Aircraft disinsection: what is the usefulness as a public health measure?

RATIONALE FOR REVIEW: Insecticide treatments in aircraft (termed 'aircraft disinsection') aim to support the containment of potentially disease-carrying vector insects. The introduction of non-endemic mosquito species is of concern as some mosquitoes can act as vectors of many serious human diseases. Expansion of vectors to previously non-endemic regions, extended flight networks and mosquito resistance to insecticides pose challenges to contemporary vector-control approaches. Despite established efficacy of aircraft disinsection in trials, there is increasing concern over its effectiveness and feasibility in flight operations, and its usefulness as a public health measure. KEY FINDINGS: We explored the literature on disinsection through a narrative approach to obtain a pragmatic assessment of existing and future implementation challenges. We describe the shortcomings that hinder evaluation of the success of aircraft disinsection. These shortcomings include operational constraints that may impact effective treatment outcomes, lack of longitudinal data on pesticide exposure scenarios, lack of compliance mechanisms, pesticide resistance in mosquitoes, and limited evidence of the extent and type of mosquito species potentially transported via aircraft. CONCLUSIONS AND RECOMMENDATIONS: Concerns about the introduction of non-endemic mosquito vectors reinforce the need for effective preventive measures. Import of disease vectors is likely to occur in the future under changing environmental and operational conditions. Optimal impact from disinsection requires appropriate deployment, commitment and use. The current system of evaluation is inadequate for producing the evidence needed for informed policy decisions. While utilizing the results of research into environmentally sustainable vector-control methods for use in aircraft, future approaches to aircraft disinsection require improved evidence of anticipated benefits and harms, reliable monitoring data on insecticide resistance, and must be supported by strong vector control at airports.

Dispersal of the Mosquito Aedes vigilax (Diptera: Culicidae) From Urban Estuarine Wetlands in Sydney, Australia.

Aedes vigilax (Skuse) is a pest and vector species associated with coastal wetlands and the abundance of this mosquito has been identified as contributing to increased risk of mosquito-borne disease outbreaks. As urban development continues to encroach on these coastal wetlands, pest and public health impacts are becoming of increasing concern and in the absence of broadscale mosquito control. Urban planners are looking to buffer zones and other land use planning options to minimize contact between mosquitoes and humans but gaps in the understanding of dispersal ranges of mosquitoes hamper the adoption of these strategies. A mark-release-recapture experiment was conducted to measure the dispersal of this mosquito from an urban estuarine wetland in Sydney, Australia. An estimated total of over 150,000 wild caught female mosquitoes were marked with fluorescent dust and then released. A network of 38 traps was then operated for 5 d within an area of 28 km2. A total of 280 marked mosquitoes was recaptured, representing less than 1% of the estimate 250,000 marked mosquitoes released. Marked mosquitoes were recaptured up to 3 km from the release point, providing an insight into the dispersal range of these mosquitoes. The mean distance traveled by marked mosquitoes was 0.83 km, a result reflecting the greater proportion of marked mosquitoes recaptured near release point. The findings of this study indicate that effective buffer zones between estuarine wetlands and high-density urban developments would be an impractical approach to minimizing pest and public health impacts associated with this mosquito.

Effects of attachment substrate, larval diet, and temperature on development and survival of immature Coquillettidia linealis (Skuse) and Coquillettidia xanthogaster (Edwards).

A sustainable colony allowed investigations into attachment substrates, diet and temperature in the development of the immature stages of Cq. linealis and its local congener Cq. xanthogaster. As immatures, these mosquitoes attach to submerged plants for respiration, and various field-collected and laboratory-raised plants were compared with non-living substrates. Hydroponically-grown wheat plant seedlings provided the most suitable attachment substrate. Development and survival of immatures to eclosion were investigated with three types and three quantities of a standardized diet. Development and survival at rearing temperatures between 10° and 30° C were also investigated. Diet type appeared to have little influence on development. However, at the lowest diet quantity, development to pupation was significantly reduced while the highest diet quantity impacted on the eclosion of pupae. Mean duration of immature development for Cq. linealis increased as temperature decreased. Time from 1st instar to median eclosion did not differ significantly between 23° C (6.0 weeks) and 25° C (5.3 weeks), although it was 10 weeks at 20° C, and 30° C was lethal. For Cq. xanthogaster, similarly, mean duration of immature development increased as temperature decreased, with development time from 1st instar to median eclosion significantly longer at 20° C (7.5 weeks) compared to 23° C (5.0 weeks) and 30° C (4.0 weeks).

Colonization of Coquillettidia linealis (Skuse) with reference to other Coquillettidia and Mansonia species.

The immature stages of Coquillettidia and Mansonia mosquitoes are cryptic and spend the duration of their development attached to the tissues of subsurface aquatic plants. This obligatory association makes them difficult to collect and has precluded detailed investigation of the biology of Coquillettidia linealis, a species of significant pest and vector status in Australia, as well as other species in the genus Coquillettidia in Australia and elsewhere. This paper describes the first successful establishment and maintenance of a colony of Cq. linealis. Blood-seeking wild adults were collected and induced to oviposit under laboratory conditions, where methods were developed to rear larval populations to adult maturity in a colony that was maintained through eight successive generations. Colonies of Coquillettidia xanthogaster and Coquillettidia sp. nr crassipes were also established and reared through at least six generations and five generations, respectively, while two species of Mansonia, Mansonia uniformis and Mansonia septempunctata, were also reared successfully for six and two generations, respectively.

Ten years of the Tiger: Aedes albopictus presence in Australia since its discovery in the Torres Strait in 2005.

The "Asian tiger mosquito", Aedes albopictus, is highly invasive, an aggressive biter and a major arbovirus vector. It is not currently present on mainland Australia despite being intercepted on numerous occasions at international ports and infesting the Torres Strait of Australia since at least 2004. In the current paper, we describe the invasion and current status of Ae. albopictus in the Torres Strait, as well as research conducted to assess the threat of this species becoming established in arbovirus transmission cycles on the Australian mainland. Genetic analysis of the invading population demonstrated that the Indonesian region was the likely origin of the invasion and not Papua New Guinea (PNG) as initially suspected. There was also intermixing between Torres Strait, PNG and Indonesian populations, indicating that the species could be re-introduced into the Torres Strait compromising any successful eradication programme. Vector competence experiments with endemic and exotic viruses revealed that Ae. albopictus from the Torres Strait are efficient alphavirus vectors, but less efficient flavivirus vectors. Ae.albopictus obtains blood meals from a range of vertebrate hosts (including humans), indicating that it could play a role in both zoonotic and human-mosquito arbovirus transmission cycles in Australia. Predictive models coupled with climate tolerance experiments suggest that a Torres Strait strain of Ae. albopictus could colonise southern Australia by overwintering in the egg stage before proliferating in the warmer months. Cohabitation experiments demonstrated that the presence of Aedes notoscriptus larvae in containers would not prevent the establishment of Ae. albopictus. Evidence from these studies, coupled with global experience suggests that we need to be prepared for the imminent invasion of Australia by Ae. albopictus by thoroughly understanding its biology and being willing to embrace emerging control technologies.

Enhanced arbovirus surveillance with deep sequencing: Identification of novel rhabdoviruses and bunyaviruses in Australian mosquitoes.

Viral metagenomics characterizes known and identifies unknown viruses based on sequence similarities to any previously sequenced viral genomes. A metagenomics approach was used to identify virus sequences in Australian mosquitoes causing cytopathic effects in inoculated mammalian cell cultures. Sequence comparisons revealed strains of Liao Ning virus (Reovirus, Seadornavirus), previously detected only in China, livestock-infecting Stretch Lagoon virus (Reovirus, Orbivirus), two novel dimarhabdoviruses, named Beaumont and North Creek viruses, and two novel orthobunyaviruses, named Murrumbidgee and Salt Ash viruses. The novel virus proteomes diverged by ≥ 50% relative to their closest previously genetically characterized viral relatives. Deep sequencing also generated genomes of Warrego and Wallal viruses, orbiviruses linked to kangaroo blindness, whose genomes had not been fully characterized. This study highlights viral metagenomics in concert with traditional arbovirus surveillance to characterize known and new arboviruses in field-collected mosquitoes. Follow-up epidemiological studies are required to determine whether the novel viruses infect humans.

Tracing the tiger: population genetics provides valuable insights into the Aedes (Stegomyia) albopictus invasion of the Australasian Region.

BACKGROUND: The range of the Asian tiger mosquito Aedes albopictus is expanding globally, raising the threat of emerging and re-emerging arbovirus transmission risks including dengue and chikungunya. Its detection in Papua New Guinea's (PNG) southern Fly River coastal region in 1988 and 1992 placed it 150 km from mainland Australia. However, it was not until 12 years later that it appeared on the Torres Strait Islands. We hypothesized that the extant PNG population expanded into the Torres Straits as an indirect effect of drought-proofing the southern Fly River coastal villages in response to El Nino-driven climate variability in the region (via the rollout of rainwater tanks and water storage containers). METHODOLOGY/PRINCIPAL FINDINGS: Examination of the mosquito's mitochondrial DNA cytochrome oxidase I (COI) sequences and 13 novel nuclear microsatellites revealed evidence of substantial intermixing between PNG's southern Fly region and Torres Strait Island populations essentially compromising any island eradication attempts due to potential of reintroduction. However, two genetically distinct populations were identified in this region comprising the historically extant PNG populations and the exotic introduced population. Both COI sequence data and microsatellites showed the introduced population to have genetic affinities to populations from Timor Leste and Jakarta in the Indonesian region. CONCLUSIONS/SIGNIFICANCE: The Ae. albopictus invasion into the Australian region was not a range expansion out of PNG as suspected, but founded by other, genetically distinct population(s), with strong genetic affinities to populations sampled from the Indonesian region. We now suspect that the introduction of Ae. albopictus into the Australian region was driven by widespread illegal fishing activity originating from the Indonesian region during this period. Human sea traffic is apparently shuttling this mosquito between islands in the Torres Strait and the southern PNG mainland and this extensive movement may well compromise Ae. albopictus eradication attempts in this region.

Is the expression of autogeny by Culex molestus Forskal (Diptera: Culicidae) influenced by larval nutrition or by adult mating, sugar feeding, or blood feeding?

Culex molestus Forskal is suspected to have been introduced into southern Australia during the 1940s. Investigations to determine factors influencing the expression of autogeny, the response of this mosquito to potential blood meals, and the subsequent influence on oviposition were undertaken. Immature mosquitoes raised at five feeding regimes had mortality rates, development rates, wing length, and autogenous egg raft size measured. All surviving female mosquitoes laid autogenous eggs but there was a significant difference between the mean number of eggs per raft. For mosquitoes raised at each of the feeding regimes, there was a significant linear relationship between the number of eggs per autogenous egg raft and wing length. Newly emerged mosquitoes were offered a blood meal (i.e., rodent) daily but no blood feeding occurred until the autogenous egg raft was laid. There was no statistical difference in the rate of autogenous oviposition or post-oviposition blood feeding between control or treatment groups. The results of this study indicate that Cx. molestus is perfectly adapted to subterranean habitats in close association with human habitation, but their preference to delay blood feeding until up to day 8 following emergence may reduce their relative importance as a vector of arboviruses.

Characterization of virulent West Nile virus Kunjin strain, Australia, 2011.

To determine the cause of an unprecedented outbreak of encephalitis among horses in New South Wales, Australia, in 2011, we performed genomic sequencing of viruses isolated from affected horses and mosquitoes. Results showed that most of the cases were caused by a variant West Nile virus (WNV) strain, WNV(NSW2011), that is most closely related to WNV Kunjin (WNV(KUN)), the indigenous WNV strain in Australia. Studies in mouse models for WNV pathogenesis showed that WNV(NSW2011) is substantially more neuroinvasive than the prototype WNV(KUN) strain. In WNV(NSW2011), this apparent increase in virulence over that of the prototype strain correlated with at least 2 known markers of WNV virulence that are not found in WNV(KUN). Additional studies are needed to determine the relationship of the WNV(NSW2011) strain to currently and previously circulating WNV(KUN) strains and to confirm the cause of the increased virulence of this emerging WNV strain.

Does the monomolecular film aquatain mosquito formula provide effective control of container-breeding mosquitoes in Australia?

The mosquito control potential of the silicone-based monomolecular film Aquatain Mosquito Formula (AMF) was investigated in field tests against the backyard mosquitoes Aedes notoscriptus and Culex quinquefasciatus. Plastic tubs, with and without emergent aquatic vegetation (Cyperus alternifolius), were sampled weekly for 2 wk prior to an application of Aquatain and up to 6 wk postapplication. The mean abundance of mosquito larvae and pupae was compared between pre- and postapplication periods as well as between treatment and control tubs. There was a significant reduction in the abundance of immature stages of both Ae. notoscriptus and Cx. quinquefasciatus within 48 h of application, and the mean weekly abundance of larvae of both species was significantly lower in treatment tubs compared with control tubs for up to 6 wk postapplication. Egg rafts, larvae, and pupae were not detected in treatment tubs until 5 wk postapplication. The results indicate that AMF holds great potential for mosquito control in backyard habitats.

Bed bugs: clinical relevance and control options.

Since the late 1990s, bed bugs of the species Cimex lectularius and Cimex hemipterus have undergone a worldwide resurgence. These bed bugs are blood-sucking insects that readily bite humans. Cutaneous reactions may occur and can start out as small macular lesions that can develop into distinctive wheals of around 5 cm in diameter, which are accompanied by intense itching. Occasionally, bullous eruptions may result. If bed bugs are numerous, the patient can present with widespread urticaria or eythematous rashes. Often, bites occur in lines along the limbs. Over 40 pathogens have been detected in bed bugs, but there is no definitive evidence that they transmit any disease-causing organisms to humans. Anemia may result when bed bugs are numerous, and their allergens can trigger asthmatic reactions. The misuse of chemicals and other technologies for controlling bed bugs has the potential to have a deleterious impact on human health, while the insect itself can be the cause of significant psychological trauma. The control of bed bugs is challenging and should encompass a multidisciplinary approach utilizing nonchemical means of control and the judicious use of insecticides. For accommodation providers, risk management procedures should be implemented to reduce the potential of bed bug infestations.

The importance of males: larval diet and adult sugar feeding influences reproduction in Culex molestus.

Culex molestus is an obligatory autogenous mosquito that is closely associated with subterranean habitats in urban areas. The objective of our study was to investigate the influence of larval and adult nutrition on the role of males in determining the expression of autogeny in Cx. molestus. Mosquitoes raised at low and high larval diets had sex ratio, wing length, mating rates, autogenous egg raft size, and hatching rates recorded. There was a higher ratio of males to females when raised at a low larval diet. Mean wing lengths of both males and females were significantly greater when raised at the high larval diet regime. Regardless of larval or adult diet, males mated with only a single female. Mosquitoes raised at the higher larval diet regimes developed significantly more autogenous eggs. However, the egg raft size was reduced when adult females were denied access to sugar. The results of this study indicate that the performance of males in the reproductive process is influenced by both larval diet and adult sugar feeding.

A review of the status and significance of the species within the Culex pipiens group in Australia.

The mosquito known in the northern hemisphere as Culex pipiens (a.k.a. Culex pipiens pipiens or Culex pipiens form pipiens) is not known from Australia. However, there are four species of the Culex pipiens group: two indigenous, Culex australicus and Culex globocoxitus, and two introduced, Culex quinquefasciatus and what is known locally as Culex molestus (? = Culex pipiens molestus or Culex pipiens form molestus), all four being members of the pipiens subgroup (= 'pipiens complex'). The species status of the indigenous Cx. australicus and Cx. globocoxitus in Australia appears to be accepted as legitimate; however, the true identity of the mosquito called 'Cx. molestus' in Australia remains contentious, even as its local profile has been increasing over the past 40 years. This paper provides an overview of the taxonomic and biologic knowledge of these species, and their public health significance as vectors of arboviruses in Australia.

Advice to travelers on topical insect repellent use against dengue mosquitoes in Far North Queensland, Australia.

Dengue outbreaks occur annually in Far North Queensland, Australia. Advice on topical insect repellents provided by health authorities rarely addresses the wide range of formulations and active ingredients currently registered for use in Australia. Recommendations on the use of registered products require review.

Bed Bugs: The Australian Response.

Australia has experienced a sudden and unexpected resurgence in bed bug infestations from both Cimex lectularius L. and Cimex hemipterus F. A survey in 2006 revealed that infestations had increased across the nation by an average of 4,500% since the start of the decade. In response, a multi-disciplinary approach to combat the rise of this public health pest was implemented and involved the coordinated efforts of several organizations. The key components of the strategy included the introduction of a pest management standard 'A Code of Practice for the Control of Bed Bug Infestations in Australia' that defines and promotes 'best practice' in bed bug eradication, the development of a policy and procedural guide for accommodation providers, education of stakeholders in best management practices, and research. These strategies continue to evolve with developments that lead to improvements in 'best practice' while bed bugs remain problematic in Australia.

Molecular phylogeny of edge hill virus supports its position in the yellow Fever virus group and identifies a new genetic variant.

Edge Hill virus (EHV) is a mosquito-borne flavivirus isolated throughout Australia during mosquito surveillance programs. While not posing an immediate threat to the human population, EHV is a taxonomically interesting flavivirus since it remains the only member of the yellow fever virus (YFV) sub-group to be detected within Australia. Here we present both an antigenic and genetic investigation of collected isolates, and confirm taxonomic classification of the virus within the YFV-group. Isolates were not clustered based on geographical origin or time of isolation, suggesting that minimal genetic evolution of EHV has occurred over geographic distance or time within the EHV cluster. However, two isolates showed significant differences in antigenic reactivity patterns, and had a much larger divergence from the EHV prototype (19% nucleotide and 6% amino acid divergence), indicating a distinct subtype or variant within the EHV subgroup.

The extinction of dengue through natural vulnerability of its vectors.

BACKGROUND: Dengue is the world's most important mosquito-borne viral illness. Successful future management of this disease requires an understanding of the population dynamics of the vector, especially in the context of changing climates. Our capacity to predict future dynamics is reflected in our ability to explain the significant historical changes in the distribution and abundance of the disease and its vector. METHODOLOGY/PRINCIPAL FINDINGS: Here we combine daily weather records with simulation modelling techniques to explain vector (Aedes aegypti (L.)) persistence within its current and historic ranges in Australia. We show that, in regions where dengue presently occurs in Australia (the Wet Tropics region of Far North Queensland), conditions are persistently suitable for year-round adult Ae. aegypti activity and oviposition. In the historic range, however, the vector is vulnerable to periodic extinction due to the combined influence of adult activity constraints and stochastic loss of suitable oviposition sites. CONCLUSIONS/SIGNIFICANCE: These results, together with changes in water-storage behaviour by humans, can explain the observed historical range contraction of the disease vector. For these reasons, future eradication of dengue in wet tropical regions will be extremely difficult through classical mosquito control methods alone. However, control of Ae. aegypti in sub-tropical and temperate regions will be greatly facilitated by government policy regulating domestic water-storage. Exploitation of the natural vulnerabilities of dengue vectors (e.g., habitat specificity, climatic limitations) should be integrated with the emerging novel transgenic and symbiotic bacterial control techniques to develop future control and elimination strategies.

Blood sources of mosquitoes collected from urban and peri-urban environments in eastern Australia with species-specific molecular analysis of avian blood meals.

To identify the hosts of mosquitoes collected from urban and peri-urban habitats in eastern Australia, 1,180 blood fed mosquitoes representing 15 species were analyzed by enzyme-linked immunosorbent assay and molecular techniques. Four common and epidemiologically important species could be classified according to their host-feeding patterns: Aedes aegypti was anthropophilic, Ae. vigilax was mammalophilic, Culex quinquefasciatus was ornithophilic, and Cx. annulirostris was opportunistic, readily feeding on birds and mammals. Mitochondrial cytochrome b DNA sequence data showed that more than 75% of avian blood meals identified from Cx. annulirostris collected from Brisbane, Newcastle, and Sydney originated from ducks (Order Anseriformes, Family Anatidae). More than 75% of avian blood meals from Cx. quinquefasciatus from Cairns belonged to one of three Passerine species, namely Sphecotheres vieilloti (figbird), Sturnus tristis (common myna), and Philemon buceroides (helmeted friarbird). This study demonstrates associations between vectors in Australia and vertebrate hosts of endemic and exotic arboviruses.