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).

Plasmodium-infected Anopheles mosquitoes collected in Virginia and Maryland following local transmission of Plasmodium vivax malaria in Loudoun County, Virginia.

Two recent outbreaks of locally acquired, mosquito-transmitted malaria in Virginia in 1998 and 2002 demonstrate the continued risk of endemic mosquito-transmitted malaria in heavily populated areas of the eastern United States. Increasing immigration, growth in global travel, and the presence of competent anopheline vectors throughout the eastern United States contribute to the increasing risk of malaria importation and transmission. On August 23 and 25, 2002, Plasmodium vivax malaria was diagnosed in 2 teenagers in Loudoun County, Virginia. The Centers for Disease Control and Prevention (CDC) deemed these cases to be locally acquired because of the lack of risk factors for malaria, such as international travel, blood transfusion, organ transplantation, or needle sharing. The patients lived approximately 0.5 mi apart; however, 1 patient reported numerous visits to friends who lived directly across the street from the other patient. Two Anopheles quadrimaculatus s.l. female pools collected in Loudoun County, Virginia, and 1 An. punctipennis female pool collected in Fairfax County, Virginia, tested positive for P. vivax 210 with the VecTest panel assay and enzyme-linked immunosorbent assay (ELISA). In addition, 2 An. quadrimaculatus s.l. female pools collected in Montgomery, Maryland, tested positive for P. vivax 210. The CDC confirmed these initial results with the circumsporozoite ELISA. The authors believe that this is the 1st demonstration of Plasmodium-infected mosquitoes collected in association with locally acquired human malaria in the United States since the current national malaria surveillance system began in 1957.

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.

Experimental transmission of St. Louis encephalitis virus by Ochlerotatus j. japonicus.

Ochlerotatus japonicus japonicus a newly discovered nonindigenous mosquito species in North America, and a colonized strain of Culex pipiens were compared for their vector competence for St. Louis encephalitis virus (SLE). Infection rates in Oc. j. japonicus were 0-33% after feeding on chickens with viremias between 10(4.1) and 10(4.7) plaque-forming units (PFU)/ml of blood. In comparison, infection rates were 12-94% for Cx. pipiens that fed on the same chickens. When fed on chickens with viremias between 10(5.3) and 10(5.6) PFU/ml of blood, infection rates for Oc. j. japonicus and Cx. pipiens were similar, 96% and 100%, respectively. After 12-14 days of extrinsic incubation at 26 degrees C, all 34 infected Oc. j. japonicus had a disseminated infection. In contrast, only 23 (43%) of 54 infected Cx. pipiens had a disseminated infection after feeding on the same chickens. If they developed a disseminated infection, both species efficiently transmitted (> or = 87%) SLE. Estimated transmission rates at viral doses sufficient to infect both of the tested species were 29-84% for Oc. j. japonicus and 30-50% for Cx. pipiens. Because of its continued geographic expansion, field and laboratory evidence incriminating it as a vector of the closely related West Nile virus, and its ability to transmit SLE in the laboratory, Oc. j. japonicus should be considered as a potential enzootic or epizootic vector of SLE.

Environmental factors associated with larval habitats of malaria vectors in northern Kyunggi Province, Republic of Korea.

The larval habitats of malaria vectors near the Demilitarized Zone of the Republic of Korea (ROK) were sampled from June through September 2000 to determine larval abundance and to identify environmental factors associated with high larval density. Six primary habitats were identified: rice fields, irrigation ditches, drainage ditches, stream pools, irrigation pools, and marshes. Most habitats harbored similar densities of larvae until August and September, when population densities in rice fields declined and those in irrigation pools increased. The primary vector in the ROK, Anopheles sinensis, occurred in water with a wide range of values for environmental factors, including pH, total dissolved solids, percent of surface covered with floating vegetation, and nitrate and phosphate concentrations. No environmental factor or combination of factors were found that were predictive of high larval densities. This study suggests that larval Anopheles are capable of developing in a wide range of stagnant, freshwater habitats in northern Kyunggi Province, ROK.

A cost comparison of two malaria control methods in Kyunggi Province, Republic of Korea, using remote sensing and geographic information systems.

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.

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.

Laboratory transmission of La Crosse virus by Ochlerotatus j. japonicus (Diptera: Culicidae).

Ochlerotatus j. japonicus, a recent introduction to the United States, was studied to determine its capability to serve as a vector of La Crosse (LAC) virus. A field-collectedpopulation of Ochlerotatus triseriatus, the primary vector of LAC virus, was similarly tested for comparison. After Oc. j. japonicus ingested virus fromhamsters with viremias of 10(3.6-5.4) plaque-forming units (PFU)/ml of blood, its estimated transmission rates were 35-88%. These rates were slightly lower than, though similar to, those for Oc. triseriatus, 75-100%. Viral titers in Oc. j. japonicus peaked at approximately 10(5.5) PFU/ mosquito about 7 d after ingesting blood meal in which the concentration of LAC virus was PFU/ml of blood; virus had disseminated from the midgut in 100% (8/8) of these specimens. These data, combined with the close association between the habitats of Oc. j. japonicus and Oc. triseriatus and the reported expansion of the range of this newly discovered species in the eastern United States, indicate that Oc. j. japonicus could function as an additional vector of LAC virus.

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).

Experimental transmission of eastern equine encephalitis virus by Ochlerotatus j. japonicus (Diptera: Culicidae).

We evaluated the potential for Ochlerotatus j. japonicus (Theobald), a newly recognized invasive mosquito species in the United States, to transmit eastern equine encephalitis (EEE) virus. Aedes albopictus (Skuse) and Culex pipiens (L.) were similarly tested for comparison. Ochlerotatus j. japonicus and Ae. albopictus became infected and transmitted EEE virus by bite after feeding on young chickens 1 d after they had been inoculated with EEE virus (viremias ranging from 10(7.0-8.7) plaque-forming units [PFU]/ml of blood). No Cx. pipiens (n = 20) had detectable levels of virus 14 d after feeding on an EEE-virus infected chicken with a viremia of 10(8.1) PFU per ml of blood. Depending on the viral titer in the donor chicken, infection rates ranged from 55-100% for Oc. j. japonicus and 93-100% for Ae. albopictus. In these two species, dissemination rates were identical to or nearly identical to infection rates. Depending on the viral titer in the blood meal, estimated transmission rates ranged from 15 to 25% for Oc. j. japonicus and 59-63% for Ae. albopictus. Studies of replication of EEE virus in Oc. j. japonicus showed that there was an "eclipse phase" in the first 4 d after an infectious blood meal, that viral titers peak by day 7 at around 10(5.7) per mosquito, and that virus escaped the mid-gut as soon as 3 d after the infectious blood meal. These data, combined with the opportunistic feeding behavior of Oc. j. japonicus in Asia and the reported expansion of its range in the eastern United States, indicate that it could function as a bridge vector for EEE virus between the enzootic Culiseta melanura (Coquillett)-avian cycle and susceptible mammalian hosts.

Vector competence of three North American strains of Aedes albopictus for West Nile virus.

To evaluate the potential for North American (NA) Aedes albopictus to transmit West Nile virus (WN), mosquito strains derived from 3 NA sources (Frederick County, Maryland, FRED strain; Cheverly, MD, CHEV strain; Chambers and Liberty counties, Texas, TAMU strain) were tested. These strains were tested along with a previously tested strain from a Hawaiian source (OAHU strain). Mosquitoes were fed on 2- to 3-day-old chickens previously inoculated with a New York strain (Crow 397-99) of WN. All of the NA strains were competent laboratory vectors of WN, with transmission rates of 36, 50, 83, and 92% for the FRED, CHEV, OAHU, and TAMU strains, respectively. The extrinsic incubation period for WN in Ae. albopictus held at 26 degrees C was estimated to be 10 days. Based on efficiency of viral transmission, evidence of natural infection, bionomics, and distribution, Ae. albopictus could be an important bridge vector of WN in the southeastern USA.

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.