitipennis larvae collected as compared to control plots. Conversely, the treatments resulted in increased larval densities of several other vector and pest mosquito species. Larval population densities of An. albimanus, Ochlerotatus taeniorhynchus, and Culex coronator were significantly higher in burn plots. In mow plots, there were significant increases in An. albimanus and Oc. taeniorhynchus larval populations. Non-target invertebrate species affected by the treatments were adult Tropisternus collaris, larval Corythrella, and adult Paraplea puella.

A life table study was conducted for recently established colonies of Anopheles albimanus and Anopheles vestitipennis in Belize, Central America. The colonies were reared in the northern Orange Walk District under uncontrolled environmental conditions (29-32 degrees C, 87-90% RH, and 13:11 L:D photoperiod). The mean time of larval development for An. albimanus was 10.8 days for males and 11.7 days for females. Mean times for An. vestitipennis larval development were 11.3 days for males and 13.5 days for females. Anopheles albimanus exhibited a 92% survival rate from egg hatch to adult emergence, while that of An. vestitipennis was 82%. Neither species showed a sex ratio that was significantly different from 1:1. Adult male An. albimanus lived for an average of 13.6 days, while the females lived for an average of 21.2 days. The An. vestitipennis adult males lived for a mean of 14.8 days, while the females lived considerably longer with a mean of 25.6 days. The reproductive rate and age of mean cohort reproduction were calculated as 287 and 11.3 days for An. albimanus and 302 and 13.4 days for An. vestitipennis. The r/B and B/D ratios of 0.13 and 1.15, respectively, for An. albimanus and 0.1 and 1.1, respectively, for An. vestitipennis indicate that these species have a low potential for colonization.

Malaria reemerged in the Republic of Korea (ROK) in 1993. While limited numbers of U.S. soldiers in high-risk areas use chloroquine/primaquine chemoprophylaxis to prevent malaria, control of mosquito larvae through larviciding also can be used to reduce the risk of malaria transmission. In order to estimate the cost of larviciding, accurate estimates of the spatial extent of mosquito larval habitats are necessary. The purpose of this study was to determine whether an accurate estimate of the area covered by mosquito larval habitats can be obtained using Landsat 7 Enhanced Thematic Mapper+ (ETM+) and/or IKONOS data for the Korean test site.To estimate the area covered by larval habitats near Camp Greaves [Paekyeon-Ri, near Tongil-Chon (village)] in the ROK, an IKONOS and a Landsat 7 ETM+ image were classified using a parallelepiped classification. In a comparison with rice paddy field sites, 24 (92%) of the sites were classified correctly on the IKONOS image and 17 (65%) were classified correctly on the Landsat image. Comparing the classifications on a pixel-by-pixel basis, the agreement between the two classifications was 79%. Part of the disagreement was due to the difference in resolution of the two images. In spite of local differences, the two classifications produced similar area estimates.Although either Landsat or IKONOS could be used in Korea for a reasonable estimate of habitat area, only IKONOS can resolve small irrigation ponds. While ponds represent a small portion of the total larval habitat, they are an important source for mosquito breeding during the late rice-growing season in the ROK since they contain higher larval densities. High-resolution imagery, such as IKONOS, would be necessary for planning and implementing treatment of these smaller habitats. (C) 2003 Elsevier Inc. All rights reserved.

Collections of Anopheles darlingi Root and An. albimanus Wiedemann from central and northern Belize were conducted as landing captures from 6:30 to 8:00 p.m. to define spatial distributions and outdoor:indoor ratios of biting during the early evening. In central Belize, collections were made at 31 houses in riparian zones (> or = 1 km from rivers) and 14 houses in upland zones (>1 km from rivers) during the dry and wet seasons of 1993 and 1994. Females of both species were abundant in houses < or = 1 km from rivers. Females were not present in houses located in upland areas during the dry season, but were present in the wet season. A total of 63 paired collections (representing 130 individual captures) from 42 houses showed An. darlingi females were more endophagic (ratio of 1:0.6) during the early evening than were An. albimanus females (ratio of 1:0.21). Paired landing collections from 22 houses in riparian zones in April-May were analyzed in an index of species abundance (ISA). ISA values rated An. darlingi as the dominant Anopheles mosquito indoors and An. albimanus was dominant outside. Although An. darlingi and An. albimanus were abundant in riparian zones, there was no association in their numerical abundance, suggesting that different environmental factors influenced their abundance. In northern Belize, one house for each of 16 villages was sampled during April and May 1994. Large numbers ofAn. albimanus were captured outdoors in houses located in riparian and marshland areas (means of 217.5 and 247.5/1.5 personhours outdoors, respectively). Numbers of An. albimanus were low at houses located away from rivers and marshes (12.2 per collection). Anopheles darlingi was uncommon at sites in northern Belize. Proportionally fewer An. albimanus females entered houses in the north (outdoor:indoor ratio of 1:0.16) compared to the central region (ratio of 1:0.21), which probably reflects differences in house construction, anti-mosquito behavior (i.e., closing windows and doors at sunset), and insecticide treatments. The ISA gave a quantitative assessment of vector dominance in relation to the parameters of spatial distribution and numerical abundance. The index was also sensitive to the variables of indoor and outdoor biting behaviors.

Bartonella bacilliformis has caused debilitating illness since pre-Incan times, but relatively little is known about its epidemiology. A population-based, prospective cohort investigation was conducted in a Peruvian community with endemic bartonellosis. By use of house-to-house and hospital surveillance methods, cohort participants were monitored for evidence of bartonellosis. Of 690 participants, 0.5% had asymptomatic bacteremia at study initiation. After 2 years of follow-up, the incidence of infection was 12.7/100 person-years. The highest rates were in children <5 years old, and there was a linear decrease in incidence with increasing age. Seventy percent of cases were clustered in 18% of households. Age and bartonellosis in a family member were the best predictors of B. bacilliformis infection. There were multiple clinical presentations and significant subclinical infection. A cost-effective control strategy should include vector control and surveillance efforts focused on children and clusters of households with highest endemicity.

A cost-comparison of two methods for the control of malaria in the Republic of Korea was performed. The cost of larviciding with methoprene granules was estimated at $93.48/hectare. The annual cost of providing chemoprophylaxis was estimated at $37.53/person. Remote sensing and geographic information systems were used to obtain estimates of the size of vector larval habitats around two U.S. Army camps, allowing an estimate of the cost of larviciding around each of the camps. This estimate was compared to the cost of providing chloroquine and primaquine chemoprophylaxis for the camp populations. Costs on each of the camps differed by the size of the larval habitats and the size of the at-risk population. These tools allow extrapolation of larval surveillance data to a regional scale while simultaneously providing site-specific cost analysis, thus reducing the cost and labor associated with vector surveillance over large areas.

The consequences of climate variability on human health, especially for poor and medically underserved populations, have received much attention in recent years. Some of the most severe health hazards induced by climate variability are epidemics of vector‐borne infectious diseases. Entomologic studies have shown that insect vectors that transmit diseases, such as malaria, yellow fever, dengue, etc., are sensitive to temperature, humidity wind, and rainfall patterns, and therefore, their abundance is potentially influenced by climate variability. Because of its geographical location, the climate of tropical South America is strongly influenced by El Niño. The episodic outbreaks of various diseases in this region have been linked to the El Niño cycles. Yet, according to a report of the World Health Organization [1999], early results from South American epidemiological studies, which were based on the aggregated national disease data irrespective of the regional meteorological impacts, found no consistent correlation between the El Niño effect with the epidemics of malaria and yellow fever.

Bartonellosis is a vector-borne, highly fatal, emerging infectious disease, which has been known in the Peruvian Andes since the early 1600s and has continued to be a problem in many mountain valleys in Peru and other Andean South American countries. The causative bacterium, Bartonella bacilliformis (Bb), is believed to be transmitted to humans by bites of the sand fly Lutzomyia verrucarum. According to available medical records, the transmission of infection often occurs in river valleys of the Andes Mountains at an altitude between 800 and 3500 meters above sea level. It shows a seasonal pattern, which usually begins to rise in December, peaks in February and March, and is at its lowest from July until November. The epidemics of bartonellosis also vary interannually, occurring every four to eight years, and appear to be associated with the El Nino cycle. In response to the National Oceanic and Atmospheric Administration (NOAA) announcement on climate variability and human health, which was constructed to stimulate integrated multidisciplinary research in the area of climate variability and health interactions, we have conducted a study to investigate the relationship between the El Nino induced regional climate variation and the outbreak of bartonellosis epidemics in Peru. Two test sites, Caraz and Cusco, were selected for this study. According to reports, Caraz has a long-standing history of endemic transmission and Cusco, which is located about five degrees poleward of Caraz, had no recorded epidemics until the most recent 1997/1998 El Nino event. The goal of this study is to clarify the relative importance of climatic risk factors for each area that could be predicted in advance, thus allowing implementation of cost-effective control measures, which would reduce disease morbidity and mortality.

Then is an increasing use of remote sensing and geographical information systems (GIS) by Earth science researchers to study public health problems such as vectorborne disease and environmental health. However, because remote sensing and GIS courses are not traditionally taught to medical personnel, there is a lack of understanding among many in the medical community about these techniques and their potential for studying health problems. In 1998, the Uniformed Services University of the Health Sciences (USUHS), a medical school under the Department of Defense, received a NASA grant to establish a Center of Excellence in Remote Sensing which enabled USUHS to begin offering a formal graduate course, "Remote Sensing and GIS Methods in Public Health". The course has been taught twice to public health students from a variety of backgrounds including medicine, entomology and environmental health. None of the students had a remote sensing background and only one student had experience in using GIS. The course emphasizes the use of remote sensing and GIS as a tool applied to better understanding of infectious disease and environmental health interactions. The goal of the course is to give students a combination of theoretical background, examples of applications in the literature and hands-on experience in using hardware and software that will enable them to use remote sensing and GIS in their research. Because most of the students are unfamiliar with remote sensing or GIS, the course must cover the basic aspects of these topics.

Females of Anopheles albimanus mosquito are known to prefer floating cyanobacterial mats over open water for oviposition. We used Solid Phase MicroExtraction (SPME) devices on-site to trap substances volatilized from these two environments, followed by analysis by GC-MS (gas chromatograph-mass spectrometer). In enclosed headspace field microcosms, an unidentified C-15 aliphatic alcohol was persistently found over cyanobacterial mats as compared to open water. Based on this finding, we conducted oviposition experiments using a commercially available compound, n-pentadecanol, close in molecular weight and mass spectral pattern to the unknown C-15 aliphatic alcohol. The results indicate a tendency of female mosquito to oviposit more eggs in containers with the tested chemical as compared to water and blank.

Surveys of larval habitats of Anopheles vestitipennis and Anopheles punctimacula were conducted in Belize, Central America. Habitat analysis and classification resulted in delineation of eight habitat types defined by dominant life forms and hydrology. Percent cover of tall dense macrophytes, shrubs, open water, and pH were significantly different between sites with and without An. vestitipennis. For An. punctimacula, percent cover of tall dense macrophytes, trees, detritus, open water, and water depth were significantly different between larvae positive and negative sites. The discriminant function for An. vestitipennis correctly predicted the presence of larvae in 65% of sites and correctly predicted the absence of larvae in 88% of sites. The discriminant function for An. punctimacula correctly predicted 81% of sites for the presence of larvae and 45% for the absence of larvae. Canonical discriminant analysis of the three groups of habitats (An. vestitipennis positive; An. punctimacula positive; all negative) confirmed that while larval habitats of An. punctimacula are clustered in the tree dominated area, larval habitats of An. vestitipennis were found in both tree dominated and tall dense macrophyte dominated environments. The forest larval habitats of An. vestitipennis and An. punctimacula seem to be randomly distributed among different forest types. Both species tend to occur in denser forests with more detritus, shallower water, and slightly higher pH. Classification of dry season (February) SPOT multispectral satellite imagery produced 10 land cover types with the swamp forest and tall dense marsh classes being of particular interest. The accuracy assessment showed that commission errors for the tall, dense marsh and swamp forest appeared to be minor; but omission errors were significant, especially for the swamp forest (perhaps because no swamp forests are flooded in February). This means that where the classification indicates there are An. vestitipennis breeding sites, they probably do exist; but breeding sites in many locations are not identified and could be more abundant than indicated.

As part of a larger on-going investigation to study the disease bartonellosis, remote sensing images are being used to map the study area and to help determine environmental factors that may influence the abundance of sand flies, the insect thought to be the vector of the disease. A plot of positive patient houses on a Landsat image shows that most of the cases occur in the agricultural areas and few cases occur in the town. The disease does not occur more frequently near the river. One of the classes produced from an unsupervised classification of a Landsat image occurs frequently with the positive houses and infrequently with the negative houses. Additional positive and negative houses are needed to confirm this result and future studies will attempt to determine what environmental factors are represented by the class and how these factors might relate to sand fly distribution.

We report on an integrated methodology of remote sensing and geographic information systems (GIS) to assess the risk of malaria transmission in the villages of southern Belize. Studies were initiated in 1990 that characterized the environmental requirements of the important Anopheles mosquitoes in Belize. A data set of environmental criteria was compiled to assess relative risk for the villages. Risk was defined as the presence and abundance of vector mosquitoes for malaria transmission based on environmental criteria. An integrated GIS was employed for differentiating villages of high and low risk. The villages were ranked according to several factors, e.g., elevation, distance to major rivers or streams, and landuse. The predictions included the identification of the 10 highest and the 10 lowest "villages of risk." A field survey team was then employed to test presence/abundance of the three important vector species in each of the 20 villages.

Culex tritaeniorhynchus is the primary vector of Japanese encephalitis virus (JEV) throughout much of the tropical and temperate climates of Asia. Several recent papers have used ecological niche modeling programs, e.g., Maxent and GARP, to predict the distribution of disease vectors (e.g. Peterson and Shaw 2003, Moffett et al. 2007). In this on-going study, we used the Maxent program to model the distribution of Cx. tritaeniorhynchus in the Republic of Korea. Using mosquito collection data, temperature, precipitation, elevation, land cover, and SPOT normalized difference vegetation index (NDVI), models were created for each month for a period of five years. Output maps from the models matched several known ecological characteristics of this species' distribution. The output maps show the highest probabilities of mosquito occurrence in August and September, which correlates to the observed mosquito population density peaks. The model demonstrated low probabilities for forest covered mountains, which corresponds to findings in the literature that Cx. tritaeniorhynchus is infrequently found above 1,000 meters. The modeling effort demonstrated several limitations in the data set, including a low number of collection sites that did not cover the full range of environmental conditions within the study area. Additional collection sites would improve the models and allow for improved testing of the results. Future goals of this project include developing real-time predictions based on NDVI data and expanding the prediction to a larger geographical area.