Cameron E. Webb

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

Abstract.  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 1948 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.

Does predation by the fish Gambusia holbrooki (Atheriniformes: Poeciliidae) contribute to declining frog populations?

Gambusia holbrooki is a small, aggressive fish introduced into Australia in 1925 to control mosquitoes. It has been suggested that this species may also prey on tadpoles and be a contributing factor in the decline of some Australian frog populations. We examined the influence of tadpole body size (10 mm. 15 mm and 20 mm). predator prey ratio (1 : 1, 1 :2 and 1 :4) and nutritional status of the predator on the level of predation by G. holbrooki on tadpoles of Limnodynasfas peronii. Unfed fish attacked all three size classes of tadpoles without any significant preference but did so more vigorously when the predator/prey ratio was densest. Predator/prey ratio had no significant overall effect on attack of tadpoles by fed fish but there was a preference for the smaller tadpoles during the first six hours of the experiment. Unfed fish also consumed more of the tadpoles they attacked than did the fed fish.Field surveys were carried out on 10 permanent water bodies in north-west Sydney to examine any correlation...

Aedes aegypti Population Sampling Using BG-Sentinel Traps in North Queensland Australia: Statistical Considerations for Trap Deployment and Sampling Strategy

Abstract BG-Sentinel mosquito traps were trialed as a tool for the rapid assessment (24-h collections) and routine monitoring (72-h collections) of adult Aedes aegypti L. populations in north Queensland. Analysis of Ae. aegypti collections using BG-Sentinels set in suburban Cairns for 24 h permitted the calculation of sample size for a range of precision levels. Clusters of houses with BG-Sentinels operating continuously for 15 d, with collections every 72 h, also permitted required sample size calculation. Evidence of Ae. aegypti spatial clustering at the house scale was revealed, with statistically significant effects detected for all collection days. Less variation was detected at each trap location, with only nine of 32 trap locations revealing significant clustering over time. Trap-out effects through continuous BG-Sentinel operation at a fixed location were absent. The findings support fixed position sampling at 72-h intervals for routine monitoring of Ae. aegypti populations in Cairns. Despite the relationship between collections of adult vectors and the incidence of disease remaining unknown, BG-Sentinel collections provide an alternative and less labor-intensive abundance measure for assessing risk of dengue virus transmission and success of dengue vector control programs.

A review of the epidemiological and clinical aspects of West Nile virus

The resurgence of West Nile virus (WNV) in North America and Europe in recent years has raised the concerns of local authorities and highlighted that mosquito-borne disease is not restricted to tropical regions of the world. WNV is maintained in enzootic cycles involving, primarily, Culex spp. mosquitoes and avian hosts, with epizootic spread to mammals, including horses and humans. Human infection results in symptomatic illness in approximately one-fifth of cases and neuroinvasive disease in less than 1% of infected persons. The most consistently recognized risk factor for neuroinvasive disease is older age, although diabetes mellitus, alcohol excess, and a history of cancer may also increase risk. Despite the increasing public health concern, the current WNV treatments are inadequate. Current evidence supporting the use of ribavirin, interferon α, and WNV-specific immunoglobulin are reviewed. Nucleic acid detection has been an important diagnostic development, which is particularly important for the protection of the donated blood supply. While effective WNV vaccines are widely available for horses, no human vaccine has been registered. Uncertainty surrounds the magnitude of future risk posed by WNV, and predictive models are limited by the heterogeneity of environmental, vector, and host factors, even in neighboring regions. However, recent history has demonstrated that for regions where suitable mosquito vectors and reservoir hosts are present, there will be a risk of major epidemics. Given the potential for these outbreaks to include severe neuroinvasive disease, strategies should be implemented to monitor for, and respond to, outbreak risk. While broadscale mosquito control programs will assist in reducing the abundance of mosquito populations and subsequently reduce the risks of disease, for many individuals, the use of topical insect repellents and other personal protective strategies will remain the first line of defense against infection.

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.

Vector Competence of Australian Mosquito Species for a North American Strain of West Nile Virus

Since the establishment of West Nile virus (WNV) into the United States, concern has arisen that this virus may also pose a serious threat to Australian biosecurity. The vector competence of 19 Australian mosquito species for a North American strain of WNV was evaluated. Mosquitoes collected from Cairns, Brisbane, and Sydney were exposed to blood containing 10(4.0+/-0.3) cell culture infectious dose(50)/mosquito WNV that was isolated from a crow during the 1999 New York outbreak. Mosquitoes were tested 12-15 days later to determine their infection, dissemination, and transmission rates. A number of Culex spp. demonstrated a high vector competence for this virus, with some populations of Culex annulirostris, the primary Australian Kunjin virus vector, displaying transmission rates up to 84%. Similarly, Cx. quinquefasciatus and Cx. gelidus were highly competent, with infection and transmission rates of >80% and >50%, respectively. Common Aedes spp., including Aedes notoscriptus, Ae. vigilax, and Ae. procax, were moderately susceptible, and some Verrallina spp. and Coquillettidia spp. were relatively refractory to infection. Thus, Australia possesses a number of competent mosquito species that could facilitate local transmission of WNV, should it be introduced.

Are commercially available essential oils from Australian native plants repellent to mosquitoes

Abstract While the use of topical insect repellents, particularly those containing synthetic active ingredients such as deet (N,N-diethyl-3-methylbenzamide), are a mainstay in personal protection strategies emphasized in public health messages, there is a growing demand in the community for alternative repellents, particularly those of botanical origin and thus deemed to be “natural.” This study evaluated the repellency of essential oils from 11 Australian native plants in 5% v/v formulations against Aedes aegypti, Culex quinquefasciatus, and Culex annulirostris under laboratory conditions. A blend of the top 3 performing oils was then compared with deet and a commercially available botanical insect repellent. All essential oils provided at least some protection against the 3 mosquito species, with the longest protection time (110 min) afforded by Prostanthera melissifolia against Cx. quinquefasciatus. Mean protection times against Ae. aegypti were substantially lower than those for the Culex spp. tested. Deet provided significantly longer protection against Ae. aegypti than both the 5% v/v blend of Leptospermum petersonii, Prostanthera melissifolia, and Melaleuca alternifolia (the 3 most effective oils) and the commercial botanical repellent. The results of this study indicate that these essential oils from Australian native plants offer limited protection against biting mosquitoes and that a blend of essential oils holds may offer commercial potential as a short-period repellent or under conditions of low mosquito abundance. However, it is important that public health messages continue to emphasize the greater effectiveness of deet-based repellents in areas with risks of mosquito-borne disease.

Arboviruses isolated from mosquitoes collected from urban and peri-urban areas of eastern Australia.

Abstract To determine the presence of arboviruses in mosquito populations from major urban areas of eastern Australia, a total of 67,825 mosquitoes, representing ∼60 species, was collected and tested from Cairns, Brisbane, and Sydney between January 2005 and April 2008. Mosquito pools were screened by inoculation onto mosquito cell cultures and the detection of viral antigen using a panel of flavivirus and alphavirus monoclonal antibodies in an enzyme-linked immunosorbent assay. Suspect positive samples were confirmed using virus-specific real-time reverse transcriptase–polymerase chain reaction assays. No flaviviruses were detected, but 2 alphaviruses were isolated from mosquito pools collected from Cairns, with 1 Barmah Forest virus isolate from a pool of 100 Aedes vigilax and 1 Ross River virus isolate from a pool of 83 Verrallina carmenti. In addition, a single Aedes alternans collected from Sydney yielded an isolate most similar to Stretch Lagoon virus, a newly described virus from the genus Orbivirus. These results suggest that during the study, arboviruses were circulating at a low level in the areas sampled. The findings from this study will promote public health awareness of the risk of arboviruses in urban areas, leading to more informative public health campaigns to safeguard the Australian public.

Integrated morphological and molecular identification of cat fleas (Ctenocephalides felis) and dog fleas (Ctenocephalides canis) vectoring Rickettsia felis in central Europe.

Fleas of the genus Ctenocephalides are the most common ectoparasites infesting dogs and cats world-wide. The species Ctenocephalides felis and Ctenocephalides canis are competent vectors for zoonotic pathogens such as Rickettsia felis and Bartonella spp. Improved knowledge on the diversity and phylogenetics of fleas is important for understanding flea-borne pathogen transmission cycles. Fleas infesting privately owned dogs and cats from the Czech Republic (n=97) and Romania (n=66) were subjected to morphological and molecular identification and phylogenetic analysis. There were a total of 59 (60.82%) cat fleas (Ctenocephalides felis felis), 30 (30.93%) dog fleas (Ctenocephalides canis), 7 (7.22%) European chicken fleas (Ceratophyllus gallinae) and 1 (1.03%) northern rat flea (Nosopsyllus fasciatus) collected in the Czech Republic. Both C. canis and C. felis felis were identified in Romania. Mitochondrial DNA sequencing at the cox1 gene on a cohort of 40 fleas revealed the cosmopolitan C. felis felis clade represented by cox1 haplotype 1 is present in the Czech Republic. A new C. felis felis clade from both the Czech Republic and Romania is also reported. A high proportion of C. canis was observed from dogs and cats in the current study and phylogeny revealed that C. canis forms a sister clade to the oriental cat flea Ctenocephalides orientis (syn. C. felis orientis). Out of 33 fleas tested, representing C. felis felis, C. canis and Ce. gallinae, 7 (21.2%) were positive for R. felis using diagnostic real-time PCR targeting the gltA gene and a conventional PCR targeting the ompB gene. No samples tested positive for Bartonella spp. using a diagnostic real-time PCR assay targeting ssrA gene. This study confirms high genetic diversity of C. felis felis globally and serves as a foundation to understand the implication for zoonotic disease carriage and transmission by the flea genus Ctenocephalides.

Ross River Virus: Many Vectors and Unusual Hosts Make for an Unpredictable Pathogen.

While most mosquito-borne viruses are associated with a narrow range of vector and reservoir host species, some pathogens have much larger vector and host assemblages. One such group is the Alphaviruses (including chikungunya virus [CHIKV]), with Ross River virus (RRV), endemic to Australia, providing a fascinating example of the complicated relationship between vector and reservoir host species across different environments (Fig 1). RRV is responsible for the most commonly reported mosquito-borne disease in Australia, and as both a reservoir host and vector generalist, the virus has complex spatial and temporal activity that makes outbreak prediction, vector and pathogen surveillance, and public health risk mitigation strategies difficult. Here, we review the unique ecology of RRV and the challenges it presents for local health authorities. Fig 1 There are complex relationships between the vectors and the zoonotic reservoirs of Ross River virus across coastal, inland, and metropolitan regions of Australia. Ross River Virus Disease Ross River virus disease (also commonly known as Ross River Fever) is not fatal. However, the associated arthralgia can be seriously debilitating. While there are a wide range of disease symptoms, they typically include arthritic joint pain, usually of the peripheral joints, which affects 83%–98% of patients; fatigue and rash, both of which affect over 50% of patients; and fever, which affects 20%–60% of patients [1]. The severity of symptoms varies, as does their duration, which can range from a few weeks to several months [2]; several studies indicate that chronic joint pain affects over 50% of RRV disease patients, which can persist for years after diagnosis [1]. The public health impacts of RRV disease are significant: it is estimated to cost Australia at least US