Local introduction and heterogeneous spatial spread of dengue-suppressing Wolbachia through an urban population of Aedes aegypti

Dengue-suppressing Wolbachia strains are promising tools for arbovirus control, particularly as they have the potential to self-spread following local introductions. To test this, we followed the frequency of the transinfected Wolbachia strain wMel through Ae. aegypti in Cairns, Australia, following releases at 3 nonisolated locations within the city in early 2013. Spatial spread was analysed graphically using interpolation and by fitting a statistical model describing the position and width of the wave. For the larger 2 of the 3 releases (covering 0.97 km² and 0.52 km²), we observed slow but steady spatial spread, at about 100–200 m per year, roughly consistent with theoretical predictions. In contrast, the smallest release (0.11 km²) produced erratic temporal and spatial dynamics, with little evidence of spread after 2 years. This is consistent with the prediction concerning fitness-decreasing Wolbachia transinfections that a minimum release area is needed to achieve stable local establishment and spread in continuous habitats. Our graphical and likelihood analyses produced broadly consistent estimates of wave speed and wave width. Spread at all sites was spatially heterogeneous, suggesting that environmental heterogeneity will affect large-scale Wolbachia transformations of urban mosquito populations. The persistence and spread of Wolbachia in release areas meeting minimum area requirements indicates the promise of successful large-scale population transformation.

Wolbachia are bacteria that live inside insect cells. In insects that act as viral vectors, Wolbachia can suppress virus transmission to new hosts. Wolbachia have been experimentally introduced into Aedes aegypti mosquito populations to reduce the transmission of dengue, Zika, and other arboviruses that cause human disease. Wolbachia invade populations by causing cytoplasmic incompatibility, a phenomenon whereby embryos from crosses between infected males and uninfected females fail to hatch. While Wolbachia have been shown to successfully invade and remain established in isolated Ae. aegypti populations, outward spread from urban release zones has not been previously documented. This is an important step in demonstrating that Wolbachia can be used to combat mosquito-borne infectious disease in cities. Here we describe Wolbachia spread from 2 introduction areas within Cairns in northeastern Australia at a rate of about 100–200 meters per year. Spread occurs only when introduction areas are sufficiently large. The slow rates of observed spread are broadly consistent with mathematical predictions based on estimated Ae. aegypti dispersal distances, Wolbachia dynamics, and effects seen in isolated populations. Spread is uneven and likely depends on local characteristics (e.g., barriers) that affect mosquito density and dispersal. Our data indicate that Wolbachia can be introduced locally in large cities, remain established where released, and slowly spread from release areas. These dynamics indicate that high Wolbachia infection frequencies can be established gradually across large urban areas through local releases.

Field evaluation of the establishment potential of wMelPop Wolbachia in Australia and Vietnam for dengue control

Background

Introduced Wolbachia bacteria can influence the susceptibility of Aedes aegypti mosquitoes to arboviral infections as well as having detrimental effects on host fitness. Previous field trials demonstrated that the wMel strain of Wolbachia effectively and durably invades Ae. aegypti populations. Here we report on trials of a second strain, wMelPop-PGYP Wolbachia, in field sites in northern Australia (Machans Beach and Babinda) and central Vietnam (Tri Nguyen, Hon Mieu Island), each with contrasting natural Ae. aegypti densities.

Methods

Mosquitoes were released at the adult or pupal stages for different lengths of time at the sites depending on changes in Wolbachia frequency as assessed through PCR assays of material collected through Biogents-Sentinel (BG-S) traps and ovitraps. Adult numbers were also monitored through BG-S traps. Changes in Wolbachia frequency were compared across hamlets or house blocks.

Results

Releases of adult wMelPop-Ae. aegypti resulted in the transient invasion of wMelPop in all three field sites. Invasion at the Australian sites was heterogeneous, reflecting a slower rate of invasion in locations where background mosquito numbers were high. In contrast, invasion across Tri Nguyen was relatively uniform. After cessation of releases, the frequency of wMelPop declined in all sites, most rapidly in Babinda and Tri Nguyen. Within Machans Beach the rate of decrease varied among areas, and wMelPop was detected for several months in an area with a relatively low mosquito density.

Conclusions

These findings highlight challenges associated with releasing Wolbachia-Ae. aegypti combinations with low fitness, albeit strong virus interference properties, as a means of sustainable control of dengue virus transmission.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-1174-x) contains supplementary material, which is available to authorized users.

Bacillus fermentation of soybeans

Kinema fermentations of Indian and Canadian No. 1 soybeans by Bacillus sp. DK-W1 and by mixed cultures of Bacillus sp. DK-W1 and Enterococcus faecium DK-C1 were essentially identical. The viable cell count of Bacillus increased from an initial 10(5) to 10(10) c.f.u./g wet wt after 48 h incubation at 37°C. The pH of the fermentation dropped from an initial 6.9 to about 6.4 after 8 h and then rose to 8.6 after 32 h, with a coincident increase in proteolytic activity and ammonia concentration. The fermentations containing E. faecium and Bacillus exhibited a greater initial pH decline and a slightly retarded subseqent increase in pH compared with fermentations with Bacillus only. The presence of E. faecium had no detectable effects on growth of the Bacillus, proteolytic activity, ammonia production or the final pH of the fermentations.

Sources of microorganisms in pozol, a traditional Mexican fermented maize dough

Freshly prepared pozol, a traditional Mexican fermented maize dough, contained (c.f.u./g wet wt): lactic acid bacteria, 10(4) to 10(6); aerobic mesophiles, 10(4) to 10(5); Enterobacteriaceae, 10(2) to 10(3); yeasts, 10(2) to 10(4); and mould propagules, <10(3). After 30 h at 28°C the numbers were, respectively: 10(9), 7×10(6), 5×10(5), 10(6) and 10(4). Soaking alkali-treated grains overnight allowed lactic acid bacteria, aerobic mesophiles and Enterobacteriaceae to grow and these then constituted the primary microbial flora of the pozol dough. Grinding in a commercial mill inoculated the dough with lactic acid bacteria, aerobic mesophiles, Enterobacteriaceae and yeasts. Other processing stages, including the nature of the surface upon which the balls were made, handling of the dough, and air, contributed only minor numbers of microbes compared with the two major sources, soaking and grinding. The pH of pozol fell from an initial value of 7.3 to 4.6 after 30 h incubation at 28°C. The numbers of Enterobacteriaceae and other aerobic mesophilic bacteria remained constant between 11 and 30 h incubation and there was no evidence of the acidic conditions having any lethal effects on these organisms.

Transcriptional profiling of Anopheles gambiae mosquitoes for adult age estimation

The age distribution of female mosquitoes in the field is a critical component of vectorial capacity because of the extrinsic incubation period of mosquito-borne pathogens. However this parameter has not been well characterized in malaria vectors because of methodological difficulties; transcriptional profiling provides a potential new approach for age determination. In Anopheles gambiae, microarrays were used to examine global gene expression over adult life. Nine genes were selected from the 2714 gene transcripts that displayed age-related transcription patterns, and quantitative reverse transcription PCR used to select the four best performing genes. The resulting age estimation assay was able to predict female age from lab-reared samples with sufficient accuracy to provide a potentially useful tool for studies of malaria epidemiology and control.

Wolbachia pipientis: an expanding bag of tricks to explore for disease control

Wolbachia pipientis are maternally inherited, endosymbiotic bacteria that are widespread among insects. Two recent studies have demonstrated that Wolbachia inhibits the ability of medically significant pathogens, including filarial nematodes, dengue virus and Plasmodium to form infections in the mosquito vector, Aedes aegypti. We highlight the added value of these traits for Wolbachia based biocontrol strategies and evaluate the evidence for the idea that the insect immune response is responsible for the pathogen inhibition.

Field validation of a transcriptional assay for the prediction of age of uncaged Aedes aegypti mosquitoes in Northern Australia

BACKGROUND

New strategies to eliminate dengue have been proposed that specifically target older Aedes aegypti mosquitoes, the proportion of the vector population that is potentially capable of transmitting dengue viruses. Evaluation of these strategies will require accurate and high-throughput methods of predicting mosquito age. We previously developed an age prediction assay for individual Ae. aegypti females based on the transcriptional profiles of a selection of age responsive genes. Here we conducted field testing of the method on Ae. aegypti that were entirely uncaged and free to engage in natural behavior.

METHODOLOGY/PRINCIPAL FINDINGS

We produced "free-range" test specimens by releasing 8007 adult Ae. aegypti inside and around an isolated homestead in north Queensland, Australia, and recapturing females at two day intervals. We applied a TaqMan probe-based assay design that enabled high-throughput quantitative RT-PCR of four transcripts from three age-responsive genes and a reference gene. An age prediction model was calibrated on mosquitoes maintained in small sentinel cages, in which 68.8% of the variance in gene transcription measures was explained by age. The model was then used to predict the ages of the free-range females. The relationship between the predicted and actual ages achieved an R(2) value of 0.62 for predictions of females up to 29 days old. Transcriptional profiles and age predictions were not affected by physiological variation associated with the blood feeding/egg development cycle and we show that the age grading method could be applied to differentiate between two populations of mosquitoes having a two-fold difference in mean life expectancy.

CONCLUSIONS/SIGNIFICANCE

The transcriptional profiles of age responsive genes facilitated age estimates of near-wild Ae. aegypti females. Our age prediction assay for Ae. aegypti provides a useful tool for the evaluation of mosquito control interventions against dengue where mosquito survivorship or lifespan reduction are crucial to their success. The approximate cost of the method was US$7.50 per mosquito and 60 mosquitoes could be processed in 3 days. The assay is based on conserved genes and modified versions are likely to support similar investigations of several important mosquito and other disease vectors.

Trends in technology, trade and consumption likely to impact on microbial food safety

Current and potential future trends in technology, consumption and trade of food that may impact on food-borne disease are analysed and the key driving factors identified focusing on the European Union and, to a lesser extent, accounting for the United States and global issues. Understanding of factors is developed using system-based methods and their impact is discussed in relation to current events and predictions of future trends. These factors come from a wide range of spheres relevant to food and include political, economic, social, technological, regulatory and environmental drivers. The degree of certainty in assessing the impact of important driving factors is considered in relation to food-borne disease. The most important factors driving an increase in the burden of food-borne disease in the next few decades were found to be the anticipated doubling of the global demand for food and of the international trade in food next to a significantly increased consumption of certain high-value food commodities such as meat and poultry and fresh produce. A less important factor potentially increasing the food-borne disease burden would be the increased demand for convenience foods. Factors that may contribute to a reduction in the food-borne disease burden were identified as the ability of governments around the world to take effective regulatory measures as well as the development and use of new food safety technologies and detection methods. The most important factor in reducing the burden of food-borne disease was identified as our ability to first detect and investigate a food safety issue and then to develop effective control measures. Given the global scale of impact on food safety that current and potentially future trends have, either by potentially increasing or decreasing the food-borne disease burden, it is concluded that a key role is fulfilled by intergovernmental organisations and by international standard setting bodies in coordinating the establishment and rolling-out of effective measures that, on balance, help ensure long-term consumer protection and fair international trade.

Immune activation by life-shortening Wolbachia and reduced filarial competence in mosquitoes

Wolbachia strain wMelPop reduces the longevity of its Drosophila melanogaster host and, when introduced into the mosquito Aedes aegypti, halves its life span. We show that wMelPop induces up-regulation of the mosquito's innate immune system and that its presence inhibits the development of filarial nematodes in the mosquito. These data suggest that wMelPop could be used in the global effort to eliminate lymphatic filariasis and possibly for the control of other mosquito-borne parasites where immune preactivation inhibits their development. The cost of constitutive immune up-regulation may contribute to the life-shortening phenotype.

Short-term starvation of immune deficient Drosophila improves survival to gram-negative bacterial infections

Background

Primary immunodeficiencies are inborn errors of immunity that lead to life threatening conditions. These predispositions describe human immunity in natura and highlight the important function of components of the Toll-IL-1- receptor-nuclear factor kappa B (TIR-NF-κB) pathway. Since the TIR-NF-κB circuit is a conserved component of the host defence in higher animals, genetically tractable models may contribute ideas for clinical interventions.

Methodology/Principal Findings

We used immunodeficient fruit flies (Drosophila melanogaster) to address questions pertaining to survival following bacterial infection. We describe here that flies lacking the NF-κB protein Relish, indispensable for countering Gram-negative bacteria, had a greatly improved survival to such infections when subject to dietary short-term starvation (STS) prior to immune challenge. STS induced the release of Nitric Oxide (NO), a potent molecule against pathogens in flies, mice and humans. Administering the NO Synthase-inhibitory arginine analog N-Nitro-L-Arginine-Methyl-Ester (L-NAME) but not its inactive enantiomer D-NAME increased once again sensitivity to infection to levels expected for relish mutants. Surprisingly, NO signalling required the NF-κB protein Dif, usually needed for responses against Gram-positive bacteria.

Conclusions/Significance

Our results show that NO release through STS may reflect an evolutionary conserved process. Moreover, STS could be explored to address immune phenotypes related to infection and may offer ways to boost natural immunity.

Horizontal gene transfer between Wolbachia and the mosquito Aedes aegypti

BACKGROUND

The evolutionary importance of horizontal gene transfer (HGT) from Wolbachia endosymbiotic bacteria to their eukaryotic hosts is a topic of considerable interest and debate. Recent transfers of genome fragments from Wolbachia into insect chromosomes have been reported, but it has been argued that these fragments may be on an evolutionary trajectory to degradation and loss.

RESULTS

We have discovered a case of HGT, involving two adjacent genes, between the genomes of Wolbachia and the currently Wolbachia-uninfected mosquito Aedes aegypti, an important human disease vector. The lower level of sequence identity between Wolbachia and insect, the transcription of all the genes involved, and the fact that we have identified homologs of the two genes in another Aedes species (Ae. mascarensis), suggest that these genes are being expressed after an extended evolutionary period since horizontal transfer, and therefore that the transfer has functional significance. The association of these genes with Wolbachia prophage regions also provides a mechanism for the transfer.

CONCLUSION

The data support the argument that HGT between Wolbachia endosymbiotic bacteria and their hosts has produced evolutionary innovation.

The use of transcriptional profiles to predict adult mosquito age under field conditions

Age is a critical determinant of an adult female mosquito's ability to transmit a range of human pathogens. Despite its central importance, relatively few methods exist with which to accurately determine chronological age of field-caught mosquitoes. This fact is a major constraint on our ability to fully understand the relative importance of vector longevity to disease transmission in different ecological contexts. It also limits our ability to evaluate novel disease control strategies that specifically target mosquito longevity. We report the development of a transcriptional profiling approach to determine age of adult female Aedes aegypti under field conditions. We demonstrate that this approach surpasses current cuticular hydrocarbon methods for both accuracy of predicted age as well as the upper limits at which age can be reliably predicted. The method is based on genes that display age-dependent expression in a range of dipteran insects and, as such, is likely to be broadly applicable to other disease vectors.

Benefits of switching from typical to atypical antipsychotic medications: a longitudinal study in a community-based setting

OBJECTIVE

This study examines the clinical and resource utilization effects of switching stable outpatients with schizophrenia from a typical to an atypical antipsychotic medication.

METHOD

We monitored 43 schizophrenia patients from a community mental health program who tolerated switching from typical to atypical antipsychotic medications. We used the Positive and Negative Syndrome Scale (PANSS), Lehman Quality of Life Interview (QOL), and service utilization data for 2 years before and 2 years after the switch.

RESULTS

The switch to atypical antipsychotics was associated with significant improvements in positive symptoms, in general psychopathology, and in quality of life. Resource requirements, including case-management and crisis services and hospitalization days, were significantly reduced. We observed no changes in the sample's already low levels of negative symptoms.

CONCLUSIONS

In stable outpatients with schizophrenia in a real-world setting, switching to an atypical antipsychotic can result in sustained, significant improvement in clinical response and quality of life, as well as in reduced need for hospitalization and community support.

Survey of local authority approaches to investigating sporadic cases of suspected food poisoning

Local authorities in England were surveyed in 1997 to document their approach to investigating sporadic cases of suspected food poisoning, the data they collect, and their objectives for doing so. Three hundred and nineteen of the 359 authorities (89%) responded. The main objectives stated were to prevent spread of infection, detect outbreaks, educate the public, and identify risk factors for infection. Most outbreaks of food poisoning were detected as a result of complaints from members of the public. Investigation of Salmonella spp and Vero cytotoxin producing Escherichia coli O157 appeared to have a higher priority than campylobacter infection and viral gastroenteritis. Eighty-five per cent (266/311) of local authorities had agreed timescales for investigating cases and 54% (165/306) reported using computer technology to collate and analyse data on sporadic cases of food poisoning. Almost all (243/244) respondents supported the idea of having a new national system for the collation of such data and 79% (244/309) expressed interest in piloting a new standard form for enhanced surveillance of food poisoning.

Evaluation of a pilot standard questionnaire for the enhanced surveillance of sporadic cases of suspected food poisoning

A national survey of local authorities, carried out in 1997, investigated how they dealt with sporadic cases of suspected food poisoning. A standard questionnaire for recording routine follow up information was then designed and piloted for three months in 30 local authorities in England. The questionnaire captured information on clinical and demographic details and exposure histories such as contact with animals, recreational exposure to water, and travel but was less successful at capturing information on domestic catering practices and food consumption. A successful surveillance questionnaire must be designed carefully to gather essential data without overburdening investigating officers.

Treatment costs of directly observed therapy and traditional therapy for Mycobacterium tuberculosis: a comparative analysis

OBJECTIVE

Treatment of tuberculosis is a time-consuming and expensive process, often complicated by patient non-adherence. Directly observed therapy (DOT), an out-patient management strategy designed to ensure adherence, is not widely used because it is perceived to be too expensive. This study compared costs of tuberculosis treatment in DOT to the same factors in traditional therapy.

DESIGN

A retrospective economic evaluation of 659 tuberculosis cases was reported to a major metropolitan county public health department between 1980 and 1994. Out-patient costs, in-patient costs and the cost impact of relapse and acquired resistance were estimated in 1995 dollars.

RESULTS

Treatment costs were lower with DOT: $15,670 per case for in-patient care and $700 per case for out-patient care (P < 0.001). These cost differences resulted from shorter therapy duration (334 vs 550 days), fewer patient hospitalizations (58 vs 75%) and shorter hospital stays (26 vs 55 days per hospitalized patient). Relapse or acquired resistance occurred in 10.9% of patients and accounted for 35.7% of cost with traditional therapy, as compared to 1.2% of patients and 6.0% of cost with observed therapy.

CONCLUSIONS

Directly observed therapy is less costly than traditional therapy.

A study of infectious intestinal disease in England: microbiological findings in cases and controls

A study was undertaken to identify the microorganisms and toxins in stool specimens associated with infectious intestinal disease (IID) among cases in the community and presenting to general practitioners (GPs) and in asymptomatic controls. Population based cohorts were recruited from practice lists in 70 practices and followed for 26 weeks (cohort component). Seven hundred and sixty-one cases of IID identified from the cohorts, 2893 cases who presented to GPs in 34 of the practices (GP component), and age/sex matched control subjects (555 and 2264, respectively) submitted stool specimens by post for comprehensive microbiological examination. Campylobacter spp (12.2% of stools tested), rotavirus group A (7.7%), and small round structured virus (SRSV) (6.5%) were the organisms most commonly detected in the GP component. SRSV was identified in 7.0% of cases in the community cohort. No target microorganisms or toxins were identified in 45.1% and 63.1% of cases in the two components. Aeromonas spp, Yersinia spp, and some enterovirulent groups of Escherichia coli were detected as frequently in controls as in cases. The higher frequency of detection of campylobacter, salmonella, and rotavirus among cases who presented to GPs than among those in the community suggests that those pathogens cause more severe illness. No enteropathogens were detected from a large proportion of cases although comprehensive standard methods were used to seek them.

Universal HIV screening at a major metropolitan TB clinic: HIV prevalence and high-risk behaviors among TB patients

OBJECTIVES

This study assessed the outcome of implementing a policy of universal screening of patients with tuberculosis (TB) for HIV infection at a major metropolitan public health TB clinic.

METHODS

HIV serologic testing was completed on 768 (93%) of 825 eligible patients. Ninety-eight HIV-positive cases (13%) were compared with 670 HIV-negative cases. The presence of adult HIV risk factors was determined by structured interview and review of medical records.

RESULTS

One or more HIV risk factors were present in 93% of HIV-positive cases and 42% of HIV-negative cases.

CONCLUSIONS

The metropolitan TB clinic is well suited for HIV screening, and HIV-antibody testing and counseling should be provided to all TB patients.

The effect of electron beam irradiation, combined with acetic acid, on the survival and recovery of Escherichia coli and Lactobacillus curvatus

The preservation of food by ionising radiation may lead to undesirable sensory changes within the food. These changes can be reduced by combining irradiation with other treatments, for example the addition of organic acids. Late exponential phase cultures of Escherichia coli and Lactobacillus curvatus were irradiated, in a liquid medium, at doses of 0-1.8 kilograys (kGy), in the presence of acetic acid (0-2%) at pH 4.6. A synergistic effect occurred when E. coli was irradiated in the presence of acetic acid (0.02-1.0%) at all doses used (0.145-1.1 kGy). There is evidence to suggest that membrane disruption occurred in the cells as a result of the combined treatments and this may account, to some extent, for the synergism observed. The addition of acetic acid up to a concentration of 2.0% had no effect upon the radiation survival or upon the subsequent growth of L. curvatus.

The effect of electron beam irradiation and modified pH on the survival and recovery of Escherichia coli

The severity of radiation processing can be reduced by combining irradiation with other treatments, such as low pH. An exponential phase culture of Escherichia coli was irradiated at doses of 0-2.4 kGy at pH values ranging between 7.0 and 4.0, in an enriched nutrient broth. At pH 4.3 and above there was no significant effect of lowering the pH prior to irradiation. At pH 4.13 and 4.0, a much higher level of cell death occurred compared with irradiation at pH 7.0. This synergistic effect was observed only when the pH was lowered before radiation processing.

Fatal overdose with amantadine

The authors describe the first case report in the psychiatric literature of death from an overdose of amantadine hydrochloride used to treat neuroleptic induced extrapyramidal side effects. The pharmacology, adverse reactions and risks of using amantadine are briefly reviewed.

Imipramine-flupenthixol decanoate interaction

The authors describe a case in which flupenthixol decanoate and imipramine were co-administered to a patient with schizophrenia, resulting in extremely high levels of imipramine and its metabolite, desipramine. The literature on the co-administration of neuroleptics and antidepressants is reviewed and guidelines for limiting possible iatrogenic effects of the combination are suggested.

Self-derogation and defense style in college students

The self-concept literature generally shows that different measures of self-acceptance and self-satisfaction are positively related to psychological adjustment and several measures of defensiveness. In order to understand clearly the relationship between self-concept and adjustment it is also important to consider characteristic defense styles. With this purpose in mind, Kaplan, and Pokorny's Self-derogation scale, three of the most commonly used measures of defensive styles, and a measures of trait-anxiety, were administered to 158 college students. Self-derogation correlated positively with repression-sensitization and trait-anxiety, and negatively with general defensiveness. A positive relationship between self-derogation and ego-control was also found. The results were interpreted as consistent with self theory.

Sex and workstyle of leaders and followers: determinants of productivity

This study investigated whether sex and workstyle interactions of leaders and followers affect team productivity. It was hypothesized that (a) task-oriented leaders would be the most productive, (b) followers with a same-sexed leader would be the most productive, and (c) the most productive subjects would rate their teams as the most pleasant. Only the final hypothesis received some support in groups formed by 168 male and 168 female undergraduates to work on a puzzle within a half-hour session and assessed by Fiedler's measures.