Aedes aegypti population sampling using BG-Sentinel traps in north Queensland Australia: statistical considerations for trap deployment and sampling strategy

BG-Sentinel mosquito traps were trialed as a tool for the rapid assessment (24-h collections) and routine monitoring (72-h collections) of adult Aedes aegypti L. populations in north Queensland. Analysis of Ae. aegypti collections using BG-Sentinels set in suburban Cairns for 24 h permitted the calculation of sample size for a range of precision levels. Clusters of houses with BG-Sentinels operating continuously for 15 d, with collections every 72 h, also permitted required sample size calculation. Evidence of Ae. aegypti spatial clustering at the house scale was revealed, with statistically significant effects detected for all collection days. Less variation was detected at each trap location, with only nine of 32 trap locations revealing significant clustering over time. Trap-out effects through continuous BG-Sentinel operation at a fixed location were absent. The findings support fixed position sampling at 72-h intervals for routine monitoring ofAe. aegypti populations in Cairns. Despite the relationship between collections of adult vectors and the incidence of disease remaining unknown, BG-Sentinel collections provide an alternative and less labor-intensive abundance measure for assessing risk of dengue virus transmission and success of dengue vector control programs.     

Integrated control of peridomestic larval habitats of Aedes and Culex mosquitoes (Diptera: Culicidae) in atoll villages of French Polynesia

An integrated larval mosquito control program was carried out in Tiputa village on Rangiroa atoll of French Polynesia. Mosquito abundance before and after treatment was compared with the abundance in an untreated village. Mosquito larval habitats consisted of large concrete or polyurethane cisterns, wells, and 200-liter drums. Depending on the target species, larval habitat category, its configuration, and purpose (drinking consumption or not), abatement methods consisted of sealing the larval habitats with mosquito gauze, treating them with 1% Temephos, covering the water with a 10-cm thick layer of polystyrene beads or introducing fish (Poecillia reticulata Rosen & Bailey). All premises of the chosen village were treated and a health education program explained basic mosquito ecology and the methods of control. A community health agent was trained to continue the control program at the end of the experiment. Entomological indices from human bait collections and larval surveys indicated that mosquito populations were reduced significantly, compared with concurrent samples from the untreated control village, and that mosquito control remained effective for 6 mo after treatment. Effects of the treatment were noticed by the inhabitants in terms of a reduction in the number of mosquito bites. In the Polynesian context, such control programs may succeed in the long-term only if strong political decisions are taken at the village level, if a community member is designated as being responsible for maintaining the program, and if the inhabitants are motivated sufficiently by the mosquito nuisance to intervene.     

Release of Mesocyclops aspericornis (Copepoda) for control of larval Aedes polynesiensis (Diptera: Culicidae) in land crab burrows on an atoll of French Polynesia.

On Tereia Island, Rangiroa Atoll, 14,321 land crab burrows were treated with the copepod Mesocyclops aspericornis from January to June 1986, to control larvae of Aedes polynesiensis marks. In October 1987, the entire island of Tereia was retreated (17,300 burrows), and the neighboring island, Voisin, was left untreated as a control. From 5 to 15 mo after treatment, burrows with M. aspericornis contained an average of 2 Ae. polynesiensis immatures compared with 97 immatures from untreated burrows. Long-term larval control was successful in low-lying areas where burrows remained wet or were reflooded. Although there may have been other contributing factors, the major reason for lack of persistence of M. aspericornis in burrows over the entire island appeared to be poor resistance to desiccation. From all treated burrows in October 1987, M. aspericornis subsequently was found in 89.5, 39.1, and 24.1% of burrows sampled 5, 8, and 15 mo after treatment, respectively. The broad-scale results for Tereia indicated that there was no reduction of adult biting indices when compared with Voisin. Mark-release experiments on four occasions indicated that Ae. polynesiensis had a limited flight range and that the probability for interisland movement was low.     

Aedes aegypti (L.) and Aedes polynesiensis Marks (Diptera: Culicidae) in Moorea, French Polynesia: a study of adult population structures and pathogen (Wuchereria bancrofti and Dirofilaria immitis) infection rates to indicate regional and seasonal epidemiological risk for dengue and filariasis

Populations of Aedes aegypti (L.) and Aedes polynesiensis (Marks) on Moorea Island, French Polynesia, the local vectors of dengue and filariasis, respectively, were sampled by landing/biting collection at nine localities on the east, north, and west coasts, during the late dry season, early and late wet season (September-May) 2003 and 2004, to investigate epidemiologically important features of the populations and compare them between regions and months. Biting rates of both species tended to increase (but not always significantly) for each species in each region each month from the late dry season to the late wet season, and the north coast region had significantly higher biting rates of Ae. aegypti. Insemination rates of Ae. polynesiensis females (94.5-98.8%) were consistently greater than those of Ae. aegypti (87.5-93.5%) throughout the study, but there was no significant difference in the insemination rates of either species between months and regions. Parity rates were generally highest in north coast samples and lowest in west coast samples for both species and generally increased (albeit not always significantly) by month for each species, with a range of 52.9-88.8% for Ae. polynesiensis and 28.6-53.6% for Ae. aegypti, although the high gravid rate (15.8-45.9%) of Ae. aegypti samples (reflecting its feeding more than once in a gonotrophic cycle) confounded both intraspecific and interspecific comparisons. Filarial infection was rare in Ae. aegypti, although both W. bancrofti and D. immitis were recorded, and infection rates in Ae. polynesiensis increased through the study period in each region for both filarias, with up to 4.6% infected and 1.4% infective for W. bancrofti and up to 6.3% infected and 2.5% infective for D. immitis. For W. bancrofti, infection rates were significantly lower on the west coast and also in the dry season, whereas rates for infective stages were significantly greater in the late wet season. For D. immitis there was no significant difference in infection rates between regions, but rates were significantly greater in the late wet season. Rainfall in all months sustains populations of both vectors and explains the relatively few significant differences between seasons; however, the wet season may provide for increased vector abundance and longevity, and present a potentially increased risk for transmission. Although the differences shown between regions also were limited in a statistical sense, there were increased risks for the northern and eastern regions, where both locals and tourists are concentrated and where the seaports and airport are located, and these areas should be priority targets for disease surveillance and vector control.     

A study on distribution and seasonal abundance of Aedes albopictus (Diptera: Culicidae) population in Athens, Greece

In September 2008, Aedes (Stegomyia) albopictus (Skuse 1894), a mosquito of great medical importance, was reported for the first time in a district of Athens, Greece. The following year, its distribution and population abundance over time around its first detection site was investigated. A network of 50 ovitraps was established in a surrounding area of 25 km2 and monitored for 17 mo from 17 August 2009 through 31 December 2010. Weekly servicing of the ovitraps and subsequent laboratory treatment of the collected mosquito eggs, revealed that Ae. albopictus is the dominant container breeding Aedes species and is widespread in the entire study area. The seasonal monitoring showed that this mosquito is continuously active from mid spring until the end of December with a considerably high oviposition activity recorded during summer and fall. Moreover, comparison of its activity during late August and end of December, between the two consecutive surveillance years, indicated a significant increase of population abundance the second year. The current study suggests the necessity of setting up in the city of Athens an integrated surveillance program in a greater scale for Asian tiger mosquito's effective control.     

Adult size and distribution of Aedes aegypti (Diptera: Culicidae) associated with larval habitats in Iquitos, Peru

Adult mosquito size may be related to longevity, feeding frequency, and other factors that impact vectorial capacity. Various investigations have shown that characteristics of larval mosquito habitats influence adult size. We studied breeding container characteristics in relation to size and abundance of Aedes aegypti larvae and pupae in Iquitos, Peru, and compared these with the size of resulting adult females. During 22 May to 20 July 2000, immature mosquitoes were collected from 12,722 containers in 2,931 houses, of which 424 held > or =1 Ae. aegypti. A subsample of larvae and all 16,433 pupae detected was removed for study. Resting adult mosquitoes were also collected from the same houses as the immatures. Adult mosquito size was determined by measuring the wing lengths of 672 aspirated adults and 2,316 adult females that emerged from container-derived pupae. Immatures were most commonly found in rain-filled containers, located outside of houses, and without lids. The average wing length of females derived from pupae varied considerably (1.67-3.83 mm), with slightly less variation for females captured as adults (1.80-3.23 mm). Linear regression showed that average wing length of pupae-derived females was positively associated with presence of larvae, container-filling method, diameter of container, and density of females. Size of pupae-derived females was correlated with that of females captured in the same houses as adults. The geographic distribution of pupae and adults indicated that the spatial pattern for Ae. aegypti is heterogeneous, with areas of higher and lower abundance. These findings provide insight for more focused control efforts aimed at reducing Ae. aegypti-borne pathogens.     

Wolbachia effects on host fitness and the influence of male aging on cytoplasmic incompatibility in Aedes polynesiensis (Diptera: Culicidae)

The endosymbiotic bacteria Wolbachia manipulate host reproduction by inducing a form of sterility known as cytoplasmic incompatibility (CI), promoting the invasion of infection into natural host populations. CI has received attention for use in applied strategies to control insect vectors of disease. Thus, to understand both naturally occurring Wolbachia invasions and evaluate potential applied strategies, it is important to understand Wolbachia interactions with its host, including impacts on fitness and the CI level. In this study, we examined for an effect of Wolbachia on survivorship, developmental time, sex ratio, longevity, fecundity, and egg hatch of Aedes polynesiensis Marks, which is the primary vector of Wuchereria bancrofti in the South Pacific. In this study, we have compared strains of A. polynesiensis that are naturally and artificially infected with Wolbachia and additional strains that are aposymbiotic (Wolbachia removed to generate an uninfected strain). Artificially infected strains were observed to have increased larval mortality and decreased adult longevity when compared with aposymbiotic strains. Naturally infected strains were observed to have decreased larval mortality, pupal mortality, increased adult longevity, and a larger adult size when compared with aposymbiotic strains. Artificially infected males that were 4 wk old were able to induce high rates of CI, similar to young males. We discuss the results in relation to the natural spread of Wolbachia and Wolbachia-based applied strategies to modify A. polynesiensis populations.     

Environmental factors associated with spatial and temporal distribution of Anopheles (Diptera: Culicidae) larvae in Sukabumi, West Java, Indonesia

A 12-mo ecological study of the spatial-temporal distribution of immature stages of Anopheles species was conducted in Sukabumi District, West Java, Indonesia. The study characterized 1,600 sites from a contiguous coastal and hill zone (0-800-m elevation) of which 64% contained Anopheles larvae. Principal component and multiple logistic regression analyses identified ecological parameters associated with presence of nine [Anopheles aconitus Doenitz, Anopheles annularis Van de Wulp, Anopheles barbirostris Van der Wulp, Anopheles flavirostris (Ludlow), Anopheles insulaeflorum (Swellengrebel and Swellengrebel de Graaf), Anopheles kochi Doenitz, Anopheles maculatus Theobald, Anopheles sundaicus (Rodenwaldt), and Anopheles vagus Doenitz] of 15 Anopheles species collected. Combined data for all nine species showed increased Anopheles presence associated with wet season periods and higher elevation habitats exhibiting reduced tree canopy coverage, higher water temperatures, and shallower water depths. Habitat variables measured included topography (elevation), water conditions (temperature, pH, salinity depth, and velocity), habitat characteristics (substrate and canopy cover), density and type of aquatic vegetation coverage (riparian, floating, and emergent), and distance from nearest human habitation. Significant relationships were found for nine species when using all habitats in the analysis. Habitat characteristics for three species were refined. An. aconitus and An. barbirostris were associated with higher elevation rice, Oryza savita L., paddies with relatively shallow water depths, higher water temperatures, higher acidity and salinity concentrations, and a greater average distance from human habitation. An. vagus presence in rice paddies was associated with lower elevation fields, deeper and cooler water, less acidic and saline conditions, and habitats closer to human dwellings. Overall, the distribution of Anopheles species in Sukabumi was found to be nonrandom and predictable on the basis of habitat characteristics.     

Oviposition behavior of Aedes triseriatus (Diptera: Culicidae): prevalence, intensity, and aggregation of eggs in oviposition traps

The oviposition behavior of the treehole mosquito Aedes triseriatus (Say) was studied by counting the eggs laid in 300 oviposition traps weekly for one season (May-October) in Illinois. Eggs were aggregated spatially among traps each week, and temporally among weekly samples and for individual traps over weekly counts. Aggregation could be associated with a nonrandom dispersion pattern of oviposition events and with the oviposition of 20-60 eggs per event. Thus, females were laying clumps of eggs in an overdispersed manner. The greatest number of eggs was found in late July when prevalence (proportion of traps with eggs) and intensity (number of eggs per positive trap) peaked simultaneously. Intensity also peaked in May and prevalence peaked in mid-June and early September. When traps from which eggs were removed each week were compared with traps in which eggs were allowed to accumulate, prevalence was naturally higher in the latter group. However, the intensity of eggs was similar in both groups, indicating that more eggs were laid in traps from which eggs were removed. Thus, the presence of eggs on oviposition surfaces was associated with a decrease in further oviposition.     

Geographic distribution and breeding site preference of Aedes albopictus and Aedes aegypti (Diptera: culicidae) in Cameroon, Central Africa

Presence in Cameroon of the recently introduced Aedes (Stegomyia) albopictus (Skuse) in association with the indigenous Aedes aegypti (L.) raises public heath concerns because it might alter the risk of arbovirus transmission. The breeding site and distribution of the two Stegomyia species are updated and reported following entomological surveys carried out in 22 localities throughout Cameroon, with a total of 1,353 containers with water visited. Ae. aegypti was found in every location sampled, showing higher infestation rates in northern Cameroon. Breeding populations of Ae. albopictus were observed in all 19 southern localities, up to the Adamaoua mountains, but the species was not recorded further north. In the area where both species are present, they were often sampled in the same larval developmental sites, suggesting convergent habitat segregation. The most frequently encountered artificial and natural breeding sites were used tires, discarded tins and plastic containers, abandoned car parts, brick holes, dead leaves on the ground, tree holes, and rock pools. Further monitoring of the demographic as well as geographic expansion of Ae. albopictus in this Afrotropical environment and its relationships with indigenous Ae. aegypti should provide insight into the biology of this highly invasive species and help to implement arboviruses surveillance programs in the area.     

Analysis of the spatial and temporal distribution of malaria in an area of Northern Guatemala with seasonal malaria transmission

Parasitology Research - The risk of malaria infection displays spatial and temporal variability that is likely due to interaction between the physical environment and the human population. In this...     

Quantitative spatial distribution of sirolimus and polymers in drug-eluting stents using confocal Raman microscopy

Raman spectroscopy was used to differentiate each component found in the CYPHER Sirolimus-eluting Coronary Stent. The unique spectral features identified for each component were then used to develop three separate calibration curves to describe the solid phase distribution found on drug-polymer coated stents. The calibration curves were obtained by analyzing confocal Raman spectral depth profiles from a set of 16 unique formulations of drug-polymer coatings sprayed onto stents and planar substrates. The sirolimus model was linear from 0 to 100 wt % of drug. The individual polymer calibration curves for poly(ethylene-co-vinyl acetate) [PEVA] and poly(n-butyl methacrylate) [PBMA] were also linear from 0 to 100 wt %. The calibration curves were tested on three independent drug-polymer coated stents. The sirolimus calibration predicted the drug content within 1 wt % of the laboratory assay value. The polymer calibrations predicted the content within 7 wt % of the formulation solution content. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra from five formulations confirmed a linear response to changes in sirolimus and polymer content.     

Metabolite images of the human arm: changes in spatial and temporal distribution of high energy phosphates during exercise.

Localized variations in metabolites in resting and exercising skeletal muscle have been studied using Chemical Shift Imaging (CSI) techniques to obtain 2-D arrays of 31P NMR spectra from a slice through the human forearm. The excitation profile of the coil resulted in a slice thickness of ca 80 mm and the planar resolution of the CSI data corresponded to either 7, 10 or 14 mm. The metabolite information was represented both as 2-D arrays of spectra and by constructing images of the spatial distribution of different metabolites. Correlation with the anatomy was clearly visualized by overlaying the metabolite images on the appropriate region of the corresponding proton images. At rest, significant variations in the intensity of Pi, phosphocreatine (PCr) and ATP were observed in different regions of the arm. Our planar spatial and temporal (1-9 min) resolution was also sufficient to follow changes in Pi, PCr and pH in response to exercise. These changes were restricted to the exercising muscle and demonstrated heterogeneity both in the kinetics and magnitude of response between different muscles.     

Chromosomal DNA fingerprinting analysis using the insertion sequence IS6110 and the repetitive element DR as strain-specific markers for epidemiological study of tuberculosis in French Polynesia.

The polymorphism of Mycobacterium tuberculosis strains was evaluated in French Polynesia, an area with a low incidence of tuberculosis and a population which has been geographically stable during recent decades. Nonrepetitive strains isolated from 64 patients during 1991 and 1992 were subjected to DNA restriction fragment length polymorphism (RFLP) analysis, using the insertion sequence IS6110 and the repetitive element DR as probes. Thirty-eight different IS6110 RFLP types were identified. They could be clustered in 11 groups. All the members of each group are identical or differ by one to three bands. All the other strains are gathered in the miscellaneous group. In some cases, transmission of strains with identical RFLP types between patients of the same family or between patients living in the same area was identified. Strains exhibiting similar IS6110 RFLP types also exhibited identical DR RFLP patterns, confirming that strains with similar types were genetically linked. Strains belonging to two different IS6110 clusters exhibited the same DR RFLP type. These data may also indicate a common origin for these strains and evolution to new IS6110 types. The results obtained in this study suggest that not only reactivation of latent tuberculous infections but also active transmissions are still occurring in French Polynesia.     

Relative effects of the spatial and temporal characteristics of scanned surfaces on human perception of tactile roughness using passive touch

The present experiments were designed to determine the ability of humans to estimate the roughness of raised dot surfaces using passive touch (subject immobile, surfaces scanned proximo-distally under the tip of the middle digit). In two initial experiments, the spatial period in the direction of the scan (longitudinal SP) was varied from 1.5 to 5 mm, while the transverse SP was kept constant at 2 mm. These surfaces were identical to those used in single unit recording experiments in primates which have shown that neurones in primary somatosensory cortex (SI) show graded changes in discharge over the same range of SPs. In the third and fourth experiments, roughness perception was studied over an extended range of longitudinal SPs (1.5-8.5 mm); transverse SP was either 1 or 2 mm. We also examined the effects on roughness perception of presenting the surfaces at two different scanning speeds (approximately 50 and approximately 95 mm/s), similar to those employed in the unit recordings. Magnitude estimates of perceived roughness increased in a nearly linear fashion as longitudinal SP was increased up to either 5 mm (experiments 1 and 2) or 8.5 mm (experiments 3 and 4). A modest increase in the transverse SP elicited a small increase in roughness estimates, with preservation of the linear relation between roughness and longitudinal SP. The roughness sensation evoked by each surface was not affected by the change of the temporal pattern of scanning (Low and High speeds). These results showed that there is perceptual constancy for roughness across a twofold change in passive scanning speed, and that roughness is a function of the spatial characteristics of these raised dot surfaces. While a spatial code may underlie this observation, it is suggested that a simpler intensive code may be sufficient to explain the psychophysical observations. Based on the results of neurophysiological recordings in SI cortex, it is suggested that an invariant central representation of surface roughness could be extracted from the ambiguous peripheral signals that covary with roughness and the stimulating conditions (e.g. speed) by means of a simple subtraction process.     

Effects of carbon dioxide, an octenol/phenol mixture, and their combination on tabanidae (Diptera) collections from French 2-tier box traps

The French 2-tier box trap was evaluated in northwestern Florida to determine its attractiveness to host-seeking tabanids (Diptera) when baited with either CO2 alone; a 4:1:8 mixture of octenol, 3-n-propylphenol, and 4-methylphenol; or a combination of CO2 plus 4:1:8 mixture. Six genera representing 43 species were obtained from this trap. Chrysops and Tabanus made up 10.3 and 87.4% of the total, respectively, with Chrysops celatus Pechuman and Tabanus pallidescens Philip as the predominate species from these two genera. CO2 alone and in combination with the octenol/phenol mixture enhanced overall tabanid collections three- to four-fold compared with no odor. Generally, more species were collected in the top tier of the French 2-tier trap regardless of treatment. Those species that showed a significant difference between top and bottom tiers in traps without odors continued this trend when traps were baited with the semiochemicals. However, Tabanus mixis Philip showed no tier preference in traps baited by CO2 alone, whereas Tabanus lineola F. showed no stratification difference with or without odors.     

Association of Ixodes pacificus (Acari: ixodidae) with the spatial and temporal distribution of equine granulocytic ehrlichiosis in California.

This study was conducted to determine if the biology of certain ticks associated with horses regulates the spatial and temporal distribution of equine granulocytic ehrlichiosis (EGE) in California north of Monterey County. We compared the spatial and temporal distribution of EGE cases with the seasons of activity and life histories of ticks that infest horses. Spatially, cases collected from equine veterinarians clustered around each other in a manner different from the way in which control cities of practice were distributed, with foci limited to the Sierra Nevada and coastal foothills. Cases also clustered seasonally: most were diagnosed between November and April. The spatial and temporal pattern of EGE cases closely parallels the well-characterized life history and distribution of Ixodes pacificus Cooley & Kohls, but not other ticks commonly associated with horses. Building on previous studies, there is compelling evidence that this tick has the vectorial capacity to transmit Ehrlichia equi to horses. Based on the life history and distribution of I. pacificus in relation to EGE cases, we reason that this tick is the only biologically plausible vector of E. equi in California, and provide evidence for a tightly linked association between I. pacificus and the epidemiology of EGE.     

Impact of source reduction on the spatial distribution of larvae and pupae of Aedes albopictus (Diptera: Culicidae) in suburban neighborhoods of a Piedmont community in North Carolina

Aedes albopictus (Skuse) is a principal nuisance mosquito species and a potential arbovirus vector throughout its geographic range in the United States. This species lays eggs, and progeny complete development in water-filled containers that are discarded in suburban landscapes. Source reduction of containers, achieved through environmental sanitation, was used to experimentally manipulate mosquito production to gain insight into the spatial structure of the population of immature Ae. albopictus. Our studies were conducted in suburban landscapes in Raleigh, NC, during the 2002 and 2003 mosquito seasons. Spatial analyses, using estimates of the mean and total standing crop of pupae and counts of the numbers of mosquito-positive containers, showed that the distribution of mosquito production was not spatially dependent on a neighborhood-wide basis. However, in all neighborhoods, mosquito production was clustered in at least one and often more than one adjacent residence. Point pattern analyses that considered only the presence or absence of pupae showed that pupae-positive residences were dispersed throughout neighborhoods receiving monthly source reduction treatments and clustered throughout control neighborhoods, indicating that source reduction affected the spatial distribution of pupae. Conversely, spatial analyses based on the presence or absence of larvae and pupae showed that mosquito production was randomly distributed among residences in both control and source reduction neighborhoods, showing that Ae. albopictus recolonized containers within several weeks after source reduction was implemented. Knowledge of the spatial distribution of production sites would allow management efforts for Ae. albopictus to be targeted to residences supporting high levels of mosquito production.     

The effects of climatic factors on the distribution and abundance of malaria vectors in Kenya

Since 1988 malaria epidemics have occurred in multiple sites in western Kenya highlands. Climatic variability has been associated with some of the recent epidemics. We examined influences of climatic factors on the distribution and abundance of three malaria vector species, Anopheles gambiae, Anopheles arabiensis, and Anopheles funestus in western Kenya and in the Great Rift Valley. Mosquito samples were collected from the lowland and highland areas with various climatic conditions. The three vector species were abundant in the lower part of western Kenya. An. arabiensis was not found in the areas above 1,400 m elevation in western Kenya Although An. gambiae and An. funestus were found in the sites above 1,700 m in western Kenya, their densities were < 1 per house. In the Great Rift Valley, An. gambiae was not recorded. An. funestus was more widely distributed than the other two species. A stepwise multiple regression analysis found that moisture index was the most important variable in shaping species composition of the An. gambiae complex. Relative abundance of An. gambiae was positively associated with moisture index, suggesting that An. gambiae is more adapted to moist climate. Seasonal differences in species composition were significant in western Kenya, and the proportion of An. funestus was higher in the dry season than the rainy season. Influence of temperature on vector density was significant for all three species. These results imply that climate changes alter the distribution and abundance of malaria vectors in future.