Urban Vector Research Articles

Dengue: An Analysis of Epidemiological Pattern Over a Six Year Period.

Dengue is an arboviral infection transmitted among humans by Aedes aegypti, the urban vector and Aedes albopictus as a maintenance vector in sub-urban and rural areas. The diagnosis is routinely established by detection of NS1 antigen and/or by IgM antibodies testing. Dengue infects 50-100 million cases per year worldwide with atleast half million serious cases needing hospitalization. Therefore, it is necessary to keep the surveillance ongoing to timely look out for changes occurring in disease pattern over a geographical area. To study the epidemiological patterns of dengue virus infection in our region over a period of six years. The present retrospective study was undertaken in the Department of Microbiology, Government Medical College Hospital, Chandigarh during time period January 2010 to December 2015 on 10,774 serum samples from patients clinically suspected to be suffering from dengue infection. Samples were selected as per World Health Organization (WHO) criteria. All the samples were processed for the presence of dengue IgM antibodies by μ anti-body-capture Enzyme Linked Immunosorbent Assay (ELISA), MAC ELISA and/or NS1Ag by ELISA as per the instructions of the manufacturer. The data was analysed from the data sheets available. During the time period, a total of 10,774 samples were processed and 2,449 (22.7%) samples came out to be positive for dengue virus infection. Marked seasonal variation was noted with 0-2 cases presenting during month of January to July but positivity peaked in post monsoon season in October (>70%) and tapered till December every year. The adult age group (16-45 yrs) showed maximum positivity (83.5%) with males affected more than females. The present study clearly shows that our region is endemic for the dengue virus infection and there is need to continuously monitor the transmission of the disease in the community, to plan effective measures, to control the spread of dengue virus infection timely.

Coevolution of the Ile1,016 and Cys1,534 Mutations in the Voltage Gated Sodium Channel Gene of Aedes aegypti in Mexico

BackgroundWorldwide the mosquito Aedes aegypti (L.) is the principal urban vector of dengue viruses. Currently 2.5 billion people are at risk for infection and reduction of Ae. aegypti populations is the most effective means to reduce the risk of transmission. Pyrethroids are used extensively for adult mosquito control, especially during dengue outbreaks. Pyrethroids promote activation and prolong the activation of the voltage gated sodium channel protein (VGSC) by interacting with two distinct pyrethroid receptor sites [1], formed by the interfaces of the transmembrane helix subunit 6 (S6) of domains II and III. Mutations of S6 in domains II and III synergize so that double mutants have higher pyrethroid resistance than mutants in either domain alone. Computer models predict an allosteric interaction between mutations in the two domains. In Ae. aegypti, a Ile1,016 mutation in the S6 of domain II was discovered in 2006 and found to be associated with pyrethroid resistance in field populations in Mexico. In 2010 a second mutation, Cys1,534 in the S6 of domain III was discovered and also found to be associated with pyrethroid resistance and correlated with the frequency of Ile1,016.Methodology/Principal FindingsA linkage disequilibrium analysis was performed on Ile1,016 and Cys1,534 in Ae. aegypti collected in Mexico from 2000–2012 to test for statistical associations between S6 in domains II and III in natural populations. We estimated the frequency of the four dilocus haplotypes in 1,016 and 1,534: Val1,016/Phe1,534 (susceptible), Val1,016/Cys1,534, Ile1,016/Phe1,534, and Ile1,016/Cys1,534 (resistant). The susceptible Val1,016/Phe1,534 haplotype went from near fixation to extinction and the resistant Ile1,016/Cys1,534 haplotype increased in all collections from a frequency close to zero to frequencies ranging from 0.5–0.9. The Val1,016/Cys1,534 haplotype increased in all collections until 2008 after which it began to decline as Ile1,016/Cys1,534 increased. However, the Ile1,016/Phe1,534 haplotype was rarely detected; it reached a frequency of only 0.09 in one collection and subsequently declined.Conclusion/SignificancePyrethroid resistance in the vgsc gene requires the sequential evolution of two mutations. The Ile1,016/Phe1,534 haplotype appears to have low fitness suggesting that Ile1,016 was unlikely to have evolved independently. Instead the Cys1,534 mutation evolved first but conferred only a low level of resistance. Ile1,016 in S6 of domain II then arose from the Val1,016/Cys1,534 haplotype and was rapidly selected because double mutants confer higher pyrethroid resistance. This pattern suggests that knowledge of the frequencies of mutations in both S6 in domains II and III are important to predict the potential of a population to evolve kdr. Susceptible populations with high Val1,016/Cys1,534 frequencies are at high risk for kdr evolution, whereas susceptible populations without either mutation are less likely to evolve high levels of kdr, at least over a 10 year period.

Best practices in school food and nutrition units of public schools of Bayeux, PB, Brazil.

The occurrence of foodborne illness outbreaks is increasing in schools, and due to the number of children who consume school meals as the only daily meal, this factor becomes even more worrisome. In this sense, the aim of this study was to evaluate the hygienic-health aspects of Food and Nutrition Units (SFNU) of public schools of Bayeux / PB in relation to the adoption of best practices in school food and nutrition. Data were collected through SFNU checklist during visits to units in 29 schools. The health risk of units evaluated was from regular to very high regarding structure and facilities, hygiene of food handlers, environment and food preparation. It was found that 10.3% of handlers used clean and adequate uniforms, and environment and equipment showed poor conservation status in 75.9% and 89.7% of Units, respectively; control of urban pests and vectors was not effective and cleaning of fresh produce was incorrectly conducted in 51.7% of SFNU of schools evaluated. It could be concluded that the production of meals in SFNU of schools evaluated does not meet the requirements established by the best practices in school food and nutrition.

Mosquito-disseminated pyriproxyfen yields high breeding-site coverage and boosts juvenile mosquito mortality at the neighborhood scale.

BackgroundMosquito-borne pathogens pose major public health challenges worldwide. With vaccines or effective drugs still unavailable for most such pathogens, disease prevention heavily relies on vector control. To date, however, mosquito control has proven difficult, with low breeding-site coverage during control campaigns identified as a major drawback. A novel tactic exploits the egg-laying behavior of mosquitoes to have them disseminate tiny particles of a potent larvicide, pyriproxyfen (PPF), from resting to breeding sites, thus improving coverage. This approach has yielded promising results at small spatial scales, but its wider applicability remains unclear.Methodology/Principal FindingsWe conducted a four-month trial within a 20-month study to investigate mosquito-driven dissemination of PPF dust-particles from 100 ‘dissemination stations’ (DSs) deployed in a 7-ha sub-area to surveillance dwellings and sentinel breeding sites (SBSs) distributed over an urban neighborhood of about 50 ha. We assessed the impact of the trial by measuring juvenile mosquito mortality and adult mosquito emergence in each SBS-month. Using data from 1,075 dwelling-months, 2,988 SBS-months, and 29,922 individual mosquitoes, we show that mosquito-disseminated PPF yielded high coverage of dwellings (up to 100%) and SBSs (up to 94.3%). Juvenile mosquito mortality in SBSs (about 4% at baseline) increased by over one order of magnitude during PPF dissemination (about 75%). This led to a >10-fold decrease of adult mosquito emergence from SBSs, from approximately 1,000–3,000 adults/month before to about 100 adults/month during PPF dissemination.Conclusions/SignificanceBy expanding breeding-site coverage and boosting juvenile mosquito mortality, a strategy based on mosquito-disseminated PPF has potential to substantially enhance mosquito control. Sharp declines in adult mosquito emergence can lower vector/host ratios, reducing the risk of disease outbreaks. This approach is a very promising complement to current and novel mosquito control strategies; it will probably be especially relevant for the control of urban disease vectors, such as Aedes and Culex species, that often cause large epidemics.

Deltamethrin induced functional mortality of Anopheles stephensi, the urban malaria vector, in relation to resistance development

Deltamethrin induced functional mortality of Anopheles stephensi, the urban malaria vector, in relation to resistance development

Disease Vector Mapping Via Environmental, Climatological and Sociological Factors

The mosquito Aedes (Ae). aegypti serves as the primary urban vector for the virus that causes dengue, the most prevalent vector-borne viral disease on Earth. The probability of contracting dengue is modulated by climatic conditions that affect both Ae. aegypti development and the incubation period of dengue virus in adult mosquitoes, as well as socio-economic and human behavioral factors that enhance risk for vector-human contact and virus transmission. Vaccines or therapeutics are not yet available for use against dengue virus. Dengue virus infections often are asymptomatic, and there is an inherent delay between the onset date of dengue illness and the date the case is reported to the public health authorities. It is therefore critical to provide public health officials with a mechanism to better prepare in advance of an impending dengue epidemic. Here we describe a new decision support tool to inform public health planning and preparedness (e.g., the development of mosquito vector intervention strategies, garnering community awareness of dengue risk and support for control interventions). The tool, developed to be run in near-real-time, consists of a linkage of new and existing physically-based models that simulate 1) meteorological conditions over an area of interest; 2) the number and types of containers in a region (which are closely linked to socioeconomic and behavioral factors); 3) the temperature and volume of water in artificial container habitats in which Ae. aegypti develops; 4) the life cycle of the mosquito itself; and 5) the development of dengue virus and its transmission be of the mosquito itself; and 5) the development of dengue virus and its transmission between Ae. aegypti and humans.

Genome analysis of a major urban malaria vector mosquito, Anopheles stephensi.

BackgroundAnopheles stephensi is the key vector of malaria throughout the Indian subcontinent and Middle East and an emerging model for molecular and genetic studies of mosquito-parasite interactions. The type form of the species is responsible for the majority of urban malaria transmission across its range.ResultsHere, we report the genome sequence and annotation of the Indian strain of the type form of An. stephensi. The 221 Mb genome assembly represents more than 92% of the entire genome and was produced using a combination of 454, Illumina, and PacBio sequencing. Physical mapping assigned 62% of the genome onto chromosomes, enabling chromosome-based analysis. Comparisons between An. stephensi and An. gambiae reveal that the rate of gene order reshuffling on the X chromosome was three times higher than that on the autosomes. An. stephensi has more heterochromatin in pericentric regions but less repetitive DNA in chromosome arms than An. gambiae. We also identify a number of Y-chromosome contigs and BACs. Interspersed repeats constitute 7.1% of the assembled genome while LTR retrotransposons alone comprise more than 49% of the Y contigs. RNA-seq analyses provide new insights into mosquito innate immunity, development, and sexual dimorphism.ConclusionsThe genome analysis described in this manuscript provides a resource and platform for fundamental and translational research into a major urban malaria vector. Chromosome-based investigations provide unique perspectives on Anopheles chromosome evolution. RNA-seq analysis and studies of immunity genes offer new insights into mosquito biology and mosquito-parasite interactions.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-014-0459-2) contains supplementary material, which is available to authorized users.

Insecticidal and growth regulating activity of crude leaf extracts of Cassia occidentalis L. (Caesalpinaceae) against the urban malaria vector, Anopheles stephensi Liston (Diptera: Culicidae)

ObjectiveTo investigate insecticidal and growth regulating activity of crude leaf extracts of Cassia occidentalis L. (Caesalpinaceae) against the urban malaria vector, Anopheles stephensi Liston. (Diptera: Culicidae). MethodsLarvicidal activity was studied against third instar larvae for 24 h at concentrations of 62.5, 125.0, 250.0, 500.0, 1 000.0, 2 000.0, 4 000.0 and 8 000.0 mg/L. The effect on development and growth of immature mosquitoes was studied at concentrations of 125.0, 250.0 and 500.0 mg/L and was assessed by growth index. Adulticidal activity on topical application was studied on test dosages of 0.01, 0.05, 0.10, 0.25 and 0.50 μg per newly emerged unfed adult female mosquito. ResultsLarvicidal activity was poor, not proportional to concentration and LC50 values were above the acceptable dose of 10 mg/L. Potential growth regulating activity was observed and the growth index was 277.5, 111.0 and 27.5 times less than control, respectively. Average larval pupal transformation was 5.8, 4.3 and 96.0 times greater than pupal adult transformation in hexane, 5.0, 4.3 and 48.4 in ethyl acetate, and 4.8, 4.2 and 10.2 in methanol extract, respectively. Adulticidal activity was the highest in ethyl acetate, followed by hexane and methanol extract with LD50 values of 0.23, 0.32 and 0.64 μg/female mosquito, respectively. ConclusionsThe crude leaf extracts of Cassia occidentalis studied showed poor larvicidal, potential growth regulating and a moderate level of adulticidal activity.

The impact of temperature on the bionomics of Aedes (Stegomyia) aegypti, with special reference to the cool geographic range margins.

The mosquito Aedes (Stegomyia) aegypti (L.), which occurs widely in the subtropics and tropics, is the primary urban vector of dengue and yellow fever viruses, and an important vector of chikungunya virus. There is substantial interest in how climate change may impact the bionomics and pathogen transmission potential of this mosquito. This Forum article focuses specifically on the effects of temperature on the bionomics of Ae. aegypti, with special emphasis on the cool geographic range margins where future rising temperatures could facilitate population growth. Key aims are to: 1) broadly define intra-annual (seasonal) patterns of occurrence and abundance of Ae. aegypti, and their relation to climate conditions; 2) synthesize the existing quantitative knowledge of how temperature impacts the bionomics of different life stages of Ae. aegypti; 3) better define the temperature ranges for which existing population dynamics models for Ae. aegypti are likely to produce robust predictions; 4) explore potential impacts of climate warming on human risk for exposure to Ae. aegypti at its cool range margins; and 5) identify knowledge or data gaps that hinder our ability to predict risk of human exposure to Ae. aegypti at the cool margins of its geographic range now and in the future. We first outline basic scenarios for intra-annual occurrence and abundance patterns for Ae. aegypti, and then show that these scenarios segregate with regard to climate conditions in selected cities where they occur. We then review how near-constant and intentionally fluctuating temperatures impact development times and survival of eggs and immatures. A subset of data, generated in controlled experimental studies, from the published literature is used to plot development rates and survival of eggs, larvae, and pupae in relation to water temperature. The general shape of the relationship between water temperature and development rate is similar for eggs, larvae, and pupae. Once the lower developmental zero temperature (10-14 degrees C) is exceeded, there is a near-linear relationship up to 30 degrees C. Above this temperature, the development rate is relatively stable or even decreases slightly before falling dramatically near the upper developmental zero temperature, which occurs at -38-42 degrees C. Based on life stage-specific linear relationships between water temperature and development rate in the 15-28 degrees C range, the lower developmental zero temperature is estimated to be 14.0 degrees C for eggs, 11.8 degrees C for larvae, and 10.3 degrees C for pupae. We further conclude that available population dynamics models for Ae. aegypti, such as CIMSiM and Skeeter Buster, likely produce robust predictions based on water temperatures in the 16-35 degrees C range, which includes the geographic areas where Ae. aegypti and its associated pathogens present the greatest threat to human health, but that they may be less reliable in cool range margins where water temperatures regularly fall below 15 degrees C. Finally, we identify knowledge or data gaps that hinder our ability to predict risk of human exposure to Ae. aegypti at the cool margins of its range, now and in the future, based on impacts on mosquito population dynamics of temperature and other important factors, such as water nutrient content, larval density, presence of biological competitors, and human behavior.

Evaluation of recreational quality, carrying capacity and ecosystem services supplied by sandy beaches of the municipality of Camaçari, northern coast of Bahia, Brazil

ABSTRACT Souza Filho, J. R., Santos, R. C, Silva, I R., Elliff, C.I., 2014. Evaluation of recreational quality, carrying capacity and ecosystem services supplied by sandy beaches of the municipality of Camacari, northern coast of Bahia, Brazil. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 527–532, ISSN 0749-0208. The coastal municipality of Camacari is currently under great real estate pressure. It is located within one of the main urban growth vectors of the State of Bahia, Brazil. In this context, the main goal of this research was to assess the recreational quality and the carrying capacity, and qualitatively evaluate the ecosystem services supplied by the beaches of the municipality of Camacari and its adjacent coastal area. In order to evaluate the recreational quality, the beaches of Busca Vida, Jaua, Interlagos, Arembepe, Barra de Jacuipe, Guarejuba and Itacimirim were class...

Long term impacts of combined sewer overflow remediation on water quality and population dynamics of Culex quinquefasciatus, the main urban West Nile virus vector in Atlanta, GA

BackgroundCombined sewers are a significant source of urban water pollution due to periodic discharges into natural streams. Such events (called combined sewer overflows, or CSOs) contribute to the impairment of natural waterways and are associated with increased mosquito productivity and elevated risk of West Nile virus transmission. ObjectivesWe investigated the impact of CSOs on water quality and immature mosquito productivity in the city of Atlanta, Georgia, one year before and four years after CSO facility remediation. MethodsWater quality (ammonia, phosphate, nitrate and dissolved oxygen concentrations), immature mosquitoes (larvae and pupae), water temperature and rainfall were quantified biweekly between June–October at two urban creeks during 2008–2012. A before–after control–intervention design tested the impact of remediation on mosquito productivity and water quality, whereas generalized linear mixed-effect models quantified the factors explaining the long term impacts of remediation on mosquito productivity. ResultsAmmonia and phosphate concentrations and late immature (fourth-instar and pupae) mosquito populations were significantly higher in CSO than in non-CSO creeks, while dissolved oxygen concentrations were lower. Remediation significantly improved water quality estimates (particularly ammonia and dissolved oxygen) and reduced the number of overflows, mosquito productivity and the overall contribution of CSO-affected streams as sources of vectors of West Nile virus. ConclusionsThe quality of water in CSOs provided a suitable habitat for immature mosquitoes. Remediation of the CSO facility through the construction of a deep storage tunnel improved water quality indices and reduced the productivity of mosquito species that can serve as vectors of West Nile virus.

Genome analysis of a major urban malaria vector mosquito, Anopheles stephensi

Anopheles stephensi is the key vector of malaria throughout the Indian subcontinent and Middle East and an emerging model for molecular and genetic studies of mosquito-parasite interactions. The type form of the species is responsible for the majority of urban malaria transmission across its range. Here, we report the genome sequence and annotation of the Indian strain of the type form of An. stephensi. The 221 Mb genome assembly represents more than 92% of the entire genome and was produced using a combination of 454, Illumina, and PacBio sequencing. Physical mapping assigned 62% of the genome onto chromosomes, enabling chromosome-based analysis. Comparisons between An. stephensi and An. gambiae reveal that the rate of gene order reshuffling on the X chromosome was three times higher than that on the autosomes. An. stephensi has more heterochromatin in pericentric regions but less repetitive DNA in chromosome arms than An. gambiae. We also identify a number of Y-chromosome contigs and BACs. Interspersed repeats constitute 7.1% of the assembled genome while LTR retrotransposons alone comprise more than 49% of the Y contigs. RNA-seq analyses provide new insights into mosquito innate immunity, development, and sexual dimorphism. The genome analysis described in this manuscript provides a resource and platform for fundamental and translational research into a major urban malaria vector. Chromosome-based investigations provide unique perspectives on Anopheles chromosome evolution. RNA-seq analysis and studies of immunity genes offer new insights into mosquito biology and mosquito-parasite interactions.

Crouching Tiger, Hidden Trouble: Urban Sources of Aedes albopictus (Diptera: Culicidae) Refractory to Source-Reduction

Our ultimate objective is to design cost-effective control strategies for Aedes albopictus, the Asian tiger mosquito, an important urban nuisance and disease vector that expanded worldwide during the last 40 years. We conducted mosquito larval surveys from May through October 2009 in the City of Trenton, New Jersey, USA, while performing intensive monthly source-reduction campaigns that involved removing, emptying, or treating all accessible containers with larvicides and pupicides. We examined patterns of occurrence of Ae. albopictus and Culex pipiens, another urban mosquito, among different container types by comparing observed and expected number of positive containers of each type. Expected use was based on the relative frequency of each container type in the environment. Aedes albopictus larvae and pupae were found significantly more often than expected in medium volumes of water in buckets and plant saucers but were rarely collected in small volumes of water found in trash items such as discarded cups and cans. They were also absent from large volumes of water such as in abandoned swimming pools and catch basins, although we consistently collected Cx. pipiens from those habitats. The frequency of Ae. albopictus in tires indicated rapid and extensive use of these ubiquitous urban containers. Standard larval-based indices did not correlate with adult catches in BG-Sentinel traps, but when based only on Ae. albopictus key containers (buckets, plant saucers, equipment with pockets of water, and tires) they did. Although we found that only 1.2% of the 20,039 water-holding containers examined contained immature Ae. albopictus (5.3% if only key containers were counted), adult populations were still above nuisance action thresholds six times during the 2009 mosquito season. We conclude that in urban New Jersey, effective source reduction for Ae. albopictus control will require scrupulous and repeated cleaning or treatment of everyday use containers and extensive homeowner collaboration.

Urban lymphatic filariasis in the city of Tanga, Tanzania, after seven rounds of mass drug administration

Urban lymphatic filariasis (LF) has been listed among the challenges to the ongoing global efforts to eliminate LF. This is partly because the control strategies developed for rural areas – where most LF occurs – do not easily comply with human organization and behaviour in urban areas, and partly because the urban vectors thrive and proliferate in poorly planned urban settlements. This study investigated LF infection, disease and transmission in the medium-sized city of Tanga (approx. 300,000 inhabitants), Tanzania, after seven rounds of mass drug administration (MDA). Three representative sites with varying distance from the city centre were selected for the study. Pupils from one public primary school at each site were screened for circulating filarial antigens (CFA; marker of adult worm infection) and antibodies to Bm14 (marker of exposure to transmission). Community members were examined for CFA, microfilariae and chronic manifestations. Questionnaires were administered to pupils and heads of community households, and vector surveys were carried out in selected households. Although there was evidence of considerable reduction in infection and transmission, there was still LF in the city, with mf and CFA prevalences well above the cut-off levels for stopping MDA. In this respect, the LF situation resembled that seen in nearby rural areas outside the city. The study emphasizes the importance of motivating the urban individuals to engage and comply with the full range of LF intervention measures (MDAs, use of mosquito proofing measures including bed nets, environmental sanitation to prevent vector breeding) in order to reach successful LF control in the city. The high LF disease burden noted, despite the reduction in infection and transmission, moreover emphasizes the importance of allocating resources for morbidity management, to ensure true elimination of LF as a public health problem.

Urban lymphatic filariasis in the metropolis of Dar es Salaam, Tanzania

BackgroundThe last decades have seen a considerable increase in urbanization in Sub-Saharan Africa, and it is estimated that over 50% of the population will live in urban areas by 2040. Rapid growth of cities combined with limited economic resources often result in informal settlements and slums with favorable conditions for proliferation of vectors of lymphatic filariasis (LF). In Dar es Salaam, which has grown more than 30 times in population during the past 55 years (4.4 million inhabitants in 2012), previous surveys have indicated high prevalences of LF. This study investigated epidemiological aspects of LF in Dar es Salaam, as a background for planning and implementation of control.MethodsSix sites with varying distance from the city center (3–30 km) and covering different population densities, socioeconomic characteristics, and water, sewerage and sanitary facilities were selected for the study. Pupils from one public primary school at each site were screened for circulating filarial antigen (CFA; marker of adult worm infection) and antibodies to Bm14 (marker of exposure to transmission). Community members were examined for CFA, microfilariae and chronic manifestations. Structured questionnaires were administered to pupils and heads of community households, and vector surveys were carried out in selected households.ResultsThe study indicated that a tremendous decrease in the burden of LF infection had occurred, despite haphazard urbanisation. Contributing factors may be urban malaria control targeting Anopheles vectors, short survival time of the numerous Culex quinquefasciatus vectors in the urban environment, widespread use of bed nets and other mosquito proofing measures, and mass drug administration (MDA) in 2006 and 2007. Although the level of ongoing transmission was low, the burden of chronic LF disease was still high.ConclusionsThe development has so far been promising, but continued efforts are necessary to ensure elimination of LF as a public health problem. These will include improving the awareness of people about the role of mosquitoes in transmission of LF, more thorough implementation of environmental sanitation to reduce Cx. quinquefasciatus breeding, continued MDA to high-risk areas, and set-up of programmes for management of chronic LF disease.

A mathematically assisted reconstruction of the initial focus of the yellow fever outbreak in Buenos Aires (1871)

We discuss the historic mortality record corresponding to the initial focus of the yellow fever epidemic outbreak registered in Buenos Aires during the year 1871 as compared to simulations of a stochastic population dynamics model. This model incorporates the biology of the urban vector of yellow fever, the mosquito Aedes aegypti, the stages of the disease in the human being as well as the spatial extension of the epidemic outbreak. After introducing the historical context and the restrictions it puts on initial conditions and ecological parameters, we discuss the general features of the simulation and the dependence on initial conditions and available sites for breeding the vector. We discuss the sensitivity, to the free parameters, of statistical estimators such as: final death toll, day of the year when the outbreak reached half the total mortality and the normalized daily mortality, showing some striking regularities. The model is precise and accurate enough to discuss the truthfulness of the presently accepted historic discussions of the epidemic causes, showing that there are more likely scenarios for the historic facts. Received: 9 October 2012, Accepted: 1 March 2013; Edited by: G. Mindlin; DOI: http://dx.doi.org/10.4279/PIP.050002Cite as: M L Fernández, M Otero, N Schweigmann, H G Solari, Papers in Physics 5, 050002 (2013)

Autosomal inheritance of alphamethrin, a synthetic pyrethroid, resistance in Anopheles stephensi – Liston, a malaria mosquito

Anopheles stephensi–Liston (Culicidae: Diptera) is an important urban malarial vector in the Indian sub-continent, accounting for about 15% of the total annual malaria incidence. Chemical control represents a key strategy in the management of this insect vector. However, owing to erratic and continuous application of insecticides, resistance has become a common phenomenon among them and their control has become an uphill task. The genetics of alphamethrin, a synthetic pyrethroid resistance was studied to determine its mode of inheritance. The late third instar larvae were selectively inbred for 27 and ten generations to synthesize homozygous resistant (R) and susceptible (S) stocks, respectively, to the diagnostic dose of 0.12 mg l−1. The log-dosage probit mortality relationships and degree of dominance (D) were calculated. Resistance was observed in both sexes, the dosage-mortality (d-m) line of F 1 was towards the resistant parent and the ‘D’ value was found to be 0.8 indicating alphamethrin resistant (amr) gene to be autosomal and incompletely dominant. The d-m lines of F 2/backcross exhibited a clear plateau of mortality across a range of doses indicating monogenic resistance. The null hypothesis for monogenic resistance was tested from mortality data of backcross progeny compared with theoretical expectations using the χ2 test and was found to be non-significant. Understanding genetics of insecticide resistance is significant in prediction and management of resistant insects. The amr genes can be used as genetic marker in A. stephensi, which can be used in several applications in conducting basic and applied genetic research.

Entomological evaluation of the risk of urban outbreak of yellow fever in 2008 in Abidjan, Côte d’Ivoire

In April 2008, seven years after the outbreak of 2001, Abidjan faced another epidemic of yellow fever. Three weeks after the case detected in the commune of Treichville at 28(th) of April 2008, two other cases were notified, the first one in Port-Bouet and the second one in Cocody located respectively in the south and north of the city of Abidjan. In order to determine a large-scale risk of urban yellow fever epidemic, epidemiological and entomological investigations were conducted by the Ministry of Health and Public Hygiene of Cote d'Ivoire with the support of the Global Outbreak Alert and Response Network. Entomological investigations revealed the predominance of Aedes ægypti, urban vector of yellow fever in neighborhood visited with larval density indices between 2 and 5, indicating the existence of a sufficient density of the vector for cause an explosion of the epidemic. In fact, the massive influx of people from inside cities towards Abidjan caused by the socio-political crisis occurred in the country in 2002, the deterioration of environment with the creation of more breeding sites of Ae.ægypti as corollary and the circulation of the virus at mosquito level were many factors favorable to the yellow fever outbreak in Abidjan city.

Additional Selection for Insecticide Resistance in Urban Malaria Vectors: DDT Resistance in Anopheles arabiensis from Bobo-Dioulasso, Burkina Faso

In the city of Bobo-Dioulasso in Burkina Faso, Anopheles arabiensis has superseded Anopheles gambiae s.s. as the major malaria vector and the larvae are found in highly polluted habitats normally considered unsuitable for Anopheles mosquitoes. Here we show that An. gambiae s.l. adults emerging from a highly polluted site in the city centre (Dioulassoba) have a high prevalence of DDT resistance (percentage mortality after exposure to diagnostic dose = 65.8% in the dry season and 70.4% in the rainy season, respectively). An investigation into the mechanisms responsible found an unexpectedly high frequency of the 1014S kdr mutation (allele frequency = 0.4), which is found at very low frequencies in An. arabiensis in the surrounding rural areas, and an increase in transcript levels of several detoxification genes, notably from the glutathione transferase and cytochrome P450 gene families. A number of ABC transporter genes were also expressed at elevated levels in the DDT resistant An. arabiensis. Unplanned urbanisation provides numerous breeding grounds for mosquitoes. The finding that Anopheles mosquitoes adapted to these urban breeding sites have a high prevalence of insecticide resistance has important implications for our understanding of the selective forces responsible for the rapid spread of insecticide resistant populations of malaria vectors in Africa.

Spatial evaluation of larvae of Culicidae (Diptera) from different breeding sites: application of a geospatial method and implications for vector control

Spatial evaluation of Culicidae (Diptera) larvae from different breeding sites: application of a geospatial method and implications for vector control. This study investigates the spatial distribution of urban Culicidae and informs entomological monitoring of species that use artificial containers as larval habitats. Collections of mosquito larvae were conducted in the São Paulo State municipality of Santa Bárbara d' Oeste between 2004 and 2006 during house-to-house visits. A total of 1,891 samples and nine different species were sampled. Species distribution was assessed using the kriging statistical method by extrapolating municipal administrative divisions. The sampling method followed the norms of the municipal health services of the Ministry of Health and can thus be adopted by public health authorities in disease control and delimitation of risk areas. Moreover, this type of survey and analysis can be employed for entomological surveillance of urban vectors that use artificial containers as larval habitat.