Zika transmission patterns: a meta-review.

OBJECTIVE: To assesses what is known and identify knowledge gaps for Zika virus (ZIKV) transmission patterns. METHODS: Meta-review searching the databases BioSys; Cochrane Infectious Diseases Group Specialised Register and Cochrane Central Register of Controlled Trials; EMBASE; Google Scholar; LILACS; MEDLINE (PubMed); Web of Science; and WHOLIS with the term 'ZIKA'. Systematic reviews and reviews specifying the search methods and describing potential modes of transmission were eligible for analysis. RESULTS: Of 5,401 hits for 'Zika', 44 studies were assessed and 11 included after applying in- and exclusion criteria: six systematic reviews and five reviews with specified methods, covering all ways of possible transmission. Results can be grouped into transmission routes with good evidence and agreement between the studies (evidence on vector, mother-to-child and sexual transmission) and transmission routes with limited evidence. Transmission by breastfeeding, intrapartum, by animal bites or laboratory-based remains inconclusive, as these routes are suggested by single studies only. The risk of transfusion transmission is described and public health measures for safe transfusion should be taken as available. CONCLUSION: Our results imply the need for public health measures to limit transmission via vectors, mother-to-child, sexual transmission and blood transfusion. Also needed are long-term prospective cohort studies covering periods of active Zika virus transmission and measuring epidemiological parameters to establish evidence on other routes of transmission; seroprevalence studies; transmission dynamics modelling and modelling health impacts by different modes of transmission.

OBJECTIF: Evaluer ce que l'on sait et identifier les lacunes dans les connaissances sur les profils de transmission du virus Zika (ZIKV). MÉTHODES: Méta-analyse de recherche dans les bases de données BioSys, Cochrane Infectious Diseases Specialised Register et le Registre Central Cochrane des Essais Contrôlés, EMBASE, Google Scholar, LILACS MEDLINE (PubMed), Web de la Science et WHOLIS avec le terme «Zika¼. Les revues systématiques et les revues spécifiant les méthodes de recherche et décrivant les modes de transmission potentiels étaient éligibles pour l'analyse. RÉSULTATS: Sur 5.401 résultats correspondant à «Zika¼, 44 études ont été évaluées et 11 incluses après application des critères d'inclusion et d'exclusion: 6 revues systématiques et 5 revues avec des méthodes spécifiées, couvrant tous les modes de transmission possibles. Les résultats peuvent être regroupés en voies de transmission avec des preuves solides et une concordance entre les études (preuves sur la transmission vectorielle, transmission mère-enfant et sexuelle) et les voies de transmission avec des preuves limitées. La transmission par l'allaitement, par voie intra-partum, par des morsures d'animaux ou via le laboratoire reste non conclusive, car ces voies ne sont suggérées que par des études uniques. Le risque de transmission par transfusion est décrit et des mesures de santé publique visant à garantir une transfusion sans danger doivent être prises dès que possible. CONCLUSION: Nos résultats insinuent la nécessité de prendre des mesures de santé publique pour limiter la transmission par le biais des vecteurs, la transmission mère-enfant, la transmission sexuelle et la transfusion sanguine. Des études de cohorte prospectives à long terme portant sur des périodes de transmission active du virus Zika et des mesures de paramètres épidémiologiques sont également nécessaires pour établir des preuves d'autres voies de transmission; des études de séroprévalence; la modélisation de la dynamique de transmission et la modélisation des impacts sur la santé par différents modes de transmission.

Rare, low frequency and common coding variants in CHRNA5 and their contribution to nicotine dependence in European and African Americans.

The common nonsynonymous variant rs16969968 in the α5 nicotinic receptor subunit gene (CHRNA5) is the strongest genetic risk factor for nicotine dependence in European Americans and contributes to risk in African Americans. To comprehensively examine whether other CHRNA5 coding variation influences nicotine dependence risk, we performed targeted sequencing on 1582 nicotine-dependent cases (Fagerström Test for Nicotine Dependence score⩾4) and 1238 non-dependent controls, with independent replication of common and low frequency variants using 12 studies with exome chip data. Nicotine dependence was examined using logistic regression with individual common variants (minor allele frequency (MAF)⩾0.05), aggregate low frequency variants (0.05>MAF⩾0.005) and aggregate rare variants (MAF<0.005). Meta-analysis of primary results was performed with replication studies containing 12 174 heavy and 11 290 light smokers. Next-generation sequencing with 180 × coverage identified 24 nonsynonymous variants and 2 frameshift deletions in CHRNA5, including 9 novel variants in the 2820 subjects. Meta-analysis confirmed the risk effect of the only common variant (rs16969968, European ancestry: odds ratio (OR)=1.3, P=3.5 × 10(-11); African ancestry: OR=1.3, P=0.01) and demonstrated that three low frequency variants contributed an independent risk (aggregate term, European ancestry: OR=1.3, P=0.005; African ancestry: OR=1.4, P=0.0006). The remaining 22 rare coding variants were associated with increased risk of nicotine dependence in the European American primary sample (OR=12.9, P=0.01) and in the same risk direction in African Americans (OR=1.5, P=0.37). Our results indicate that common, low frequency and rare CHRNA5 coding variants are independently associated with nicotine dependence risk. These newly identified variants likely influence the risk for smoking-related diseases such as lung cancer.

Human myelomeningocele risk and ultra-rare deleterious variants in genes associated with cilium, WNT-signaling, ECM, cytoskeleton and cell migration.

Myelomeningocele (MMC) affects one in 1000 newborns annually worldwide and each surviving child faces tremendous lifetime medical and caregiving burdens. Both genetic and environmental factors contribute to disease risk but the mechanism is unclear. This study examined 506 MMC subjects for ultra-rare deleterious variants (URDVs, absent in gnomAD v2.1.1 controls that have Combined Annotation Dependent Depletion score ≥ 20) in candidate genes either known to cause abnormal neural tube closure in animals or previously associated with human MMC in the current study cohort. Approximately 70% of the study subjects carried one to nine URDVs among 302 candidate genes. Half of the study subjects carried heterozygous URDVs in multiple genes involved in the structure and/or function of cilium, cytoskeleton, extracellular matrix, WNT signaling, and/or cell migration. Another 20% of the study subjects carried heterozygous URDVs in candidate genes associated with gene transcription regulation, folate metabolism, or glucose metabolism. Presence of URDVs in the candidate genes involving these biological function groups may elevate the risk of developing myelomeningocele in the study cohort.

Reducing costs and operational constraints of dengue vector control by targeting productive breeding places: a multi-country non-inferiority cluster randomized trial.

OBJECTIVES: To test the non-inferiority hypothesis that a vector control approach targeting only the most productive water container types gives the same or greater reduction of the vector population as a non-targeted approach in different ecological settings and to analyse whether the targeted intervention is less costly. METHODS: Cluster randomized trial in eight study sites (Venezuela, Mexico, Peru, Kenya, Thailand, Myanmar, Vietnam, Philippines), with each study area divided into 18-20 clusters (sectors or neighbourhoods) of approximately 50-100 households each. Using a baseline pupal-demographic survey, the most productive container types were identified which produced >or=55% of all Ae. aegypti pupae. Clusters were then paired based on similar pupae per person indices. One cluster from each pair was randomly allocated to receive the targeted vector control intervention; the other received the 'blanket' (non-targeted) intervention attempting to reach all water holding containers. RESULTS: The pupal-demographic baseline survey showed a large variation of productive container types across all study sites. In four sites the vector control interventions in both study arms were insecticidal and in the other four sites, non-insecticidal (environmental management and/or biological control methods). Both approaches were associated with a reduction of outcome indicators in the targeted and non-targeted intervention arm of the six study sites where the follow up study was conducted (PPI, Pupae per Person Index and BI, Breteau Index). Targeted interventions were as effective as non-targeted ones in terms of PPI. The direct costs per house reached were lower in targeted intervention clusters than in non-targeted intervention clusters with only one exception, where the targeted intervention was delivered through staff-intensive social mobilization. CONCLUSIONS: Targeting only the most productive water container types (roughly half of all water holding container types) was as effective in lowering entomological indices as targeting all water holding containers at lower implementation costs. Further research is required to establish the most efficacious method or combination of methods for targeted dengue vector interventions.

Parental history of stroke predicts subclinical but not clinical stroke: the Atherosclerosis Risk in Communities Study.

BACKGROUND AND PURPOSE: An individual with a positive family history of a disease may be at increased risk for the disease. We sought to examine whether parental history of stroke is associated with subclinical or clinical stroke in the Atherosclerosis Risk in Communities (ARIC) Study, and whether any observed association is independent of established stroke risk factors. METHODS: Parental history of stroke was determined by home interview at the baseline examination. Cerebral MRI was performed on individuals from 2 ARIC field centers. Subclinical cerebral infarct cases (n=202) were defined by the presence of cerebral infarcts >3 mm. The comparison group for the subclinical cases included all individuals participating in the MRI examination who were not identified as a subclinical case (n=1533). Incidence of clinical ischemic stroke was determined by following the ARIC cohort for potential cerebrovascular events. Two hundred sixty-one validated ischemic strokes were identified; 13 775 individuals from the ARIC cohort did not experience an ischemic event. RESULTS: Parental history of stroke was significantly associated with subclinical stroke after adjusting for age, gender, and race (OR 1.67, 95% CI1.23 to 2.26) and after further adjustment for multiple stroke risk factors (OR1. 64, 95% CI1.20 to 2.24). Parental history of stroke was not a significant predictor of clinical stroke in either adjustment model. CONCLUSIONS: The observed increased risk of subclinical stroke among individuals with a parental history of stroke is consistent with the expression of genetic susceptibility, a shared environment, or both in the etiology of stroke. This effect did not appear to be mediated by established stroke risk factors. Parental history of stroke does not confer an increased risk of clinical stroke in this sample of middle-aged Americans.

G-protein beta3 subunit and alpha-adducin polymorphisms and risk of subclinical and clinical stroke.

BACKGROUND AND PURPOSE: Essential hypertension is a significant risk factor for stroke. Genes contributing to interindividual variation in blood pressure levels and essential hypertension status may play a role in the etiology of stroke either through their effects on blood pressure levels or through separate pathways. For this reason, we sought to examine the association between the alpha-adducin (ADD1) G/W460 and G-protein beta3 subunit (GNbeta3) 825C/T polymorphisms and subclinical and clinical stroke in the Atherosclerosis Risk in Communities (ARIC) Study. METHODS: Subclinical stroke was determined by cerebral MRI. Subclinical cerebral infarct cases (n=202) were compared with a stratified random sample (MRI-CRS) identified from individuals participating in the MRI examination (n=211). Incidence of clinical ischemic stroke was determined by following the ARIC cohort for an average of 7.2 years for potential cerebrovascular events; 231 validated clinical ischemic strokes were identified. A stratified random sample of the ARIC cohort (CRS) (n=984) was used as the comparison group for the clinical cases. RESULTS: The frequency of the ADD1 W460 allele was determined for the subclinical cases (0.12), MRI-CRS (0.16), clinical cases (0.14), and CRS (0.17). The frequency of the GNbeta3 825T allele was determined in whites and blacks, respectively, for the subclinical cases (0.26, 0.73), MRI-CRS (0.31, 0.75), clinical cases (0.36, 0.72), and CRS (0.30, 0.72). The ADD1 W460 and GNbeta3 825T alleles were not significantly associated with subclinical stroke. The ADD1 W460 allele was also not a significant predictor of clinical stroke. The GNbeta3 825T allele was significantly associated with clinical stroke in whites after adjustment for age and sex (hazard rate ratio, 1.45; 95% CI, 1.05 to 2.00) and after further adjustment for multiple stroke risk factors (hazard rate ratio, 1.68; 95% CI, 1.18 to 2.41). The GNbeta3 825T allele was not significantly associated with clinical stroke in blacks for either adjustment model. CONCLUSIONS: The GNbeta3 gene 825C/T polymorphism is significantly associated with incident clinical ischemic stroke in a white middle-aged American population, but not in blacks. This association does not appear to be mediated by established stroke risk factors, specifically blood pressure levels or hypertension status.

Characterization of an influenza A (H3N2) virus resistant to the cyclopentane neuraminidase inhibitor RWJ-270201.

The novel influenza virus neuraminidase (NA) inhibitor, (1S,2S,3R,4R)-3-[(1S)-(acetylamino)-2-ethylbutyl]-4-[(aminoiminomethyl)amino]-2-hydroxy-cyclopentanecarboxylic acid (RWJ-270201, BCX-1812), is a potent inhibitor of influenza A and B viruses in cell culture and in infected mice. A mouse-adapted strain of influenza A/Shangdong/09/93 (H3N2) virus was serially passaged in the presence of 1 microM compound. After the fourth passage, breakthrough of resistant virus occurred. By the tenth passage, a twice plaque purified isolate was obtained which could replicate in 10 microM inhibitor. The 50% effective concentration (EC(50)) values for RWJ-270201 against wild-type and resistant viruses, determined by using a cytopathic effect inhibition assay, were 0.007 and 23 microM, respectively. Cross-resistance to zanamivir and oseltamivir carboxylate was observed. The hemagglutinin (HA) and NA genes of the virus were sequenced to determine the mutation(s) which conferred drug resistance. No differences were found between the resistant and wild-type viruses in the NA gene. However, a point mutation resulting in a single amino acid change (Lys189Glu) was found in the resistant viral HA. The wild-type and resistant viruses were compared for virulence in BALB/c mice. The resistant virus was approximately tenfold less virulent than the wild-type virus based upon virus challenge dose. Mice infected with a lethal dose of the resistant virus could still be effectively treated with RWJ-270201. Thus, the HA mutation may allow for the spread of the virus in cell culture in the presence of the NA inhibitor, but not in mice.

Host preferences of the sand fly Lutzomyia longipalpis at an endemic focus of American visceral leishmaniasis in Colombia.

Blood meals from 579 Lutzomyia longipalpis (Diptera:Psychodidae), collected in an endemic focus of American visceral leishmaniasis in Colombia, were identified by precipitin test. Sand fly collections were made during a 16-month period from the inside walls of two houses, a pigpen, and rock crevices in a small community (El Callejon) within the endemic area. Feeding patterns of the sand flies varied with locality and date of collection. Overall, bovine feedings predominated, but feedings were also recorded on pigs, equines, humans, dogs, opossums, birds, and reptiles. Calculation of the forage ratios for each host species indicated that cows and pigs were the preferred hosts of Lu. longipalpis in El Callejon. Results of this study suggest that Lu. longipalpis is an opportunistic feeder and is not highly anthropophilic nor strongly attracted to dogs.

Exploratory space-time analysis of reported dengue cases during an outbreak in Florida, Puerto Rico, 1991-1992.

The spatial and temporal distributions of dengue cases reported during a 1991-1992 outbreak in Florida, Puerto Rico (population = 8,689), were studied by using a Geographic Information System. A total of 377 dengue cases were identified from a laboratory-based dengue surveillance system and georeferenced by their residential addresses on digital zoning and U.S. Geological Survey topographic maps. Weekly case maps were generated for the period between June and December 1991, when 94.2% of the dengue cases were reported. The temporal evolution of the epidemic was rapid, affecting a wide geographic area within seven weeks of the first reported cases of the season. Dengue cases were reported in 217 houses; of these 56 (25.8%) had between two and six reported cases. K-function analysis was used to characterize the spatial clustering patterns for all reported dengue cases (laboratory-positive and indeterminate) and laboratory-positive cases alone, while the Barton and David and Knox tests were used to characterize spatio-temporal attributes of dengue cases reported during the 1991-1992 outbreak. For both sets of data significant case clustering was identified within individual households over short periods of time (three days or less), but in general, the cases had spatial pattern characteristics much like the population pattern as a whole. The rapid temporal and spatial progress of the disease within the community suggests that control measures should be applied to the entire municipality, rather than to the areas immediately surrounding houses of reported cases. The potential for incorporating Geographic Information System technologies into a dengue surveillance system and the limitations of using surveillance data for spatial studies are discussed.

PIP: Through use of the Geographic Information System (GIS), the spatial and temporal distributions of dengue cases reported during a 1990-91 outbreak in Florida, Puerto Rico, were reviewed. The GIS, a computer system that can store, assemble, manipulate, and analyze geographically referenced material, offers a new approach to the study of disease patterns. A total of 377 dengue cases were identified from a laboratory-based dengue surveillance system and georeferenced by their residential addresses on digital zoning and US Geological Survey topographic maps. Weekly case maps were generated for the period June-December 1991, when 94.2% of dengue cases were reported. The epidemic's temporal evolution was rapid, affecting a wide geographic region within 7 weeks of the first reported cases of the season. Cases were reported in 217 houses, 56 (25.8%) of which had 2-6 cases each. Both K-function analysis, and the Barton and David-Knox tests, revealed significant case clustering within individual households over a period of 3 days or less. In general, however, cases had spatial pattern characteristics similar to the population pattern as a whole. The rapid spatial and temporal progress of dengue cases within the community suggests that vector control measures (e.g., source reduction) should be applied to the entire municipality, rather than to the areas immediately surrounding houses of reported cases.

Larval microhabitats of Lutzomyia longipalpis (Diptera: Psychodidae) in an endemic focus of visceral leishmaniasis in Colombia.

An intensive search for the larval habitats of Lutzomyia longipalpis (Lutz & Neiva) was conducted from November 1992 to October 1993 at a small rural community in Colombia where American visceral leishmaniasis is endemic. Emergence traps constructed from polyvinyl chloride pipes were used to sample a variety of soil microhabitats that included edge areas of covered pigpens, cattle corrals, the base of trees, and leaf litter at sites within 40 m of a house, rocks in fields located between 50 and 500 m from houses, and sites within a patch of secondary forest (rocks, base of palm trees, and leaf litter). The teneral status of the sand flies captured in the emergence traps was confirmed by laboratory studies that determined the rate of terminalia rotation in male L. longipalpis and the rate of cuticular growth layer formation of the thoracic phragma in both sexes of this species. A total of 58 teneral sand flies was captured during the study period (49 wk). Fifteen specimens were L. longipalpis; of these 11 (5 sand flies per square meter) were captured near pigpens, 3 (1.4 sand flies per square meter) were captured near rock resting sites, and 1 (1.6 sand flies per square meter) was collected at the base of a tree. The remainder of the sand flies were either L. trinidadensis (Newstead) or L. cayennensis (Flock & Abonnenc). Our results indicate that L. longipalpis larvae were dispersed widely in sites near houses, rather than concentrated in a few optimal microhabitats.

Dispersal of the sand fly Lutzomyia longipalpis (Diptera: Psychodidae) at an endemic focus of visceral leishmaniasis in Colombia.

Mark-release-recapture studies were carried out during 1990-1991 in El Callejón, Colombia, an endemic focus of American visceral leishmaniasis, to study the longevity, dispersal, and flight range of the principal vector, Lutzomyia longipalpis Lutz & Neiva. Several groups of wild-caught (n = 1,539) and laboratory-reared F1 (n = 2,208) sand flies were marked with fluorescent dusts and released. Recaptures at daytime resting sites, on animal bait, and in CDC light traps were made for 20 d following each release. From 2 to 9% of L. longipalpis were recaptured, a rate which differed between the sexes (7.7% male, 1.5% female). Overall, 49% of the L. longipalpis were recaptured between 0 and 50 m, 48% within 100 and 300 m, and nearly 3% at > or = 0.5 km from the release site. Sex differences in recapture site, distance flown, and direction were observed. Our results indicate that the dispersal behavior of peridomestic populations of L. longipalpis compares more closely with that of Old World sand fly species from similar habitats than to the sylvan Neotropical phlebotomines.

Species composition and relative abundance of sand flies of the genus Lutzomyia (Diptera: Psychodidae) at an endemic focus of visceral leishmaniasis in Colombia.

Ecological studies on the sand fly Lutzomyia longipalpis (Lutz & Neiva) were conducted during 1990-1993 at a small rural community in Colombia where American visceral leishmaniasis is endemic. Weekly sand fly collections were made from pigpens, houses, and natural resting sites, using hand-held aspirators, sticky (oiled) paper traps, and opossum-baited Disney traps. In total, 263,094 sand flies were collected; L. longipalpis predominated (86.1%), followed by L. trinidadensis (11.0%), L. cayennensis (2.7%), and 8 other Lutzomyia species. The species composition and sex ratio of these sand flies varied among sites and by collection method. L. longipalpis were captured most efficiently by direct aspiration from animal bait. Conversely, sticky paper traps, especially inside houses and at rock resting sites, collected a greater diversity of species, but a lower relative abundance of L. longipalpis.

Genetic structure of local populations of Lutzomyia longipalpis (Diptera: Psychodidae) in central Colombia.

Lutzomyia longipalpis (Lutz & Neiva), the sand fly vector of American visceral leishmaniasis in the New World tropics, has a broad but discontinuous geographical distribution from southern Mexico to Argentina. A baseline for population genetic structure and genetic variability for this species was obtained by analyzing 5 local, peridomestic populations at the approximate center of its distribution, the Magdalena River Valley of central Colombia. Three populations of L. longipalpis from El Callejón, a small rural community, were compared with 2 populations from neighboring areas 12 and 25 km distant for genetic variation at 15 isoenzyme loci. The mean heterozygosity ranged from 11 to 16%, with 1.2 to 2.3 alleles detected per locus. Nei's genetic distances among the populations were very low, ranging from 0.001 to 0.007. Gene flow estimates based on FST indicated high levels of gene flow among local L. longipalpis populations, with minimal population substructuring.

Age structure, blood-feeding behavior, and Leishmania chagasi infection in Lutzomyia longipalpis (Diptera: Psychodidae) at an endemic focus of visceral leishmaniasis in Colombia.

Ecological studies on the sand fly Lutzomyia longipalpis (Lutz & Neiva) were conducted during 1990-1992 in a small rural community in Colombia where American visceral leishmaniasis (AVL) is endemic. Subsamples of sand flies collected weekly from pigpens, the interior of houses, and natural outdoor resting sites were dissected to determine physiological age and Leishmania chagasi Cunha & Chagas infection rates. Eleven female L. longipalpis had flagellates in their gut, 2 of which were successfully cultured and identified as Leishmania chagasi. The reproductive status, stage of ovarian development, and trophic history of female sand flies varied among sites, habitats, and time of collection. The percentage of parous females ranged from about one-third to two-thirds overall and varied seasonally. Of most relevance to AVL transmission was the finding that 8% of L. longipalpis females were multiparous. In addition, our data suggest that L. longipalpis rest inside houses after blood-feeding outdoors, and that this species can blood-feed more than once during a single gonotrophic cycle.

Nocturnal activity patterns of Lutzomyia longipalpis (Diptera: Psychodidae) at an endemic focus of visceral leishmaniasis in Colombia.

Nocturnal activity of the sand fly Lutzomyia longipalpis (Lutz & Neiva) was studied from August 1991 to July 1992 in a small rural community in Colombia where American visceral leishmaniasis is endemic. During 2 or 3 nights each month, sand flies were collected with hand-held aspirators each hour between 1730 and 0630 hours, from a pigpen and a cattle corral located 30 m apart. Host-seeking activity of L. longipalpis adults was characterized by 2 general patterns: (1) adult sand fly activity increased shortly after sunset and continued until just after sunrise, and (2) peak sand fly activity was greatest early in the evening (1830-2330 hours) and then declined steadily toward morning. Female L. longipalpis activity generally increased after 2030 hours, whereas that of males remained constant or declined as the evening progressed. There were seasonal differences in sand fly abundance between the 2 sites: peak abundance in the cattle corral occurred during hot, dry periods, whereas maximum abundance in the pigpen occurred when relative humidity was higher. Influence of relative humidity on activity varied with season. Sand fly activity tended to decrease at temperatures below 24 degrees C and increase in the presence of moonlight.

Longitudinal studies of Aedes aegypti (Diptera: Culicidae) in Thailand and Puerto Rico: blood feeding frequency.

We used a histologic technique to study multiple blood feeding in a single gonotrophic cycle by engorged Aedes aegypti (L.) that were collected weekly for 2 yr from houses in a rural village in Thailand (n = 1,891) and a residential section of San Juan, Puerto Rico (n = 1,675). Overall, mosquitoes from Thailand contained significantly more multiple meals (n = 1,300, 42% double meals, 5% triple meals) than mosquitoes collected in Puerto Rico (n = 1,156, 32% double meals, 2% triple meals). The portion of specimens for which frequency of feeding could not be determined was 31% at both sites. We estimated that on average Ae. aegypti take 0.76 and 0.63 human blood meals per day in Thailand and Puerto Rico, respectively. However, frequency of multiple feeding varied among houses and, in Puerto Rico, the neighborhoods from which mosquitoes were collected. In Thailand 65% of the mosquitoes fed twice on the same day, whereas in Puerto Rico 57% took multiple meals separated by > or = 1 d. At both sites, the majority of engorged specimens were collected inside houses (Thailand 86%, Puerto Rico 95%). The number of blood meals detected was independent of where mosquitoes were collected (inside versus outside of the house) at both sites and the time of day collections were made in Puerto Rico. Feeding rates were slightly higher for mosquitoes collected in the afternoon in Thailand. Temperatures were significantly higher and mosquitoes significantly smaller in Thailand than in Puerto Rico. At both sites female size was negatively associated with temperature. Rates of multiple feeding were associated positively with temperature and negatively with mosquito size in Thailand, but not in Puerto Rico. Multiple feeding during a single gonotrophic cycle is a regular part of Ae. aegypti biology, can vary geographically and under different climate conditions, and may be associated with variation in patterns of dengue virus transmission.

Longitudinal studies of Aedes aegypti (Diptera: Culicidae) in Thailand and Puerto Rico: population dynamics.

Aspiration collections of adult Aedes aegypti (L.) were made weekly from inside and outside of houses for 3 yr in a rural Thai village (n = 9,637 females and n = 11,988 males) and for 2 yr in a residential section of San Juan, Puerto Rico (n = 5,941 females and n = 6,739 males). In Thailand, temperature and rainfall fell into distinct seasonal categories, but only temperature was correlated with fluctuations in female abundance. Average weekly temperature 6 wk before mosquitoes were collected and minimum weekly temperature during the week of collection provided the highest correlations with female abundance. Accounting for annual variation significantly improved Thai models of temperature and mosquito abundance. In Puerto Rico, temperature, but not rainfall, could be categorized into seasonal patterns. Neither was correlated with changes in female abundance. At both sites the vast majority of females were collected inside houses and most contained a blood meal. Most teneral females were collected outside. Wing length--an indicator of female size--and parity, egg development or engorgement status were not correlated, indicating that feeding success and survival were not influenced by female size. At both sites, females fed almost exclusively on human hosts (> or = 96%), a pattern that did not change seasonally. In Puerto Rico more nonhuman blood meals were detected in mosquitoes collected outside than inside houses; no such difference was detected in Thailand. Gut contents of dissected females indicated that females in the Thai population had a younger age distribution and fed more frequently on blood than did Ae. aegypti in Puerto Rico. Our results indicated that aspects of this species' biology can vary significantly from one location to another and 1 yr to the next.

Seasonal abundance of Lutzomyia longipalpis (Diptera: Psychodidae) at an endemic focus of visceral leishmaniasis in Colombia.

Ecological studies on the sand fly Lutzomyia longipalpis (Lutz & Neiva) were conducted during 1990-1993 in a small rural community in Colombia where American visceral leishmaniasis is endemic. Standardized weekly sand fly collections made from pigpens and natural resting sites displayed a bimodal annual abundance cycle, with a small peak occurring in October-November and a larger one in April-May. Time series analysis was employed to quantify the associations between sand fly abundance and weather factors (temperature, relative humidity, and rainfall). In addition to a prominent 6-mo cycle. Fourier analysis of the collection data demonstrated that the L. longipalpis population also exhibited a 5- to 8-wk cycle that may represent the length of larval development. Autoregressive moving average models were fit to weekly collection data and their residuals were regressed against rainfall, temperature, and relative humidity. A significant positive association between female L. longipalpis abundance and the relative humidity and rainfall recorded 3 wk earlier was found, indicating that these factors may be of value in predicting sand fly abundance. Additionally, these data indicated that L. longipalpis larvae may become quiescent during adverse conditions.

Evaluation of a sampling methodology for rapid assessment of Aedes aegypti infestation levels in Iquitos, Peru.

An epidemic of dengue during 2001 in Northwestern Peru reemphasized the need for efficient, accurate, and economical vector surveillance. Between November 1998 and January 1999, we carried out extensive entomological surveys in two neighborhoods of approximately 600 contiguous houses located in the Amazonian city of Iquitos, providing a unique opportunity to evaluate the Aedes aegypti (L.) rapid assessment survey strategy. Based on Pan American Health Organization recommendations, this strategy is used by the Peruvian Ministry of Health (MOH). In our analysis all household locations, including closed and unoccupied houses, were georeferenced and displayed in a geographic information system, which facilitated simulations of MOH surveys based on hypothetical systematic sampling transects. Larval, pupal, and adult mosquito indices were calculated for each simulation (n = 10) and compared with the indices calculated from the complete data set (n = 4). The range of indices calculated from simulations was moderately high, but included actual indices. For example, simulation ranges for house indices (HI, percentage of infested houses from complete survey) were 38-56% (45%), 36-42% (38%), 21-34% (30%), and 13-33% (27%) in four surveys. HI, Breteau index, pupae per hectare, adult index, and adults per hectare were more robust entomological indicators (coefficient of variation [CV]/mean = 0.1-2.9) than the container index, pupae per person, pupae per house, adults per person, and adults per house (CV/mean >20). Our results demonstrate that the MOH's Ae. aegypti risk assessment program provides reasonable estimates of indices based on samples from every house. However, it is critical that future studies investigate the association of these indices with rates of virus transmission to determine whether sampling variability will negatively impact the application of indices in a public health context.

Aedes aegypti (Diptera: Culicidae) movement influenced by availability of oviposition sites.

Marked Aedes aegypti (L.) (5-6 d old) were released inside 2 groups of 5 houses (100 females per house) in a residential community in Florida, PR, to compare behavior of gravid females at sites where oviposition containers were absent to sites where containers were abundant (i.e., 2 tires and 10 ovipots were added to each yard). Two sequential releases were made so that both groups of houses were evaluated with oviposition containers removed and added. Mosquitoes resting inside the 10 release houses plus 20 additional neighboring houses were collected with backpack aspirators for 4 consecutive days, beginning 2 d after release. Because 172 of the 185 recaptured females (93%) were collected in the same houses in which they had been released, dispersal patterns were not directly comparable. However, the recapture rate in houses with containers added (13%) was significantly higher (P < 0.0001) than in houses with containers removed (6%). No difference was observed in the mean number of potential oviposition containers among the nonrelease houses at the 2 sites (3.9 versus 3.8 aquatic containers per house in the prerelease survey). Our results are consistent with the hypothesis that availability of oviposition sites is inversely correlated with the potential for female Ae. aegypti to disperse. These results have important implications because campaigns to reduce Ae. aegypti larval sites during dengue epidemics could have the undesirable effect of inducing the dispersal of infected adult female mosquitoes.