Importance of socioeconomic status and tree holes in distribution of Aedes mosquitoes (Diptera: Culicidae) in Jodhpur, Rajasthan, India

Mathematics of dengue transmission dynamics: Roles of vector vertical transmission and temperature fluctuations

A new deterministic model is designed and used to gain insight into the effect of seasonal variations in temperature and vector vertical transmission on the transmission dynamics of dengue disease. The model, which incorporates (among many other features) the dynamics of the immature dengue-competent mosquitoes, vertical transmission in the vector population, density-dependent larval mortality and temperature effects, is rigorously analysed and simulated using data relevant to the disease dynamics in Chiang Mai province of Thailand. The non-trivial disease-free equilibrium of the model is shown to be globally-asymptotically stable when the associated basic reproduction number of the model is less than unity. Numerical simulations of the model, using data relevant to the disease dynamics in the Chiang Mai province of Thailand, show that vertical transmission in the vector population has only marginal impact on the disease dynamics, and that the effect of vertical transmission is temperature-dependent (in particular, the effect of vertical transmission on the disease dynamics increases for values of the mean monthly temperature in the range[ 16 - 28 ] ∘ C, and decreases with increasing mean monthly temperature thereafter). It is further shown that dengue burden (as measured in terms of disease incidence) is maximized when the mean monthly temperature is in the range[ 26 - 28 ] ∘ C (and dengue burden decreases for mean monthly temperature values above28 ∘ C). Thus, this study suggests that anti-dengue control efforts should be intensified during the period when this temperature range is recorded in the Chiang Mai province (this occurs between June and August).

Comparative analysis of midgut bacterial communities in three aedine mosquito species from dengue-endemic and non-endemic areas of Rajasthan, India

Dengue viruses are transmitted to humans through the bites of infected female aedine mosquitoes. Differences in the composition and structure of bacterial communities in the midguts of mosquitoes may affect the vector's ability to transmit the disease. To investigate and analyse the role of midgut bacterial communities in viral transmission, midgut bacteria from three species, namely Stegomyia aegypti (= Aedes aegypti), Fredwardsius vittatus (= Aedes vittatus) and Stegomyia albopicta (= Aedes albopictus) (all: Diptera: Culicidae), from dengue-endemic and non-endemic areas of Rajasthan, India were compared. Construction and analyses of six 16S rRNA gene libraries indicated that Serratia spp.-related phylotypes dominated all clone libraries of the three mosquito species from areas in which dengue is not endemic. In dengue-endemic areas, phylotypes related to Aeromonas, Enhydrobacter spp. and uncultivated bacterium dominated the clone libraries of S. aegypti, F. vittatus and S. albopicta, respectively. Diversity indices analysis and real-time TaqMan polymerase chain reaction assays showed bacterial diversity and abundance in the midguts of S. aegypti to be higher than in the other two species. Significant differences observed among midgut bacterial communities of the three mosquito species from areas in which dengue is and is not endemic, respectively, may be related to the vectorial capacity of mosquitoes to carry dengue viruses and, hence, to the prevalence of disease in some areas.

Zika: As an emergent epidemic

Zika virus is a new global threat for 2016 that has been swept to almost all Americas and is now posing serious threats to the entire globe. This deadly virus is playing havoc to unborn lives because of its reported association with upsurge of fetal deformation called microcephaly and neuropathic disorders including Guillain-Barré syndrome. Till today, there is no vaccine prospect, antiviral therapy or licensed medical countermeasures to curb the teratogenic outcomes of this destructive viral infection. Diagnosis, treatment, chronicity and pathogenesis are still vague and unsettled. Therefore, this review article addresses all the aspects related to this disease to mitigate the explosive rise in Zika virus infection.

Effectiveness of Print Education at Reducing Urban Mosquito Infestation through Improved Resident-Based Management

Improving resident-based management and knowledge of mosquitoes is often an integral component of integrated mosquito management, especially in urban landscapes with considerable mosquito habitat on privately owned lands. This study tested the effectiveness of print education materials at reducing urban mosquito exposure through improving resident knowledge of, and attitudes towards, mosquitoes and mosquito management in Washington DC, USA. There was a specific focus on the removal of water-filled containers that are utilized by the developmental stages of the two most common vector species in the region, Aedes albopictus and Culex pipiens. Households in six neighborhoods that varied in socio-economic status were administered knowledge, attitude, and practice (KAP) surveys in 2010 and 2012, and had their yards surveyed for container habitats and immature mosquitoes (larvae and pupae) in 2010, 2011, and 2012. Half the households (intervention, n = 120) received education materials in 2011 and 2012 to yield a before-after control-intervention (BACI) design. Unexpectedly, residents in intervention households were more likely to show decreased concern for mosquito-borne illnesses than residents in control households, which did not receive materials. Moreover, there was a greater probability that control households reduced containers in 2012 than intervention households, particularly when they had low numbers of baseline (2010) containers. Irrespective of control, reductions in containers were associated with decreased abundances of immature mosquitoes. Overall, our findings suggest that print education materials may have unintended negative effects on resident attitudes and household management of mosquito production. We recommend that mosquito control agencies need to carefully consider their content of print messages and the effectiveness of strategies that passively convey information with little or no engagement with control professionals.

The ecological foundations of transmission potential and vector-borne disease in urban landscapes

Urban transmission of arthropod-vectored disease has increased in recent decades. Understanding and managing transmission potential in urban landscapes requires integration of sociological and ecological processes that regulate vector population dynamics, feeding behavior, and vector-pathogen interactions in these unique ecosystems. Vectorial capacity is a key metric for generating predictive understanding about transmission potential in systems with obligate vector transmission. This review evaluates how urban conditions, specifically habitat suitability and local temperature regimes, and the heterogeneity of urban landscapes can influence the biologically-relevant parameters that define vectorial capacity: vector density, survivorship, biting rate, extrinsic incubation period, and vector competence.Urban landscapes represent unique mosaics of habitat. Incidence of vector-borne disease in urban host populations is rarely, if ever, evenly distributed across an urban area. The persistence and quality of vector habitat can vary significantly across socio-economic boundaries to influence vector species composition and abundance, often generating socio-economically distinct gradients of transmission potential across neighborhoods.Urban regions often experience unique temperature regimes, broadly termed urban heat islands (UHI). Arthropod vectors are ectothermic organisms and their growth, survival, and behavior are highly sensitive to environmental temperatures. Vector response to UHI conditions is dependent on regional temperature profiles relative to the vector's thermal performance range. In temperate climates UHI can facilitate increased vector development rates while having countervailing influence on survival and feeding behavior. Understanding how urban heat island (UHI) conditions alter thermal and moisture constraints across the vector life cycle to influence transmission processes is an important direction for both empirical and modeling research.There remain persistent gaps in understanding of vital rates and drivers in mosquito-vectored disease systems, and vast holes in understanding for other arthropod vectored diseases. Empirical studies are needed to better understand the physiological constraints and socio-ecological processes that generate heterogeneity in critical transmission parameters, including vector survival and fitness. Likewise, laboratory experiments and transmission models must evaluate vector response to realistic field conditions, including variability in sociological and environmental conditions.

A tale of two city blocks: differences in immature and adult mosquito abundances between socioeconomically different urban blocks in Baltimore (Maryland, USA)

Infrastructure degradation in many post-industrial cities has increased the availability of potential mosquito habitats, including container habitats that support infestations of invasive disease-vectors. This study is unique in examining both immature and adult mosquito abundance across the fine-scale variability in socio-economic condition that occurs block-to-block in many cities. We hypothesized that abundant garbage associated with infrastructure degradation would support greater mosquito production but instead, found more mosquito larvae and host-seeking adults (86%) in parcels across the higher socio-economic, low-decay block. Aedes albopictus and Culex pipiens were 5.61 (p < 0.001) and 4.60 (p = 0.001) times more abundant, respectively. Most discarded (garbage) containers were dry during peak mosquito production, which occurred during the 5th hottest July on record. Containers associated with human residence were more likely to hold water and contain immature mosquitoes. We propose that mosquito production switches from rain-fed unmanaged containers early in the season to container habitats that are purposefully shaded or watered by mid-season. This study suggests that residents living in higher socioeconomic areas with low urban decay may be at greater risk of mosquito-borne disease during peak mosquito production when local container habitats are effectively decoupled from environmental constraints.

Linking mosquito infestation to resident socioeconomic status, knowledge, and source reduction practices in suburban Washington, DC

Eliminating water-holding containers where mosquitoes oviposit and develop (source reduction) can help manage urban disease-vector mosquitoes. Source reduction requires residents to be knowledgeable of effective practices and motivated to implement them. We tested relationships between demographics, resident knowledge, attitudes, and practices (KAP), and mosquito infestation by administering larval mosquito surveys and KAP questionnaires in Washington, DC. Respondents who reported practicing source reduction had lower numbers of pupae-positive containers and Culex pipiens-positive containers, but not Aedes albopictus-positive containers or water-holding containers, in their yards. When controlling for numbers of water-holding containers in statistical models, residents who reported source reduction had lower numbers of A. albopictus-positive containers in addition to numbers of pupae-positive containers and C. pipiens-positive containers. These results suggest that while active container reduction may be effective at reducing C. pipiens and overall pupal production, it may be offset by other resident activities that add containers to yards, and that source reduction that involves mosquito habitat management without outright container removal can also be effective at reducing A. albopictus. Source reduction was related to respondent knowledge of mosquitoes and, in particular, specific knowledge of mosquito development, which both varied with demographics alongside respondent motivation to control mosquitoes. Respondents from high socioeconomic status households reported greater knowledge but lower motivation than respondents from middle and low socioeconomic-status households. We conclude that mosquito-related education will help promote community-based container management as part of integrated mosquito management programs, particularly in middle and low socioeconomic status neighborhoods with lower knowledge and high motivation.

First dengue virus detection in Aedes albopictus from Delhi, India: its breeding ecology and role in dengue transmission

OBJECTIVE

To report dengue virus and its disease transmission in Aedes albopictus in the National Capital Territory of Delhi, India.

METHODS

Monthly Aedes surveys were carried out in 126 urban localities of Delhi in 2008 and 2009. Pools of all three species of Aedes mosquitoes were tested for Dengue virus (DENV) using an antigen-capture enzyme-linked immunosorbent assay.

RESULTS

Aedes aegypti was the most prevalent species, breeding throughout the year. Aedes albopictus was found in 9.52% of surveyed localities including the central urban part of Delhi, in March and from August to October. Aedes albopictus and Aedes vittatus are adapting to breed in manmade containers in the urban areas of Delhi in addition to their natural habitats of bamboo bushes and rock pits. Of the 229 pools of Ae. aegypti and 34 pools of Ae. albopictus tested, 10.5% and 11.76% were positive for dengue virus, respectively. No dengue virus infection was recorded in Ae. vittatus.

CONCLUSION

This is the first report of dengue virus in Ae. albopictus from north India. Because DENV was detected in Ae. albopictus, which adapted to manmade containers, both its spread and transmission dynamics should be checked.

Higher temperature and urbanization affect the spatial patterns of dengue fever transmission in subtropical Taiwan

Our study conducted spatial analysis to examine how temperature and other environmental factors might affect dengue fever distributions, and to forecast areas with potential risk for dengue fever endemics with predicted climatic change in Taiwan. Geographic information system (GIS) was used to demonstrate the spatial patterns of all studied variables across 356 townships. Relationships between cumulative incidence of dengue fever, climatic and non-climatic factors were explored. Numbers of months with average temperature higher than 18 degrees C per year and degree of urbanization were found to be associated with increasing risk of dengue fever incidence at township level. With every 1 degrees C increase of monthly average temperature, the total population at risk for dengue fever transmission would increase by 1.95 times (from 3,966,173 to 7,748,267). A highly-suggested warmer trend, with a statistical model, across the Taiwan Island is predicted to result in a sizable increase in population and geographical areas at higher risk for dengue fever epidemics.

Evidence of vertical transmission of dengue virus in two endemic localities in the state of Oaxaca, Mexico

BACKGROUND

Dengue virus is spread in tropical areas of the world and is the causative agent of dengue fever and dengue hemorrhagic fever. It is horizontally transmitted to humans by infected Aedes mosquitoes, but it is also able to be vertically or transovarially transmitted to insect progeny.

OBJECTIVE

In this work, we analyzed the vertical transmission of dengue virus in Aedes aegypti mosquitoes collected in two endemic localities in the state of Oaxaca, Mexico.

METHODS

The collected larvae were grown in the laboratory and transovarial transmission of dengue virus, either in larvae or newly emerged mosquitoes, was investigated using a semi-nested reverse transcription-polymerase chain reaction method.

RESULTS

Although the presence of dengue virus in larvae could not be demonstrated, the viral genome was amplified in 4 out of 43 pools of in-cage born mosquitoes: DEN 2, 3 and 4 serotypes were detected in 2 pools from Tuxtepec and two from Juchitán.

CONCLUSION

The results presented here strongly suggest that dengue virus can be vertically transmitted in mosquitoes from Oaxaca, but more studies will be necessary to analyze the epidemiological impact of this mechanism of transmission.