RESUMO
During the last 50 years, the geographic range of the mosquito Aedes aegypti has increased dramatically, in parallel with a sharp increase in the disease burden from the viruses it transmits, including Zika, chikungunya, and dengue. There is a growing consensus that vector control is essential to prevent Aedes-borne diseases, even as effective vaccines become available. What remains unclear is how effective vector control is across broad operational scales because the data and the analytical tools necessary to isolate the effect of vector-oriented interventions have not been available. We developed a statistical framework to model Ae. aegypti abundance over space and time and applied it to explore the impact of citywide vector control conducted by the Ministry of Health (MoH) in Iquitos, Peru, over a 12-year period. Citywide interventions involved multiple rounds of intradomicile insecticide space spray over large portions of urban Iquitos (up to 40% of all residences) in response to dengue outbreaks. Our model captured significant levels of spatial, temporal, and spatio-temporal variation in Ae. aegypti abundance within and between years and across the city. We estimated the shape of the relationship between the coverage of neighborhood-level vector control and reductions in female Ae. aegypti abundance; i.e., the dose-response curve. The dose-response curve, with its associated uncertainties, can be used to gauge the necessary spraying effort required to achieve a desired effect and is a critical tool currently absent from vector control programs. We found that with complete neighborhood coverage MoH intra-domicile space spray would decrease Ae. aegypti abundance on average by 67% in the treated neighborhood. Our framework can be directly translated to other interventions in other locations with geolocated mosquito abundance data. Results from our analysis can be used to inform future vector-control applications in Ae. aegypti endemic areas globally.
Assuntos
Aedes/fisiologia , Controle de Mosquitos/métodos , Mosquitos Vetores/fisiologia , Aedes/efeitos dos fármacos , Aedes/crescimento & desenvolvimento , Animais , Cidades , Feminino , Inseticidas/farmacologia , Masculino , Mosquitos Vetores/efeitos dos fármacos , Mosquitos Vetores/crescimento & desenvolvimento , Peru , Dinâmica Populacional , Estações do Ano , Análise Espaço-TemporalAssuntos
Desastres , Terremotos , Traumatismos Faciais/parasitologia , Lacerações/parasitologia , Infecção por Mosca da Bicheira/complicações , Infecção dos Ferimentos/terapia , Adolescente , Criança , Traumatismos Faciais/complicações , Feminino , Haiti , Humanos , Masculino , Infecções por Pseudomonas/complicações , Pseudomonas aeruginosa , Infecção por Mosca da Bicheira/terapia , Infecção dos Ferimentos/complicaçõesRESUMO
Vector control is a key means of combating mosquito-borne diseases and the only tool available for tackling the transmission of dengue, a disease for which no vaccine, prophylaxis, or therapeutant currently exists. The most effective mosquito control methods include a variety of insecticidal tools that target adults or juveniles. Their successful implementation depends on impacting the largest proportion of the vector population possible. We demonstrate a control strategy that dramatically improves the efficiency with which high coverage of aquatic mosquito habitats can be achieved. The method exploits adult mosquitoes as vehicles of insecticide transfer by harnessing their fundamental behaviors to disseminate a juvenile hormone analogue (JHA) between resting and oviposition sites. A series of field trials undertaken in an Amazon city (Iquitos, Peru) showed that the placement of JHA dissemination stations in just 3-5% of the available resting area resulted in almost complete coverage of sentinel aquatic habitats. More than control mortality occurred in 95-100% of the larval cohorts of Aedes aegypti developing at those sites. Overall reductions in adult emergence of 42-98% were achieved during the trials. A deterministic simulation model predicts amplifications in coverage consistent with our observations and highlights the importance of the residual activity of the insecticide for this technique.
Assuntos
Aedes/efeitos dos fármacos , Dengue/prevenção & controle , Ecossistema , Insetos Vetores/efeitos dos fármacos , Hormônios Juvenis/toxicidade , Metamorfose Biológica/efeitos dos fármacos , Controle de Mosquitos/métodos , Aedes/ultraestrutura , Animais , Simulação por Computador , Inseticidas , Microscopia Eletrônica de Varredura , Modelos Biológicos , PeruRESUMO
Endemic dengue transmission has been documented in the Amazonian city of Iquitos, Peru, since the early 1990s. To better understand the epidemiology of dengue transmission in Iquitos, we established multiple active surveillance systems to detect symptomatic infections. Here we compare the efficacy of distinct community-based (door to door) and school absenteeism-based febrile surveillance strategies in detecting active cases of dengue. Febrile episodes were detected by both systems with equal rapidity after disease onset. However, during the period that both programs were running simultaneously in 2004, a higher number of febrile cases in general (4.52/100 versus 1.64/100 person-years) and dengue cases specifically (2.35/100 versus 1.29/100 person-years) were detected in school-aged children through the community-based surveillance program. Similar results were obtained by direct comparison of 435 participants concurrently enrolled in both programs (P < 0.005). We conclude that, in Iquitos, community-based door-to-door surveillance is a more efficient and sensitive design for detecting active dengue cases than programs based on school absenteeism.
Assuntos
Dengue/epidemiologia , Vigilância da População/métodos , Adolescente , Criança , Pré-Escolar , Estudos de Coortes , Feminino , Humanos , Masculino , Peru/epidemiologia , Instituições AcadêmicasRESUMO
Malaria transmission from humans to mosquitoes is modulated by human host immune factors. Understanding mechanisms by which the human host response may impair parasite infectivity for mosquitoes has direct implications for the development of transmission-blocking vaccines. We hypothesized that despite a low transmission intensity of malaria in the Peruvian Amazon region of Iquitos, transmission-blocking immunity against Plasmodium vivax might be common, given an unexpectedly high proportion of asymptomatic parasitemic individuals in this region. To test this hypothesis, the ability of symptomatic P. vivax malaria patients to experimentally infect wild-caught outbred Anopheles darlingi mosquitoes was tested using the indirect membrane feeding technique. Only half (52/102) of P. vivax parasitemic patients successfully infected mosquitoes. Transmitters were more likely to have gametocytes (OR 6.35, P = 0.003), high parasitemia (OR 3.79, P = 0.024), and, in terms of basic clinical parameters, a slower pulse rate (mean +/- SD: 82.3 +/- 12.3 versus 88.7 +/- 13.5, P = 0.016) than non-transmitters. Log(10) gametocytemia and log(10) real-time reverse transcriptase Pvs25 PCR quantifying gametocytes were significantly and positively correlated with oocyst counts (correlation coefficient 0.505, R2 = 0.26, P = 0.001). These experiments are the first to establish a system of determining transmission patterns in experimental infection of outbred natural neotropical malaria vectors in the Amazon region. Patients with P. vivax inefficiently infect outbred An. darlingi mosquitoes, raising the possibility that some degree of naturally occurring transmission-blocking immunity is present on a population basis in the Peruvian Amazon, an area of low intensity of malaria transmission.
Assuntos
Anopheles/parasitologia , Insetos Vetores/parasitologia , Malária Vivax/transmissão , Plasmodium vivax/fisiologia , Adolescente , Adulto , Animais , Feminino , Humanos , Modelos Lineares , Malária Vivax/imunologia , Malária Vivax/parasitologia , Masculino , Pessoa de Meia-Idade , Parasitemia/imunologia , Parasitemia/transmissão , Peru , Plasmodium vivax/genética , Plasmodium vivax/imunologia , RNA Mensageiro/análise , RNA de Protozoário/análise , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
The effects of pyriproxyfen were tested against a local population of Aedes aegypti (L.) in Iquitos, Perú. Bioassays showed that, when applied to late instars, pyriproxyfen prevented adult emergence at extremely low concentrations (LC50 = 0.012 ppb). There was no adult emergence from water sampled from storage tanks that had been seeded with the equivalent of 50-83 ppb (AI) pyriproxyfen. Five months after treatment, despite constant dilution of these tanks, water sampled from these sources continued to be lethal to larvae and pupae. Additional studies, carried out in the laboratory, showed that groups of five or 20 female blood-fed mosquitoes, exposed to residues of approximately 0.003 g (AI) pyriproxyfen/m2, could transfer enough chemical to new oviposition sites to prevent approximately 80% of adult emergence from larvae developing in that previously uncontaminated water. Moreover, although the fecundity of the adult females used as the transfer vehicles in these tests was unaffected, the subsequent eclosion of the eggs that these mosquitoes laid was decreased by 70-90%. It also was shown that, at very high concentrations (>30,000 ppb), pyriproxyfen-treated water sources were as likely to be used as oviposition sites as untreated sources. These data suggest that treated sites might act as sinks for mosquito reproduction and moreover that such sites might act as dissemination sources for the horizontal transfer of larvicides to new environments by mature females. We review the literature on the environmental and human health effects of this compound and discuss its potential for use as a mosquito control agent in the field.
Assuntos
Aedes , Inseticidas , Controle de Mosquitos/métodos , Piridinas , Aedes/crescimento & desenvolvimento , Animais , Repelentes de Insetos , Hormônios Juvenis , PeruRESUMO
Large-scale longitudinal cohort studies are necessary to characterize temporal and geographic variation in Aedes aegypti (L.) (Diptera: Culicidae) production patterns and to develop targeted dengue control strategies that will reduce disease. We carried out pupal/demographic surveys in a circuit of approximately 6,000 houses, 10 separate times, between January 1999 and August 2002 in the Amazonian city of Iquitos, Peru. We quantified the number of containers positive for Ae. aegypti larvae and/or pupae, containers holding pupae, and the absolute number of pupae by 4-mo sampling circuits and spatially by geographic area by using a geographic information system developed for the city. A total of 289,941 water-holding containers were characterized, of which 7.3% were positive for Ae. aegypti. Temporal and geographic variations were detected for all variables examined, and the relative importance of different container types for production of Ae. aegypti was calculated. Ae. aegypti larvae and pupae were detected in 64 types of containers. Consistent production patterns were observed for the lid status (lids: 32% wet containers, 2% pupal production), container location (outdoor: 43% wet containers, 85% pupal production), and method by which the container was filled with water (rain filled: 15% wet containers, 88.3% pupal production); these patterns were consistent temporally and geographically. We describe a new container category (nontraditional) that includes transient puddles, which were rare but capable of producing large numbers of pupae. Because of high variable pupal counts, four container categories (large tank, medium storage, miscellaneous, and nontraditional) should be targeted in addition to outdoor rain-filled containers that are not covered by a lid. The utility of targeted Ae. aegypti control is discussed, as well as the ability to achieve control objectives based on published but untested threshold values.
Assuntos
Aedes/crescimento & desenvolvimento , Animais , Demografia , Geografia , Humanos , Larva , Peru , Densidade Demográfica , Pupa , Fatores de Tempo , Saúde da População UrbanaRESUMO
Objetivos: Demostrar la presencia de An. (Nys. ) benarrochi en áreas de transmisión malárica, donde es frecuentemente identificado como An. evansae. Materiales y métodos: Se colectaron mosquitos en San José (Pucallpa), Muniches y Andoas (Alto Amazonas), localidades con transmisión de malaria. Con estos mosquitos se efectuaron crías biológicas en laboratorio con la finalidad de obtener material de estudio como son exuvias de larvas, pupas, adultos hembras y machos. Se efectuaron montajes de exuvias de larvas y pupas asociados con sus respectivos adultos, disecciones de las genitalias de machos y biometría de los adultos machos y hembras. Resultados: Además de las verificaciones efectuadas en el campo, basadas en el estudio de inmaduros y adultos, las crías biológicas efectuadas confirmaron la presencia de An. benarrochi en las localidades mencionadas. Asimismo, confirmaron también la existencia de gran variabilidad de los caracteres morfológicos externos, que pueden inducir al error en las identificaciones. Conclusiones: En las áreas maláricas estudiadas, la especie identificada como An. (Nys.) evansae corresponde a An. (Nys. ) benarrochi, demostrado con nuestros estudios. Dada la variabilidad de caracteres que dificultan la identificación de las especies afines, es necesario realizar estudios completos con la finalidad de conocer la fauna local de anofelinos.
Objective: Determine the presence of An. (Nys.) benarrochi in those malaria transmission areas where it is often identified as An. evansae. Material and methods: Collections were conducted in San José (Pucallpa), Muniches and Andoas (Alto Amazonas), localities where malaria transmission occurs. Mosquitoes were reared in the laboratory where larval and pupal exuviae were preserved along with corresponding adults specimens, dissection of male genitalia and biometry of male and female adult mosquitoes was also conducted. Results: The presence of An. benarrochi in the above localities was confirmed with both field collected adults and laboratory-reared specimens. Considerable morphological variability was noted in the laboratory-reared specimens, which has likely contributed to previous incorrect identifications. Conclusions: Based on these studies, the species identified as An. (Nys.) evansae correspond to An. (Nys.) benarrochi, in these malaria endemic areas. Morphological variability makes identification of similar species difficult, thus it is necessary to conduct thorough studies to know local fauna of anophelines.