Extensive public health initiatives drive the elimination of Aedes aegypti (Diptera, Culicidae) from a town in regional Queensland: A case study from Gin Gin, Australia

Aedes aegypti is the primary vector of exotic arboviruses (dengue, chikungunya and Zika) in Australia. Once established across much of Australia, this mosquito species remains prevalent in central and northern Queensland. In 2011, Ae. aegypti was re-discovered in the town of Gin Gin, Queensland, by health authorities during routine larval surveillance. This town is situated on a major highway that provides a distribution pathway into the highly vulnerable and populous region of the state where the species was once common. Following the detection, larval habitat and adult control activities were conducted as a public health intervention to eliminate the Ae. aegypti population and reduce the risk of exotic disease transmission. Importantly, genetic analysis revealed a homogenous cluster and small effective population vulnerable to an elimination strategy. By 2015, adult surveillance revealed the population had expanded throughout the centre of the town. In response, a collaboration between research agencies and local stakeholders activated a second control program in 2016 that included extensive community engagement, enhanced entomologic surveillance and vector control activities including the targeting of key containers, such as unsealed rainwater tanks. Here we describe a model of the public health intervention which successfully reduced the Ae. aegypti population below detection thresholds, using source reduction, insecticides and novel, intensive genetic surveillance methods. This outcome has important implications for future elimination work in small towns in regions sub-optimal for Ae. aegypti presence and reinforces the longstanding benefits of a partnership model for public health-based interventions for invasive urban mosquito species.

Past and future epidemic potential of chikungunya virus in Australia

Background

Australia is theoretically at risk of epidemic chikungunya virus (CHIKV) activity as the principal vectors are present on the mainland Aedes aegypti) and some islands of the Torres Strait (Ae. aegypti and Ae. albopictus). Both vectors are highly invasive and adapted to urban environments with a capacity to expand their distributions into south-east Queensland and other states in Australia. We sought to estimate the epidemic potential of CHIKV, which is not currently endemic in Australia, by considering exclusively transmission by the established vector in Australia, Ae. aegypti, due to the historical relevance and anthropophilic nature of the vector.

Methodology/Principal findings

We estimated the historical (1995–2019) epidemic potential of CHIKV in eleven Australian locations, including the Torres Strait, using a basic reproduction number equation. We found that the main urban centres of Northern Australia could sustain an epidemic of CHIKV. We then estimated future trends in epidemic potential for the main centres for the years 2020 to 2029. We also conducted uncertainty and sensitivity analyses on the variables comprising the basic reproduction number and found high sensitivity to mosquito population size, human population size, impact of vector control and human infectious period.

Conclusions/Significance

By estimating the epidemic potential for CHIKV transmission on mainland Australia and the Torres Strait, we identified key areas of focus for controlling vector populations and reducing human exposure. As the epidemic potential of the virus is estimated to rise towards 2029, a greater focus on control and prevention measures should be implemented in at-risk locations.

Chikungunya virus (CHIKV) is transmitted primarily by Aedes aegypti and Aedes albopictus mosquitoes and causes a potentially debilitating febrile and arthralgic disease. The virus is a threat to public health in regions where the primary vectors are established, as evidenced by past epidemics in the Indian Ocean Islands, South America and the Caribbean. In Australia, there are established populations of Ae. aegypti both on the mainland and in the Torres Strait, and of Ae. albopictus in the Torres Strait. This provides a theoretical potential for CHIKV transmission, as seen historically with dengue virus (DENV). It is therefore important to understand the epidemic potential of CHIKV in Australia. We estimated the basic reproduction number (R₀) of CHIKV during the years 1995–2019 for 11 Urban Centres and Localities (UCLs) in Australia, and found that Brisbane, Cairns, Darwin, Rockhampton, Thursday Island, and Townsville were all susceptible to CHIKV epidemics. We then forecasted epidemic potential from 2020–2029 and found an increase in R₀ across the six main UCLs. By highlighting factors that significantly influence the epidemic potential of CHIKV in Australia, our study supports evidence-based decision making for vector control and public health programs.

Estimation of mosquito-borne and sexual transmission of Zika virus in Australia: Risks to blood transfusion safety

BACKGROUND

Since 2015, Zika virus (ZIKV) outbreaks have occurred in the Americas and the Pacific involving mosquito-borne and sexual transmission. ZIKV has also emerged as a risk to global blood transfusion safety. Aedes aegypti, a mosquito well established in north and some parts of central and southern Queensland, Australia, transmits ZIKV. Aedes albopictus, another potential ZIKV vector, is a threat to mainland Australia. Since these conditions create the potential for local transmission in Australia and a possible uncertainty in the effectiveness of blood donor risk-mitigation programs, we investigated the possible impact of mosquito-borne and sexual transmission of ZIKV in Australia on local blood transfusion safety.

METHODOLOGY/PRINCIPAL FINDINGS

We estimated 'best-' and 'worst-' case scenarios of monthly reproduction number (R0) for both transmission pathways of ZIKV from 1996-2015 in 11 urban or regional population centres, by varying epidemiological and entomological estimates. We then estimated the attack rate and subsequent number of infectious people to quantify the ZIKV transfusion-transmission risk using the European Up-Front Risk Assessment Tool. For all scenarios and with both vector species R0 was lower than one for ZIKV transmission. However, a higher risk of a sustained outbreak was estimated for Cairns, Rockhampton, Thursday Island, and theoretically in Darwin during the warmest months of the year. The yearly estimation of the risk of transmitting ZIKV infection by blood transfusion remained low through the study period for all locations, with the highest potential risk estimated in Darwin.

CONCLUSIONS/SIGNIFICANCE

Given the increasing demand for plasma products in Australia, the current strategy of restricting donors returning from infectious disease outbreak regions to source plasma collection provides a simple and effective risk management approach. However, if local transmission was suspected in the main urban centres of Australia, potentially facilitated by the geographic range expansion of Ae. aegypti or Ae. albopictus, this mitigation strategy would need urgent review.

Epidemiologic, Entomologic, and Virologic Factors of the 2014-15 Ross River Virus Outbreak, Queensland, Australia

Australia experienced its largest recorded outbreak of Ross River virus (RRV) during the 2014-15 reporting year, comprising >10,000 reported cases. We investigated epidemiologic, entomologic, and virologic factors that potentially contributed to the scale of the outbreak in Queensland, the state with the highest number of notifications (6,371). Spatial analysis of human cases showed that notifications were geographically widespread. In Brisbane, human case notifications and virus detections in mosquitoes occurred across inland and coastal locations. Viral sequence data demonstrated 2 RRV lineages (northeastern genotypes I and II) were circulating, and a new strain containing 3 unique amino acid changes in the envelope 2 protein was identified. Longitudinal mosquito collections demonstrated unusually high relative abundance of Culex annulirostris and Aedes procax mosquitoes, attributable to extensive freshwater larval habitats caused by early and persistent rainfall during the reporting year. Increased prevalence of these mosquitoes probably contributed to the scale of this outbreak.

Establishment of wMel Wolbachia in Aedes aegypti mosquitoes and reduction of local dengue transmission in Cairns and surrounding locations in northern Queensland, Australia

Background: The wMel strain of Wolbachia has been successfully introduced into Aedes aegypti mosquitoes and subsequently shown in laboratory studies to reduce transmission of a range of viruses including dengue, Zika, chikungunya, yellow fever, and Mayaro viruses that cause human disease. Here we report the entomological and epidemiological outcomes of staged deployment of Wolbachia across nearly all significant dengue transmission risk areas in Australia. Methods: The  wMel strain of  Wolbachia was backcrossed into the local  Aedes aegypti genotype (Cairns and Townsville backgrounds) and mosquitoes were released in the field by staff or via community assisted methods. Mosquito monitoring was undertaken and mosquitoes were screened for the presence of  Wolbachia. Dengue case notifications were used to track dengue incidence in each location before and after releases. Results: Empirical analyses of the Wolbachia mosquito releases, including data on the density, frequency and duration of Wolbachia mosquito releases, indicate that Wolbachia can be readily established in local mosquito populations, using a variety of deployment options and over short release durations (mean release period 11 weeks, range 2-22 weeks). Importantly, Wolbachia frequencies have remained stable in mosquito populations since releases for up to 8 years. Analysis of dengue case notifications data demonstrates near-elimination of local dengue transmission for the past five years in locations where Wolbachia has been established. The regression model estimate of Wolbachia intervention effect from interrupted time series analyses of case notifications data prior to and after releases, indicated a 96% reduction in dengue incidence in Wolbachia treated populations (95% confidence interval: 84 - 99%). Conclusion: Deployment of the wMel strain of Wolbachia into local Ae. aegypti populations across the Australian regional cities of Cairns and most smaller regional communities with a past history of dengue has resulted in the reduction of local dengue transmission across all deployment areas.

Establishment of wMel Wolbachia in Aedes aegypti mosquitoes and reduction of local dengue transmission in Cairns and surrounding locations in northern Queensland, Australia

Background: The wMel strain of Wolbachia has been successfully introduced into Aedes aegypti mosquitoes and subsequently shown in laboratory studies to reduce transmission of a range of viruses including dengue, Zika, chikungunya, yellow fever, and Mayaro viruses that cause human disease. Here we report the entomological and epidemiological outcomes of staged deployment of Wolbachia across nearly all significant dengue transmission risk areas in Australia.

Methods: The  wMel strain of  Wolbachia was backcrossed into the local  Aedes aegypti genotype (Cairns and Townsville backgrounds) and mosquitoes were released in the field by staff or via community assisted methods. Mosquito monitoring was undertaken and mosquitoes were screened for the presence of  Wolbachia. Dengue case notifications were used to track dengue incidence in each location before and after releases.

Results: Empirical analyses of the Wolbachia mosquito releases, including data on the density, frequency and duration of Wolbachia mosquito releases, indicate that Wolbachia can be readily established in local mosquito populations, using a variety of deployment options and over short release durations (mean release period 11 weeks, range 2-22 weeks). Importantly, Wolbachia frequencies have remained stable in mosquito populations since releases for up to 8 years. Analysis of dengue case notifications data demonstrates near-elimination of local dengue transmission for the past five years in locations where Wolbachia has been established. The regression model estimate of Wolbachia intervention effect from interrupted time series analyses of case notifications data prior to and after releases, indicated a 96% reduction in dengue incidence in Wolbachia treated populations (95% confidence interval: 84 – 99%).

Conclusion: Deployment of the wMel strain of Wolbachia into local Ae. aegypti populations across the Australian regional cities of Cairns and most smaller regional communities with a past history of dengue has resulted in the reduction of local dengue transmission across all deployment areas.

Epidemic potential of Zika virus in Australia: implications for blood transfusion safety

BACKGROUND

Zika virus (ZIKV) is transfusion-transmissible. In Australia the primary vector, Aedes aegypti, is established in the north-east, such that local transmission is possible following importation of an index case, which has the potential to impact on blood transfusion safety and public health. We estimated the basic reproduction number (R ₀ ) to model the epidemic potential of ZIKV in Australian locations, compared this with the ecologically similar dengue viruses (DENV), and examined possible implications for blood transfusion safety.

STUDY DESIGN AND METHODS

Varying estimates of vector control efficiency and extrinsic incubation period, "best-case" and "worst-case" scenarios of monthly R ₀ for ZIKV and DENV were modeled from 1996 to 2015 in 11 areas. We visualized the geographical distribution of blood donors in relation to areas with epidemic potential for ZIKV.

RESULTS

Epidemic potential (R ₀ > 1) existed for ZIKV and DENV throughout the study period in a number of locations in northern Australia (Cairns, Darwin, Rockhampton, Thursday Island, Townsville, and Brisbane) during the warmer months of the year. R ₀ for DENV was greater than ZIKV and was broadly consistent with annual estimates in Cairns. Increased vector control efficiency markedly reduced the epidemic potential and shortened the season of local transmission. Australian locations that provide the greatest number of blood donors did not have epidemic potential for ZIKV.

CONCLUSION

We estimate that areas of north-eastern Australia could sustain local transmission of ZIKV. This early contribution to understanding the epidemic potential of ZIKV may assist in the assessment and management of threats to blood transfusion safety.

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.

Rapid Surveillance for Vector Presence (RSVP): Development of a novel system for detecting Aedes aegypti and Aedes albopictus

Background

The globally important Zika, dengue and chikungunya viruses are primarily transmitted by the invasive mosquitoes, Aedes aegypti and Aedes albopictus. In Australia, there is an increasing risk that these species may invade highly urbanized regions and trigger outbreaks. We describe the development of a Rapid Surveillance for Vector Presence (RSVP) system to expedite presence- absence surveys for both species.

Methodology/Principal findings

We developed a methodology that uses molecular assays to efficiently screen pooled ovitrap (egg trap) samples for traces of target species ribosomal RNA. Firstly, specific real-time reverse transcription-polymerase chain reaction (RT-PCR) assays were developed which detect a single Ae. aegypti or Ae. albopictus first instar larva in samples containing 4,999 and 999 non-target mosquitoes, respectively. ImageJ software was evaluated as an automated egg counting tool using ovitrap collections obtained from Brisbane, Australia. Qualitative assessment of ovistrips was required prior to automation because ImageJ did not differentiate between Aedes eggs and other objects or contaminants on 44.5% of ovistrips assessed, thus compromising the accuracy of egg counts. As a proof of concept, the RSVP was evaluated in Brisbane, Rockhampton and Goomeri, locations where Ae. aegypti is considered absent, present, and at the margin of its range, respectively. In Brisbane, Ae. aegypti was not detected in 25 pools formed from 477 ovitraps, comprising ≈ 54,300 eggs. In Rockhampton, Ae. aegypti was detected in 4/6 pools derived from 45 ovitraps, comprising ≈ 1,700 eggs. In Goomeri, Ae. aegypti was detected in 5/8 pools derived from 62 ovitraps, comprising ≈ 4,200 eggs.

Conclusions/Significance

RSVP can rapidly detect nucleic acids from low numbers of target species within large samples of endemic species aggregated from multiple ovitraps. This screening capability facilitates deployment of ovitrap configurations of varying spatial scales, from a single residential block to entire suburbs or towns. RSVP is a powerful tool for surveillance of invasive Aedes spp., validation of species eradication and quality assurance for vector control operations implemented during disease outbreaks.

Aedes (Stegomyia) vectors of dengue, Zika and chikungunya viruses utilize artificial and natural containers as larval habitats. Adults do not usually disperse far (< 500 m) from these larval habitats in urban and peri-urban environments. Highly heterogeneous distributions raise significant logistic challenges to conduct informative surveillance. Public health imperatives require contemporaneous vector mosquito presence-absence data for highly urbanized regions that are both vulnerable to invasions and have frequent exposure to viremic travellers. We developed a promising tool to expedite presence-absence surveillance of Aedes aegypti and Aedes albopictus by integrating molecular diagnostics with ovitraps and automated egg quantification software. The high sensitivity of the molecular assays enabled samples from multiple ovitraps to be pooled and processed for each diagnostic test. This innovation resolves the considerable logistic constraints inherent in traditional ovitrap surveillance programs. Proof of concept was evaluated in field trials in Queensland geographies where Ae. aegypti is considered either absent, present or at the margin of its range (Brisbane, Rockhampton and Goomeri, respectively). Aedes aegypti was detected in Goomeri and Rockhampton and not detected in Brisbane. Further investigation is required to address the inaccuracy of automated egg counting software whenever contaminants are present. RSVP can accommodate varied ovitrap designs and deployment configurations, improves efficiency in laboratory and labor costs for high volumes of samples, and enables a rapid turnaround of results. The RSVP system can innovate surveillance programs for early-warning of invasion, eradication, and quality assurance for vector control in disease response contexts.

Combining contact tracing with targeted indoor residual spraying significantly reduces dengue transmission

The widespread transmission of dengue viruses (DENV), coupled with the alarming increase of birth defects and neurological disorders associated with Zika virus, has put the world in dire need of more efficacious tools for Aedes aegypti-borne disease mitigation. We quantitatively investigated the epidemiological value of location-based contact tracing (identifying potential out-of-home exposure locations by phone interviews) to infer transmission foci where high-quality insecticide applications can be targeted. Space-time statistical modeling of data from a large epidemic affecting Cairns, Australia, in 2008-2009 revealed a complex pattern of transmission driven primarily by human mobility (Cairns accounted for ~60% of virus transmission to and from residents of satellite towns, and 57% of all potential exposure locations were nonresidential). Targeted indoor residual spraying with insecticides in potential exposure locations reduced the probability of future DENV transmission by 86 to 96%, compared to unsprayed premises. Our findings provide strong evidence for the effectiveness of combining contact tracing with residual spraying within a developed urban center, and should be directly applicable to areas with similar characteristics (for example, southern USA, Europe, or Caribbean countries) that need to control localized Aedes-borne virus transmission or to protect pregnant women's homes in areas with active Zika transmission. Future theoretical and empirical research should focus on evaluation of the applicability and scalability of this approach to endemic areas with variable population size and force of DENV infection.

Epidemic Potential for Local Transmission of Zika Virus in 2015 and 2016 in Queensland, Australia

INTRODUCTION

Zika virus could be transmitted in the state of Queensland, Australia, in parts of the state where the mosquito vectors are established.

METHODS

We assessed the epidemic potential of Zika in Queensland from January 2015 to August 2016, and estimate the epidemic potential from September to December 2016, by calculating the temperature-dependent relative vectorial capacity (rVc), based on empirical and estimated parameters.

RESULTS

Through 2015, we estimated a rVc of 0.119, 0.152, 0.170, and 0.175, respectively in the major cities of Brisbane, Rockhampton, Cairns, and Townsville. From January to August 2016, the epidemic potential trend was similar to 2015, however the highest epidemic potential was in Cairns. During September to November 2016, the epidemic potential is consistently the highest in Cairns, followed by Townsville, Rockhampton and Brisbane. Then, from November to December 2016, Townsville has the highest estimated epidemic potential.

DISCUSSION

We demonstrate using a vectorial capacity model that ZIKV could have been locally transmitted in Queensland, Australia during 2015 and 2016. ZIKV remains a threat to Australia for the upcoming summer, during the Brazilian Carnival season, when the abundance of vectors is relatively high. Understanding the epidemic potential of local ZIKV transmission will allow better management of threats to blood safety and assessment of public health risk.

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.

Novel estimates of Aedes aegypti (Diptera: Culicidae) population size and adult survival based on Wolbachia releases

The size of Aedes aegypti (L.) mosquito populations and adult survival rates have proven difficult to estimate because of a lack of consistent quantitative measures to equate sampling methods, such as adult trapping, to actual population size. However, such estimates are critical for devising control methods and for modeling the transmission of dengue and other infectious agents carried by this species. Here we take advantage of recent releases of Wolbachia-infected Ae. aegypti coupled with the results of ongoing monitoring to estimate the size of adult Ae. aegypti populations around Cairns in far north Queensland, Australia. Based on the association between released adults infected with Wolbachia and data from Biogents Sentinel traps, we show that data from two locations are consistent with population estimates of approximately 5-10 females per house and daily survival rates of 0.7-0.9 for the released Wolbachia-infected females. Moreover, we estimate that networks of Biogents Sentinel traps at a density of one per 15 houses capture around 5-10% of the adult population per week, and provide a rapid estimate of the absolute population size of Ae. aegypti. These data are discussed with respect to release rates and monitoring in future Wolbachia releases and also the levels of suppression required to reduce dengue transmission.

Culex annulirostris (Diptera: Culicidae) host feeding patterns and Japanese encephalitis virus ecology in northern Australia

Japanese encephalitis virus (JEV) transmission in northern Australia has, in the past, been facilitated by Culex annulirostris Skuse feeding on domestic pigs, the primary amplifying hosts of the virus. To further characterize mosquito feeding behavior in northern Australia, 1,128 bloodmeals from Cx. annulirostris were analyzed using a double-antibody enzyme-linked immunosorbent assay. Overall, Cx. annulirostris obtained > 94% of blood meals from mammals, comprising marsupials (37%), pigs (20%), dogs (16%), and cows (11%), although the proportion feeding on each of these host types varied between study locations. Where JEV activity was detected, feeding rates on pigs were relatively high. At the location that yielded the first Australian mainland isolate of JEV from mosquitoes, feral pigs (in the absence of domestic pigs) accounted for 82% of bloodmeals identified, representing the first occasion that feeding on feral pigs has been associated with JEV transmission in Australia. Interestingly, < 3% of Cx. annulirostris had fed on pigs at locations on Badu Island where JEV was detected in multiple pools of mosquitoes in a concurrent study. This suggests that either alternative hosts, such as birds, which comprised 21% of blood meals identified, or infected mosquitoes immigrating from areas where domestic pigs are housed, may have contributed to transmission at this location. Because Cx. annulirostris is both an opportunistic feeder and the primary JEV vector in the region, environmental characteristics and host presence can determine JEV transmission dynamics in northern Australia.

Successful establishment of Wolbachia in Aedes populations to suppress dengue transmission

Genetic manipulations of insect populations for pest control have been advocated for some time, but there are few cases where manipulated individuals have been released in the field and no cases where they have successfully invaded target populations. Population transformation using the intracellular bacterium Wolbachia is particularly attractive because this maternally-inherited agent provides a powerful mechanism to invade natural populations through cytoplasmic incompatibility. When Wolbachia are introduced into mosquitoes, they interfere with pathogen transmission and influence key life history traits such as lifespan. Here we describe how the wMel Wolbachia infection, introduced into the dengue vector Aedes aegypti from Drosophila melanogaster, successfully invaded two natural A. aegypti populations in Australia, reaching near-fixation in a few months following releases of wMel-infected A. aegypti adults. Models with plausible parameter values indicate that Wolbachia-infected mosquitoes suffered relatively small fitness costs, leading to an unstable equilibrium frequency <30% that must be exceeded for invasion. These findings demonstrate that Wolbachia-based strategies can be deployed as a practical approach to dengue suppression with potential for area-wide implementation.

The effects of sustained release metofluthrin on the biting, movement, and mortality of Aedes aegypti in a domestic setting

The impact of a sustained release metofluthrin emanator and an allethrin-based mosquito coil on biting, movement and mortality of female Aedes aegypti was assessed in an apartment. In the room in which the metofluthrin emanator was activated, mosquito biting counts were reduced to zero. Metofluthrin also had a spillover effect, significantly (P < 0.001) reducing biting counts in a neighboring room 1, 4, and 24 hours after the emanator was activated when compared with either the coil or control (untreated) treatment. Mosquitoes were neither repelled nor expelled from a room exposed to metofluthrin. Indeed, a significantly (P = 0.023) greater proportion of mosquitoes were found in the treated room after exposure to metofluthrin when compared with either the coil or control treatment. Furthermore, in the room treated with metofluthrin the majority of mosquitoes died and a spillover effect into the neighboring room caused greater than one-third mortality of the mosquitoes. Metofluthrin could be used to prevent dengue transmission within a household.

Dengue in north Queensland, 2005-2008

The dengue vector, the mosquito Aedes aegypti, is present in urban settings in north Queensland, thereby putting the region at risk of outbreaks of dengue. This review describes some features of the 9 outbreaks of dengue that occurred in north Queensland over the 4 years, 2005-2008.

Operational trials of remote mosquito trap systems for Japanese encephalitis virus surveillance in the Torres Strait, Australia

Japanese encephalitis virus (JEV) appears nearly annually in the Torres Strait in far northern Queensland, Australia, and is a threat to invade the Australian mainland. Surveillance has involved the use of sentinel pigs that develop detectable viremias and antibody titers to JEV. However, pigs are amplifying hosts for JEV, and thus pose a health risk to the public and to pig handlers who bleed the pigs. A remote mosquito trap system would not have these risks. We report on trials using a remote mosquito trap system for the surveillance of JEV in the Torres Strait. The Mosquito Magnet (MM) Pro, MM Liberty Plus, and a novel updraft trap, the NAQS Mozzie Trap, were run at Badu and Moa islands in the Torres Strait and at Bamaga in the northern Cape York Peninsula from 2002-2005. TaqMan real-time polymerase chain reaction (PCR) was used to detect JEV nucleic acid in weekly mosquito collections. Sentinel pigs located at Badu were also bled and the serum processed by reverse transcriptase (RT)-PCR for JEV antigen and enzyme-linked immunosorbent assay (ELISA) for anti-JEV antibodies. JEV was detected in mosquito collections each year but not in each trap. No JEV was detected in trapped mosquitoes before detection in sentinel pigs. The mosquito trap system cost ca. AU$10,000 per site, about AU$5,000 less than a pig-based system. However, trap failures caused by mosquito-clogged motors, electrical faults, and blocked gas lines reduced the efficacy of some mosquito traps. Nonetheless, a remote mosquito trap system, employing stand alone traps and PCR for viral antigen detection, can be a safe, economical way to detect arbovirus activity in remote areas.

Multiple outbreaks of dengue serotype 2 in north Queensland, 2003/04

OBJECTIVES

To describe the various investigations and responses to multiple outbreaks of dengue serotype 2 that occurred in north Queensland in 2003/04.

METHODS

Details about each case were collated so as to target mosquito-control responses including control of mosquito breeding sites, interior spraying of selected premises, and a novel 'lure and kill' approach using lethal ovitraps. Phylogenetic analyses were undertaken to determine the genetic relatedness of viruses isolated during the outbreaks.

RESULTS

Except for a two-month hiatus in mid-2003, the outbreaks continued for 16 months and included approximately 900 confirmed cases, with three severe cases and one death. The available evidence suggests that the mosquito-control measures were effective, but delays in recognising the outbreaks in Cairns and the Torres Strait coupled with intense mosquito breeding contributed to the extensive nature of the outbreaks. Phylogenetic analyses showed that there had been only two major outbreaks, one that spread from Cairns to Townsville, the other from the Torres Strait to Cairns; both were initiated by viraemic travellers from Papua New Guinea.

CONCLUSIONS

Phylogenetic analyses were essential in understanding how the outbreaks were related to each other, and in demonstrating that dengue had not become endemic. Further innovative approaches to dengue surveillance and mosquito control in north Queensland are necessary.

IMPLICATIONS

Dengue outbreaks have become more frequent and more severe in north Queensland in recent years, raising the possibility that dengue viruses could become endemic in the region leading to outbreaks of dengue haemorrhagic fever.

Short report: the first isolation of Japanese encephalitis virus from mosquitoes collected from mainland Australia

In response to an incursion of Japanese encephalitis virus (JEV) on Cape York Peninsula, Australia, in 2005, 23,144 Culex mosquitoes were processed for virus detection. A single isolate of JEV was obtained from a pool of Culex sitiens subgroup mosquitoes. This is the first reported mosquito isolate of JEV from the Australian mainland.

Does 1-octen-3-ol enhance trap collections of Japanese encephalitis virus mosquito vectors in northern Australia?

The responses of Japanese encephalitis virus (JEV) mosquito vectors to 1-octen-3-ol (octenol) and CO2 were evaluated using Centers for Disease Control (CDC) light traps at 3 sites in northern Australia. There was no significant difference between the number of Culex sitiens subgroup mosquitoes or Cx. gelidus collected in CDC light traps baited with either CO2 alone or CO2 + octenol on Badu Island. At both mainland locations, using octenol in combination with CO2 significantly increased collections of Cx. sitiens subgroup mosquitoes. Collections of nontarget species, such as Ochlerotatus spp., Anopheles spp., and Verrallina spp. were also significantly increased with the addition of octenol. At all 3 locations, reducing collections of nontarget mosquitoes by not using octenol increased the proportion of Culex spp. collected, thus potentially reducing the time and resources required to sort and process collections for JEV detection. Our results also indicate that trials into the efficacy of using octenol as an attractant should be carried out in each area prior to the implementation of a mosquito-based arbovirus surveillance system.

Field evaluation of New Mountain Sandalwood Mosquito Sticks and New Mountain Sandalwood Botanical Repellent against mosquitoes in North Queensland, Australia

The mosquito repellent efficacy of New Mountain Sandalwood Mosquito Sticks (containing 0.5% w/w essential oils) and New Mountain Sandalwood Botanical Repellent (containing soybean and geranium oils) was assessed. Tests were conducted in the field with 4 volunteers in a wooded area near Cairns, North Queensland, Australia. Predominant biting species were Verrallina funerea and Ve. lineata. A pair of burning Mosquito Sticks immediately upwind of the subject (acting as an area repellent) provided a 73.1% mean reduction in mosquito landing and probing over the 3-h test period. The Botanical Repellent and a DEET-based control were both 100% effective in preventing mosquito probing for 3 h. These data are consistent with other studies of area repellents in that such products provide significant protection from mosquito bites, albeit inferior to the protection provided by topically applied repellents.

Subsoil drain sumps are a key container for Aedes aegypti in Cairns, Australia

The contribution of subterranean drain sumps to pupal and adult populations of Aedes aegypti is reported for the 1st time in Cairns, Australia. Pupal surveys were used to quantify the relative contribution of drain sumps to the total population of Ae. aegypti by concurrent survey of sump and water-bearing containers in yards of inner-city premises. A total of 854 mosquito pupae were collected, predominantly Ae. aegypti and Culex quinquefasciatus (26.3 and 69.8%, respectively). Drain sumps provided a relatively uncommon (n = 4) but productive source for pupal Ae. aegypti, producing 14.7% of the combined yard and drain sump population. Drain sumps in inner-city Cairns most commonly occurred in parking lots (52.6%). Subsequently, a sticky emergent adult trap (SEAT) was developed to provide a pragmatic method to assess production of Ae. aegypti by drain sumps. A total of 866 adult mosquitoes were trapped from 162 drain sumps over a 48-h exposure period, comprising Ae. aegypti and Cx. quinquefasciatus (21 and 79%, respectively). Advantages of the SEAT are an ability to rapidly count, identify, and sex mosquitoes and to provide specimens for molecular analysis where necessary. The treatment of water-bearing drain sumps is a critical element of control campaigns against Ae. aegypti.

An outbreak of Plasmodium vivax malaria in Far North Queensland, 2002

OBJECTIVE

To describe an outbreak of Plasmodium vivax malaria in Far North Queensland in 2002.

DESIGN

Epidemiological and entomological investigations; molecular analyses of the infecting parasites.

MAIN OUTCOME MEASURES

Case characteristics, adult and larval mosquito counts at the outbreak location, haplotyping of parasites in blood samples from different cases determined through sequencing of AMA1 and MSP1 genes.

RESULTS

A man with imported P. vivax malaria stayed at a camping ground 95 km north of Cairns in late September 2002. This led to an outbreak of P. vivax malaria in 10 adults who stayed at the camping ground in October. Large numbers of Anopheles farauti sensu lato larvae were present in stagnant pools in a creek at the camping ground, and many adult mosquitoes were collected nearby. Not only had most of the infected patients been exposed to mosquitoes at night, they were also less likely than other campers to have used insect repellents appropriately (odds ratio, 0.01; P < 0.001). Two different haplotypes of P. vivax, only one of which was detected in the imported case, were involved in the outbreak.

CONCLUSIONS

Although local transmission of malaria is rare in Far North Queensland, the risk is probably higher in the dry season (September to December). Campers need to be aware of the increased risk of mosquito-borne diseases. Sexual recombination of multiple gametocytes in mosquitoes infected by the imported case may have resulted in the two haplotypes of P. vivax involved in the outbreak.

Efficacies of the mosquitomagnet and counterflow geometry traps in North Queensland, Australia

We conducted three trials near Cairns, Australia, to compare the numbers of mosquitoes collected with the standard Encephalitis Vector Surveillance (EVS) and Centers for Disease Control (CDC) light traps with the new MosquitoMagnet (MM) and counterflow geometry (CFG) traps with the use of a 4 x 4 latin square experimental design. The MM was generally equal to the performance of the CDC and CFG traps, ranking ahead of or equal to one or both traps in 2 of 3 trials, although there were no significant differences in the performances of the MM, CDC, and CFG traps. The EVS trap ranked last in all trials. The MM, being self powered and self baited via combustion of propane for up to 20 days without requiring a propane refill, would be suitable for collection of adult mosquitoes in remote areas that do not have access to dry ice.

Field evaluation of a sentinel mosquito (Diptera: Culicidae) trap system to detect Japanese encephalitis in remote Australia

Incursions of Japanese encephalitis (JE) virus into northern Queensland are currently monitored using sentinel pigs. However, the maintenance of these pigs is expensive, and because pigs are the major amplifying hosts of the virus, they may contribute to JE transmission. Therefore, we evaluated a mosquito-based detection system to potentially replace the sentinel pigs. Single, inactivated JE-infected Culex annulirostris Skuse and C. sitiens Wiedemann were placed into pools of uninfected mosquitoes that were housed in a MosquitoMagnet Pro (MM) trap set under wet season field conditions in Cairns, Queensland for 0, 7, or 14 d. JE viral RNA was detected (cycling threshold [CT] = 40) in 11/12, 10/14, and 2/5 pools containing 200, 1,000, and 5,000 mosquitoes, respectively, using a TaqMan real-time reverse transcription-polymerase chain reaction (RT-PCR). The ability to detect virus was not affected by the length of time pools were maintained under field conditions, although the CT score tended to increase with field exposure time. Furthermore, JE viral RNA was detected in three pools of 1,000 mosquitoes collected from Badu Island using a MM trap. These results indicated that a mosquito trap system employing self-powered traps, such as the MosquitoMagnet, and a real-time PCR system, could be used to monitor for JE in remote areas.

Dengue in north Queensland, 2002

In 2002 three separate outbreaks of dengue were detected in north Queensland, including the first documented outbreak of dengue 4 in Australia. Molecular analyses identified Thailand and Indonesia as the likely origin of two of the outbreaks. Investigations during 2002 also included a suspected dengue outbreak in the Torres Strait which proved to be a false alarm, and a number of imported cases of dengue in north Queensland.

Roof gutters: a key container for Aedes aegypti and Ochlerotatus notoscriptus (Diptera: Culicidae) in Australia

The contribution of roof gutters to Aedes aegypti (L.) and Ochlerotatus notoscriptus (Skuse) pupal populations was quantified for the first time in Cairns, Australia. Concurrent yard and roof surveys yielded an estimated 6,934 mosquito pupae, comprising four species. Roof gutters were an uncommon but productive source of Ae. aegypti in both wet season (n = 11) and dry season (n = 2) surveys, producing 52.6% and 39.5% of the respective populations. First story gutters accounted for 92.3% of the positive gutters. Therefore, treatment of roof gutters is a critical element in Ae. aegypti control campaigns during dengue outbreaks. In wet season yards, the largest standing crops of Ae. aegypti occurred in garden accoutrements, discarded household items, and rubbish (36.4%, 28.0%, and 20.6%, respectively). In dry season yards, rubbish produced 79.6% of the Ae. aegypti pupae. The number of Ae. aegypti pupae/person was 2.36 and 0.59 for the wet and dry season surveys, respectively.

Efficacy of an aerosol surface spray against container-breeding Aedes

The effectiveness of a residual insect surface spray against container-breeding mosquitoes was tested in Cairns, Australia. A formulation containing imiprothrin and cypermethrin (Mortein Plus Cockroach Lure 'n' Kill High Performance Surface Spray) was selected based on the label claim to "kill continuously for up to 6 months." A 1-sec spray was applied to the water and interior surface of partially flooded tires and terra-cotta pots. Treatments were paired with a control and replicated at 2 sites within 3 residential properties for a total of 6 replicates. All mosquito larvae were removed and counted weekly, and a representative sample was identified in the laboratory. Complete control of Aedes species was achieved for 4 and 5 months in all tires and pots, respectively.

First records of Culex gelidus from Australia

Culex gelidus Theobald was recorded for the 1st time in Australia in May 1999 from 2 locations (Brisbane and Mackay, Queensland) approximately 820 km apart. Larval samples were collected from a semi-permanent freshwater swamp and an open drain and reared to adults in laboratories. Implications for Australia are discussed.

Biliverdin reductase-induced phytochrome chromophore deficiency in transgenic tobacco

Targeted expression of mammalian biliverdin IXalpha reductase (BVR), an enzyme that metabolically inactivates linear tetrapyrrole precursors of the phytochrome chromophore, was used to examine the physiological functions of phytochromes in the qualitative short-day tobacco (Nicotiana tabacum cv Maryland Mammoth) plant. Comparative phenotypic and photobiological analyses of plastid- and cytosol-targeted BVR lines showed that multiple phytochrome-regulated processes, such as hypocotyl and internode elongation, anthocyanin synthesis, and photoperiodic regulation of flowering, were altered in all lines examined. The phytochrome-mediated processes of carotenoid and chlorophyll accumulation were strongly impaired in plastid-targeted lines, but were relatively unaffected in cytosol-targeted lines. Under certain growth conditions, plastid-targeted BVR expression was found to nearly abolish the qualitative inhibition of flowering by long-day photoperiods. The distinct phenotypes of the plastid-targeted BVR lines implicate a regulatory role for bilins in plastid development or, alternatively, reflect the consequence of altered tetrapyrrole metabolism in plastids due to bilin depletion.

Modification of distinct aspects of photomorphogenesis via targeted expression of mammalian biliverdin reductase in transgenic Arabidopsis plants

The phenotypic consequences of targeted expression of mammalian biliverdin IXalpha reductase (BVR), an enzyme that metabolically inactivates the linear tetrapyrrole precursors of the phytochrome chromophore, are addressed in this investigation. Through comparative phenotypic analyses of multiple plastid-targeted and cytosolic BVR transgenic Arabidopsis plant lines, we show that the subcellular localization of BVR affects distinct subsets of light-mediated and light-independent processes in plant growth and development. Regardless of its cellular localization, BVR suppresses the phytochrome-modulated responses of hypocotyl growth inhibition, sucrose-stimulated anthocyanin accumulation, and inhibition of floral initiation. By contrast, reduced protochlorophyll levels in dark-grown seedlings and fluence-rate-dependent reduction of chlorophyll occur only in transgenic plants in which BVR is targeted to plastids. Together with companion analyses of the phytochrome chromophore-deficient hy1 mutant, our results suggest a regulatory role for linear tetrapyrroles within the plastid compartment distinct from their assembly with apophytochromes in the cytosol.

Evacuation of an Aboriginal community in response to an outbreak of blistering dermatitis induced by a beetle (Paederus australis)

OBJECTIVE

To describe an outbreak of dermatitis induced by the beetle Paederus australis and the public health measures implemented to control it.

SETTING

A remote Aboriginal community in the Northern Territory of Australia.

METHODS

Inspection of the community and interviews with residents to document skin lesions, sleeping locations and beetle activity. Samples of the beetle were collected for identification.

RESULTS

The community was affected by a plague of beetles. All 40 residents reported painful, blistering, skin lesions. Four required hospitalisation for treatment of an extensive exfoliating and ulcerating dermatitis. The community was evacuated to allow skin lesions to heal and the beetle plague to decline.

CONCLUSION

This is the first reported en masse outbreak of Paederus dermatitis in Australia. Paederus dermatitis should be considered as a differential diagnosis of vesicular dermatitis in tropical Australia.