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?

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

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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10 things to love about mosquitoes!

I was recently invited by Associate Professor Chris Buddle (McGill University, Montreal Canada) to contribute to his SciLogs blog, Expiscor. With the brief to produce a series of ten interesting facts about mosquitoes, it would be easy to concentrate on their public health significance. “Ten potentially life threatening pathogens or parasites transmitted by mosquitoes” would have been an obvious choice! However, instead of going down that path, I chose the less obvious route and decided to go with “Ten Things to Love About Mosquitoes“!

Please follow the link to read about some of the fascinating, and potentially ecologically important, things to love about mosquitoes; from singing sexy love songs to cleaning up ant vomit to cooling down hot drinks to pollinating plants. Haters love to hate but how about some love for the mosquitoes that aren’t all that bad….

Why not contribute to the conversation on Twitter? Tell me what you love about mosquitoes….

You can also follow Chris on Twitter @CMBuddle, or check out his wonderful blog at http://www.arthropodecology.com

 

 

 

Can we genetically modify malaria mosquitoes to extinction?

Malaria 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

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 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)

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?

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

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