Asian tigers and shifting mosquito control from the swamps to the suburbs

aedes_albopictus_SteveDoggettOne of the world’s most troublesome nuisance-biting mosquitoes is perfectly adapted to summer life in southern cities in Australia. This is bad news for communities in temperate climate regions in Australia that would otherwise be immune from the threats of exotic mosquito vectors of dengue and chikungunya virus otherwise limited to tropical regions of the world.

I’ve been invited to speak in the “Managing Current & Future Exotic Mosquito Threats” symposium at the Australian Entomological Society conference to share some of the experiences in temperate Australia regarding exotic and endemic mosquito threats and how the threat of the Asian Tiger Mosquito is being addressed.

Australia has annual activity of mosquito-borne disease. Around 5,000 people a year fall ill following a mosquito bite each year in Australia, most commonly due to Ross River virus. These pathogens are generally spread by native “wetland” mosquitoes such as Aedes vigilax or Culex annulirositrs). Australia has also had major outbreaks of dengue in the past but the only mosquito in Australia able to spread the viruses, Aedes aegypti, is restricted to far north QLD. It is unlikely to spread to southern cities beyond Brisbane based on temperature change alone but there is another mosquito that may pose a threat of dengue or chikungunya virus transmission in southern regions.

The Asian Tiger Mosquito (Aedes albopictus), poses a significant threat to Australia. It was discovered in the Torres Strait in 2005, having thought to have hitchhiked on fishing boats from Indonesia. Although the mosquito hasn’t yet managed to set up home on mainland Australia, its a more likely a question of when, not if, this mosquito will make its way here.

The container-inhabiting (not wetland living) mosquito has already hitchhiked to Europe and North America with eggs carried with people and their belongings. Movement of people, not shifts in climate is the biggest risk. Should it reach one of our major southern cities, there is little doubt that mosquito could become a persistent summer pest and possible public health threat. The way we respond to water shortages in our cities, by increasing water storage around our homes, may set the scene for this mozzie to move in.

Once the mosquito is established in our cities, all we need are travellers to bring in the viruses. Travellers introduce dengue virus into Far North QLD every year. Last year Japan experienced its biggest outbreak of dengue in over 70 years thanks to a traveller introducing the virus to local mosquitoes in downtown Tokyo. This Tokyo outbreak of dengue has implications for local authorities in Australia.

In my presentation at the Australian Entomological Society conference, I’ll highlight some of the issues to consider when assessing the risks posed by exotic mosquitoes in New South Wales as well as outline some of the problems local authorities may have to face when dealing with these mosquitoes that differ from the current focus of mosquito and mosquito-borne disease surveillance and control strategies.

You can view my presentation slides and abstract below:

Developing a strategic response to exotic mosquito threats in NSW

Cameron E Webb (1,2), Jay Nicolson (3), Andrew van den Hurk (4) & Stephen L Doggett (1)

(1)Department of Medical Entomology, Pathology West – ICPMR Westmead, Level 3, ICPMR, Westmead Hospital, Westmead NSW 2145 Australia; (2) Marie Bashir Institute of Infectious Disease and Biosecurity, University of Sydney, NSW 2006, Australia; (3) School of Pathology and Laboratory Medicine, The University of Western Australia, Nedlands, WA 6009, Australia; (4) Virology, Public and Environmental Health, Forensic and Scientific Services, Department of Health, Queensland Government, Brisbane, QLD 4108, Australia.

Mosquito-borne disease management in Australia faces challenges on many fronts. Home growth threats posed by endemic mosquito-borne pathogens (e.g. Ross River virus (RRV)) may increase with a changing climate but exotic mosquitoes and pathogens are an emerging threat. In the absence of a national strategy to address these exotic threats, local authorities must develop regionally specific surveillance and response programs to identify and respond to exotic mosquito incursion. The Asian tiger mosquito, Aedes albopictus, poses the greatest risk to temperate regions of Australia due to their close ecological associations with urban habitats and ability to transmit exotic pathogens (e.g. dengue viruses (DENV) and chikungunya virus (CHIKV)). The mosquito is widespread in local regions, has been detected at international ports and, given the increasing frequency of local travellers to regions where this mosquito is abundant, it raises the potential that an incursion into metropolitan Sydney in the coming years is probable. When this happens, what is the likelihood that this mosquito becomes established? Laboratory studies have confirmed Ae. albopictus could survive in the egg stage under climatic conditions typical of a Sydney winter. Despite the endemic mosquito, Aedes notoscriptus, sharing the same ecological niche to Ae. albopictus, cohabitation studies demonstrated that no interspecies competition would act to limit the local spread of Ae. albopictus and the mosquito could proliferating in the summer. Critically, vector competence experiments have demonstrated the ability of Ae. albopictus to transmit endemic pathogens and, given their propensity to bite humans, could contribute to human-mosquito-human outbreaks of RRV in urban areas of NSW, complementing the enzootic vectors that currently limit transmission to the metropolitan fringe. Local authorities need to develop a multiagency strategic approach to surveillance concomitant with strategic response to reduce the pest and public health threats associated with exotic mosquitoes.

Make sure you check out the tweets from the Australian Entomological Society Annual Conference in Cairns, QLD, 27 September through 1 October 2015, by clicking on #AusEntoSoc15

Are mosquito coils making us sick?

coilWe burn them to beat the bite of mosquitoes but could they actually be making us sick? Is breathing the smoke from a smouldering mosquito coil really the same as smoking a pack of cigarettes?

In summary, should I use mosquito coils to protect my family from mosquito bites?

  • Only use commercial products that have been registered by local authorities
  • Products that contain pyrethroids will provide better protection from mosquitoes than those that contain only botanical extracts
  • The byproducts of combustion, not insecticides, associated with mosquito coils may pose a health risk in some circumstances
  • Best to limit use of coils to outdoor or well ventilated indoor areas
  • Don’t sleep next to a smouldering mosquito coil
  • Consider plug-in “smokeless” mosquito repellent devices
  • Sleeping under a mosquito net is the best non-chemical approach to overnight mosquito bite prevention
The Saltmarsh Mosquito (Aedes vigilax) (Photo: Stephen Doggett)

The Saltmarsh Mosquito (Aedes vigilax) (Photo: Stephen Doggett)

Here is the background…

For centuries we’ve burnt substances, particularly aromatic plants, to keep mosquitoes away. The clouds of smelly smoke can often ward off the swarms of blood sucking mosquitoes.

The use of pyrethrum in incense gained popularity and became common practice in Asia but it wasn’t until the early 1900s that the mosquito coil was born thanks to Japanese entrepreneurs Eiichiro and Yuki Ueyama and their katori senkō (mosquito-killing incense).

Modern mosquito coils, mostly containing the pyrethroid insecticides, are an almost permanent fixture at camp sites and backyard during summer. Millions of families across the tropics use them as their primary source of mosquito-borne disease prevention. They’re cheap and generally effective. We burn them to reduce the risks of mosquito-borne disease but could they actually be making us sick?

Health concerns of mosquito coils

There is growing concern about the adverse health impacts associated with the burning of mosquito coils and sticks indoors. A recently presentation to the 48th National Conference of Indian College of Allergy, Asthma and Applied Immunology has again raised the issue of potential health impacts associated with mosquito coils with media coverage given to Dr Sundeep Salvi in the lead up to the conference. He is quoted as saying “Burning one mosquito coil in a closed room amounts to smoking roughly 100 cigarettes”. The key point in Dr Salvi’s comment is “closed room”.

When assessing the real risks posed by mosquito coils, it is important to consider not just what is released by these smouldering products but actual likelihood it poses a serious health risk. How do you balance these potential health risks of burning coils with those posed by the bite of infected mosquitoes?

Total daily rainfall recorded at Sydney Olympic Park (Data source Bureau of Meteorology)

Do you really need to weigh up the risks of breathing in smoke from a mosquito coil with the risks of mosquito bites? (Image: Joel Sartore, National Geographic)

Who checks the safety of mosquito coils?

In Australia, all substances that purport to kill or repel mosquitoes must be registered by the Australian Pesticides and Veterinary Medicines Authority (APVMA). Similar regulatory authorities exist in other jurisdictions.

Mosquito repellents, whether they’re topical or spatial or whether they contain “chemical” or “natural” substances will need to be tested for efficacy and safety. Check the packaging for a registration number. There are dozens of different variations on “mosquito coils” including sticks, coils, candles and a variety of “plug in” devices. You’ll find the shelves of the local supermarket, camping and hardware store fully stocked almost all year round!

Despite the wide range of products available, the active ingredients (that is the mosquito repelling or killing products) don’t vary too much. There are either synthetic pyrethroids or botanical extracts (e.g. citronella oil, eucalytpus oil). You may be surprised to know that some contain a combination of the two. Just because “citronella” is written in bold on the packaging, it may still contain one of the synthetic pyrethroids. Check the label.

repellentrackDoes burning mosquito coils really make us sick?

A study of mosquito coils sold in the U.S. and found that some mosquito coils contain octachlorodipropyl ether (s-2) that, during the smouldering of the coils, produces an extremely potent lung carcinogen as a byproduct called (bis(chloromethyl)ether (BCME)). Fortunately, s-2 is banned in many countries. It is no longer used commercially in the U.S. and prompted by reports of the risks associated with mosquito coils, Hong Kong authorities released a statement in 2005 regarding the recall of mosquito coils containing s-2.

It is not listed as an active ingredient in mosquito coils registered for use in Australia. Given that in most circumstances, particularly in Australia, mosquito coils don’t contain s-2, it is the particulate matter that is of greatest concern.

An often quoted study published in 2003 titled “Mosquito coil emissions and health implications” analysed the components of commercially available mosquito coils from China and Malaysia and found that burning mosquito coils in an enclosed room may pose “significant acute and chronic health risks” with the fine and ultra fine particulate matter released from a single mosquito coil equaling that of up to 137 cigarettes!

In addition, they found that emission of formaldehyde (a by product of the combustion process) from burning one coil can be as high as that released from burning 51 cigarettes.

Doesn’t sound too good does it? The combustion of the coil itself is the main concern, not the insecticides used.

More recent studies have indicated that changing the base materials used in mosquito coils (i.e. switching to charcoal from other organic material) can reduce the volume of particulate matter substantially. Would these “smokeless” mosquitoes be more “healthy”? Probably.

Does what happens in the lab stays in the lab?

Billions of mosquito coils are sold across Asia every year. Millions of families use them as their primary mosquito bite prevention strategy. Why aren’t we seeing more substantial health impacts in local communities?

It is worth noting that two papers published in 2006 investigated the different methods used to assess the health risks associated with burning mosquito coils. The researchers tested different methods to expose laboratory rats to particulate matter from mosquito coils. They firstly reported that “protocols devised evaluate and assess the acute inhalation toxicity of mosquito coil smoke demonstrating that the nose-only mode of exposure of rats to the smoke of mosquito coils is suitable to assess the toxic potency of different coils.

The nose-only mode has clear advantages over the whole-body exposure mode.” Then, using the “nose-only” exposure method that they proposed, the researchers concluded that “overnight exposure to the smoke from burning mosquito coils (manufactured in Indonesia) is unlikely to be associated with any unreasonable health risk.” This is a noteworthy conclusion given that the level of exposure to those rats (6 h a day, 5 days a week for 13 weeks) was substantial.

What about “smokeless” mosquito coils?

There is a paucity of studies investigating the potential human health impacts of “smokeless” mosquito repellents. The few studies that do exist are inconclusive or use animals to test health impacts under conditions unlikely to occur in most circumstances.

A 2005 review of pyrethroid poisoning reported “Despite their extensive world-wide use, there are relatively few reports of human pyrethroid poisoning. Less than ten deaths have been reported from ingestion or following occupational exposure. Occupationally, the main route of pyrethroid absorption is through the skin. Inhalation is much less important but increases when pyrethroids are used in confined spaces.” Again, this highlights the critical issue here, exposure to insecticides in confined and/or enclosed situations.

It is worth remembering that pyrethroids are over 2000 times more toxic to insects than mammals. That means that the concentrations used to kill insects are unlikely to have adverse health impacts on humans, particularly if commercial formulations are used as recommended. Given the billions of people who use mosquito coils to prevent mosquito bites, perhaps the more important question to ask is, does burning mosquito coils actually prevent mosquito-borne disease? Perhaps that is a discussion for another time….

sp-breweries-mozzie-boxPerhaps one of the most interesting ideas this year was the “mosquito repellent beer carton”. More marketing than public health initiative but I like the idea. The carton is infused with citronella so that when you’re sitting about the campfire enjoying a few beers, you can toss bits of the carton into the fire and keep mosquitoes away. It is unlikely many mosquitoes will be actively repelled. However, I do like the idea of using the beer carton as an opportunity to raise awareness of mosquito-borne disease.

Perhaps it is this little bit of public health communication that will actually stop a few people becoming infected.

Do you use mosquito coils and sticks to prevent mosquito bites? Join the conversation on Twitter and let me know what you think.

Want to learn more about the amazing world of Australian mosquitoes? Check out “A Field Guide to Mosquitoes of Australia” out now through CSIRO Publishing. Over 200 pages containing a pictorial guide to almost 100 different mosquitoes along with tips on beating their bite and protecting your family from the health risks of mosquitoes. You can order online or through your favourite local bookstore or online retailer.


Read more at The Conversation: Are mosquito coils good or bad for our health?


Read more at The Conversation: What can I eat to stop mosquitoes biting me?


Read more at The Conversation: The best (and worst) ways to beat mosquito bites



 

Don’t let mozzie bites spoil your tropical “Schoolies” celebrations

With cheap international travel luring plenty of school leavers away from traditional “Schoolies” locations, concerns have been raised regarding a new set of health risks.

Traditionally, the Gold Coast in QLD was the main destination for “end of school” celebrations. Commonly known as “Schoolies”, these celebrations are generally portrayed in the media as pretty wild affairs. It is estimated that around 30,000 people will travel to the Gold Coast in 2013 (around 10,000 will celebrate an hour or so further south in Byron Bay). In recent years, there have also been discussions about alternatives to traditional “Schoolies” activities.

There are plenty of health concerns every year for those partying and this year, CSIRO has teamed up with local health authorities to create a tool to reduce the strain on hospitals. The software predicts how many patients will arrive at emergency, their medical needs and how many will be admitted or discharged. As the Brisbane Times reported:

The most common injuries among 17 to 19 year-olds are expected to include acute drunkenness from alcohol, grazes and cuts to feet, hands and heads, ankle and foot sprains, drug poisoning, asthma attacks, reaction to severe stress, lower abdominal pain and broken noses.  Intoxication is the single biggest reason schoolies turn up to hospitals or at medical tents for treatment, with the number of schoolies presenting for alcohol intoxication tripling between 2011 and 2012.

Lets hope that with a bit of help from some new technology, there is a downturn in injuries and hospitalisations this year. There has even been the suggestion that day-time naps could help prevent many injuries!

While the Gold Coast and Byron Bay continue to be popular destinations, cheap overseas holiday options in Bali are also attracting plenty of school leavers.

Don’t try to shake off that “Schoolies” hangover with a trip to McDonalds, try the local street food in Bali (Photo: Streetfood Blog)

Taking celebrations overseas

While there are many health risks associated with “Schoolies” celebrations across Australia, many are now looking to travel to Bali. Additional concerns are then thrown into the mix.

Health authorities have been issuing warnings about increased measles risks in Bali and encouraging travellers to ensure that they’re vaccinated. The Australian Government’s “Smart Traveller” website warns of measles, magic mushrooms and potentially poisoned drinks.

In addition, there are warnings on the risk of rabies and a range of mosquito-borne diseases (e.g. dengue, Chikunguya, Japanese encephalitis). In particular, there have been reports of surging dengue activity in Bali in recent years. Notwithstanding the risk to travellers, the burden of disease on local communities, particularly children, is significant.

Aedes aegypti (Photo: Stephen Doggett)

One of the key mosquitoes internationally that is responsible for the spread of dengue viruses, Aedes aegypti (Photo: Stephen Doggett)

From a mosquito perspective, the big difference between the Gold Coast and Bali is the presences of mosquitoes that can transmit dengue and Chikungunyna viruses. The risks are different, not only due to the activity of these pathogens but the mosquitoes display a different pattern of biting activity. They bite during the day as opposed to most “Aussie Mozzies” that bite in the late afternoon and evening. This has implications for the effectiveness of topical mosquito repellents against these mosquitoes/pathogens.

In the latest issue of the Broad Street Pump (Newsletter of the Centre for Infectious Diseases and Microbiology & Marie Bashir Institute of Infectious Diseases and Biosecurity), I wrote a piece titled “Are we providing the right advice on personal protection measures against endemic and exotic mosquito-borne diseases?”. The thrust of the paper is that we should be providing specific advice on how to choose and use repellents in these dengue-receptive regions.

The most important issue is that topical repellents should be applied in the morning, and reapplied during the day, to provide protection from mosquito bites. It is equally important that travellers aren’t complacent about the risks of mosquitoes in urban areas. While the preventative measures against malaria (i.e prophylaxis and bed nets) are well know, I suspect that they are mostly associated with travel to rural and “jungle” locations. The problem is, dengue is a disease of urban areas. Perhaps Australian travelers are being complacent?

Rather than being associated with wetlands or rice paddies, the mosquitoes that spread dengue and Chikungunya viruses are closely associated with “man made” water holding containers. Pot plant saucers, discarded tyres, rainwater tanks, uncovered water drums and, probably most importantly, discarded containers ranging from takeaway food containers to bottles and cans.

It isn’t just the parties, the wonderful surf in Bali is surf to attract a few extra Australian travellers to “Schoolies” celebrations (Photo: Aquabumps)

Australia has seen a steady rise in travellers returning with dengue and chikungunya infections. Dengue infection in returning travelers is not uncommon. The majority of dengue infections have occurred in Indonesia. This increase in imported cases may also be a risk to trigger local epidemics in QLD.  Even the movement of infected mosquitoes on aircraft have caused suspected cases of “airport dengue” in NT and WA.

It is important to note that there are some regions in Australia where mosquitoes responsible for the spread of dengue viruses are present. In particular, Far North Queensland experiences annual activity of dengue with occasional small clusters of locally acquired cases. Local mosquitoes typically pick up the virus by biting an infected traveller and then, subsequently, spreading to local residents. There have been about 30 cases of locally acquired dengue in FNQ since the start of the year.

Across Australia, according to the statistics provided by Australian National Notifiable Diseases Surveillance System, we are currently on track to record the highest number of dengue and Chikungunya cases. As of 16 November 2013, there had been 1563 cases of dengue reported and 121 cases of Chikungunya. Compared to the number of cases of dengue, Chikungunya may not seem so bad, until you realise that the highest number of cases previously was only 63 in 2010. The reasons for this increase are probably due to increasing movement of Australian travellers to dengue endemic regions as well as increasing activity of dengue and Chikungunya at these destinations.

What do you do?

Firstly, you head off to Bali to have a great time and, as well as celebrating the end of school with your friends, get a chance to experience another culture (and possibly some good waves). As they say, be alert but not alarmed.

Here are three tips on protecting yourself against mosquito-borne disease:

1. Protect yourself against day-biting mosquitoes. Apply a repellent before breakfast.

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 or picaridin. These two products are most effective.

3. Apply the repellent like sunscreen, not perfume. An even coating on exposed skin is required. Don’t bother applying it to clothing or “spraying it around the room”, that won’t protect you from bites.

Don’t forget to check out Smart Traveller before heading off to Bali…or anywhere else for that matter. Consult your GP before traveling regarding the appropriateness of anti-malarial drugs. This is particularly the case if you’re traveling to rural areas in Indonesia or heading off to another tropical location for celebrations.

The photo at the top of this post was taken from the 2012 piece “Sex, drugs, cheap beer and ignorance – schoolies completely lose it in Bali