About cameronwebb

Dr Cameron Webb is a Medical Entomologist with NSW Health Pathology and The University of Sydney. His research is focused on the management of mosquitoes and mosquito-borne disease risk associated with constructed, rehabilitated and natural wetlands in Australia.

Unintended consequences of wildlife conservation, could more frogs mean more mosquitoes?

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We need to do all we can to protect our urban wildlife but what if the ways we do that increases mosquito risk? PhD candidate Jayne Hanford will be presenting the results of her research at the Ecological Society of Australia conference in Tasmania.

Mosquitoes can share their aquatic habitats with many other animals.

The 2019 Ecological Society of Australia conference will be held in Tasmania, 24-29 November. The conference theme, “Ecology: science for practical solutions”, is closely aligned with much of the work my collaborators and myself undertake each summer. We’re trying to ensure that recommendations on managing the pest and public health risks associated with mosquitoes is informed by the best available science.

Practical solutions to the challenges of balancing mosquito management while also ensuring positive outcomes from the environment too.

Jayne Hanford will be presenting her research in the “Field-based manipulative experiments for under-standing environmental change” symposium. She has been studying the aquatic biodiversity of urban wetlands as part of her PhD. This recent project aimed to determine what impacts management of urban wetlands to enhance conditions for local frog populations may have on local mosquito populations.

The research was undertaken at Sydney Olympic Park where an extensive network of freshwater ponds make up Narawang Wetlands. These wetlands are home to the endangered Green and Golden Bell Frog (Litoria aurea) but they’re also home to the plague minnow (Gambusia holbrooki). The plague minnow is essentially the cane toad of Australia’s waterways, introduced around 100 years ago to control mosquito populations, this aggressive predatory fish has impacted much of our local aquatic life, especially frogs. Populations of this fish need to be managed to enhance conditions for local frogs and, especially, their tadpoles.

Jayne has already found that mosquitoes avoid water bodies where the fish are found. The next step was to see how the seasonal draining of the local wetlands impacted the abundance and diversity of mosquito populations.

Immature mosquitoes and other aquatic macroinvertebrates were sampled from drained and undrained ponds within the wetland network. Once the drained ponds had been at least partially reflooded, mosquitoes were more likely to be found. This wasn’t too surprising given the results of previous experiments. Mosquitoes like to avoid habitats with fish but also, if they do lay eggs in those habitats, mosquito larvae aren’t likely to last long!

The results are useful for those authorities looking to manage waterbodies for wildlife conservation. Removal of the plague minnow may result in more suitable conditions being created for mosquitoes. It may be good for the frogs but we also know that their tadpoles aren’t eating the mosquito larvae. Strategies may be required to manage the pest and public health risks associated with local mosquitoes in these habitats.

You can catch Jayne’s work in the poster session but also as part of the symposium at 3pm on Monday 25 November in Chancellor 5!

The full abstract for Jayne’s presentation is below:

Unintended impacts of managing urban wetlands for conservation

Jayne K. Hanford1,2*, Cameron E. Webb2,3 , Dieter F. Hochuli1

1 School of Life and Environmental Sciences, The University of Sydney, Australia; 2 Marie Bashir Institute for Infectious Diseases and Biosecurity, The University of Sydney, Australia; 3 Medical Entomology, NSW Health Pathology, Westmead Hospital, Westmead, Australia.

Urban wetlands are increasingly being recognised as valuable conservation resources that support significant biodiversity. Concerns around the pest and public health risks of mosquitoes will restrict how we manage these wetlands, as outbreaks of mosquito-borne diseases fuel public fear and foster dislike of mosquitoes. Understanding the ecological and public health consequences of wetland management practices is vital to maximise the conservation value of urban wetlands without negatively impacting public health. Our aim was to determine how wetland management to benefit a threatened species affects mosquitoes and aquatic biodiversity. A group of six urban wetlands in Sydney, Australia, were drained to reduce the abundance of an invasive fish, Gambusia holbrooki, and then refilled to provide breeding habitat for a threatened frog, Litoria aurea. We collected and compared aquatic macroinvertebrates, mosquito larvae, and mosquito adults from these refilled wetlands, and six adjacent undrained wetlands, on four occasions across summer and autumn. Wetland draining had a significant effect on aquatic macroinvertebrates and larval mosquitoes, although differences between drained and undrained wetlands decreased over time. Draining did not affect adult mosquito assemblages associated with the wetlands. The number of constructed and rehabilitated wetlands in urban areas continues to grow, and while conserving threatened habitats and species is imperative, our results highlight how wetland management can impact non-target species with potentially negative effects on humans. It is vital that future design and management of urban wetlands around the world also considers the impact on vectors of human disease.

 

If you’re at the conference, why not join the conversation on Twitter using the official conference hashtag #ESAus19 or reaching out to Jayne or myself!

 

 

 

 

 

 

School is out (but don’t let mosquitoes bite)

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“School’s out forever
School’s out for summer
School’s out with fever
School’s out completely” Alice Cooper

The end of the school year for students completing high school is here. School is out so the partying can start! Lets hope fever isn’t part of the story too.

For many students, this means traveling overseas for “schoolies” celebrations. The health and wellbeing of students attending “schoolies” has been front of mind of many parents and local authorities. This isn’t surprising given the risk taking behaviours many engage in.

Health authorities are often warning about potential health risks. However, with many travelling overseas for end of school celebrations, a range of mosquito related health risks may be experienced. The steps taking to avoid mosquito bites at home need to be changed if travelling to regions of the world where different mosquitoes and more serious mosquito-borne pathogens are found.

Overseas travel brings different risks

The risks may be significantly greater if travelling overseas to tropical regions such as SE Asia and the Pacific. Bali is a particularly popular party destination and also one with a high risk of mosquito-borne disease, especially dengue.

There are other mosquito-borne diseases to be wary of. Fortunately, the steps taken to avoid dengue will also assist in preventing exposure to Zika or Chikungunya too. There are occasionally cases of Japanese encephalitis virus in Australian travellers but they are rare.

Some regions will have a risk of malaria too. If you’re traveling to one of those regions, best consult your local travel health professional.

One of the main differences Australian travellers will face when spending time in regions prone to dengue outbreaks is that the mosquitoes that spread the virus bite during the day. We’re familiar with the local warnings to avoid mosquitoes at dawn, dusk, and overnight here in Australia. The mosquito that drives dengue outbreaks is most commonly Aedes aegypti, a mosquito that bites during the day.

We’re also likely to reach for the mosquito repellent when mosquitoes are abundant, as they often are, during summer coastal holidays. Bu Aedes aegypti is generally not that abundant. Don’t wait to notice the mosquitoes biting before putting on repellent.

These mosquitoes are also most likely to be present around urban areas and villages. These mosquitoes aren’t found in wetlands, they like living in water-filled containers where people live. Don’t think that just because you aren’t visiting wetlands or rainforests that there won’t be a risk of mosquito-borne disease!

Here are three tips on protecting yourself against mosquito-borne disease if you’re travelling overseas for “schoolies” celebrations:

1. Protect yourself against day-biting mosquitoes. Apply a repellent before breakfast and apply it like sunscreen. An even cover of exposed skin is required. Don’t bother applying it to clothing or “spraying it around the room”, that won’t protect you from bites.

2. Take repellent with you. Australian repellents must be registered with the Australian Pesticides and Veterinary Medicines Authority who test for efficacy and safety. You may not be able to get a hold of similar products overseas. Use a repellent that contains either diethyltoluamide (aka DEET) or picaridin; these formulations are readily available in local supermarkets and pharmacies. Oil of Lemon Eucalyptus is useful too but these formulations are often difficult to find.

3. Even if you’re staying at an expensive resort, where mosquito control is probably in place, take insect repellent for those day trips to local villages or markets. These are places and times where you may be exposed to “dengue mosquitoes”.

Don’t forget to check out Smart Traveller before heading off to Bali…or anywhere else for that matter. They provide all the updates on health and security concerns.

Photo at top of this post by Jed Villejo on Unsplash

How does a mosquito researcher mark the passing of seasons?

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Winter has come and gone for another year. For many people it means packing away the footy boots and starting to shop for swimwear. What about mosquito researchers? How does the passing of seasons change their work?

One of the things I love about my job (and occasionally loathe) is that it is primarily driven by the weather. On a weekly basis, i have to keep an eye on local rainfall, temperature fluctuations, and tidal cycles. All these things have a strong influence on local mosquito abundance and diversity. Add extreme weather events into the mix and things can become quite unpredictable! I can’t ignore the wind either, ever tried catching a mosquito in a howling gale?

Mosquitoes can be found right through the year in Sydney. Generally though, the year for me is divided into a series of milestones.

Goodbye winter, hello spring (plus migratory birds, daylight saving and end to rugby league)

There is a sound I’ve come to dread in recent years. The “awk-awk-awk…” of the channel-billed cuckoo. This migratory bird moves into Sydney from New Guinea and Indonesia around August and it’s call is a kind of siren that warns of the upcoming mosquito season. Once I start hearing those calls, I better start planning the field work season ahead.

The long weekend in October, that coincides with an end to the rugby league season, means field work planning should really be in full swing.

If these birds and farewell to footy season aren’t strong enough reminders, once daylight savings kicks in from early October, I know I’ve got to start moving!

In Sydney, “mosquito season” has historically run from the start of November through to the end of April. Field work is well underway by the time the Melbourne Cup is run and won.

One of the interesting trends in recent years has been are ever increasing early start to mosquito season. While the start of spring if often punctuated by occasional hot conditions, mosquitoes have usually be slow to kick into gear. It isn’t until late spring that serious pest problems are reported. However, in recent years, the start of the season has got earlier and earlier.

It is becoming so common to see boosts in mosquito numbers in late September and early October that start dates of mosquito control and surveillance programs are moving forward.

Say goodbye to summer holidays

My summers are dictated by tides and rainfall. These are the events that bring water into local wetlands and trigger hatches of mosquitoes. My schedule will shift from year with differences in the timing of king tides and the pattern of rainfall.

What these shifts in environmental conditions mean is that I can be in the wetlands on Christmas Day or New Years Eve. Sometimes mosquito season sucks.

The Australia Day holiday is often an important date, especially if it occurs just as mosquito populations are on the rise or there is increased activity of mosquito-borne pathogens. I’m often dealing with plenty of media enquiries at this time.

The kids are back in school by February and Sydney is well and truly out of holiday mode. For me, this means much earlier and later working times as I try to dodge peak-hour traffic getting from field site to field site. There is nothing more likely to take the gloss off some early morning time in the wetlands than spending twice as long as usually in crawling traffic as I try to get mosquitoes back to the laboratories.

Easter bunnies, chocolate eggs, and outbreaks of mosquito-borne disease

While it may be tempting to think the Easter Long-weekend may mark the end of the mosquito season and chocolate egg fueled celebrations can commence, it is important to keep in mind that Easter moves about from year to year. This can have important implications for mosquito monitoring and public health interventions.

When the Easter falls at the end of March or early April, there can be greater mosquito-borne disease risks. In many areas of Australia, mosquito-borne disease caused by Ross River virus is more commonly reported in autumn than summer or spring. Depending on the temperatures, tides, and rainfall, there can be very abundant populations of mosquitoes and elevated mosquito-borne disease risk just as everyone is taking off on long-weekend camping trips or school holidays. In 2020, with Easter falling in the middle or April, the risks shouldn’t be too high (but lets just wait to see what the weather and mosquito populations are like).

An end to daylight savings is usually a pretty good marker. I’m often caught out the first week after our clocks go back and need a head lamp or torch to finish setting mosquito traps! However, the real end point to mosquito season is typically ANZAC Day. While there may be some mosquitoes about through to the early stages of May, it is usually only under exceptional circumstances (at least around Sydney).

Bring on the cold (and report writing)

Between May and September, temperatures get too cold for mosquitoes to be a problem. It is the cold overnight temperatures (as opposed to the occasional warm daily temperatures) that influence mosquito populations. As soon as we start getting overnight minimums consistently dropping below 10oC, mosquito activity generally starts to decline.

Winter is spent writing, teaching, sleeping, conferences, planning, and trying to sneak in some kind of holiday….

If you’re a scientist, how do the seasons shift your schedule throughout the year? Join the conversation on Twitter!

 

 

 

Global Health Security 2019 – Mosquito threats and community engagement

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While we can embrace technology to track pathogens and diseases, engaging the community to be more aware of the risk and the ways to avoid them will be critical in reducing the public health burden across the globe. This was a key message repeated again and again throughout the sessions at the inaugural Global Health Security conference in Sydney.

The event around 800 delegates representing academia, local, national and international governmental and non-governmental organizations, public and animal health and security professionals, and the private sector. There were representatives from over 65 countries.

I had the opportunity to contribute in a couple of sessions, firstly the ‘Emerging Infectious Diseases in a Changing Global Environment’ workshop at the university of Sydney. This was co-presented by the Marie Bashir Institute for Infectious Diseases and Biosecurity and CREID – NHMRC Centre of Research Excellence in Emerging Infectious Disease. It was described as an “event is an opportunity for policy makers, public health and clinical researchers, veterinarians, scientists, and WHO representatives to come together and define the health security issues related to emerging infectious diseases (EIDs) and antimicrobial resistance (AMR) in the Asia-Pacific region.”

I spoke about mosquitoes in Australian cities and the challenges facing the management of issues associated with urban planning, constructed and rehabilitated wetlands, endemic mosquito-borne disease risk, and exotic mosquito threats. A little nervous having the Chief Medical Officer of Australia (Prof Brendan Murphy) in the front row, along with representatives of WHO and CDC but a wonderful opportunity to share my research and perspectives on these local issues.

The following day, I spoke in the “Challenges with Zoonotic Diseases” session alongside Elpidius Rukambile and Berihun Afera Tadele. An interesting session (chaired by Siobhan Mor) that, through the panel discussion, highlighted the importance of community engagement, as well as communications between policy makers and those “on the ground” in improving public health outcomes in the “one health” space.

I spoke about the issues surrounding exotic mosquito threats in Australia with a focus on the results of recent work on the far north coast of NSW. The work we did there highlighted the need for cooperation between all levels of government but also the critical importance of engaging the local community. Notwithstanding the effort required to go from property to property searching for introduced mosquitoes, such as Aedes aegypti or Aedes albopictus, understanding the role of the community in this response provided essential. Successful local eradication of any introduced mosquito will require assistance from the local community.

The abstract of my presentation is below:

Building capacity to address the unexpected challenges associated with the emerging threat of exotic mosquitoes in Australia

Webb C (1,2),  Doggett S (2), Piazza K (3), McNicoll D (3), Sly A (4), Neilson J (4), Dean A (5), Bethmont A (6).

1 University Of Sydney, Westmead NSW, Australia; 2 NSW Health Pathology, Westmead NSW, Australia; 3 Tweed Shire Council, Tweed Heads NSW, Australia; 4 Department of Agriculture and Water Resources, Canberra ACT, Australia; 5 University of Queensland, Brisbane QLD, Australia; 6 NSW Health, North Sydney NSW, Australia

Introduction. Ongoing evolution of trade pathways increases the risk of exotic mosquitoes, especially Aedes albopictus and pesticide resistant Ae. aegypti, establishing or expanding their range in Australia. This highlights the need for health authorities to develop strategic response plans considering different risk scenarios. Context and Aim. Key challenges to exotic mosquito response in Australian include capacity at local government level and community acceptance of measures. Several strategic initiatives were used to study these challenges in the NSW Northern Rivers region. Method. Field exercises were undertaken with representatives of 11 local and state authority stakeholders, surveying approximately 300 residential properties for potential mosquito habitats. A survey of community attitudes to mosquito threats and responses was also conducted, with over 700 responses collected. Findings. Surveys found almost 4,000 actual and potential container breeding sites, demonstrating potential for exotic mosquito establishment and subsequent need to manage local transmission risks of pathogens including dengue, chikungunya and Zika viruses. Surveys of community attitudes found significant community resistance to required mosquito control activities, indicating responses would be challenging and need strategic planning. Innovative contribution to policy and practice. Strategic response plans must address mosquito biology but also not underestimate the need for active community engagement.

Overall, it was a wonderful meeting. It was, however, unfortunate that I couldn’t spend as much time in sessions as I would have liked. There were plenty of tweets so check in on the hashtag #GHS2019. There is also the very important “The Sydney Statement on Global Health Security” to come out of the meeting, please check it out.

Were you at the meeting? What did you think? Join the conversation on Twitter.

 

 

How far do mosquitoes fly?

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There is no single answer to one of the most commonly asked questions I’m asked. “How far does a mosquito fly?” Notwithstanding those blown long distances by cyclonic winds or transported in vehicles, the distances travelled by mosquitoes varies greatly from mosquito to mosquito. But how do scientists work it out?

My latest published research demonstrates that Australia’s saltmarsh mosquito (Aedes vigilax) flies many kilometres from urban estuarine wetlands. This has great implications for improving our understanding of their role in outbreaks of mosquito-borne disease as well as designing mosquito control programs.

There are a few different ways you can work out how far mosquitoes fly.

Firstly, given we know that mosquitoes are closely associated with certain habitats, it is sometimes possible to track back collections of mosquitoes to their preferred habitats. For example, knowing a coastal wetlands mosquito is found many kilometres away from the nearest estuarine wetland may indicate it disperses widely.

Secondly, scientists can conducted mark-release-recapture experiments. In these studies, mosquitoes are marked with some kind of substance, released, and then specimens collected in traps operated in a surrounding network can be checked to see how many of those marked mosquitoes have been recaptured and how far they’ve travelled.

In this recently published study, I marked over 200,000 Aedes vigilax with a fluorescent powder (usually used to create paint) and released them close to their larval habitats in estuarine wetlands along the Parramatta River. For the next week, I set dozens of traps around the local area hoping to recollect some of those marked mosquitoes. By scanning the mosquitoes under a UV light, the marked mosquitoes were (relatively) easily identified.

Recapture rates for these types of experiments are notoriously low. While I was only able to recapture less than 1% of those marked mosquitoes released, marked mosquitoes were recaptured many kilometres from their release point. The results demonstrated that these mosquitoes of pest and public health concern disperse so widely from saltmarsh and mangrove habitats that their impacts can be felt quite widely, highlighting the need for targeted mosquito control to minimise potentially widespread pest and public health impacts.

There is an important implication here for current “mosquito aware” urban planning strategies. The incorporation of “buffer zones” between residential developments and mosquito habitats is often proposed but this research clearly demonstrated that this strategy just isn’t practical when it comes to saltmarsh mosquitoes. They just fly too far!

While this study demonstrated marked mosquitoes were travelling up to 3km, other work I’ve done has highlighted how differently the dispersal ranges of mosquitoes can be.  In a study of yellow fever mosquitoes (Aedes aegypti) in far north QLD, we found marked mosquitoes were only traveling between 100-200m. Similarly, other work with Australian backyard mosquitoes (e.g. Aedes notoscriptus) has shown they don’t fly more than 200m. That’s still enough to fly over from your neighbour’s backyard full of mosquito breeding opportunities.

There is a practical application to this work for the management of dengue in far north QLD. Knowing that the mosquitoes involved in transmission are flying less than 200m, mosquito surveillance and control can be concentrated around the homes of those infected individuals. A great example of how understanding mosquito biology can better inform cost-effective response strategies.

There is still plenty to learn about the dispersal of mosquitoes in Australia. I’ve got some ideas so if you’re looking for a research projects, get in touch!

Check out the Journal of Medical Entomology for the full paper titled “Dispersal of the Mosquito Aedes vigilax (Diptera: Culicidae) From Urban Estuarine Wetlands in Sydney, Australia“.

The abstract is below:

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.

Join the conversation on Twitter or check out some of the other articles I’ve written on mosquitoes and other biting insects at The Conversation. You can also learn more about Australia’s wonderful mosquitoes in the award winning field guide available from CSIRO Publishing.

 

 

 

The long hot summer of mosquito and media wrangling

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“Webb’s a mosquito researcher with NSW Health Pathology, and while it may sound like potentially the worst job in the world to the rest of us, it’s important work.” – Ten Daily, 14 Jan 2019.

Every summer I’m required to juggle those pesky mosquitoes and help out with requests from media. Over the past 6 months or so I’ve responded to about 70 media requests and here is a round up of some fun highlights and other bits and pieces.

There was a wide range of media requests this summer, from morning TV through to talkback radio, podcasts and live interviews via Skype. There was once a time when the only acceptable way to do a radio interview was via landline connected phone. This summer I did interviews via mobile, Skype, and various  smartphone apps! Times are a changing.

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A fun segment on Channel 7’s ‘Sunrise’ breakfast show on why mosquitoes bite some people more than others; always a challenge taking in a cage a live mosquitoes to the studio, especially travelling in via public transport!

A hot and dry summer must mean less mosquitoes, right?

The outlook for the 2018-2019 “mosquito season” was for it to be fairly routine. The Bureau of Meteorology was predicting a hot and dry summer under the influence of El Nino. At the time I wrote a piece for The Conversation highlighting that just because it was dry, that didn’t mean we wouldn’t see plenty of mosquitoes.

In coastal regions of Australia, tidal flooding of local wetlands often offsets any impact due to lack of rainfall. Mosquitoes such as Aedes vigilax certainly respond well and there were some very high mosquito numbers recorded in early spring. Usually, the media interest in mosquitoes starts increasing once the politicians break for the summer, this year there was plenty of interest early on!

NSW Health also issued a media release to get the community thinking about the potential mosquito impacts ahead of the summer holiday period and asked me to be the spokesperson. These warnings often prompt a different range of media interest, usually news bulletins for radio. Unlike the traditional radio interviews in which you’re responding to the host’s questions, only “grabs” (short statements regarding the topic) are required. I’ve learned there is a fine art to being concise in these statements and it pays to give some thought to what you’ll say ahead of calling up the news desk!

Some of the media coverage in early summer was less about bites and more about why mosquitoes disturb your sleep! I spoke with Channel Ten about how you can beat these bedroom buzzers! Here are some tips on beating the buzz of mosquitoes in the bedroom.

These concerns about mosquitoes in the bedroom prompted questions about the suitability of mosquito coils as a person protection measures. I’d written about this issue before but there was also some media coverage at the Daily Telegraph and Sydney Morning Herald.

There was also a funny segment on The Project:

Warm weather, warm blood, and hungry mosquitoes

As summer kicked in, I did a bunch of “pre-season” interviews about the outlook for the mosquito activity ahead. One of them was with the Sydney Morning Herald. There was also a piece in Illawarra Murcury on the mosquitoes around Newcastle. I even chatted with ABC Illawarra about the mosquitoes bringing in the new year along the NSW coast. I also chatted with the team at the Daily Mail. Also the Daily Telegraph.

Once summer really hit (and the mosquitoes really started biting following heavy rains), everyone’s mind turned to one of the most commonly asked questions….why do mosquitoes bite me more than my friends? You can check out my contribution to a story by ABC Science below:

The usual coverage of mosquito impacts during the Australia Day holiday also popped up. Will my diet influence the likelihood of being bitten? I spoke with Channel Ten. The University of Sydney media team also put out a piece on why what you eat or drink makes not difference when it comes to stopping mosquito bites. A story picked up and republished by ABC News.

Combining fieldwork and media requests

“Ballina council is calling in an expert to hunt for some ladies – Medical Entomologist Dr Cameron Webb will visit the area next week in search of blood sucking girls.” – EchoNet Daily, Ballina

While undertaking some work for Ballina Shire Council on the NSW far north coast, I helped out managing a few media requests associated with local mosquito problems and the work of council. It was fun squeezing in some print, TV, radio, and social media activities between the work in the wetlands.

I also participated in a “Q and A” on the Ballina Shire Council Facebook page where residents could ask questions about how best to protect themselves from mosquitoes. See here.

Mosquito-borne disease in the city

The detection of Ross River virus in mosquitoes around Sydney sparked some additional interest from media (and anxiety from local community). Coverage in Sydney Morning Herald here.  It prompted me to write an article about what the actual health implications were of finding the pathogen in a heavily urbanised areas such as the Parramatta River compared to the more bushland dominated Georges River.

The issue of wildlife and their role in urban transmission cycles of Ross River virus is always a tricky one. How do you balance wildlife conservation and mitigation of health risks? Together will colleagues I wrote about this at The Conversation.

The media coverage of the Ross River virus detection provided an opportunity for NSW Health Pathology to share some insights into how we research local mosquitoes and the pathogens they’re carrying. See below for a short video from the mangroves along the Parramatta River.

Declining insects, increasing mosquitoes, and the need to spray our backyards

One of the other stories bubbling along during the last year or so were the reports of declining global insect populations. I first spoke to the media about this issue back in early 2018. I was quoted in a couple of other stories too, clearly there was a lot of interest in this issue. This story gained plenty of attention and I spoke with various radio and print media about this challenge were facing with potential insect declines and how we can measure them. I even wrote an article about whether mosquitoes may be in decline too!

I spoke about this issue, and more generally about mosquitoes on an episode of the Science on Top podcast too.

There has been suggestions that insecticides may be contributing to declining insect populations. Earlier in the year, I was one of the coauthors of a paper that called for the need to better understand integrated pest control in our cities and become less reliant on insecticides. There was also an associated article at The Conversation. This was also republished at Domain.

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Floods in the north, floods in the south

The incredible flooding around Townsville in far north QLD created some major concern. Despite some initial concerns about increased mosquito risk, there weren’t any substantial increases in mosquito-borne disease reported. I spoke to ABC News about the potential risks.

The flooding that did trigger a big boost in mosquito numbers occurred in SE QLD and northern NSW. Local wetlands were inundated by tides and rain, resulting in some phenomenal numbers of mosquitoes in early autumn. I spoke to ABC and Great Lakes Advocate about the climatic factors that triggered this unusual mosquito activity.

Everyone was on weather watch late in the season too. A few extra downpours prompted concerns about more increases in autumn mosquito populations. I spoke with Sydney Morning Herald after a particularly wet weekend in March.

Finally, I helped the Australian Academy of Science make a video exploring why mosquitoes bite and how to stop them!

Join the conversation on Twitter, did you catch me talking mosquitoes this summer? Did it help you protect your family from mosquito bites?

Could a boombox (playing Skrillex) save you from mosquito bites?

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There has been quite a buzz about some new research that suggests the music playing at your next backyard party may keep the mosquitoes at bay. Could it actually be true?

“As music is loved by many people, the development of music-based anti-mosquito control measures may represent an appealing alternative to strategies involving the use of harmful chemical insecticides.” – Dieng et al. 2019

Are mosquitoes monsters or sprites?

The study was recently published in the peer-reviewed journal Acta Tropica. The researchers (including one of my previous PhD students) exposed mosquitoes to the song “Scary Monsters And Nice Sprites” by U.S. electronic dub-step artist Skrillex while recording how long it took Aedes aegypti (these are the mosquitoes that transmit dengue viruses) to find a blood meal, how long they spent feeding, as well as tracking how much time was spent mating. The “blood meal” was provided by a restrained hamster and all experiments were conducted in the laboratory.

Adults entertained with music copulated far less than their counterparts kept in the environment where there was no music entertainment.” – Dieng et al. 2019

Unfortunately, the researchers didn’t explain why they decided to use this particular song, only describing it as “…characterized as noisy based on the resulting vibragram and strong sound pressure/vibration with constantly rising pitches”. It would have been interesting to include a couple of other songs in the testing too. Perhaps something a little more downbeat?

Once they had the song playing (ensuring the speakers weren’t located close enough to cause vibration to the cage containing mosquitoes), mosquitoes were released into the cage and behaviour was recorded for 10 minutes. Researchers recorded the time to first blood feeding attempt, number of blood feeding events, and number of mating events.

The results were interesting. Mosquitoes took longer to find a host, spent less time blood feeding and mated less often when exposed to the music. These differences in each measurement were statistically different too.

What does this mean for prevention of mosquito-borne disease?

This study has received plenty of media attention. See here and here and here. I spoke to ABC Sydney about it too (tune in from the 1:07).

While the results demonstrated some reduced likelihood of biting, it shouldn’t be interpreted that playing Skrillex’s music will protect yourself from mosquito bites. The reduced likelihood was pretty short lived, you’re pretty much guaranteed to get bitten despite the dub step blasting from the boombox.

There has always been an interest in understanding how sound impacts the behaviour of mosquitoes. Ultrasonic insect repellents have been sold in one way or another for a couple of decades. Now you can download apps to your smartphone that purport to use sound to repel mosquitoes. There really is no evidence that sound can provide protection from mosquito bites.

Digging deeper into the “Skrillex study”, the results indicate that even though there may be less chance you’ll be bitten while listening to this music, you’ll still be bitten. Even over the relatively short exposure periods in the laboratory study, the mosquitoes were still biting. Notwithstanding your tolerance of Skrillex’s brand of electronic music, who knows how loud you need to be playing it or how shifts in songs (and their associated pitches, frequencies, buzzes, and beats) may change the activity of local mosquitoes.

To prevent mosquito-borne disease, you need to stop all bites, not just some of them. Topical insect repellents will still provide better protection. Keep in mind that even a low dose DEET-based insect repellent will prevent all bites from Aedes aegypti for a few hours in laboratory testing.

See the full paper here:

Dieng, H., Chuin, T.C., Satho, T., Miake, F., Wydiamala, E., Kassim, N.F.A., Hashim, N.A., Vargas, R.E.M. and Morales, N.P., 2019. The electronic song “Scary Monsters and Nice Sprites” reduces host attack and mating success in the dengue vector Aedes aegypti. Acta Tropica. [online]

 

Join the conversation on Twitter, if music could keep mosquitoes away, what music would you want that to be?

Photo at the top of this article by Eric Nopanen on Unsplash

Why has mosquito-borne disease hit Tasmania?

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Are there even mosquitoes in Tasmania?

You could be forgiven thinking that Australia’s southern most state, Tasmania, is probably free of mosquitoes and certainly the chances of an outbreak of mosquito-borne disease would be rare. Is it even possible?

Health authorities in Tasmania have recently warned residents and visitors to avoid mosquito bites following reports of locally acquired infections of Barmah Forest virus.

Ross River virus may be the best known of Australia’s local mosquito-borne pathogens but Barmah Forest isn’t far behind. Infection can cause an illness similar to Ross River virus disease, its typically marked by joint pain and inflammation, fatigue, rash, headaches, muscle pain, fever and chills.

Fortunately the disease is not fatal.

There have been outbreaks of Barmah Forest virus in many parts of Australia, not just in the tropical north. Significant outbreaks have occurred in NSW and southern Western Australia.

While Tasmania may be cold, that doesn’t mean there aren’t mosquito problems. There is a range of mosquitoes found in Tasmania, including Aedes camptorhynchus, a key species of pest and public health concern. This mosquito is closely associated with coastal estuarine wetlands, especially saltmarsh environments.

Tasmania has also had outbreaks of mosquito-borne disease. More than 100 people were infected with Ross River virus in the coastal region just to the east of Hobart in 2002. Specimens of Aedes camptorhynchus collected in the region tested positive to the virus making transmission risk most likely influenced by an abundance of this mosquito.

Like Ross River virus, Barmah Forest virus is spread by mosquitoes to people from local wildlife. It is likely that the virus quietly circulates between native animals, such as birds and mammals, but when favorable conditions for mosquitoes occur and populations increase, the risks of transmission to people increase.

While there is only a hand full of cases confirmed to date, a total of five with an additional two to be confirmed, it may not seem significant. However, it is a reminder that wherever mosquitoes, wetlands, and wildlife occur, there can also be a risk of mosquito-borne disease transmission.

With a warmer Tasmania possibly resulting from climate change and a concomitant extension of the “mosquito season” in coming years, perhaps the public health risks associated with mosquitoes will be something for health authorities to keep a closer eye on in the future. Importantly, is it time for local authorities to proactively monitor mosquitoes and the activity of mosquito-borne pathogens?

The image used at the top of this post comes from John Tann via Flickr; a mosquito (possibly Aedes alboannulatus) from Strahan, Tasmania.

Find out more about the amazing mosquitoes of Australia by picking up a copy of the award winning “A Guide to Mosquitoes of Australia” from CSIRO Publishing.

 

Mosquitoes feed on frogs, very small frogs…

I was excited to be asked back on the Science on Top podcast recently to record an episode about mosquitoes, currently declines in insect populations (are mosquitoes on the way out too?), and whether recent flooding in north QLD would result in increased mosquito populations and risk of mosquito-borne disease outbreak.

Please subscribe to the podcast, its a really fun and relaxed look at whats making headlines in the science world. The crew themselves describe the podcast as:

The Australian podcast about science, health and technology news. Join Ed Brown and his panel of co-hosts each week as we talk about the latest and coolest research and discoveries in the world of science. We’re joined by special guests from all over the science field: doctors, professors, nurses, teachers and more.

If you’re interested, you can chase up my previous guest spot with them talking “Everything Zika” back in 2016.

I still hold some aspirations of starting my own podcast. Problem is finding the time (there isn’t even enough time to catch up on my podcast “to do” list). Perhaps this is a project for the coming summer.

Would you listen to a podcast about mosquitoes and the people who study them?

You can catch up on a couple of other podcasts I’ve guested on over the past few years. Check out Flash Forward (The Ultimate Swatting) and Arthropod (Getting to Know Mosquitoes).

Oh, and mosquitoes do feed on frogs. Frog blood, not the whole thing. It would have to be a very small frog…

 

 

 

Ross River virus in Sydney, should we be worried?

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Health authorities in NSW recently released warnings to avoid mosquito bites following the detection of Ross River virus in wetlands along two major river systems in metropolitan Sydney. Whats going on and should these findings be something to be worried about?

What is Ross River virus?

Ross River virus is the most commonly reported mosquito-borne disease in Australia. The virus is spread by the bite of a mosquito and about 40 different mosquito species have been implicated in its transmission.

The disease caused by Ross River virus is not fatal but it can be severely debilitating.

Thousands of Australian’s are infected each year. We have some idea of the quantity of infections as Ross River virus disease is classified as a notifiable disease. While the official statistics indicate there are around 5,000 cases of illness across the country (there are between 500 and 1,500 cases per year in NSW), there are likely to be many more people that experience a much milder illness and so never get blood tests to confirm infection. These people won’t appear in official statistics.

What makes Ross River virus a fascinating pathogen to study is also what makes it extremely difficult to predict outbreaks. Transmission cycles require more than just mosquitoes. Mosquitoes don’t emerge from local wetlands infected with the virus, they need to bite an animal first and become infected themselves before then being able to pass on the pathogen to people.

It is generally thought that kangaroos and wallabies are the most important animals driving outbreak risk. However, we’re starting to better understand how the diversity of local wildlife may enhance, or reduce, likely transmission risk.

How was the virus found in Sydney?

The recent warnings have been triggered by the results of mosquito trapping and testing around Sydney. NSW Health coordinates an arbovirus and mosquito monitoring program across the state and this includes surveillance locations within metropolitan Sydney.

Mosquitoes are collected using traps baited with carbon dioxide. They trick the mosquitoes into thinking the trap is an animal. By catching mosquitoes, we can better understand how the pest and public health risks vary across the city and the conditions that make mosquitoes increase (or decrease) in numbers.

It mostly occurs around the metropolitan region’s northern and southern river systems and generally associated with estuarine or brackish-water wetlands. In these areas, there are often abundant mosquitoes and wildlife. Along the Parramatta River, there are often abundant mosquito populations but given the heavily urbanised landscape, there aren’t many kangaroos and wallabies.

The nuisance impacts of mosquitoes, such as Aedes vigilax, dispersing from the estuarine wetlands of the Parramatta River can create challenges for local authorities. These challenges include targeted wetland conservation and rehabilitation strategies along with ecologically sustainable mosquito control programs.

Is the detection of the virus in Sydney unusual?

The detection of Ross River virus is not that unusual. Detection of Ross River virus (as well as other mosquito-borne viruses such as Stratford virus) along the Georges River in southern Sydney is an almost annual occurrence. The local health authorities routinely issue warnings and in recent years have successfully used social media to spread their messages.

Ross River virus has also previously been detected along the Parramatta River.

While there have been confirmed local clusters of locally acquired Ross River virus in the suburbs along the Georges River, there have been no confirmed cases of Ross River virus disease in the suburbs along the Parramatta River.

There are a few reasons why more disease isn’t reported. Health authorities are active in promoting personal protection measures, sharing recommendations on insect repellent use and providing regular reminders of the health risks associated with local mosquitoes. It isn’t unreasonable to think these actions raise awareness and encourage behaviour change that reduces mosquito bites and subsequent disease.

Along the Georges River, there is clearly a higher risk of infection given the more significant wildlife populations, especially the wallabies common throughout Georges River National Park. By comparison, along the Parramatta River there are fewer bushland areas and virtually no wallabies (except for the occasional one hopping across the Sydney Harbour Bridge). Even in the wetland areas around Sydney Olympic Park, there is abundant bird life, meaning mosquitoes are probably more likely to be biting the animals than people. A study looking at the blood feeding preferences of mosquitoes in the local area found that animals were more likely to be bitten, mosquitoes actually only fed on humans about 10% of the time.

It is important that if you’re spending a lot of time outdoors in these areas, especially close to wetlands and bush land areas at dawn and dusk when mosquitoes are most active, take measure to reduce the risk of being bitten. Cover up with long sleeved shirts and long pants and apply an insect repellent. Choose a repellent that contains either DEET (diethlytoluamide), picaridin, or oil of lemon eucalyptus. Apply it to all exposed skin to ensure there is a thin even coat – a dab “here and there” doesn’t provide adequate protection. More tips here.

Also, keep in mind that just because cooler weather has arrived, the health risks associated with mosquitoes remain. That means keeping in mind that mosquitoes will be out and about just as football and netball seasons start so take along some mosquito repellent to training nights.

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