West Aussies versus the local mozzies

This is a special guest post from Dr Abbey Potter, Senior Scientific Officer, Environmental Health Hazards, WA Health. I’m currently mentoring Abbey as part of The Public Health Advocacy Institute of WA (PHAIWA) Mentoring Program. Its been a great experience as we navigate through some of the strategies to raise awareness of mosquito-borne disease and advocate for better approaches to addressing the public health risks associated with mosquitoes.

Living in WA, we’re all too familiar with the pesky mosquito. We know they bite but what we often don’t consider is that they can transmit serious and sometimes deadly diseases. In fact, a recent survey of locals indicated that knowledge of mosquito-borne disease is pretty limited, particularly among younger adults aged 18-34 years and those living in the Perth Metro. It’s pretty important we’re aware of the risks posed by these pint-sized blood suckers and how you can avoid them… and here’s why!

The Facts

On average, more than 1,000 people will be infected with a mosquito-borne disease in WA every year. Our mossies can transmit Ross River virus, Barmah Forest virus, West Nile virus (Kunjin substrain) and Murray Valley encephalitis virus. All four cause diseases that are debilitating at best, causing weeks to months of symptoms. Murray Valley encephalitis is limited to the north of the State but is so serious it can result in seizures, coma, brain damage and even death.

Forget the bush, most people bitten in their own backyard. West Aussies are all very prone to getting eaten alive while socialising outdoors but if you’re up in the north of the State, you’ve also got a much higher likelihood of being bitten while boating, camping or fishing or working outside, compared to the rest of the state.

And don’t think you’re off the hook when you head off on holidays. A further 500 WA residents return from overseas travel with an exotic mosquito-borne disease every year. Heading to Bali? Beware of dengue, especially young adult males who return home with the illness more than others. There is limited mosquito management in many overseas countries where disease-transmitting mozzies can bite aggressively both indoors and throughout the day. This catches West Aussies off guard, as we are accustomed to mozzies biting outdoors, around dusk and dawn. When you’re in holiday mode it’s likely that you’ll be relaxing, having a couple of drinks and not thinking about applying repellent. Oddly enough, mosquitoes may actually be more attracted to people whose body temperature is higher. This happens naturally when you consume alcohol, so best pull out the repellent before you crack your first beer.

Despite our attractiveness to mosquitoes, we aren’t really aware of the most effective ways to avoid bites or how we can do our bit to reduce breeding in our own backyards. If you live by the mantra Cover Up. Repel. Clean Up you’ll have no problems!

Western Australia has some amazingly beautiful wetlands but these saltmarshes around Mandurah can produce large populations of nuisance-biting mosquitoes!

Cover Up

If you know you are going to be outdoors when mosquitoes are active, wear loose, long-fitting clothing that is light in colour. Believe it or not, mosquitoes can bite through tight pants as tough as jeans – I’ve witnessed it!

If you’re staying in accommodation that isn’t mosquito-proof, consider bed netting.

Try to keep children indoors when mosquitoes are most active. If exposure can’t be avoided, dress them appropriately and cover their feet with socks and shoes. Pram netting can also be really useful.

Admittedly, it’s not always practical to wear long sleeves during our warm summer nights, so there are going to be times when you need to use repellent. Choose a product that actually works and apply it appropriately so it does the job. Despite our best intentions, this is where we often go wrong. There are a few basic things to cover here, so stick with it!

Ingredient: Science tells us that the best active ingredient for repelling mosquitoes is diethyltoluamide (DEET for short) or picaridin. You need to look for either one of these names on the repellent label under the ‘active constituents’ section.

Unfortunately, natural repellents and anything wearable (e.g. bands, bracelets or patches) have very limited efficacy. Experts don’t recommend you use them and I consider this very wise advice. It only takes a single mosquito bite to become infected and chances are you will receive at least one if you rely solely on a product of this nature. It just isn’t worth the risk.

Percentage: The next thing to consider is the percentage of the active ingredient. This can range anywhere from 7% to 80% which can make choosing a repellent confusing. Just remember, the higher the percentage, the LONGER the product will remain active for. It doesn’t mean it will repel mosquitoes better.

A repellent containing 16-20% DEET will provide around 4-6 hours of protection, and is a good place to start. Repellents labelled ‘tropical strength’ usually contain greater than 20% DEET – they are useful when you spend longer periods exposed to mosquitoes or if you are heading to a region where dengue, malaria or Zika is problematic. Kids repellents usually contain picaridin or <10% DEET.

Sometimes it can be tricky to work out the percentage of the active ingredient. You can see the Bushmans example below states this clearly, but the other bottles list the ingredient in grams per litre (g/L). No need for complex maths – just divide by 10 and you have the magic number! For example, the RID label below reports the product contains 160g/L of DEET. This would convert to 16% DEET – easy!

You can see a few examples here of effective repellents:

How to Apply: No doubt we would all prefer if repellents didn’t feel quite so gross on our skin or didn’t smell so bad. Even I have to admit that before I moved into this field, I was guilty of putting just a dab here and a dab there. Unfortunately, this is flawed logic that will only result in you being bitten!

Repellents must be applied correctly to be effective. That means reading the label and applying it evenly to all areas of exposed skin. Remember to reapply the product if you are exposed to mosquitoes for longer than the repellent protects you for. You’ll also have to reapply the repellent after sweaty activity or swimming.

For more information on repellent use in adults and children, click here.

Clean Up

Mosquitoes need water to breed, but only a very small amount. Water commonly collects in a range of things you may find in your backyard including pot plant drip trays, toys, old tyres, trailers and clogged up gutters. Mosquitoes also love breeding in pet water bowls, bird baths and pools if the water is not changed weekly or they are not well maintained. Rain water tanks can also be problematic so place some insect proof meshing over any outlets. When you’re holidaying, cover up or remove anything that may collect water.

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If you need more official info from WA Health about mosquito-borne disease or simple ways to prevent being bitten click here. And if you want to read more about how much West Aussies know (or don’t know) about mossies, check out Abbey’s excellent paper here! Joint the conversation too on Twitter by following Abbey and Cameron.

Mosquitoes, Gold Coast and the latest arbovirus research

This week I’ve been on the Gold Coast for the 12th Mosquito Control Association of Australia and Arbovirus Research in Australia Symposium. The theme of the meeting was “Managing challenges and threats with new technology” and included presentations covering a range of topics, from remote piloted aircraft for mosquito control to the discovery of insect-specific viruses and their potential to stop outbreaks of mosquito-borne disease.

You can check out some of the tweets shared during the meeting here.

I found myself on ten papers presented at the meeting and I’ve provided the abstracts below!

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Does surrounding land use influence the mosquito populations of urban mangroves?

Suzi B. Claflin¹ and Cameron E. Webb^2,3

¹Department of Entomology, Cornell University, Ithaca, NY, USA; ²Marie Bashir Institute of Infectious Diseases and Biosecurity, University of Sydney, Sydney, NSW; ³Department of Medical Entomology, NSW Health Pathology, Westmead Hospital, NSW 2145, Australia

Mosquitoes associated with mangrove habitats pose a pest and public health risk. These habitats in urban environments are also threatened by urbanisation and climate change. As a consequence, urban mangrove management must strike a balance between environmental conservation and minimising public health risks. Land use may play a key role in shaping the mosquito community within urban mangroves through either species spillover or altering the abundance of mosquitoes associated with the mangrove. In this study, we explore the impact of land use within 500m of urban mangroves on the abundance and diversity of adult mosquito populations. Carbon dioxide baited traps were used to sample host-seeking female mosquitoes around nine mangrove forest sites along the Parramatta River, Sydney, Australia. Specimens were identified to species and for each site, mosquito species abundance, species richness and diversity were calculated and were analyzed in linear mixed effects models. We found that the percentage of residential land and bushland in the surrounding area had a negative effect on mosquito abundance and species richness. Conversely, the amount of mangrove had a significant positive effect on mosquito abundance, and the amount of industrial land had a significant positive effect on species richness. These results demonstrate the need for site-specific investigations of mosquito communities to assist local authorities develop policies for urban development and wetland rehabilitation.

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Do urban wetlands increase mosquito-related public health risks?

Jayne K. Hanford¹, Cameron E. Webb^2,3, Dieter F. Hochuli¹

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

Wetlands in urban areas are frequently constructed or rehabilitated to improve stormwater quality and downstream aquatic health. In addition to improving water quality, these wetlands can provide aesthetic, recreational and biodiversity values to communities. However, urban wetlands are often perceived to proliferate nuisance-biting and pathogen-transmitting mosquitoes which can, in severe cases, erode goodwill in the community for protecting these valuable ecosystems.  We compared mosquito assemblages at 24 natural and constructed wetlands in the greater Sydney region, Australia. Our aims were to determine if wetlands with high aquatic biodiversity posed reduced mosquito-related public health risks, and if these links vary across the urban-rural gradient. At each wetland we sampled adult and larval mosquitoes, aquatic macroinvertebrates and physical habitat variables on two occasions through summer and autumn.  Although larval mosquito abundance was low across all sites, there was a high diversity of adult mosquito species, and assemblages varied greatly between sites and seasons. Species of wetland-inhabiting mosquitoes showed vastly different responses to aquatic biodiversity and physical habitat variables. There were strong relationships between the abundance of some mosquito species and aquatic macroinvertebrate richness, while others mosquito species showed strong relationships with the percentage of urbanisation surrounding the wetland.  Effectively integrating wetlands into cities requires balancing wetland design for water infrastructure purposes, biodiversity resources and public health and wellbeing requirements. Understanding relationships between biodiversity value and mosquito-related public health risks will enhance the value of constructed urban wetlands in cities while minimising risks posed by mosquitoes.

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Aedes aegypti at Sydney Airport; the detections and response

Doggett, S.L. and Webb C.E

Department of Medical Entomology, CIDMLS, Pathology West, ICPMR,
Westmead Hospital, Westmead, NSW.

Despite a huge increase in the detections of exotic vectors at ports around Australia, up until 2016 there had been no detection of Aedes aegypti at the Sydney International Airport. However, this changed on 14/Jan/2016 when two larvae were observed in an ovitrap serviced by the Department of Agriculture and Water Resources (formerly AQIS), as part of their routine surveillance activities for the detection of exotic vectors. These larvae were confirmed as being Ae. aegypti. Thereafter, there were a further nine separate detections of Ae. aegypti up until 4/Mar/2016. Six were via BG traps, one in an ovitrap, and there were two separate instances of an adult mosquito being collected in open areas. The majority of detections occurred in areas of the airport known as the ‘basement areas’. This is where the bags are unloaded from the air cans onto convey belts for collection directly upstairs by the passengers. Response measures undertaken included: (1) enhanced surveillance; BG traps were increased in number from 2 to 12, and traps inspected at more frequent intervals; (2) insecticide treatments; thermal fogging and surface sprays were conducted of the relevant areas; (3) vector surveys; a comprehensive audit of the airport was undertaken to examine the potential for localized mosquito breeding. In the case of the vector surveys, some 107 potential sites were identified and grouped into risk categories. No Ae. aegypti were discovered breeding, although Cx. quinquefasciatus and Ae. notoscriptus were found, and recommendations to prevent future localized breeding were made.

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Communicating the risks of local and exotic mosquito-borne disease threats to the community through social and traditional media

Cameron E Webb^1,2

¹Department of Medical Entomology, NSW Health Pathology, Level 3, ICPMR, Westmead Hospital, WESTMEAD NSW 2145 AUSTRALIA; ²Marie Bashir Institute of Infectious Diseases and Biosecurity, University of Sydney, NSW 2006, AUSTRALIA

Mosquito-borne disease management in Australia faces challenges on many fronts. Many gaps exist in our understanding of the drivers of exotic and endemic mosquito-borne disease risk but also the pathways to ensuring the community embrace personal protection measures to avoid mosquito bites. While traditional media has been the mainstay of public health communications by local authorities, social media provides a new avenues for disseminating information and engaging with the wider community. This presentation will share some insights into how the use of social media has connected new and old communications strategies to not only extend the reach of public health messages but also provide an opportunity to promote entomological research and wetland conservation. A range of social media platforms, including Twitter, Instagram and WordPress, were employed to disseminate public health messages and engage the community and traditional media outlets. Engagement with the accounts of traditional media (e.g. radio, print, television, online) was found to be the main route to increased exposure and, subsequently, to increased access of public health information online. With the increasing accessibility of the community to online resources via smartphones, researchers and public health advocates must develop strategies to effectively use social media. Many people now turn to social media as a source of news and information and those in the field of public health, as well as entomological research more generally, must take advantage of these new opportunities.

See the slides here.

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So, you want to write a field guide?

Cameron E. Webb^1,2, Stephen L. Doggett¹ and Richard C. Russell²

¹Department of Medical Entomology, NSW Health Pathology, Level 3, ICPMR, Westmead Hospital, WESTMEAD NSW 2145 AUSTRALIA; ²Marie Bashir Institute of Infectious Diseases and Biosecurity, University of Sydney, NSW 2006, AUSTRALIA

We know a lot about Australian mosquitoes. They’re one of the most studied insects in the country. Their pest and public health threats warrant a better understanding of their biology and ecology. There is still plenty we don’t know. We may not understand their ecological role in the local environment very well and there are many mosquitoes we know exist but have very little information about them. We still need to give many mosquitoes a formal scientific name. There is a reason why so many field guides are written by retired scientists. It’s not just about expertise, it’s about time too! In early 2016, “A Guide to Mosquitoes of Australia” to was published by CSIRO Publishing and marked the culmination of many years work. This work involved chasing mosquitoes from coastal rock pools to snow melt streams. We carried eskies of buzzing mosquitoes on airplanes from northern Australia to laboratories in Western Sydney and there were many late nights of wrangling those mosquitoes to get the perfect photo. Lots of mosquito bites too. Many, many mosquito bites. Putting together this field guide wasn’t an easy task and for all those involved it proved a challenge in many different ways. Digging out old papers to colour-correcting digital photographs proved time consuming but the biggest delays in finishing this project was a problem that plagues many field guide writer, “species creep”! Completing the guide was only possible with the kindness, generosity and co-operation of many mosquito researchers around the country.

See the slides here.

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Arbovirus and vector surveillance in NSW, 2014/15-2015/16

 Doggett, S.L., Clancy, J., Haniotis, J., Webb C. and Toi, C.

Department of Medical Entomology, CIDMLS, Pathology West, ICPMR,
Westmead Hospital, Westmead, NSW.

The NSW Arbovirus Surveillance and Vector Monitoring Program acts as an early warning system for arbovirus activity. This is achieved through the monitoring of mosquito abundance, detection of arboviruses from mosquitoes, and the testing for seroconversions to MVEV and KUNV in sentinel chickens. A summary of the last two seasons will be presented. The 2014-2015 season started early with elevated temperatures through late 2014, however conditions were relative dry with neither Forbes’ nor the Nicholls’ hypothesis being suggestive of an MVEV epidemic. Despite this, for the inland region, human notifications were close to average, with 260RRV & 11BFV). There were 12 arboviral detections from the inland including 5BFV, 6RRV & 1STR, with no seroconversions. In contrast, the coastal strip experienced the largest epidemic of RRV in recorded history. The 1,225 cases were close to double the average, with much of the activity occurring in the far north coast. There were 41 isolates from the mosquitoes trapped along the coast and included 6BFV, 29RRV, 4EHV and 2STRV. An intense El Niño occurred during the 2015-2016 season and thus it was extremely dry across the state. Again the Forbes’ and the Nicholls’ hypothesis were not suggestive of an MVEV outbreak. For the inland, mosquito numbers were well below average and there were only two arboviral detections from the mosquitoes (1RRV & 1 BFV), with no seroconversions. Similarly, mosquito collections were below average and there were also two arboviral detections from the trapped mosquitoes (1BFV & 1EHV). Human cases were below average.

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Are remote piloted aircraft the future of mosquito control in urban wetlands?

Cameron E Webb^1,2 Stephen L. Doggett¹ and Swapan Paul³

¹Department of Medical Entomology, NSW Health Pathology, Level 3, ICPMR, Westmead Hospital, WESTMEAD NSW 2145 AUSTRALIA; ²Marie Bashir Institute of Infectious Diseases and Biosecurity, University of Sydney, NSW 2006, AUSTRALIA; ³Sydney Olympic Park Authority, 8 Australia Ave, Sydney Olympic Park NSW 2127, AUSTRALIA

Mosquito control in urban wetlands will become increasing important. The expansion of residential areas will continue to encroach on natural mosquito habitats, particularly coastal wetlands, and expose the community to the health risks associated with mosquitoes. In many existing areas, ever increasing density of human populations associated with high rise residential developments will further expose people to mosquitoes. The increasing urban development adjacent to wetlands can restrict the ability to use traditional larvicide and insect growth regulator application methods. In 2016 a trial of larvicide application via remote piloted aircraft was undertaken in an area of estuarine wetlands at Sydney Olympic Park. An existing mosquito control program involving helicopter application of larvicides has been in place for over a decade. Post-treatment mortality of Aedes vigilax and Culex sitiens larvae was compared between bioassay and long-term surveillance sites within the wetlands. While there was a substantial reduction in larval densities post-treatment, the treatments via remote piloted aircraft were less effective than those of traditional piloted aircraft. The results of this preliminary trial suggest that the use of remote piloted aircraft has potential but the operational aspects of this application method requires careful consideration if there are to be as effective as existing strategies.

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Seasonal Activity, Vector Relationships and Genetic Analysis of Mosquito-Borne Stratford Virus

Cheryl S. Toi¹, Cameron E. Webb^1,2, John Haniotis¹, John Clancy¹ and Stephen Doggett¹

¹Department of Medical Entomology, Centre for Infectious Diseases and Microbiology Laboratory Services, Pathology West – Institute for Clinical Pathology and Medical Research, Westmead Hospital, NSW; ²Marie Bashir Institute for Infectious Diseases and Biosecurity, University of Sydney, Institute for Clinical Pathology and Medical Research, Westmead Hospital, NSW;

There are many gaps to be filled in our understanding of mosquito-borne viruses, their relationships with vectors and reservoir hosts, and the environmental drivers of seasonal activity. Stratford virus (STRV) belongs to the genus Flavivirus and has been isolated from mosquitoes and infected humans in Australia. However, little is known of its vector and reservoir host associations. A total of 43 isolates of STRV from field collected mosquitoes collected in NSW between 1995 and 2013 were examined to determine the genetic diversity between virus isolates and their relationship with mosquito species by year of collection. The virus was isolated from six mosquito species; Aedes aculeatus, Aedes alternans, Aedes notoscriptus, Aedes procax Aedes vigilax, and Anopheles annulipes. While there were distinct differences in temporal and spatial activity of STRV, with peaks of activity in 2006, 2008, 2010 and 2013, there was a high degree of sequence homology (89.1% – 97.7%) found between isolates with no evidence of mosquito species, geographic, or temporal divergence. The result suggests the virus is geographically widespread in NSW (albeit only from coastal regions) and increased local STRV activity is likely to be driven by reservoir host factors and local environmental conditions influencing vector abundance. While STRV may not currently be associated with major outbreaks of human disease, with the potential for urbanisation and climate change to increase mosquito-borne disease risks, and the potential for genomic changes which could produce pathogenic strains, understanding the drivers of STRV activity may assist the development of strategic response to public health risks posed by zoonotic flaviviruses in Australia.

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Insect specific flaviviruses suppress West Nile virus replication and transmission

Sonja Hall-Mendelin¹, Breeanna McLean², Helle Bielefeldt-Ohmann³, Cameron E. Webb⁴ Jody Hobson-Peters², Roy Hall², Andrew van den Hurk¹

¹Public Health Virology, Forensic and Scientific Services, Department of Health, Queensland Government, PO Box 594, Archerfield 4108, Queensland, Australia; ²Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia 4072, Queensland, Australia; ³School of Veterinary Science, The University of Queensland, Gatton Campus, Gatton 4343, Queensland, Australia; ⁴Medical Entomology, Marie Bashir Institute of Infectious Diseases and Biosecurity, The University of Sydney, NSW, Australia

Diseases caused by mosquito-borne flaviviruses, including dengue (DENV), Zika and West Nile viruses (WNV), are a global problem. New molecular tools have led to recent discoveries of a plethora of insect-specific flaviviruses (ISF) that infect mosquitoes but not vertebrates. Preliminary reports have suggested that transmission of WNV can be suppressed by some ISFs in co-infected mosquitoes, thus the ecology of ISFs and their potential as natural regulators of flaviviral disease transmission is intriguing. In vitro studies with two ISFs discovered in Australia, Palm Creek virus (PCV) and Parramatta River virus (PaRV), demonstrated suppression of WNV, Murray Valley encephalitis virus (MVEV) and DENV replication in mosquito cells (C6/36) previously infected with either of these ISFs. Further in vivo experiments indicated that these ISFs were not transmitted horizontally in the saliva, and that PaRV relied on vertical transmission through the mosquito egg to the progeny. Additional studies revealed a significant reduction of infection and transmission rates of WNV when Culex annulirostris were previously infected with PCV, compared to control groups without PCV. Of particular interest was the specific localisation of ISFs to the midgut epithelium of mosquitoes infected via natural route (vertical transmission – PaRV) or by intrathoracic injection (PCV). Overall these results confirm a role for ISFs in regulating the transmission of pathogenic flaviviruses by mosquitoes and that this interference may occur in the midgut where initial infection occurs. Further research is needed to determine the precise mechanism of this phenomenon and its potential for mosquito-borne disease management.

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Neges, Nidos and Nings – so that’s what’s killing my mossie cells!

Roy Hall¹, Jody Hobson-Peters¹, Helle Bielefeldt-Ohmann¹, Caitlin O’Brien¹, Breeanna McLean¹, Agathe Colmant¹, Jessica Harrison¹, Thisun Piyasena¹, Natalee Newton¹, Waylon Wiseman¹, Marcus Mah^1,2, Natalie Prow², Andreas Suhrbier², David Warrilow³, Andrew van den Hurk³, Sonja Hall-Mendelin³, Cheryl Johansen⁴, Steven Davis⁵, Weng Chow⁶, Stephen Doggett⁷, John Haniotis⁷ and Cameron Webb⁷.

¹Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, Australia; ²QIMR Berghofer Medical Research Institute, Herston, Brisbane, Australia; ³Public Health Virology, Forensic and Scientific Services, Coopers Plains, Queensland, Australia; ⁴Arbovirus Surveillance and Research, Infectious Diseases Surveillance Unit, PathWest Laboratory Medicine WA, Western Australia; ⁵Berrimah Veterinary Laboratories, Department of Primary Industry and Fisheries, Darwin, Northern Territory, Australia; ⁶Vector Surveillance and Control, Australian Army Malaria Institute, Enoggera, Queensland, Australia; ⁷Department of Medical Entomology, West Westmead Hospital, Westmead, NSW, Australia.

Isolation of viruses from mosquitoes is an important component of arbovirus surveillance and virus discovery programs. In our lab, these viruses are detected in inoculated cultures by the appearance of cytopathic effects (CPE) in mosquito cell monolayers or by reactivity of monoclonal antibodies to viral antigens or dsRNA intermediates. Isolates are then identified by RT-PCR or deep sequencing.  We detected extensive CPE in many mosquito cell cultures inoculated with mosquito homogenates from several regions of Australia, however these isolates were not identified by specific mAbs or RT-PCRs designed to detect known arboviruses.  When we investigated their identity by deep sequencing, a new species (Castlerea virus – CsV) in the unclassified taxon Negevirus, was identified in several mosquito species from WA and Brisbane. Two viruses in the newly established Mesoniviridae family (order Nidovirales) were also identified; a novel species named Casuarina virus (CASV) from Coquillettidia xanthogaster in Darwin and from Culex annulirostris in Cairns, and the first Australian isolates of Nam Dinh virus from several mosquito species in Brisbane and Perth. Many isolates of a new genetic lineage of Liao Ning virus, a member of the Seadornavirus genus (family Reoviridae), were also obtained from several mosquito species from different regions of Australia.  These new viruses were isolated at very high frequency in some mosquito collections, and were often found to co-infect isolates of other mosquito-borne viruses making it difficult to obtain pure cultures. We have now developed neutralising antibodies to each virus to facilitate selective removal of these viruses from mixed cultures.

 

That was a busy meeting. I’m exhausted but cannot wait until the next meeting in 2018. Are you a member of the Mosquito Control Association of Australia?

 

 

What can the outbreak of dengue in Japan tell us about future mosquito-borne disease risk?

Considered free of dengue for around 70 years, Japan is now facing an outbreak of mosquito-borne dengue virus centered around a popular Tokyo city park. How could this happen?

Dengue is typically associated with tropical regions. However, outbreaks of dengue have occurred in temperate regions historically. That includes major outbreaks in Japan. In fact, dengue has been a notifiable disease in Japan since 1999; regulated by the Infectious Disease Control Law.

The last major outbreak was in 1942-1945. Breaking out in Nagasaki in August 1942, over 200,000 cases were suspected to have occurred, making it one of the largest temperate zone dengue outbreaks on record. It is interesting that, at the time, there was an extensive network of water tanks to enable response to fires triggered by bombing during the war. These tanks supported “innumerable” populations of the Asian Tiger Mosquito, Aedes albopictus. Also contributing to the problem was an inability to undertake large-scale insecticide applications at the time.

Then, for around 70 years, dengue disappeared. Until 2014.

Local authorities undertake spraying in Tokyo’s Yoyogi Park. (Photo Source: AFP via ABC News)

The first case of dengue in this current outbreak was reported at the end of August 2014 but in the space of a week or so, many more cases were identified. To date (9 October 2014) there has been a total of 151 confirmed locally acquired cases of dengue (this includes an Australian traveller). The majority to these cases have been centred around the popular Yoyogi Park in Tokyo.

[update 1 November 2014] Tokyo’s Yoyogi Park finally reopened after the outbreak was first detected but it was closed for 57 days. As well as a serious inconvenience to the people of Tokyo, there is little doubt this has had a substantial economic impact on the city. It would be fascinating to know if the outbreak impacted tourism.

[update 5 December 2014] A newly published paper reports on the molecular analysis of isolates of dengue virus from 19 confirmed cases of infection from Tokyo. The analysis showed that the outbreak was triggered by a single incursion of dengue virus type 1 (DENV-1) and that analysis of the envelope protein genome sequence from 3 patients revealed 100% identity with the strain from the first patient.

Some of the media coverage has focused in the role that climate change may have played on triggering this outbreak. However, the outbreak is not the result of a changing climate. International travel and a cool climate tolerant mosquito are to blame. Perhaps complacency regarding the risks associated with this mosquito predisposed the region to this outbreak too?

The Asian Tiger Mosquito, Aedes albopictus. (Source: Stephen Doggett, Pathology West – ICPMR Westmead)

The Asian Tiger Mosquito, Aedes albopictus, is a cool climate tolerant mosquito closely associated with water holding containers in urban environments. The mosquito is a severe nuisance-biting pest and second only to the Yellow Fever Mosquito (Aedes aegypti) in its importance in transmitting dengue virus. It is also very effective at transmitting chikungunya viruses. The expanding range of Aedes albopictus internationally is of critical importance to outbreaks of the disease. It is raising concerns regarding the transmission of chikungunya virus in North America this year.

Aedes albopictus provided the tinder that an infected traveller ignited to kick off this dengue outbreak.

There were warnings this was coming. Much of the media coverage has emphasised that this is the first local outbreak of dengue in 70 years. In fact, there was an intriguing case last year that should have put local authorities on notice.

In January 2014 there was news that a German tourist had contracted dengue. In Japan.

In a published case report, a woman sought treatment in a hospital in Berlin, Germany, in after returning from two weeks of travel in August-September 2013 to Honshu Island, Japan. Her travel route was via Frankfurt International Airport to Tokyo Narita International Airport and return. She did not visit any regions considered to have endemic dengue activity. The authors note that this case was “the first recognised case of locally acquired dengue (DENV) infection in Japan for more than 60 years”.

Following this reported case, authorities undertook surveys that revealed high population densities of Aedes albopictus within the urban areas of Japan. It is interesting to note that, despite using a surveillance method that is typically not effective at collecting Aedes albopictus (carbon dioxide baited light traps), some of the largest densities of mosquitoes were collected from Tokyo. Interestingly, a 2010 study into the blood feeding behaviour of Aedes albopictus in Japan showed that over 68% of mammalian blood meals identified were human and the authors concluded that the mosquito may play a role in outbreaks of dengue and chikungunya viruses.

I cannot find any reports of mosquito control, either source reduction or insecticide treatment, were undertaken in response to these findings.

Average number of Aedes albopictus collected using human bait collection and CDC miniature traps in urban areas of Japan in September 2013 (Source: International Journal of Infectious Diseases)

There are clearly some warnings that authorities, both in Japan and elsewhere, should take from this event. Most importantly, the presence of Aedes albopictus should not be underestimated in increasing the risk of local dengue outbreaks. While the published report of the dengue infection in the German tourist prompted debate (see here and here) about the future of local dengue outbreaks in Japan, it is clear now that where Aedes albopictus occurs, so does the risk of dengue. Control of this mosquito should be undertaken, not only to reduce the nuisance-biting impacts but to also reduce public health risk. Clearly, August and September seem to be a high risk period around Tokyo.

While locally acquired cases of dengue were unknown since the 1945, Japanese travellers were regularly returning home infected with the pathogens. A recent study of 540 Japanese travellers demonstrated that, not only was Indonesia and the Phillippines destinations of high risk, but that August and September were peak periods when infected travellers were returning home from these endemic regions. An eerie coincidence considering the cases in August/September in both 2013 and 2014. Where these traveller, not climate change, triggered outbreaks in Japan? (the debate about climate change driven dengue outbreaks in other regions of SE Asian could be left for another day)

Rate of reported dengue cases per 100 000 Japanese travellers by month and country visited, 2006–2010. It is interestign to note that only data for 2010 on travellers to Indonesia is reported. (Source: Western Pacific Surveillance Response Journal)

Australian authorities should take note of what has happened in Japan. While understanding the routes of entry of Aedes albopictus into new regions is critical, developing strategic surveillance and control responses to the introduction of the mosquito are of equal importance.

Since the discovery of Aedes albopictus in the Torres Strait in 2005, there has been much debate, together with data crunching and computer modelling, with regard to the possible spread of the mosquito across the mainland. There is evidence that the mosquito can survive at cooler climates in Australia and can spread some of our local pathogens. What will it mean for Australia to have a severe nuisance-biting pest and potential vector of dengue and chikungunya viruses inhabiting our major cities such as Brisbane, Sydney, Melbourne and Perth?

We should be mindful that this mosquito may not naturally spread south from the north, it may sneak in through the back door. It already has. The mosquito was discovered, and fortunately eradicated, from Melbourne in 2012. Exotic mosquitoes continue to be intercepted at our ports.

Perhaps we can’t stop Aedes albopictus reaching mainland Australia. Efforts continue to keep the mosquitoes at bay but, in reality, we may be overwhelmed. We cannot fill enough cracks to stop them slipping through.

What we need are strategic responses to the incursions of the mosquito. Authorities need to build capacity for quick response surveillance and control. Traps and insecticides are cheap, expertise on the ground by those responsible for catching and killing the mosquitoes is not. The traps and control measures currently used to control pest mosquitoes associated with wetlands will not be easily be transferable to the control of container-inhabiting mosquitoes. We need to review our approaches to mosquito control should Aedes albopictus be introduced. Time may be on our side for the moment but for how long? Will we one day see outbreaks of dengue in Sydney’s Centennial Park?

Why not join the conversation on Twitter?