A mark release-recapture study to define the flight behaviors of Anopheles vestitipennis and Anopheles albimanus in Belize, Central America.

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.

A mark-release-recapture study to define the flight behaviors of Anopheles vestitipennis and Anopheles albimanus in Belize, Central America

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 September­October 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.

Biting patterns and seasonal densities of Anopheles mosquitoes in the Cayo District, Belize, Central America with emphasis on Anopheles darlingi.

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.

Experimental evaluation of overhanging bamboo in Anopheles darlingi larval habitat selection in Belize, Central America.

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.

Use of remote sensing and geographic information systems to predict locations of Anopheles darlingi-positive breeding sites within the Sibun River in Belize, Central America.

Previous studies have identified several anopheline species integral to the transmission of malaria in Belize. The highly efficient vector, Anopheles darlingi Root, is currently considered the most important. The preferred larval habitat of An. darlingi has been described as floating detritus patches, which are commonly associated with overhanging spiny bamboo, Guadua longifolia (E. Fourn.), along river margins. The objectives of this study were to use remote sensing and geographic information system (GIS) tools to 1) define the landscape features (i.e., river curvature, land cover, and house locations) associated with An. darlingi-positive breeding habitats and 2) determine the association between cleared land cover and the growth of spiny bamboo. A systematic survey was conducted in which all detritus patches of at least 1 m2 were sampled, mapped using GPS, and characterized by cause of habitat lodging. Bamboo stretches growing along the river margins also were mapped. Spatial analyses of satellite imagery found no associations between river characteristics or land cover with positive An. darlingi habitats. In addition, there was no significant difference in cleared versus forested land cover in relation to the presence or absence of bamboo. Results indicate that the average distance from homes to negative habitats was significantly greater than from positive detritus mats. Based on the land cover and river characteristics used, our results do not support the use of remote sensing as a predictive tool to locate specific areas within rivers positive for An. darlingi habitats.

Comparative susceptibility of three species of Anopheles from Belize, Central America, to Plasmodium falciparum (NF-54).

In August of 2000, a comparative susceptibility study was conducted using 3 species of Anopheles mosquitoes from Belize, Central America, and a standard species used in laboratory infection studies, Anopheles stephensi. Test populations were fed human blood infected with cultured Plasmodium falciparum (NF-54 strain) parasites via a membrane feeder. The control species, An. stephensi, exhibited the highest infections, with 73.8% of dissected specimens positive for sporozoites in the salivary glands. The control species also showed heavier sporozoite loads; 74.0% of positive glands having greater than 200 sporozoites. Of species from Belize, Anopheles darlingi was the most susceptibile, e.g., 41.0% of salivary glands were positive, with more than 200 sporozoites per gland. Anopheles vestitipennis had a low salivary gland infection rate (9.3%) and a moderate number of sporozoites in glands (i.e., 85.7% containing 50-250 sporozoites). Anopheles albimanus was the least susceptible species to infection. No specimens of An. albimanus from the Golden Stream population developed sporozoites in the salivary glands, yet 20.7% of dissected specimens had positive midgut infections. The An. albimanus Buena Vista population showed similar results with only a 2.2% salivary gland infection rate and a 21.5% midgut infection rate. Oocysts in An. stephensi increased in size by 20% after day 10. Development peaked at day 12, with a mean oocyst diameter of 58 microm at onset of oocyst differentiation. Oocysts developed more slowly in An. vestitipennis until day 10. After day 10, there was a 53% increase in oocyst development over the previous 10 days. Oocyst differentiation was not observed until day 13 postfeed. As with An. vestitipennis, both populations of An. albimanus showed similar slow rates of oocyst development; however, no dramatic growth increase occurred after day 10. The oocysts in the Golden Stream population exhibited a cessation of growth after day 10, peaking at a mean of 30 microm. The Buena Vista population did not exhibit the same level of reduced oocyst development. A gradual increase in growth continued until days 13 and 14 (36.7 and 35.7 microm, respectively).

Evaluation of habitat management strategies for the reduction of malaria vectors in northern Belize.

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 subaquatic 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 ofAn. 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 Parapleapuella.

A mark-release-recapture study using a novel portable hut design to define the flight behavior of Anopheles darlingi in Belize, Central America.

Knowledge of the flight behavior of local vectors is of paramount importance in mosquito control programs. The following study defined the recapture rate of wild-caught, unengorged Anopheles darlingi females at 0, 400, and 800 m from a fixed release point in Belize, Central America, using a newly designed portable experimental hut. Three sampling trials, each consisting of 2 12-h collections, were performed at all distances from July 2002 to June 2003. A total of 1,185 An. darlingi were marked and released during the course of the study. The recapture rate was greatest at 0 m (29.0%; 124/428) and declined from 11.6% (37/318) at 400 m to 5.8% (21/361) at the 800-m site. There was no difference between the average number of marked mosquitoes recaptured inside the experimental hut versus outside the hut at any distance location. Recapture rates of each trial were highest during the first night's collection at all locations. Further examination of the first night data revealed a variation in the peak time of recapture by distances from the release point. The peak in nightly recapture at both the 0- and 400-m sites occurred within the first 2 h after sunset, and the peak recapture at the 800-m site occurred during the 7th h after sunset. Information from the present study is the first to describe the flight behavior of An. darlingi in Belize and will benefit in the development of adult-density risk assessments at the house level based on distances from potential vector breeding sites.

A mark-release-recapture study using a novel portable hut design to define the flight behavior of Anopheles darlingi in Belize, Central America

Knowledge of the flight behavior of local vectors is of paramount importance in mosquito control programs. The following study defined the recapture rate of wild-caught, unengorged Anopheles darlingi females at 0, 400, and 800 m from a fixed release point in Belize, Central America, using a newly designed portable experimental hut. Three sampling trials, each consisting of 2 12-h collections, were performed at all distances from July 2002 to June 2003. A total of 1,185 An. darlingi were marked and released during the course of the study. The recapture rate was greatest at 0 m (29.0%; 124/428) and declined from 11.6% (37/318) at 400 m to 5.8% (21/361) at the 800-m site. There was no difference between the average number of marked mosquitoes recaptured inside the experimental hut versus outside the hut at any distance location. Recapture rates of each trial were highest during the first night's collection at all locations. Further examination of the first night data revealed a variation in the peak time of recapture by distances from the release point. The peak in nightly recapture at both the 0- and 400-m sites occurred within the first 2 h after sunset, and the peak recapture at the 800-m site occurred during the 7th h after sunset. Information from the present study is the first to describe the flight behavior of An. darlingi in Belize and will benefit in the development of adult-density risk assessments at the house level based on distances from potential vector breeding sites.

Epidemiology of endemic Bartonella bacilliformis: a prospective cohort study in a Peruvian mountain valley community.

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.

Role of residual spraying for malaria control in Belize.

We studied the impact of reduced residual spraying in Belize by developing a logistic regression model on relationships between numbers of houses sprayed (mostly with DDT) and numbers of malaria cases. We defined the "minimum effective house spray rate" (MEHSR) as the level of spraying that will prevent increases in malaria rates for a defined population. Under the total coverage approach (all houses sprayed), the MEHSR for Belize was 134.6. The model also showed that the odds for decreasing malaria is 1.086 for each increase of 10 houses sprayed per 1,000 population. In further testing, highly significant and differential changes in malaria rates were documented for paired groups of years with house spray rates that were either above or below the MEHSR. Numbers of malaria cases since 1995 are used to show how stratification methods are used in Belize to spray fewer houses (at levels below the MEHSR of 134.6).

Host feeding preferences of Anopheles species collected by manual aspiration, mechanical aspiration, and from a vehicle-mounted trap in the Toledo District, Belize, Central America.

The host-feeding patterns of Anopheles albimanus, Anopheles vestitipennis, and Anopheles punctimacula from the Toledo District in southern Belize were studied with blood-fed females that were collected by manual aspiration, a backpack aspirator, and a vehicle-mounted trap for sampling in-flight mosquito populations. Female An. vestitipennis collected from both inside and outside house walls by manual aspiration tested positive for human blood meals (88 and 67%, respectively). At increasing distances from the houses, specimens of An. vestitipennis collected from vegetation with the backpack aspirator were equally positive for human and cattle blood (44 and 43%, respectively). In contrast, 68% of the An. albimanus specimens (148) collected by backpack aspiration tested positive for cattle blood. Engorged An. vestitipennis from vehicle-mounted trap collections tested positive for cattle (108) and human (52) blood. Almost all specimens of An. albimanus from these collections were positive for cow (95%). After analyzing the data from the An. vestitipennis samples using the feeding index, the ratio of human blood to all other bloodmeal sources showed indices greater than 1. Both An. albimanus and An. punctimacula fed mostly on cattle and rarely fed on humans. Foraging ratios for the 3 Anopheles species were very similar to the feeding indexes. Ratios based on data from all collection methods showed that An. vestitipennis feeds predominately on humans. The foraging ratios for An. albimanus demonstrated consistent preferences for nonhuman hosts. As with previous studies. An. albimanus seemed to prefer cattle and pigs to almost all other host species.