Talking wetlands, wildlife and mosquitoes at the 2017 Australian Entomological Society Meeting

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I’ll be in Terrigal, on the NSW Central Coast, for the 2017 Australian Entomological Society conference and taking the opportunity to present a summary of a number of collaborative projects undertaken in recent years, from working out how surrounding landuse influences the mosquito populations in urban mangroves to how important mosquitoes are to the diet of local bats.

Together with a range of colleagues, I’ve been undertaking research into the factors driving mosquito and mosquito-borne disease risk in urban wetlands. It is a complex puzzle to solve with more than just mosquitoes determining local pest and public health risks. However, with outbreaks of mosquito-borne Ross River virus on the rise in recent years, including urban areas of Australia, there is a need to better understand the factors at play.

There is a range of factors that may increase the risk of Ross River virus, they include suitable wetlands, wildlife reservoirs of the pathogen and mosquitoes. Understanding the mosquitoes associated with urban estuarine and freshwater wetlands is critical.

Investigating the role of surrounding landuse in determining the mosquito communities of urban mangroves, we found that industrial and residential areas tended to increase abundance of mosquitoes, perhaps due to direct or indirect impacts on the health of those mangroves. We’ve found previously that mosquitoes problems are often associated with estuarine wetlands suffering poor health, perhaps this is determining the increased mosquito risk we identified? You can read more in our publication here.

Expanding the investigation to look at urban freshwater wetlands, it was found that there was a high degree of variability in local mosquito populations and that each wetland needed to be assessed with consideration to be given to site-specific characteristics. You can read more about our work investigating mosquito assemblages associated with urban water bodies in our publication here.

More research is underway in this field and my PhD student, Jayne Hanford, has already started collecting some fascinating data on wetland biodiversity and local mosquito populations.

While the focus of our studies is often prompted by concern about Ross River virus, interestingly, in recent years we’ve found considerable activity of Stratford virus. This is not currently considered a major human health concern but given how widespread it is, it raises concerns about the suitability of local wildlife, even in Western Sydney, to represent important reservoirs of mosquito-borne pathogens. You can read more about Stratford virus in our publication here.

The final piece of the puzzle is to understand the ecological role of mosquitoes. Where their potential health threats are deemed significant, how could management of mosquito populations have unintended consequences for other wildlife. What about the animals that eat mosquitoes? A number of years ago we did some research to determine the importance of mosquitoes in the diet of coastal bats. While there was no indication that mosquitoes are a critical component of their diet, they are still being snacked on and mosquito control programs need to consider any local ecological impacts.

Now, how am I going to squeeze all this into 15 minutes….

The presentation abstract is below:

What drives mosquito-borne disease risk in urban wetlands?

Webb, C. (1, 2), J. Hanford (3), S. Claflin (4), W. Crocker (5), K. Maute (5), K. French (5), L. Gonsalves (6) & D. Hochuli (3)

(1) Department of Medical Entomology, NSW Health Pathology, Westmead Hospital, NSW 2145; (2) Marie Bashir Institute of Infectious Diseases and Biosecurity, University of Sydney, Camperdown, NSW 2006; (3) School of Life and Environmental Sciences, Faculty of Science, The University of Sydney, Camperdown, NSW, 2006; (4) Menzies Institute for Medical Research, University of Tasmania, Hobart, TAS, 7000; (5) Centre for Sustainable Ecosystem Solutions, Biological Sciences, Faculty of Science, Medicine & Health, University of Wollongong NSW, 2522; (6) School of Arts and Sciences, Australian Catholic University, North Sydney, NSW, 2060.

Managing pest and public health risks associated with constructed and rehabilitated urban wetlands is of increasing concern for local authorities. While strategic conservation of wetlands and wildlife is required to mitigate the impacts of urbanisation and climate change, concomitant increases in mosquitoes and mosquito-borne disease outbreak risk must be addressed. However, with gaps in our understanding of the ecological role of mosquitoes, could control strategies have unintended adverse impacts on vertebrate and invertebrate communities? A series of studies were undertaken in urban wetlands of greater Sydney to investigate the role of land use, wetland type and wetland aquatic biodiversity in driving the abundance and diversity of mosquito populations. A diverse range of mosquitoes, including key pest an vector species, were found in urban environments and mosquito-borne pathogens were detected in local populations, implicating local wildlife (e.g. water birds and macropods) as potential public health risk factors. Estuarine wetlands are locally important with the percentage of residential land and bushland surrounding wetlands having a negative effect on mosquito abundance and species richness while the amount of industrial land had a significant positive effect on species richness. Mosquito control in these habitats is required but insectivorous bats were identified as mosquito predators and the indirect implications of mosquito control should be considered. The aquatic biodiversity of urban freshwater wetlands influenced the species richness of local mosquito populations indicating vegetation plays an important role in determining local pest species. However, the matrix of wetland types also influences the abundance of mosquitoes in the local area. These results demonstrate the need for site-specific investigations of mosquito communities to assist local authorities develop policies for urban development and wetland rehabilitation that balance the need for conservation with reduced public health risks.

To keep up to date on what’s happening at the conference, check out the program online or follow the conversation on Twitter.

 

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Could a podcast stop mosquito bites?

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This week I’m attending OzPod 2016: the Australian Podcast Conference, a workshop at the ABC, Ultimo. Celebrating International Podcast Day, the workshop brings together podcasters for “an event for the expanding podcast industry to escape the studio or office and meet with peers to share experiences, information, insights and ideas around audience acquisition and retention, new technologies, the rise of the podcast in traditional media, monetizing and of course the fine art of storytelling.”

 So, why am I going? I don’t even have a podcast!

I may not have a podcast now but I hope to start playing around with the platform soon as a complement to my other efforts to spread the word on science communication and public health awareness.

I’ve been thinking about kicking off a podcast for a while but have been a little reluctant due to time commitments. More importantly, I’ve also wanted to have a clear idea of what exactly I want to do.

In a previous life, I co-hosted a radio show on FBI Radio (during their test broadcast days) with my wife called “Good Morning Gidget”. It was a Saturday morning show of surf music and interviews with professionals involved in a wide range of coastal-based activities, from marine biologists to surf shop owners. Despite the early start on a Saturday morning, it was a load of fun. I’d also worked behind the scenes producing a couple of music shows. If I had more time, I really would have liked to pursue more work with community radio.

Perhaps podcasting will be the backup plan.

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It’s great to listen back to packaged interviews with radio, like the Health Report (I’m talking zika virus) but I was also lucky enough to have a chance to contribute to a few podcasts this year. I spoke with Science On Top about the outbreak of Zika virus and the implications it has for Australia, Flash Forward on what will happen if we eradicate mosquitoes from the planet and ArthroPod on what its like to study mosquitoes for a living!

All these were a lot of fun and were really motivating for me to want to get started with podcasting myself.

I feel like my experience with sound recording and ongoing engagement with media provides a solid background in most of the technical skills I need to get started. I’m hoping I’ll leave the OzPod 2016 conference with a few more tips on story telling and structuring a podcast too.

What I’ve been struggling with is format. I like the conversational nature of most podcasts but as I’ll probably be doing everything myself, perhaps a more structured and edited podcast is the go?

There are very few podcasts I listen to that are built around a one-person show. I’m not sure I could pull it off. Does anyone really want to listen to me ramble on for 20 mins about mosquitoes? 40minutes?

Sometime over the coming summer I hope to launch a short series of podcasts covering some of the basics of mosquito biology and how that relates to the ways we protect ourselves and our families from mosquito bites and mosquito-borne disease. I want to share my fascination with mosquitoes and explore some of the gaps in our understanding of mosquitoes, particularly their role in our local environment. 

Hopefully I can recruit some of my colleagues from around Australia for a chat too so we can share a little about the science behind our public health messages and what life is like to be chasing mosquitoes around swamps all summer

Sound like a good idea? Join the conversation on Twitter and let me know what you think, would you listen to a podcast about Australian mosquitoes?

 

 

 

 

 

 

Taking Australian wetland research to China

jayne_mosquitotrap

My PhD student Jayne Hanford has been super busy this year. Not much more than a year into her candidature and she has already locked away a summer of research and has been presenting her findings at conferences here in Australia as well as overseas.

After recently sharing our research at the Society for Wetland Scientists Annual Conference held in Corpus Christi, Texas, USA and the Mosquito Control Association of Australia conference on the Gold Coast, Jayne is off to China for the 10th INTECOL International Wetlands Conference.

Her research is focused on understanding the links between wetland vegetation, aquatic biodiversity and mosquito populations. Better understanding of these links will assist management strategies that minimise actual and potential pest and public health risks associated with mosquitoes and urban wetlands.

Our abstract for the conference is below:

Is the Biodiversity Value of Constructed Wetlands Linked to their Potential Mosquito-Related Public Health Risks?

Jayne Hanford1, Cameron Webb2, Dieter Hochuli1

1School of Life and Environmental Sciences, The University of Sydney, Australia; 2Department of Medical Entomology, Westmead Hospital and The University of Sydney, Westmead, Australia

 Stormwater treatment wetlands constructed in cities can enhance the sustainability of urban biodiversity by providing wildlife refuge areas and habitat connectivity. However, the creation of wetlands for stormwater infrastructure can increase risks to public health and wellbeing by proliferating nuisance-biting and pathogen-transmitting mosquitoes. In severe cases, this proliferation can erode goodwill in the community for creating and protecting valuable wetland systems.  We compared mosquito assemblages at 24 natural and constructed urban wetlands in the greater Sydney region, Australia. Our aim was to determine if stormwater wetlands constructed with the goal to support high biodiversity value also had reduced associated mosquito risks. Wetlands were located across a gradient of urbanisation determined by surrounding human population density, and included sites with different aquatic and riparian habitat complexity and availability. Adult and larval mosquitoes and aquatic macroinvertebrates were sampled on two occasions through summer and autumn. Aquatic macroinvertebrates were used to derive health indices, as well as being a relative measure of aquatic diversity.  Diversity of adult mosquito species was high, and abundance varied greatly between wetlands. Macroinvertebrate assemblages were also highly variable between sites. Wetlands with greater habitat complexity had lower adult mosquito abundance and greater mosquito species diversity, compared to stormwater-specific wetlands with minimal available habitat. As expected, mosquito assemblages did not respond to urbanisation and aquatic macroinvertebrate assemblages per se, but appeared to respond to a complex suite of coarse and fine-scale features that may affect a wetland’s biodiversity value.  Effectively integrating wetlands into cities requires balancing their design for water infrastructure purposes, biodiversity resources and public health and wellbeing requirements. Understanding the risks as well as the benefits will enhance the value of constructed urban wetlands in sustainable cities while minimising public health risks posed by mosquitoes.

Jayne will be speaking in the “The next generation of wetland science: ecosystems, applications, and engineering” session in the Nanhu Room 1520-1530 on Wednesday 21 September.

You can keep an eye on whats happening in China by following Jayne on Twitter and checking the hashtag

westernsydneywetlands

The Society for Wetland Scientists Annual Conference held in Corpus Christi, Texas, USA back in May included a paper by Jayne titled “Risky Wetlands? Conflicts between biodiversity value and public health” and prompted some great feedback and discussion among wetland scientists at the meeting. It was a successful trip and a timely reminder that I must get to one of the SWS meetings sometime soon, perhaps Puerto Rico?

Keep an eye out for Jayne’s research publications soon!

 

 

 

Why don’t mosquitoes spread Ebola?

13717624625_cd5f3df570_zAuthorities are quick to remind the community that Ebola virus is spread by blood and bodily fluids so it is hardly surprising that many are asking, “can mosquitoes spread Ebola”?

The 2014 Ebola outbreak in West Africa is the largest in history. As of mid-October, there have been approximately 9,000 cases and 4,500 deaths. The World Health Organisation warned that the infection rate could reach 5000 to 10000 new cases a week by the end of the year.

The virus is primarily transmitted from sick to healthy people by blood or body fluids (including but not limited to urine, saliva, sweat, feces, vomit, breast milk, and semen). In addition, objects contaminated with the virus (including needles and syringes) and direct contact with infected animals also play a role. Given this knowledge, it is not an unreasonable question to ask if blood feeding mosquitoes could spread the virus from infected people or animals.

Mosquitoes are just flying syringes aren’t they?

Mosquitoes are not flying syringes. They don’t transmit pathogens by transferring small infected droplets of blood. There is a complex biological process between the mosquito and the pathogen that must be completed before transmission can occur. In addition, there are ecological questions regarding the diversity, abundance, distribution and host-feeding patterns of local mosquitoes that can all influence the importance of mosquitoes in outbreaks of disease.

Unraveling these biological factors can be a complex process.

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

The saltmarsh mosquito (Aedes vigilax) (Photo: Stephen Doggett)

What happens inside the mosquito?

The mouth parts of a mosquito are made up of small tubes that either suck or spit. For a mosquito to effectively transmit a virus, the virus must make its way from the mosquito gut to the mosquito saliva.

If a mosquito takes a blood meal from an infected animal that contains the virus, the virus must infect the cells of the gut and then pass through to the body of the mosquito, replicate and then disseminate throughout the mosquito until the salivary glands are infected. This process is known as the extrinsic incubation period and can take anywhere from a few days to over two weeks. Once the salivary glands are infected, the mosquito may pass the virus to a new host through the saliva she injects while taking a blood meal.

There can be many barriers in this process. It may simply be the case that the virus cannot survive long enough in the gut of a mosquito. If it does survive, the virus may not “escape” the gut of the mosquito. In this case, the pathogen is excreted and the mosquito does not become infected.  Even if most of the body of the mosquito becomes infected, the salivary glands may remain uninfected and the pathogen is not transmitted through the bite of the mosquito.

vcexperiments

To test the ability of mosquitoes to become infected and transmit pathogens requires laboratory studies (Source: Stephen Doggett, Pathology West – ICPMR Westmead)

Experiments to determine the ability of individual mosquito species to transmit pathogens are known as “vector competence” experiments. Hundreds of these have been conducted in many countries to assess the ability of local mosquito species to transmit endemic and exotic pathogens. These studies typically involve the exposure of mosquitoes to an infected blood meal and then testing, at various times following infection, the legs, wings and body of the mosquito (to determine infection) and salivary glands or saliva specifically.

There are very few published vector competence studies on Ebola. In one, three species of mosquito (Aedes albopictus, Aedes taeniorhynchus, and Culex pipiens) were infected with Ebola Reston virus but no virus replication was recorded. What was interesting about this study was that, by attempting to inoculate the mosquitoes through intrathoracic injection rather than orally (i.e. via an infected blood meal), the researchers were able to bypass the mid-gut barrier. It gave the virus the best chance of infection. However, the lack of virus replication in the mosquitoes suggests they are unlikely to be natural hosts of the virus.

What happens outside the mosquito?

When assessing the role of mosquitoes in outbreaks of disease, it is important to look at not only how competent the mosquito is at becoming infected and transmitting a virus. What happens in the laboratory may not reflect what is happening in the field.

For example, a mosquito that preferentially feeds on birds may be an effective vector but will play a minor role in transmission of the pathogen to humans as it will rarely, if ever, bite a person. These mosquitoes, however, may play an important role in spreading the pathogens amongst wildlife and this may indirectly increase the risk of exposure to humans. There may also be mosquitoes that are effective vectors but are naturally found at such low densities (due to reliance on specific environmental conditions) they rarely bite humans.

The natural reservoir host for Ebola virus appears to be bats. However, it is suspected that one of the most likely routes of transmission from bats to humans could be via the spread of the virus to primates (who are infected by bat droppings or bodily fluids of diseased bats) and then to humans through expose to the infected primate. There are likely to be plenty of mosquitoes that readily bite both bats and various primates in regions where Ebola is endemic but there is no evidence that mosquitoes play a role in these endemic enzootic transmission cycles.

During an outbreak of Ebola in Kikwit (Democratic Republic of the Congo) in 1995, researchers collected approximately 35,000 arthropods and tested them for the presence of the virus. 15,118 mosquitoes were tested and no Ebola virus was detected.

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Ebola virus transmission cycles between enzootic and epidemic conditions (Source: CDC)

While mosquito-borne pathogens have emerged (or reemerged) in various parts of the world, this has primarily been driven through the movement of vectors and infected individuals through international travel. There is no evidence that mosquitoes have played a role in the transmission of any of the emerging zoonotic pathogens that have jumped from animals to humans in recent times.

There are also other factors to take into consideration. One critical factor with regard to the current Ebola outbreak is the epidemiological data. As described in this review of transmission, human cases are driven by direct contact with the blood or other body fluids of infected patients. If mosquitoes were capable of transmitting Ebola virus, there would likely be a very different distribution of cases with many people becoming infected who hadn’t had prior contact with an infected person.

Unfortunately, while the mosquitoes in West Africa are not transmitting Ebola virus, they are transmitting malaria parasites. Malaria will kill many times more people in West Africa than Ebola this year. Perhaps the most significant public health impact of the Ebola outbreak in West Africa will be the disruption of anti-malaria campaigns?

The photo at the top of this piece is taken from European Commission Humanitarian Aid & Civil Protection.

Solving the common mystery of the cat flea

You may be inclined to think that we know everything we need to know about the flea but we don’t. They infest our pets and our homes; we treat them with a variety of substances and yet they are near impossible to exterminate. Importantly, they occasionally bite people, causing annoyance and sometimes severe skin reactions. You may also think this is all we really need to know them. In fact, these parasites are often overlooked in terms of their significance to animal health, their competence as disease vectors and the impacts they make on our everyday lives. There is much more to these irritating insects than meets the eye.

This is the first “guest post” on my blog and comes from my PhD student Andrea Lawrence (University of Sydney) ahead of her presentations at the Australian Society for Parasitology conference in Canberra next week (looks like a wonderful program of events this year!). I’m hoping that there will be plenty more guest posts from Andrea and my other students in the near future.

The most common flea encountered in Australia is the cat flea, Ctenocephalides felis. Just because your dog has fleas, it doesn’t mean it has dog fleas (Ctenocephalides canis). This is a common misconception. In fact, it appears as if the dog flea is something of a mythical creature in Australia. Despite historical records and anecdotal reports of dog flea infestations, there is no recent literature confirming their presence. A recent study of over 2,500 pets failed to find a dog flea. As such, if your pet is troubled with fleas, you can likely lay the blame solely on the cat flea.

The cat flea is the top ectoparasite affecting cats and dogs globally for a variety of reasons. They are the cause of up to 50% of all dermatological cases presented to vet clinics world-wide. Pet owners are spending $40 to $70 on flea and tick control products per month and, based on figures from the United States, over $1 billion annually. That is a lot of money to spend only to have the fleas come back time after time.

As well as the nuisance-biting, the cat flea also carries zoonotic pathogens such as Bartonella (bacteria that causes cat scratch disease in hypersensitive or immunocompromised people) and Rickettsia (bacteria that causes murine typhus and flea-borne spotted fever).

There may also be many cases of underdiagnosed febrile illnesses caused by flea-borne pathogens that fly under the radar due to the presentation of generic fever and flu-like symptoms that rarely warrant further pathological investigation. Of course, the most famous and historically significant pathogen spread by fleas is the plague bacteria: Yersinia pestis. Plague is certainly not a thing of the past with recent outbreaks in Madagascar and up to 17 cases reported from North America each year. Considering the highly ubiquitous nature of fleas in human environments, and many species’ tendency to be host generalists – particularly the cat flea – shouldn’t we be more concerned, or at least more aware, of their biology, taxonomy and potential public health risks?

Professional Ratcatchers from Views taken during Cleansing Operations, Quarantine Area, Sydney, 1900

Although the pathogens that cause plague are not endemic to Australia, plague has touched Australia with significant impact. Here are some professional ratcatchers from Sydney, Australia, during the plague outbreak in 1900 (Source: State Library Image Collection)

Given the impact these little parasites have on our lives, it is baffling how little we know about them. The genetic profile of the cat flea is highly understudied and yet within the genetic code lies hidden implications for the evolution of insecticide resistance, disease transmission and the passage of fleas across continents and the global sphere. A study from the Veterinary Parasitology unit at the University of Sydney found that in 2011 across 5 states of Australia cat fleas collected from veterinary practices were 100% genetically identical at the mitochondrial DNA. This was a very unusual result as populations of other flea species are generally very diverse. The result was comforting news at the time for the regulation of veterinary pharmaceuticals as the efficacy of flea control products were able to be compared against flea populations across the entire country.

Taken from “How to get rid of fleas at home” via Appliances online blog.

We know fleas from Australia are genetically similar but what about elsewhere? We broadened the scope of the investigation and compared the fleas from Australia to those collected from Thailand, Fiji and Seychelles: a group of Islands north-east of Madagascar. These results showed that from a global perspective, cat fleas are genetically diverse. The 2013 flea season yielded a novel second Australian haplotype found in north-east Australia which contradicts the unanimous results from the previous study in 2011. This haplotype was shared with most fleas tested from Fiji, suggesting some recent flea transfer between the two countries. With the rapid emergence of this second haplotype since the previous study, it sparks the question of whether there may be a division of fitness between the two haplotypes. Could this division be resulting in a steady ‘invasion’ of Australia by the second haplotype?

To investigate the haplotype diversity in this study we developed a novel genetic marker capable of clearly delineating different flea species, subspecies and haplotypes. Previously, genetic studies primarily used a mitochondrial DNA marker called cox2. However, there is an emerging global standard of genetic taxonomy called DNA barcoding, which uses a similar gene called cox1. This method involves storing massive amount of short DNA sequences in an electronic database, accessible to anyone with internet access. Currently the database called Barcode of Life Database or BOLD holds 3 million ‘barcodes’, 2 million of which are arthropod barcodes. I wanted to align fleas with this emerging global standard by developing a cox1 marker that would work for fleas. It is surprising given the global significance fleas that the marker has not been optimised before. The ‘barcodes’ collected from this study are now available on BOLD and can be searched allowing greater dissemination of and accessibility to flea genetic data.

A change in the genetic makeup of Australia’s flea population as discovered recently has implications for the pharmaceutical companies who can no longer apply a blanket approach to flea control efficacy testing. Research is continuing this year in the Veterinary Parasitology Unit at The University of Sydney to monitor the rate of spread of this second haplotype. In time I hope this may yield greater understanding of the cat flea genetic puzzle that will lead to finding the key to effective control of these tenacious blood-sucking creatures and the diseases they carry.

The abstract for Andrea’s paper is below:

The cat flea, Ctenocephalides felis (Siphonaptera: Pulicidae) (Bouché), is the most common flea species found on cats and dogs worldwide. We investigated the genetic identity of the cosmopolitan subspecies C. felis felis and evaluated diversity of cat fleas from Australia, Fiji, Thailand and Seychelles using mtDNA sequences from cytochrome c oxidase subunit I (cox1) and II (cox2) genes. Both cox1 and cox2 confirmed the high phylogenetic diversity and paraphyletic origin of C. felis felis. The African subspecies C. felis strongylus (Jordan) is nested within the paraphyletic C. felis felis. The south East Asian subspecies C. felis orientis (Jordan) is monophyletic and is supported by morphology. We confirm that Australian cat fleas belong to C. felis felis and show that in Australia they form two distinct phylogenetic clades, one common with fleas from Fiji. Using a barcoding approach, we recognize two putative species within C. felis (C. felis and C. orientis). Nucleotide diversity was higher in cox1 but COX2 outperformed COX1 in amino acid diversity. COX2 amino acid sequences resolve all phylogenetic clades and provide an additional phylogenetic signal. Both cox1 and cox2 resolved identical phylogeny and are suitable for population structure studies of Ctenocephalides species.

The full reference of the paper is:

Lawrence, A. L., Brown, G. K., Peters, B., Spielman, D. S., Morin-Adeline, V. and Šlapeta, J. (2014), High phylogenetic diversity of the cat flea (Ctenocephalides felis) at two mitochondrial DNA markers. Medical and Veterinary Entomology [early view]doi: 10.1111/mve.12051 [Online]

(The image of the cat flea, Ctenocephalides felis, at the top of this blog post is taken from the PaDIL image collection by K Walker)

Jumping about in muddy puddles

I was kindly invited to contribute to Sarah Keenihan’s wonderful “Science For Life 365” blog recently. Please share some of the joys of “bush combing” in freshwater rock pools with me! (Also, please drop by Sarah’s blog for some excellent examples of how science can impact our day to day lives!)

Science for Life. 365

freshwaterrockpool

Sarah: Some scientists just inherently know how to communicate.

Entomologist Dr Cameron Webb is one of those people. This week he sent me a wonderful idea for a blog post, and followed up a few days later with this story: 

Cameron: The joys of beach combing are well known but what about “bush combing”? Perhaps not quite the same, but after a bit of rain, there is much joy to be had splashing about in puddles, ponds and potholes in your local bushland.

A wet winter weekend is just the time to start sloshing about.

Most of my summer is spent chasing mosquitoes about the wetlands of NSW, from coastal saltmarshes and mangroves to constructed waste-water treatment wetlands. I’m generally targeting specific mosquitoes, tracking changes in abundance and processing them for the detection of pathogens such as Ross River virus. However, Australia boasts a diverse mosquito fauna and many species are found in highly…

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Can we genetically modify malaria mosquitoes to extinction?

angambiae_wikicommonsMalaria no more? A new study has provided a pathway to possibly driving one of the most important malaria transmitting mosquitoes to extinction by using genetically modified mosquitoes that produce almost entirely male offspring. Without many females, the mosquito population will crash. A decline in the number of malaria cases should similarly follow.

There has been much research, as well as community discussion, regarding the use of genetically modified mosquitoes (and sometimes the pathogens themselves) to reduce the impacts of mosquito-borne disease. The recent proposals around the use of genetically modified mosquitoes to assist in the control of dengue outbreaks have been attracting many headlines, including both excitement and concern.

The new study, “A synthetic sex ratio distortion system for the control of the human malaria mosquito” (published in Nature Communications), reports on the genetic modification of mosquitoes that only produce sperm that result in (mostly) only male offspring. The researchers used a modified enzyme that attacks a specific region of the X-chromosome, preventing it being passed onto the next generation. Mating between GM mosquitoes and “wild type” mosquitoes produced up to 97.4% male mosquitoes.

In addition, the researchers demonstrated that once the wheels are set in motion, there is the potential that the spread of these  mosquitoes carrying “male only sperm” pass on the trait to their offspring and then their offspring. It is hoped that as these mosquitoes spread throughout the environment, eventually, the population of mosquitoes will crash as female mosquitoes are removed. The theory was tested in the laboratories and the researchers found that it took about 6 generations for the populations to crash (but they did need to start off with three times as many genetically modified mosquitoes to “wild type” mosquitoes).

While the technology is new, the idea was first proposed in the 1950s. The idea that you can distort the sex ratio of insect populations to control pest impacts had been proposed with various approaches to achieve it. The latest approach provides a novel way to apply the strategy to mosquitoes.

An illustration taken from "This is Ann, she's dying to meet you" produced by US War Department, 1943

An illustration taken from “This is Ann, she’s dying to meet you” produced by US War Department, 1943

Doesn’t this latest research mean, in theory, you could make mosquitoes extinct?

The results from the current study are fascinating but it is still very early days before it is known if this approach works under field conditions and can actually reduce malaria, let alone drive mosquitoes to extinction. Keep in mind that this study focuses on just one of the thousands of mosquito species found throughout the world.

The mosquito the researchers from the Imperial College of London used was one of the key vectors of malaria parasites, Anopheles gambiae. This species belongs to a group of mosquitoes that contain up to 40 different species that may play a role in the transmission of malaria parasites. The fact that there are so many mosquito species capable of transmitting malaria parasites makes developing a “silver bullet” approach to control difficult.

Global distribution of potentially important malaria vectors (Taken from: Kiszewksi et al., 2004. American Journal of Tropical Medicine and Hygiene 70(5):486-498.)

Global distribution of potentially important malaria vectors (Taken from: Kiszewksi et al., 2004. American Journal of Tropical Medicine and Hygiene 70(5):486-498 via CDC)

There are many ecological and operational issues surrounding the release of genetically modified mosquitoes. Notwithstanding any fitness cost (e.g. less effective mating with “wild type” mosquitoes, lower fecundity, lower survival of immature stages, smaller dispersal ranges) that may put the genetically modified mosquitoes at a competitive disadvantage in the field, there are the issues of determining when, how many, and how frequently, genetically modified mosquitoes must be released into the environment. Some of these issues are discussed in this discussion paper and I’ve written about regulation here.

Even if the laboratory technique is translated to the field, and it worked, what would happen if you drove local populations of Anopheles gambiae to extinction?

I’m not sure that there is any research that identifies the ecological role of these mosquitoes. There certainly hasn’t been any work, to my knowledge, that addresses the issue in the same way we studied the ecological role of the Australian mosquitoes that spread Ross River virus. However, the potential ecological impacts of genetically modified mosquitoes have been identified.

Putting aside the issues of ecological impact (perhaps there wouldn’t be any significant ecological impact?), what would be the impact on human health? This is the critical issue. We know that by reducing the contact between mosquitoes and humans through the use of bed nets and insecticides can reduce the incidents of malaria, what if populations of Anopheles gambiae were significantly reduced or eradicated?

Malaria eradication campaigns have been with us for decades but are they now transitioning from spraying insecticides to releases genetically modified mosquitoes? (Source: National Library of Medicine)

Malaria eradication campaigns have been with us for decades but are they now transitioning from spraying insecticides to releases genetically modified mosquitoes? (Source: National Library of Medicine)

One of the problems may be that the ecological niche exploited by Anopheles gambiae is simply taken up by another of the mosquitoes able to transmit malaria. Anopheles gambiae is a pretty good competitor and if you take it out of the environment, another Anopheles species may move in. There is no doubt that Anopheles gambiae is one of the most important vectors of malaria parasites but even if a “replacement” species moves in, outbreaks of disease may still be less than before. However, health authorities will still need to call on traditional mosquito control and malaria prevention strategies. A balance is required when assessing the cost effectiveness of the new and old strategies.

Amongst the wave of new technologies purported to aid in the battle against malaria, it is worth noting that current methods of prevention (e.g. bed nets) and control (e.g. insecticides), in combination with better diagnosis and treatment, have contributed to a reduction in world wide malaria mortality rates by 42% since 2000. Combining different mixes of approaches (e.g. bed nets and residual insecticide treatments) has been shown to be potentially significant. In the future, perhaps genetically modified mosquitoes should be added to this mix too.

You can listen (stream or download) to me chat with James Carleton about the implications of the research on Radio National’s Breakfast. There has also been plenty of news coverage following the publication of the research, a good overview is here.

Why not join the conversation by following me on Twitter?

The photo of the malaria vector, Anopheles gambiae, at the top of this post is taken from here (CDC/James Gathany)