Assessment of the effect of the COVID-19 lockdown on glycaemic control in people with type 1 diabetes using flash glucose monitoring

AIM

To describe the effect of the stringent lockdown measures, introduced in the UK on 23 March 2020 to curtail the transmission of COVID-19, on glycaemic control in people with type 1 diabetes using flash glucose monitoring.

METHODS

We undertook an observational study of 572 individuals with type 1 diabetes for whom paired flash glucose monitoring data were available between early March and May 2020. The primary outcome was change in flash glucose monitoring variables. We also assessed clinical variables associated with change in glycaemic control.

RESULTS

Percentage of time in range increased between March and May 2020 [median (interquartile range) 53 (41-64)% vs 56 (45-68)%; P < 0.001], with associated improvements in standard deviation of glucose (P <0.001) and estimated HbA_1c (P <0.001). There was a small reduction in the number of individuals meeting the hypoglycaemia target of <5% per day (64% vs 58%; P = 0.004). Comparing changes in flash glucose monitoring data from March to May in 2019 with the same period in 2020 confirmed that these differences were confined to 2020. Socio-economic deprivation was an independent predictor of a ≥5% reduction in time in range during lockdown (odds ratio 0.45 for people in the two most affluent Scottish Index of Multiple Deprivation quintiles; P <0.001).

CONCLUSIONS

Lockdown was not associated with a significant deterioration in glycaemic control in people with type 1 diabetes using flash glucose monitoring. However, socio-economic deprivation appeared to increase the risk of decline in glycaemic control, which has implications for how support is focused in challenging times.

Modelling the Wolbachia incompatible insect technique: strategies for effective mosquito population elimination

BACKGROUND

The Wolbachia incompatible insect technique (IIT) shows promise as a method for eliminating populations of invasive mosquitoes such as Aedes aegypti (Linnaeus) (Diptera: Culicidae) and reducing the incidence of vector-borne diseases such as dengue, chikungunya and Zika. Successful implementation of this biological control strategy relies on high-fidelity separation of male from female insects in mass production systems for inundative release into landscapes. Processes for sex-separating mosquitoes are typically error-prone and laborious, and IIT programmes run the risk of releasing Wolbachia-infected females and replacing wild mosquito populations.

RESULTS

We introduce a simple Markov population process model for studying mosquito populations subjected to a Wolbachia-IIT programme which exhibit an unstable equilibrium threshold. The model is used to study, in silico, scenarios that are likely to yield a successful elimination result. Our results suggest that elimination is best achieved by releasing males at rates that adapt to the ever-decreasing wild population, thus reducing the risk of releasing Wolbachia-infected females while reducing costs.

CONCLUSIONS

While very high-fidelity sex separation is required to avoid establishment, release programmes tend to be robust to the release of a small number of Wolbachia-infected females. These findings will inform and enhance the next generation of Wolbachia-IIT population control strategies that are already showing great promise in field trials.

The impact of insecticide-treated cloth targets on the survival of Stegomyia polynesiensis (= Aedes polynesiensis) under laboratory and semi-field conditions in French Polynesia

The impact of deltamethrin-impregnated cloth targets on Stegomyia polynesiensis (= Aedes polynesiensis) (Marks) (Diptera: Culicidae) was assessed under laboratory and semi-field settings in French Polynesia. Stegomyia polynesiensis females were released into small laboratory cages and large field cages containing either a deltamethrin-treated or an untreated navy blue cloth, and mosquito knock-down and mortality were assessed. The 24-h mortality rate in mosquitoes exposed to the insecticide-treated target in small cages was 98.0%. These mosquitoes also demonstrated significantly higher levels of knock-down than those exposed to the untreated target. Mortality in field cages was assessed at 24 and 48 h. The 24-h mortality rate in mosquitoes exposed to the control target was 31.2%, whereas that in those exposed to the deltamethrin-treated target was 54.3%. The 48-h mortality rate was also elevated in mosquitoes exposed to the deltamethrin-treated target, but this result did not differ significantly from that observed in mosquitoes exposed to the control target. The significant suppression of female S. polynesiensis by deltamethrin-treated resting targets in this study indicates that these targets could play a role in the control of an important disease vector in the South Pacific region.

Effects of Cohabitation on the Population Performance and Survivorship of the Invasive Mosquito Aedes albopictus and the Resident Mosquito Aedes notoscriptus (Diptera: Culicidae) in Australia

The presence of Aedes albopictus (Skuse) in the Torres Strait of northern Australia increases the potential for colonization and establishment on the mainland. However, there is a possibility that native species that occupy the same habitats may influence the population performance of Ae. albopictus, potentially affecting the establishment of this species in Australia. Cohabitation experiments were performed with the endemic Aedes notoscriptus (Skuse), which has been found occupying the same larval habitats as Ae. albopictus in the Torres Strait and is the most widespread container-inhabiting Aedes species in Australia. The influence of environmental factors and cohabitation between the two species was examined using different climates, food resource levels, food resource types, and species densities. Survivorship proportions and a population performance index (λ') were calculated and compared. The consequences of increased Ae. notoscriptus densities were reduced survivorship and λ' for Ae. albopictus. Despite this, the mean λ' of Ae. albopictus and Ae. notoscriptus was consistently ≥ 1.06, indicating both species could increase under all conditions, potentially due to increasing conspecific densities negatively affecting Ae. notoscriptus. The outcomes from this study suggest that the preexisting presence of Ae. notoscriptus may not prevent the establishment of Ae. albopictus in Australia.

Ability for Aedes albopictus (Diptera: Culicidae) to survive at the climatic limits of its potential range in eastern Australia

Aedes albopictus (Skuse) is one of the most invasive mosquito species in the world and has infested islands in the Torres Strait, off the northern coast of Australia since at least 2004. This has led to fears that it may establish on the Australian mainland, including highly populated cities in southern temperate regions. To supplement theoretical projections addressing the range expansion of Ae. albopictus into Australia, laboratory-based trials were conducted to assess the performance of a Torres Strait Ae. albopictus population under a range of Australian conditions. First-instar larvae were placed in individual microcosms and maintained on a natural food resource, under average climatic conditions representing different regions of Australia's east coast. Larvae could not survive winter conditions in southern Australia. As the population performance index was >1.0 for tropical winter and summer conditions, and temperate summer conditions, populations would likely increase during these times. To test whether Ae. albopictus could overwinter during adverse conditions as eggs, we exposed cohorts to four different temperature (7, 17, 27, and 33 degrees C) and relative humidity (35, 55, and 80%) combinations for up to 3 mo. High temperatures and low humidity were most detrimental to egg survival. However, those eggs maintained under cooler climates remained viable after 3 mo, including 17% of eggs kept at 7 degrees C. Overall, this study suggests that a Torres Strait Ae. albopictus strain could proliferate all year round under northern tropical conditions and could overwinter in the egg stage before proliferating in the summer in southern temperate regions.

Invasion of Wolbachia at the residential block level is associated with local abundance of Stegomyia aegypti, yellow fever mosquito, populations and property attributes

Wolbachia can suppress dengue and control mosquito populations and this depends on the successful invasion of Wolbachia-infected mosquitoes into local populations. Ovitrap data collected during the recent invasion of wMel-infected Stegomyia aegypti (Diptera: Culicidae) (Linnaeus) into Gordonvale near Cairns, Australia, were used to identify variables that help predict the success of localized invasion. Based on the variance in Wolbachia frequencies across Gordonvale as well as at another release site at Yorkeys Knob in comparison to simulations, it was estimated that on average 2-4 females contributed eggs to an ovitrap. By collating ovitrap data from two collection periods at the start of the release from residential blocks, it was found that uninfected mosquitoes had a patchy distribution across the release site. Residential blocks with relatively high uninfected mosquito numbers were less easily invaded by Wolbachia than blocks with low numbers. The numbers of uninfected mosquitoes in ovitraps were negatively correlated with the proportion of brick houses in a residential block, whereas local Wolbachia frequencies were correlated positively with this variable as well as negatively with the amount of shading in a yard and availability of breeding sites. These findings point to proxy measures for predicting the ease of localized invasion of Wolbachia.

Aedes albopictus (Diptera: Culicidae) as a potential vector of endemic and exotic arboviruses in Australia

In 2005, established populations of Aedes albopictus (Skuse) were discovered in the Torres Strait, the region that separates Papua New Guinea from northern Australia. This increased the potential for this species to be introduced to mainland Australia. Because it is an arbovirus vector elsewhere, we undertook laboratory-based infection and transmission experiments to determine the potential for Ae. albopictus from the Torres Strait to become infected with and transmit the four major Australian endemic arboviruses--Murray Valley encephalitis virus, West Nile virus Kunjin strain (WNV(KUN)), Ross River virus (RRV), and Barmah Forest virus--as well as the exotic Japanese encephalitis virus. Ae. albopictus is susceptible to infection with all viruses, with infection rates ranging between 8% for WNV(KUN) and 71% for RRV. Transmission rates of approximately 25% were observed for RRV and Barmah Forest virus, but these were < 17% for Murray Valley encephalitis virus, WNV(KUN), and Japanese encephalitis virus. Given its relative vector competence for alphaviruses, we also examined the replication kinetics and extrinsic incubation periods required for transmission of RRV and chikungunya virus. Despite lower body titers, more mosquitoes reared and maintained at 28 degrees C became infected with and transmitted the virus than those reared and maintained at 22 degrees C. The minimum time between Ae. albopictus consuming an infected bloodmeal and transmitting chikungunya virus was 2 d at 28 degrees C and 4 d at 22 degrees C, and for RRV, it was 4 d, irrespective of the temperature. Given its opportunistic feeding habits and aggressive biting behavior, the establishment of Ae. albopictus on the Australian mainland could have a considerable impact on alphavirus transmission.

Overcoming the challenges of mosquito (Diptera: Culicidae) sampling in remote localities: a comparison of CO2 attractants on mosquito communities in three tropical forest habitats

Emerging infectious diseases are on the rise with future outbreaks predicted to occur in frontier regions of tropical countries. Disease surveillance in these hotspots is challenging because sampling techniques often rely on vector attractants that are either unavailable in remote localities or difficult to transport. We examined whether a novel method for producing CO2 from yeast and sugar produces similar mosquito species captures compared with a standard attractant such as dry ice. Across three different vegetation communities, we found traps baited with dry ice frequently captured more mosquitoes than yeast-baited traps; however, there was little effect on mosquito community composition. Based on our preliminary experiments, we find that this method of producing CO2 is a realistic alternative to dry ice and would be highly suitable for remote field work.

Landing response of Aedes (Stegomyia) polynesiensis mosquitoes to coloured targets

Aedes polynesiensis Marks (Diptera: Culicidae) is the primary vector of lymphatic filariasis (LF) in the island countries and territories of the South Pacific. In the development of a novel control tool, the response of Ae. polynesiensis to six different colours (three solid fabrics, two patterned fabrics and a plastic tarp) was measured using a digital photographic system. Adult mosquitoes were placed into an environmental chamber and allowed to choose between a white target and one of six experimental targets. Mosquito landing frequency and landing duration were calculated. Adult female Ae. polynesiensis preferred all of the experimental targets to the white control target. Mosquito landing frequency was highest for the solid targets (black, navy blue and red) followed in turn by the two colour pattern targets and the polyethylene target. Mosquito landing duration was greater for experimental targets when compared with white control targets. Mosquito landing frequencies did not change over time during the course of the assay. The response of male Ae. polynesiensis was also measured when exposed to a 100% cotton black target. Male mosquitoes preferred the black target to the white control target, although at levels lower than that observed in female mosquitoes. The results suggest that future investigations evaluating the visual responses of Ae. polynesiensis mosquitoes are warranted, with a special emphasis on semi-field and field-based experiments.

Field sampling rate of BG-sentinel traps for Aedes aegypti (Diptera: Culicidae) in suburban Cairns, Australia

Mini-mark-release-recapture experiments were conducted in suburban Cairns, Australia to establish the sampling rate of the Biogents-Sentinel (BGS) trap for adult Aedes aegypti (L.). Small cohorts of marked mosquitoes (30 females and 15 males) were released at typical Cairns residences, and the number of marked mosquitoes recaptured in the BGS trap after 24 h was recorded. The sampling rate was compared between two seasons and two common housing styles (high-set 'Queenslander-style' timber and low-set brick houses), between old gravid and young nulliparous females, and between mosquitoes released in different areas of a house. Overall, the BGS traps recaptured a mean (+/- SEM) of 24.6% (+/- 1.9) of the released marked female mosquitoes in 24 h. The mean recapture rate for females was significantly higher in the dry season (30.4% +/- 2.8) compared with the wet (18.8% +/- 2.2). The overall recapture rates did not differ significantly between the two house types, but variability between the individual premises was high. An overall mean of 18.2% (+/- 1.7) of males was collected. Recapture rates of young nullipars and older gravid females were similar. These recapture rates can be used to estimate the population density of Ae. aegypti females in north Queensland, although it will provide an underestimate as trap sample was largely representative of mosquitoes present in the same area as the trap, and not from other areas of the house.

Changes in the genetic structure of Aedes aegypti (Diptera: Culicidae) populations in Queensland, Australia, across two seasons: implications for potential mosquito releases

Diseases transmitted by mosquitoes could be controlled if vector populations were replaced with strains that have reduced vector competency. Such a strategy is being developed for control of dengue virus which is transmitted by Aedes aegypti (L.) (Diptera: Culicidae). Mosquitoes artificially infected with the bacterium, Wolbachia pipientis Hertig, are being assessed as candidates for release at the adult stage with the aim of replacement of the wild population. Wolbachia can reduce the capacity of Ae. aegypti to transmit dengue virus and has potential to be driven through the natural population via a system of cytoplasmic incompatibility. Deployment of benign mosquito strains will be influenced by population size and structure of wild-type Ae. aegypti in proposed release areas, as well as rates of gene flow among populations in the wet and dry tropical seasons. Mosquitoes from northern Queensland were screened with genetic markers to find an optimal locality for release of a benign strain of Ae. aegypti. The inland towns of Chillagoe and Charters Towers and the coastal town of Ingham had mosquito populations that were partly genetically isolated from mosquitoes in other areas across both seasons. These locations may be suitable release sites if it is important for the released strain to be restricted during initial phases of implementation. Smaller genetic differences were also evident among other regions and were consistent over two seasons (wet and dry).

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.

Improved accuracy of the transcriptional profiling method of age grading in Aedes aegypti mosquitoes under laboratory and semi-field cage conditions and in the presence of Wolbachia infection

Transcriptional profiling is an effective method of predicting age in the mosquito Aedes aegypti in the laboratory, however, its effectiveness is limited to younger mosquitoes. To address this we used a microarray to identify new gene candidates that show significant expression changes in older mosquitoes. These genes were then used to create a revised model, which upon evaluation in both laboratory and semi-field conditions, proved to have improved accuracy overall and for older mosquitoes. In association with the development of symbiont-based control strategies for Ae. aegypti, we also tested the model's accuracy for Wolbachia-infected mosquitoes and found no decline in performance. Our findings suggest that the new model is a robust and powerful tool for age determination in Australian Ae. aegypti populations.

A lethal ovitrap-based mass trapping scheme for dengue control in Australia: II. Impact on populations of the mosquito Aedes aegypti

In Cairns, Australia, the impacts on Aedes aegypti L. (Diptera: Culicidae) populations of two types of 'lure & kill' (L&K) lethal ovitraps (LOs), the standard lethal ovitrap (SLO) and the biodegradable lethal ovitrap (BLO) were measured during three mass-trapping interventions. To assess the efficacy of the SLO, two interventions (one dry season and one wet season) were conducted in three discrete areas, each lasting 4 weeks, with the following treatments: (i) SLOs (>200 traps, approximately 4/premise), BG-sentinel traps (BGSs; approximately 15, 1/premise) and larval control (container reduction and methoprene treatment) and (ii) larval control alone, and (iii) untreated control. Female Ae. aegypti populations were monitored for 4 weeks pre- and post-treatment in all three areas using BGSs and sticky ovitraps (SOs) or non-lethal regular ovitraps (ROs). In the dry season, 206 SLOs and 15 BGSs set at 54 and 15 houses, respectively, caught and killed an estimated 419 and 73 female Ae. aegypti, respectively. No significant decrease in collection size of female Ae. aegypti could be attributed to the treatments. In the wet season, 243 SLOs and 15 BGSs killed approximately 993 and 119 female Ae. aegypti, respectively. The mean number of female Ae. aegypti collected after 4 weeks with SOs and BGSs was significantly less than the control (LSD post-hoc test). The third mass-trapping intervention was conducted using the BLO during the wet season in Cairns. For this trial, three treatment areas were each provided with BLOs (>500, approximately 4/premise) plus larval control, and an untreated control area was designated. Adult female Ae. aegypti were collected for 4 weeks pre- and post-treatment using 15 BGSs and 20 SOs. During this period, 53.2% of BLOs contained a total of 6654 Ae. aegypti eggs. Over the intervention period, collections of Ae. aegypti in the treatment areas were significantly less than in the control area for BGSs but not SOs. An influx of relatively large numbers of young females may have confounded the measurement of changes in populations of older females in these studies. This is an important issue, with implications for assessing delayed action control measures, such as LOs and parasites/pathogens that aim to change mosquito age structure. Finally, the high public acceptability of SLOs and BLOs, coupled with significant impacts on female Ae. aegypti populations in two of the three interventions reported here, suggest that mass trapping with SLOs and BLOs can be an effective component of a dengue control strategy.

A lethal ovitrap-based mass trapping scheme for dengue control in Australia: I. Public acceptability and performance of lethal ovitraps

We report on the first field evaluation of the public acceptability and performance of two types of lethal ovitrap (LO) in three separate trials in Cairns, Australia. Health workers were able to set standard lethal ovitraps (SLOs) in 75 and 71% of premise yards in the wet and dry season, respectively, and biodegradable lethal ovitraps (BLOs) in 93% of yards. Public acceptance, measured as retention of traps by residents, was high for both trap types, with <9% of traps missing after 4 weeks. Traps retaining water after 4 weeks were 78 and 34% for the two SLO trials and 58% for the BLOs. The 'failure rate' in the 535 BLOs set in the field for 4 weeks was 47%, of which 19% were lost, 51% had holes from probable insect chewing, 23% were knocked over, 7% had dried by evaporation and 1% were split. There was no significant difference in the failure rate of BLOs set on porous (grass, soil and mulch) versus solid (tiles, concrete, wood and stone) substrates. The SLOs and the BLOs were readily acceptable to ovipositing Aedes aegypti L. (Diptera: Culicidae); the mean number of eggs/trap was 6 and 15, for the dry season and wet season SLO trial, respectively, and 15 for the BLO wet season trial. Indeed, 84-94% of premise yards had egg positive SLOs or BLOs. A high percentage of both wet and dry season SLOs (29 and 70%, respectively) and BLOs (62%) that were dry after 4 weeks were egg positive, indicating the traps had functioned. Lethal strips from SLOs and BLOs that had been exposed for 4 weeks killed 83 and 74%, respectively, of gravid Ae. aegypti in laboratory assays. These results indicate that mass trapping schemes using SLOs and BLOs are not rejected by the public and effectively target gravid Ae. aegypti. The impact of the interventions on mosquito populations is described in a companion paper.

The link between abdominal obesity, metabolic syndrome and cardiovascular disease

AIM

The prevalence of metabolic syndrome has increased dramatically in recent years, and the cluster of metabolic abnormalities it encompasses results in increased cardiovascular morbidity and mortality. The role of abdominal (visceral) obesity and the underlying molecular and cellular mechanisms central to this association have been the subject of intensive research in recent times. The aim of this review is to correlate data in this area, highlighting the central role of excess visceral fat and its secreted adipokines, and to review existing and emerging therapies.

DATA SYNTHESIS

Data were generated from a search of the PubMed database using the terms 'abdominal obesity', 'metabolic syndrome', 'insulin resistance', 'adipokines', 'interleukin-6 (IL-6)', 'adiponectin', 'tumour necrosis factor-alpha (TNF-alpha)' and 'cardiovascular disease'.

CONCLUSION

Metabolic syndrome is associated with a pro-inflammatory state, and the role of visceral obesity is thought to be central to this. Visceral obesity leads to alteration of the normal physiological balance of adipokines, insulin resistance, endothelial dysfunction and a pro-atherogenic state. In association with this, the presence of conventional cardiovascular risk factors such as hypertension, dyslipidaemia and smoking results in a significantly elevated cardiovascular and metabolic (cardiometabolic) risk. Better understanding of the molecular mechanisms central to this association has led to the development of potential therapeutic agents.

Mark-release-recapture study to measure dispersal of the mosquito Aedes aegypti in Cairns, Queensland, Australia

In Queensland, Australia, in response to isolated cases of dengue infection, larval control of the vector Aedes aegypti (L.) (Diptera: Culicidae) is targeted at breeding sites within 200 m of a case and interior spraying with a pyrethroid adulticide is targeted at premises within 100 m. To ascertain whether these limits are appropriate, we conducted a mark-release-recapture study to measure the dispersal of female Ae. aegypti in the city of Cairns where transmission occurs. Female mosquitoes reared from wild collected eggs were differentially marked with fluorescent dust depending on whether they were to be released blood-fed or non-blood-fed, and a total of 1,948 females was released. A total of 132 sticky ovitraps was set at 64 premises within a 200 m radius and collections of trapped adults were made at 5-15 days post-release. Sixty-seven females (3.4%) were recaptured, with the furthest being caught 200 m from the release point, and the mean distance travelled was 78 m. Overall, 23.1% of the recaptures outside the release site were taken beyond 100 m by day 15. Dispersal was comparable for both blood-fed and non-blood-fed releases. There was a significant tendency for dispersal to be in a north-westerly direction, probably because of the presence of numerous containers and heavy shading by trees in this direction and a busy road to the south of the release point that appeared to inhibit dispersal. The results suggest that adulticiding may have to be extended beyond 100 m if more than 8 days have elapsed since female Ae. aegypti could have fed upon a viraemic dengue case. The study also shows that dispersal is not random, and that it may be possible to maximize vector control by taking into account environmental factors that affect the direction of female mosquito flight.

Flavivirus isolations from mosquitoes collected from Saibai Island in the Torres Strait, Australia, during an incursion of Japanese encephalitis virus

Adult mosquitoes (Diptera: Culicidae) were collected in January and February 2000 from Saibai Island in the Torres Strait of northern Australia, and processed for arbovirus isolation during a period of Japanese encephalitis (JE) virus activity on nearby Badu Island. A total of 84 210 mosquitoes were processed for virus isolation, yielding six flavivirus isolates. Viruses obtained were single isolates of JE and Kokobera (KOK) and four of Kunjin (KUN). All virus isolates were from members of the Culex sitiens Weidemann subgroup, which comprised 53.1% of mosquitoes processed. Nucleotide sequencing and phylogenetic analysis of the pre-membrane region of the genome of JE isolate TS5313 indicated that it was closely related to other isolates from a sentinel pig and a pool of Cx. gelidus Theobald from Badu Island during the same period. Also molecular analyses of part of the envelope gene of KUN virus isolates showed that they were closely related to other KUN virus strains from Cape York Peninsula. The results indicate that flaviviruses are dynamic in the area, and suggest patterns of movement south from New Guinea and north from the Australian mainland.

Mosquito host-feeding patterns and implications for Japanese encephalitis virus transmission in northern Australia and Papua New Guinea

Japanese encephalitis (JE) virus spread to northern Australia during the 1990s, transmitted by Culex annulirostris Skuse and other mosquitoes (Diptera: Culicidae). To determine the relative importance of various hosts for potential vectors of JE virus, we investigated the host-feeding patterns of mosquitoes in northern Australia and Western Province of Papua New Guinea, with particular attention to pigs, Sus scrofa L. - the main amplifying host of JE virus in South-east Asia. Mosquitoes were collected by CDC light traps baited with dry ice and 1-octen-3-ol, run 16.00-08.00 hours, mostly set away from human habitations, if possible in places frequented by feral pigs. Bloodmeals of 2569 mosquitoes, representing 15 species, were identified by gel diffusion assay. All species had fed mostly on mammals: only <10% of bloodmeals were from birds. The predominant species was Cx. annulirostris (88%), with relatively few (4.4%) bloodmeals obtained from humans. From all 12 locations sampled, the mean proportion of Cx. annulirostris fed on pigs (9.1%) was considerably lower than fed on other animals (90.9%). Highest rates of pig-fed mosquitoes (>30%) were trapped where domestic pigs were kept close to human habitation. From seven of eight locations on the Australian mainland, the majority of Cx. annulirostris had obtained their bloodmeals from marsupials, probably the Agile wallaby Macropus agilis (Gould). Overall proportions of mosquito bloodmeals identified as marsupial were 60% from the Gulf Plains region of Australia, 78% from the Cape York Peninsula and 64% from the Daru area of Papua New Guinea. Thus, despite the abundance of feral pigs in northern Australia, our findings suggest that marsupials divert host-seeking Cx. annulirostris away from pigs. As marsupials are poor JE virus hosts, the prevalence of marsupials may impede the establishment of JE virus in Australia.

Population structure and dispersal of the freshwater mosquitoes Culex annulirostris and Culex palpalis (Diptera: Culicidae) in Papua New Guinea and northern Australia

In 1995 and 1998, outbreaks of Japanese encephalitis (JE) virus occurred for the first time in Australia. Virus isolation from pools of mosquitoes indicated Culex annulirostris Skuse was the most likely vector. It was hypothesized that wind-blown mosquitoes introduced JE from Papua New Guinea to the Torres Strait and Cape York, northern Australia. This study used levels of genetic differentiation, as indirect evidence of dispersal of mosquitoes between the two continents. The results have demonstrated that in the region incorporating Western Province in PNG, the Torres Strait and Cape York Peninsula, Cx. annulirostris is represented by a panmictic population, indicating frequent widespread dispersal throughout the region of investigation. The closely related Cx. Palpalis Taylor was also present at some locations but the population structure of this species is uncertain. This supports the hypothesis that wind-blown Cx. annulirostris and possibly Cx. Palpalis could be a possible mechanism for introduction of JE virus into Australia.

Collection of wind-borne haematophagous insects in the Torres Strait, Australia

Circumstantial evidence has implicated wind-borne mosquitoes (Diptera: Culicidae) in the introduction of Japanese encephalitis (JE) virus into Australia from the New Guinea mainland. A study was initiated on Saibai Island in the northern Torres Strait, during January and February 2000, to identify the potential source of insects collected in aerial (kytoon) and surface-level traps. Wind speed and direction were recorded to determine wind profiles during insect sampling. Northerly winds capable of carrying insects from New Guinea to Saibai Island were only present on three out of 18 nights sampled. Only three male mosquitoes, comprising two Verrallina funerea (Theobald) and one Ochlerotatus vigilax (Skuse), were collected in aerial samples, and were most likely of local origin. Culicoides midges were also collected in aerial nets and included gravid/parous C. bundyensis Lee and Reye, and one parous C. histrio Johannsen. Highest densities of arthropods (up to 1562/million m3) were on 30 January 2000 when NW winds, sustained for six hours, probably introduced midges from the New Guinea mainland. Adult mosquitoes (including three female Ve. funerea and a single female Ficalbia) and Culicoides (including two gravid C. bundyensis and one parous C. cordiger Macfie) were also collected in 2 m high mast nets during northerly surface winds. Although the results do not provide evidence that wind-blown mosquitoes introduced JE from New Guinea into Australia, they do not preclude that strong N winds associated with low pressure systems SW of the Torres Strait could have done so. However, results suggest that Culicoides were more likely than mosquitoes to reach high altitude and travel long distances during the light N winds experienced during the study.

Vector competence of Australian mosquitoes (Diptera: Culicidae) for Japanese encephalitis virus

Australian mosquitoes were evaluated for their ability to become infected with and transmit a Torres Strait strain of Japanese encephalitis virus. Mosquitoes, which were obtained from either laboratory colonies and collected using Centers for Disease Control and Prevention light traps baited with CO2 and octenol or reared from larvae, were infected by feeding on a blood/sucrose solution containing 10(4.5 +/- 0.1) porcine stable-equine kidney (PS-EK) tissue culture infectious dose50/mosquito of the TS3306 virus strain. After 14 d, infection and transmission rates of 100% and 81%, respectively, were obtained for a southeast Queensland strain of Culex annulirostris Skuse, and 93% and 61%, respectively, for a far north Queensland strain. After 13 or more days, infection and transmission rates of > 90% and > or = 50%, respectively, were obtained for southeast Queensland strains of Culex sitiens Wiedemann and Culex quinquefasciatus Say, and a far north Queensland strain of Culex gelidus Theobald. Although infection rates were > 55%, only 17% of Ochlerotatus vigilax (Skuse) and no Cx. quinquefasciatus, collected from far north Queensland, transmitted virus. North Queensland strains of Aedes aegypti L., Ochlerotatus kochi (Dönitz), and Verrallina funerea (Theobald) were relatively refractory to infection. Vertical transmission was not detected among 673 F1 progeny of Oc. vigilax. Results of the current vector competence study, coupled with high field isolation rates, host feeding patterns and widespread distribution, confirm the status of Cx. annulirostris as the major vector of Japanese encephalitis virus in northern Australia. The relative roles of other species in potential Japanese encephalitis virus transmission cycles in northern Australia are discussed.

Isolation of arboviruses from mosquitoes (Diptera: Culicidae) collected from the Gulf Plains region of northwest Queensland, Australia

As part of investigations into Japanese encephalitis (JE) virus and related flaviviruses in northern Australia, 153,529 mosquitoes were collected and processed for virus isolation from the Gulf Plains region of northwest Queensland. Collections from within 30 km of each of the townships of Croydon, Normanton and Karumba yielded 3,087 (2.0%), 66,009 (43.0%), and 84,433 (55.0%) mosquitoes, respectively, from which 16 viruses were isolated. Four isolates of Murray Valley encephalitis (MVE), two of Kunjin (KUN), three of Ross River (RR), and one of Sindbis (SIN) viruses were obtained from Culex sitiens subgroup mosquitoes. Molecular identification of the mosquito species composition of these virus positive pools revealed that most isolates were from pools containing mainly Culex annulirostris Skuse and low numbers of Culex palpalis (Taylor). Only three pools, one each of MVE, KUN, and RR, were from mosquitoes identified exclusively as Cx. annulirostris. Other viruses isolated include one Edge Hill virus from Ochlerotatus normanensis (Taylor), an isolate of SIN from Anopheles meraukensis Venhuis, two isolates of RR from Anopheles amictus Edwards, and single isolates of RR from Anopheles bancroftii Giles andAedes lineatopennis (Ludlow). The isolate of RR from Ae. lineatopennis was the first reported from this species. The public health implications of these isolations in the Gulf Plains region are discussed briefly.

The appearance of a second genotype of Japanese encephalitis virus in the Australasian region

In mid-January 2000, the reappearance of Japanese encephalitis (JE) virus activity in the Australasian region was first demonstrated by the isolation of JE virus from 3 sentinel pigs on Badu Island in the Torres Strait. Further evidence of JE virus activity was revealed through the isolation of JE virus from Culex gelidus mosquitoes collected on Badu Island and the detection of specific JE virus neutralizing antibodies in 3 pigs from Saint Pauls community on Moa Island. Nucleotide sequencing and phylogenetic analyses of the premembrane and envelope genes were performed which showed that both the pig and mosquito JE virus isolates (TS00 and TS4152, respectively) clustered in genotype I, along with northern Thai, Cambodian, and Korean isolates. All previous Australasian JE virus isolates belong to genotype II, along with Malaysian and Indonesian isolates. Therefore, for the first time, the appearance and transmission of a second genotype of JE virus in the Australasian region has been demonstrated.

Japanese encephalitis on Badu Island, Australia: the first isolation of Japanese encephalitis virus from Culex gelidus in the Australasian region and the role of mosquito host-feeding patterns in virus transmission cycles

During investigation of an outbreak of Japanese encephalitis (JE) in the Torres Strait, Australia, in 2000, mosquitoes were collected in Badu Island community and at a newly established communal piggery about 3 km from the community. A total of 94,285 mosquitoes, comprising 91,240 (96.8%) unengorged females, 1630 (1.7%) blood-engorged females and 1415 (1.5%) males, were processed for virus isolation. One isolate of JE virus was obtained from Culex gelidus, with a minimum infection rate of 12.4:1000. This is the first isolate of JE virus from Cx. gelidus in the Australasian region. No isolates were obtained from Cx. annulirostris, the primary implicated Australian JE vector. Analysis of mosquito host-feeding patterns, using gel diffusion, demonstrated that Cx. annulirostris and 5 other species fed predominately on mammals. Analysis of blood-fed mosquitoes collected within the community demonstrated that the proportion of Cx. annulirostris feeding on pigs in 2000 (2.3%) was significantly lower than that for the 1995-97 period (31.3%). The removal of the pigs from Badu Island community has limited the contact between potential amplifying hosts and mosquitoes, thus potentially reducing the risk of transmission of JE virus to the human population.

Effect of some animal feeds and oviposition substrates on Aedes oviposition in ovitraps in Cairns, Australia

Animal feed pellets containing lupin seed or alfalfa were added to ovitraps set in Cairns, Australia. Although they collected fewer Aedes eggs than Centers for Disease Control enhanced ovitraps, they did outperform tap water alone. A wooden tongue depressor collected comparable number of Aedes eggs as a Masonite board and seed germination paper.

Entomological investigations of an outbreak of Japanese encephalitis virus in the Torres Strait, Australia, in 1998

Japanese encephalitis (JE) virus first appeared in Australia in 1995, when three clinical cases (two fatal) were diagnosed in residents on Badu Island in the Torres Strait, northern Queensland. More recently, two confirmed human JE cases were reported in the Torres Strait Islands and Cape York Peninsula, in northern Queensland in 1998. Shortly after JE virus activity was detected in humans and sentinel pigs on Badu Island in 1998, adult mosquitoes were collected using CO2 and octenol-baited CDC light traps; 43 isolates of JE virus were recovered. Although Culex sitiens group mosquitoes yielded the majority of JE isolates (42), one isolate was also obtained from Ochlerotatus vigilax (Skuse). Four isolates of Ross River virus and nine isolates of Sindbis (SIN) virus were also recovered from members of the Culex sitiens group collected on Badu Island in 1998. In addition, 3,240 mosquitoes were speciated and pooled after being anesthetized with triethylamine (TEA). There was no significant difference in the minimum infection rate of mosquitoes anesthetized with TEA compared with those sorted on refrigerated tables (2.8 and 1.6 per 1,000 mosquitoes, respectively). Nucleotide analysis of the premembrane region and an overlapping region of the fifth nonstructural protein and 3' untranslated regions of representative 1998 Badu Island isolates of JE virus reveled they were identical to each other. Between 99.1% and 100% identity was observed between 1995 and 1998 isolates of JE from Badu Island, as well as isolates of JE from mosquitoes collected in Papua New Guinea (PNG) in 1997 and 1998. This suggests that the New Guinea mainland is the likely source of incursions of JE virus in Australia.

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.

Efficacy of Australian quarantine procedures against the mosquito Aedes aegypti

Methods employed by Australian quarantine officers to control Aedes mosquitoes in containers were tested against all stages of Aedes aegypti. Saltwater emersion killed all larvae but not pupae or eggs that were briefly exposed. Swimming pool chlorine, methyl bromide fumigation, and permethrin (2% active ingredient) spray provided 100% mortality of eggs, larvae, and pupae. Aerosol sprays incorporating synthetic pyrethrins are practical and also provide effective control of adults.

Murray Valley encephalitis virus surveillance and control initiatives in Australia. National Arbovirus Advisory Committee of the Communicable Diseases Network Australia

Mechanisms for monitoring Murray Valley encephalitis (MVE) virus activity include surveillance of human cases, surveillance for activity in sentinel animals, monitoring of mosquito vectors and monitoring of weather conditions. The monitoring of human cases is only one possible trigger for public health action and the additional surveillance systems are used in concert to signal the risk of human disease, often before the appearance of human cases. Mosquito vector surveillance includes mosquito trapping for speciation and enumeration of mosquitoes to monitor population sizes and relative composition. Virus isolation from mosquitoes can also be undertaken. Monitoring of weather conditions and vector surveillance determines whether there is a potential for MVE activity to occur. Virus isolation from trapped mosquitoes is necessary to define whether MVE is actually present, but is difficult to deliver in a timely fashion in some jurisdictions. Monitoring of sentinel animals indicates whether MVE transmission to vertebrates is actually occurring. Meteorological surveillance can assist in the prediction of potential MVE virus activity by signalling conditions that have been associated with outbreaks of Murray Valley encephalitis in humans in the past. Predictive models of MVE virus activity for south-eastern Australia have been developed, but due to the infrequency of outbreaks, are yet to be demonstrated as useful for the forecasting of major outbreaks. Surveillance mechanisms vary across the jurisdictions. Surveillance of human disease occurs in all States and Territories by reporting of cases to health authorities. Sentinel flocks of chickens are maintained in 4 jurisdictions (Western Australia, the Northern Territory, Victoria and New South Wales) with collaborations between Western Australia and the Northern Territory. Mosquito monitoring complements the surveillance of sentinel animals in these jurisdictions. In addition, other mosquito monitoring programs exist in other States (including South Australia and Queensland). Public health control measures may include advice to the general public and mosquito management programs to reduce the numbers of both mosquito larvae and adult vectors. Strategic plans for public health action in the event of MVE virus activity are currently developed or being developed in New South Wales, the Northern Territory, South Australia, Western Australia and Victoria. A southern tri-State agreement exists between health departments of New South Wales, Victoria and South Australia and the Commonwealth Department of Health and Aged Care. All partners have agreed to co-operate and provide assistance in predicting and combatting outbreaks of mosquito-borne disease in south-eastern Australia. The newly formed National Arbovirus Advisory Committee is a working party providing advice to the Communicable Diseases Network Australia on arbovirus surveillance and control. Recommendations for further enhancement of national surveillance for Murray Valley encephalitis are described.

Flaviviruses isolated from mosquitoes collected during the first recorded outbreak of Japanese encephalitis virus on Cape York Peninsula, Australia

In response to an outbreak of Japanese encephalitis (JE) virus on Cape York Peninsula, Australia, in 1998, mosquitoes were collected using CO2 and octenol-baited Centers for Disease Control and Prevention light traps. A total of 35,235 adult mosquitoes, comprising 31 species, were processed for virus isolation. No isolates of JE virus were recovered from these mosquitoes. However, 18 isolates of Kokobera virus, another flavivirus were obtained from Culex annulirostris. Twelve isolates were from western Cape York (minimum infection rate (MIR) of 0.61: 1,000 mosquitoes) and 6 were from the Northern Peninsula Area (MIR of 1.0:1,000). Potential explanations for the failure to detect JE virus in mosquitoes collected from Cape York Peninsula include the timing of collections, the presence of alternative bloodmeal hosts, differences in pig husbandry, asynchronous porcine seroconversion, and the presence of other flaviviruses.

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.

An epidemic of dengue 3 in far north Queensland, 1997-1999

OBJECTIVES

To describe an epidemic of dengue type 3 that occurred in far north Queensland in 1997-1999 and its influence on the further development of dengue prevention and control strategies.

DESIGN

Epidemiological and laboratory investigation of cases, entomological surveys and phylogenetic analysis of dengue virus isolates.

MAIN OUTCOME MEASURES

Numbers and characteristics of confirmed cases; Breteau Index (BI; number of containers breeding Aedes aegypti per 100 premises); effect of control measures on mosquito populations; genetic homology of epidemic virus with other dengue virus isolates.

RESULTS

The epidemic lasted 70 weeks and comprised 498 confirmed cases in three towns (Cairns, Port Douglas and Mossman); 101 patients (20%) were admitted to hospital. Median interval between symptom onset and notification was seven days (range, 0-53 days), and cumulative duration of viraemia of public health significance was 2,072 days. BIs in affected areas were high, particularly in Mossman (45) and Port Douglas (31). Control measures significantly reduced mosquito populations (assessed as number of ovitraps containing Ae. aegypti eggs and mean number of eggs per trap [P< 0.05 for both]). However, transmission persisted in several foci, in part due to undetected waterfilled containers breeding Ae. aegypti. The epidemic virus belonged to serotype 3; phylogenetic analysis suggested it was imported from Thailand.

CONCLUSIONS

The epidemic had greater morbidity than other recent Queensland epidemics of dengue and was harder to control, necessitating substantial revision of the Dengue Fever Management Plan for North Queensland. The epidemic's severity supports the hypothesis that dengue viruses from South East Asia are more virulent than others.

Wind-blown mosquitoes and introduction of Japanese encephalitis into Australia

Backtrack simulation analysis indicates that wind-blown mosquitoes could have traveled from New Guinea to Australia, potentially introducing Japanese encephalitis virus. Large incursions of the virus in 1995 and 1998 were linked with low-pressure systems that sustained strong northerly winds from New Guinea to the Cape York Peninsula.

Emerging viral diseases of Southeast Asia and the Western Pacific

Over the past 6 years, a number of zoonotic and vectorborne viral diseases have emerged in Southeast Asia and the Western Pacific. Vectorborne disease agents discussed in this article include Japanese encephalitis, Barmah Forest, Ross River, and Chikungunya viruses. However, most emerging viruses have been zoonotic, with fruit bats, including flying fox species as the probable wildlife hosts, and these will be discussed as well. The first of these disease agents to emerge was Hendra virus, formerly called equine morbillivirus. This was followed by outbreaks caused by a rabies-related virus, Australian bat lyssavirus, and a virus associated with porcine stillbirths and malformations, Menangle virus. Nipah virus caused an outbreak of fatal pneumonia in pigs and encephalitis in humans in the Malay Peninsula. Most recently, Tioman virus has been isolated from flying foxes, but it has not yet been associated with animal or human disease. Of nonzoonotic viruses, the most important regionally have been enterovirus 71 and HIV.

An alternative, human SRC promoter and its regulation by hepatic nuclear factor-1alpha

The SRC gene encodes the proto-oncogene pp60(c-)(src), a tyrosine kinase implicated in numerous signal transduction pathways. In addition, the SRC gene is differentially expressed, developmentally regulated, and frequently overexpressed in human neoplasia. However, the mechanisms regulating its expression have not been completely explored. Here we describe the isolation of a new distal SRC promoter and associated exon, designated 1alpha, which we mapped to a position 1.0 kilobase upstream of the previously described SRC1A housekeeping promoter. Differential use of these promoters and their associated exons coupled with subsequent splicing to a common downstream exon results in c-Src transcripts with different 5' ends but identical coding regions. Promoter analysis following transient transfections into HepG2 cells mapped the minimal 1alpha promoter to a region 145 bp upstream of the major transcription start site. This region contained a consensus binding site for hepatic nuclear factor-1 (HNF-1), a liver-enriched transcription factor implicated in the regulation of a number of genes in liver, kidney, stomach, intestine, and pancreas. Subsequent mobility shift assays confirmed that HNF-1alpha isoform was the predominant factor interacting with this region of the promoter. Mutation of the HNF-1 site resulted in a dramatic reduction in SRC promoter activity. Cotransfection studies demonstrated the promoter could be strongly transactivated by the HNF-1alpha isoform but not by the related HNF-1beta factor. Consistent with these results, we demonstrated that transcripts originating from the SRC1alpha promoter display a tissue restricted pattern of expression with highest levels present in stomach, kidney, and pancreas. These results indicate that SRC transcriptional regulation is much more complex than previously realized and implicates HNF-1 in both the tissue-specific regulation of the SRC gene in normal tissues and the overexpression of c-Src in certain human cancers.

Definition of species in the Culex sitiens subgroup (Diptera: Culicidae) from Papua New Guinea and Australia

Japanese encephalitis is a disease of major importance in Asia, which from 1995 has extended its range into the north of Australia. Culex annulirostris Skuse of the Culex sitiens subgroup of Culex was incriminated as the most likely mosquito vector. Because misidentifications previously have occurred within this subgroup, our paper defines electrophoretic methods to identify Culex specimens from Queensland and the Northern Territory in Australia and from Western Province in Papua New Guinea. In collections from 1996 to 1998 Culex sitiens Wiedemann, Cx. palpalis Taylor, and Cx. annulirostris comprised 93.1% of the total banded proboscis Culex mosquitoes collected; 6.9% remained unidentified to species by morphological or electrophoretic examination. The prevalence of Cx. palpalis was variable and appeared to be associated with below average rainfall during 1997. In Papua New Guinea, this species comprised up to 97.4% of banded proboscis Culex, with smaller numbers collected from the Torres Strait Islands and Cape York; none was collected from other Queensland localities. Cx. annulirostris was more prevalent during years of average or above average rainfall and was predominant in most localities, especially in the Torres Strait and Queensland. These data confirmed the problems in separating Cx. sitiens from Cx. palpalis and Cx. annulirostris using morphological characters.

Isolation of Japanese encephalitis virus from mosquitoes (Diptera: Culicidae) collected in the Western Province of Papua New Guinea, 1997-1998

After Japanese encephalitis (JE) virus emerged in the Torres Strait in Australia in 1995, investigations were initiated into the origin of the incursion. New Guinea was considered the most likely source, given its proximity to islands of the Torres Strait. Almost 400,000 adult mosquitoes were processed for virus isolation from 26 locations in the Western Province of Papua New Guinea (PNG) between February 1996 and February 1998, yielding three isolates of JE virus. Two isolates of Murray Valley encephalitis, 17 isolates of Sindbis, and 1 each of Sepik and Ross River viruses were also obtained. Nucleic acid sequences of the PNG JE isolates were determined in the prM region, and in a region overlapping a part of the fifth nonstructural protein and the 3' untranslated region. The PNG isolates belonged to genotype II, and shared > 99.2% identity with isolates from humans and mosquitoes from the Torres Strait, suggesting that PNG is the source of incursions of JE virus into Australia.

Seasonal abundance of Anopheles farauti (Diptera: Culicidae) sibling species in far north Queensland, Australia

In the Cairns area of far north Queensland, Australia, the seasonal abundance of Anopheles farauti Laveran sibling species was studied at 6 locations, representing 3 habitat types, between August 1995 and September 1997. A total of 45,401 An. farauti s.l. was collected using CO2 + octenol baited CDC light traps, and consisted of 29,565 An. farauti No. 2, 14,214 An. farauti No. 3, and 1,622 An. farauti s.s. The relative abundance of all 3 species differed significantly by season and location. An. farauti No.2 was the dominant species except in Cairns, where An. farauti s.s. was most abundant, and at Ninds Creek, where An. farauti No. 3 predominated. The dominant species at each location was present year round, although peaks in seasonal abundance were observed. An. farauti s.s. populations were highest during the wet season (January-April). In lowland freshwater swamp habitats and 1 brackish location, An. farauti No. 2 was more abundant during the wet season. However, at the highland freshwater swamp habitat, populations of An. farauti No. 2 were highest during the late dry season and early wet season (October-December). There was a significant positive correlation of both temperature and rainfall with An. farauti s.s. and An. farauti No. 2 trap collections. There was a negative correlation between An. farauti No. 3 and temperature, indicating that this species may be more abundant during cool weather. Although there were significant relationships among weather variables and An. farauti s.l. collections, correlation values were generally low, indicating that other factors may contribute to variability among An. farauti sibling species trap collections.

Population structure and dispersal of the saltmarsh mosquito Aedes vigilax in Queensland, Australia

Population genetics of the mosquito Aedes vigilax (Skuse) (Diptera: Culicidae), a major vector of arboviruses (e.g. Barmah Forest, Ross River), were investigated to obtain an indirect estimate of mosquito dispersal characteristics in typical habitats of Aedes vigilax in south-east Queensland: on the off-shore islands of Moreton Bay and on the mainland where disjunct breeding populations of Ae. vigilax are distributed along intertidal marsh. Six allozyme loci were assessed for genetic differentiation between samples from 11 localities. Significant larval variation between some breeding sites was attributed to site-specific selection. Nonsignificant genetic differentiation was found among collections of adult mosquitoes caught in light traps throughout the study area (exceeding 60x27 km), indicating widespread dispersal. As distances of < or = 9 km over water did not appear to act as effective barriers to Ae. vigilax dispersal, localized control activities applied to Ae. vigilax breeding sites are unlikely to be effective against the vagile adult population. Therefore, the contiguous shires programme of broad acre control is endorsed to prevent the spread of arboviruses carried by Ae. vigilax

Japanese encephalitis in north Queensland, Australia, 1998

OBJECTIVE

To describe the circumstances of two cases of Japanese encephalitis (JE) in north Queensland in 1998, including one acquired on the Australian mainland.

DESIGN

Serological surveillance of sentinel pigs for JE virus activity; serological surveys of humans and pigs and viral cultures of mosquito collections.

SETTING

Islands in the Torres Strait and communities in the Northern Peninsula Area (NPA) and near the mouth of the Mitchell River in Cape York, Queensland, in the 1998 wet season (December 1997-May 1998).

RESULTS

Sentinel pigs in the Torres Strait began to seroconvert to JE virus in February 1998, just before onset of JE in an unvaccinated 12-year-old boy on Badu island. By mid-April, most sentinel pigs had seroconverted. Numerous JE viruses were isolated from Culex annulirostris mosquitoes collected on Badu. In early March, a person working at the mouth of the Mitchell River developed JE. Serological surveys showed recent JE virus infection in 13 young pigs on a nearby farm, but not in 488 nearby residents. In NPA communities, sentinel pigs seroconverted slowly and JE viruses were isolated from three, but none of 604 residents showed evidence of recent infection. Nucleotide sequencing showed that 1998 JE virus isolates from the Torres Strait were virtually identical not only to the 1998 isolate from an NPA pig, but also to previous (1995) Badu isolates.

CONCLUSIONS

JE virus activity was more widespread in north Queensland in the 1998 wet season than in the three previous wet seasons, but ecological circumstances (e.g., less intensive pig husbandry, fewer mosquitoes) appear to have limited transmission on the mainland. Nucleotide sequencing indicated a common source for the 1995 and 1998 JE viruses. Circumstantial evidence suggests that cyclonic winds carried infected mosquitoes from Papua New Guinea.

Eggshell sampling: quantitative or qualitative data?

This research evaluated the use of qualitative presence/absence data compared with quantitative real number counts of Aedes vigilax eggshell data to obtain information on the spatial distribution of eggshells in several salt marsh vegetation types. Eggshells were extracted by subsampling and flotation, a method that does not recover all eggshells. The results of the analysis of presence/absence data were compared with those of real numbers. The general conclusions were similar by either method, suggesting that presence/absence data may be sufficient to rapidly determine eggshell distribution patterns.

The first report of Anopheles farauti sensu stricto below the nineteenth parallel at Mackay, Queensland

Fifty-six adult female mosquitoes of the species Anopheles farauti sensu stricto--the arthropod vector for malaria--were collected from Mackay, central Queensland, at latitude 21 degrees 09'S, between August 1996 and August 1997. This is the southernmost record of this species, and may indicate that the malaria-receptive zone in Queensland needs to be expanded.

Arboviruses in the Australian region, 1990 to 1998

Arboviruses continue to be major human pathogens in the Australian region. This report provides a summary of the activities of these viruses over the past eight years, and comments on new findings relevant to their respective ecologies. Of particular interest and concern is the propensity of these viruses to spread. The examples discussed include the initiation of dengue epidemics in north Queensland by virus imported in viraemic travellers; the spread of Japanese encephalitis virus to the Australasian region and its probable enzootic establishment in the south-west of Papua New Guinea; the potential spread of Ross River virus to other countries, as demonstrated by the 1979-80 outbreak in the South Pacific, and the recent occurrence in military personnel from the United States of America after an exercise; and the recent spread of Barmah Forest virus into Western Australia.

An overview of remote sensing and GIS for surveillance of mosquito vector habitats and risk assessment

This paper provides a brief nontechnical overview of the use of remote sensing to achieve multiple objectives, focusing on mosquito management. It also shows how Geographic Information Systems, combined with remote sensing analysis, have the potential to assist in minimizing disease risk. Examples are used from subtropical Queensland, Australia, where the salt marsh mosquito, Aedes vigilax, and the freshwater species, Culex annulirostris, are vectors of human arbovirus diseases such as Ross River and Barmah Forest virus disease. Culex annulirostris is also implicated in the transmission of Japanese Encephalitis. Mapping the breeding habitats of the species facilitates assessment of the risk of contracting the diseases and also assists in control of the vectors. First, it considers a simple risk model that is applied to data for the city of Brisbane in southeast Queensland. This is then linked to computer-aided analysis of remotely sensed data to map potential ephemeral freshwater breeding sites of Cx. annulirostris. This has the potential to guide control at critical times, for example after heavy summer rainfall or when there is an outbreak of Ross River virus disease. Second, the use of color infrared aerial photography is used to identify the specific parts of the salt marsh in which larvae and eggs of Ae. vigilax are found. Finally, we explore novel ways to map the detailed pattern of water under mangrove forest canopy to identify where mosquitoes are breeding and as an aid to planning modification. For each we discuss the limitations and advantages and the possibilities for combining methods and/or using a single method for multiple objectives.

Malaria and its implications for public health in Far North Queensland: a prospective study

This prospective study's objectives were to describe the features of all episodes of malaria diagnosed in Far North Queensland (excluding the Torres Strait) and to assess how much of a threat they posed to the area's public health. Over a three-year period, 216 episodes of malaria were diagnosed (158 Plasmodium vivax and 68 P. falciparum infections). Most (82%) of the infections were acquired in Papua New Guinea (PNG). Approximately 70% of the episodes occurred in Australian citizens, about half of whom were in malaria-endemic countries for work; the remainder travelled abroad for recreation. Three-quarters of the Australian citizens with malaria had taken either no or inadequate prophylaxis. Australian citizens who had taken adequate prophylaxis were much less likely to develop P. falciparum than other types of malaria compared to those who took either no or inadequate prophylaxis (p = 0.01). Gametocytes were present in 121 (56%) of the episodes of malaria. Mosquito surveillance was carried out in response to 38 (31%) of these gametocytaemic episodes. Significant numbers of Anopheles farauti sensu lato mosquitoes were found close to the residence of a patient in 4 (11%) of these episodes. Only two occasions when local transmission could have possibly occurred were recognised. We do not believe malaria poses an important threat to the health of the public in Far North Queensland. Nevertheless, it remains an important problem for those who travel abroad to malarious areas.

Two contiguous outbreaks of dengue type 2 in north Queensland

OBJECTIVES

To investigate two outbreaks of dengue type 2 in north Queensland, one in the Torres Strait beginning in late 1996, the other in a Cairns suburb in early 1997.

DESIGN

Epidemiological investigation of all laboratory-confirmed cases of dengue, entomological investigation of the local environment, and laboratory analysis of the isolated dengue viruses.

MAIN OUTCOME MEASURES

Numbers of confirmed and of locally acquired cases; virus serotype; comparison of nucleotide sequences between viruses isolated from the two outbreaks; and Breteau Index (BI = number of containers with larvae of the mosquito vector Aedes aegypti found per 100 houses investigated) on the affected islands and in the Cairns suburb.

RESULTS

There were 201 confirmed cases of dengue in the Torres Strait outbreak, which lasted nearly seven months, and seven confirmed cases in the Cairns outbreak, which lasted about nearly 11 weeks. Most (190) were confirmed as dengue type 2. Nucleotide sequencing of viruses isolated from the two outbreaks showed they were identical. Ae. aegypti breeding sites were very common on the five Torres Strait islands surveyed (BIs, 73-219--high risk), but less so in the Cairns suburb (BI, 23). The most common breeding sites were water storage reservoirs, particularly rainwater tanks, on the outer Torres Strait islands, discarded containers (such as plastic containers, buckets and tyres) on Thursday Island, and garden items (such as flowerpot bases and jars) in Cairns.

CONCLUSIONS

The virus responsible for the Cairns outbreak was most probably introduced from the Torres Strait, whereas the virus responsible for the Torres Strait outbreak was imported from Papua New Guinea. Preventive strategies tailored to specific locations are needed to reduce breeding of Ae. aegypti in north Queensland, and the consequent risk of future outbreaks of dengue.

Acute and sublethal effects of (S)-methoprene on some Australian mosquitoes

Laboratory bioassays were used to determine the efficacy of (S)-methoprene against 7 species of Australian mosquitoes. The 90% lethal concentration (LC90) ranged from 0.17 ppb for Aedes vigilax to 6.54 ppb for Culex sitiens. The survival of adults exposed as larvae to 2 sublethal dosages of (S)-methoprene was compared to a control group. Little effect was noted for Cx. sitiens and Culex annulirostris. However, survival of male and female Ae. vigilax was significantly reduced and appeared to be dose related. Bloodfeeding success of female Ae. vigilax was also significantly reduced.