Testing the claims of new mosquito repellents

aedes_aegypti_doggettHaving worked in the field of “mosquito research” for over 10 years, I’m no stranger to new mosquito repellent formulations or mosquito traps that purport to provide a breakthrough in the prevention of mosquito-borne disease. I’ve tested dozens of these products, both in a research capacity and as part of the registration process of new products here and overseas.

Since DEET first become widely available in the 1950s, there really hasn’t been many new topical mosquito repellents reaching the market AND accepted by health authorities. Picaridin and PMD are probably the two exceptions. For the most part, the vast majority of mosquito repellents currently available contain one of these three active ingredients. Most of the recent developments have been in the formulations, making them “nicer” to use. I’ve written about these various repellents elsewhere (try here, here or here) so won’t repeat it here. I must say though that although these products are often claimed to contain “toxic chemicals”, reviews of the literature repeatedly find that these products are safe to use, even on young children.

The patch that makes you invisible to mosquitoes!

This week, a new mosquito repellent formulation/device was grabbing headlines. The  Kite™ Mosquito Patch repellent is currently a runaway success on crowd funding website Indiegogo. Their website is here. At the time of writing, they’d already raised close to US$190,000. That is a lot of money. If nothing else, it demonstrates the willingness of the community to support the development of new approaches to reducing the burden of mosquito-borne disease.

The promotional video for Kite™ Mosquito Patch campaign can be seen here.

The developers claim:

Kite™ Mosquito Patch is a small, powerful patch that allows humans to go virtually undetected by mosquitoes for up to 48 hours. Kite’s compounds act as a non-topical, spatial repellent, blocking mosquitoes’ ability to detect carbon dioxide – their primary method of tracking human blood meals. Indiegogo

Firstly, it would be fantastic if this worked. One of the biggest obstacles to the effective use of repellents is the need to apply a topical formulation correctly, as well as overcoming any actual or perceived unpleasantness of using any of the currently available formulations. If there was a “stick on” device that protected an individual or household from mosquito bites, it would go a long way in our battle to reduce the burden of mosquito-borne disease.

It is important to note that the developers state on their website that Kite™ Mosquito Patch is not a substitute for bed nets, rather it is an alternative product to topical repellents.

With regard to the Kite™ Mosquito Patch, I’m a little skeptical as to how effective it will be outside of the laboratory. I hate to sound negative about this but from personal experience, I have not tested a “spatial” repellent that worked effectively in a field-based situation. Even in a laboratory setting, a small device worn on one part of the body won’t provide “whole body” protection against bites. A number of reputable organisations have provided funding to the various stages of this product’s development so it isn’t fair to dismiss their claims too quickly. However, in the absence of published laboratory trials, it is difficult to make an assessment of just how effective this “spatial repellent” product will be.

Products claiming to be “spatial repellents” such as mosquito coils and sticks offer some protection if they contain insecticides (and therefore “knock down” of near by mosquitoes) but there is growing opinion amongst experts that these provide only limited protection against nuisance-biting and/or mosquito-borne disease risk. Australian studies have shown that burning devices like this that contain botanical products provide a reduction in landing mosquitoes of approximately 70%. The same study found that a topical application of DEET stopped 100% of landings.

Probably the most exciting development in “spatial repellents” is metofluthrin. This is often called the “smokeless mosquito coil”. Studies have suggested this is a potentially effective tool in controlling dengue outbreaks.

The team behind Kite™ Mosquito Patch claim that the product makes the person wearing the patch “practically invisible” to mosquitoes by blocking the detection of carbon dioxide. It is true that mosquitoes use carbon dioxide, as well as the smell of the chemical cocktail of microbes on our skin, to determine who and where to bite. I’ve written about this here.  This is essentially the same process in play with DEET. It blocks the blood feeding urges of mosquitoes. It essentially makes the person wearing the repellent “invisible” to mosquitoes for various periods of time depending on the concentration of DEET in the specific formulation.

Will this new repellent device work? The team behind Kite™ Mosquito Patch haven’t really provided enough detail in their promotional material to make a good assessment of the effectiveness of this product. I don’t want to tear apart their claims but it is worth taking a look at the processes behind assessing new mosquito repellents.

Taking Australia as an example, any product claiming to repel mosquitoes must be registered with the Australian Pesticides and Veterinary Medicines Authority (APVMA). The APVMA assesses new products for both safety and effectiveness.

Do you just stick your arm in a cage of mozzies?

There are a few different ways to test repellents but one of the most common methods remains the “arm in cage” test. This seems to be one of the methods used by the developers of the Kite™ Mosquito Patch. As this repellent isn’t a topical formulation, they need some alternative strategies to test the methodology.

The shot below is taken from their promotional material. It is a neat idea to test the effectiveness of a repellent without directly exposing researchers to mosquito bites. Similar techniques are used to test the effectiveness of insecticide and/or repellent treated clothing. The team at USDA are undertaking some great work in this area as part of the Deployed War-Fighter Protection (DWFP) Program.

An example of the testing methodology of the Kite repellent as depicted in promotional material. Taken from The Australian.

As I mentioned earlier, without more detail on the laboratory methods, it is difficult to assess the links between the work with Kite™ Mosquito Patch in the laboratory and its application in the field. I appreciate that the promotional video isn’t claiming to be a factual presentation of their laboratory procedures. While the presence of a patch (or the candidate repellent substances), may reduce the number of mosquito bites in the nearby area, what about elsewhere?

In 2011, I published a paper on the testing of mosquito repellent “wrist bands”. These were bands that contained botanical products. The laboratory test results showed that there was a significant difference in the landing rates of mosquitoes (Aedes aegypti) adjacent to the band, compared to “untreated” arms. However, landing rates 10cm away from the band were no different to “untreated” arms. This supports previous studies that have reported similar results with wrist bands containing botanical extracts. We tested a wide range of essential oils from Australian native plants as topical repellents also and found only very limited protection.

When I’ve tested similar products (i.e. devices containing botanical ingredients) in the field, I get the same result. A product that provides some limited spatial protection in the lab, does not provide “whole body” protection under field conditions. I’ve never found them to provide the same level of protection as a DEET-based topical repellent. However, some researchers have found that DEET-impregnated anklets, wristbands, shoulder, and pocket strips do offer some protection against biting mosquitoes in the field (up to 5h).

What mosquito was the repellent tested against?

This may seem a strange question to ask. However, it is critically important. There are thousands of mosquito species worldwide. Some are far more important as nuisance-biting pests than others. Many don’t even bite humans. The vast majority of mosquito repellent tests published in the scientific literature use Aedes aegypti (the dengue/yellow fever mosquito). This is pretty much the lab rat of the mosquito world. It is a great species to work with as it is a day-biting species and has a relatively consistent biting rate. Testing a repellent against Aedes aegypti is pretty much the way to go. In malaria prone regions, testing against the malaria-vector and avid nuisance-biting species Anopheles gambiae is useful too.

If, however, a repellent is tested against a species such Culex quinquefasciatus, a species generally associated with bird-feeding, it is difficult to be confident with the results. We have this species is colony and whenever it is used for repellent tests, we get greatly different results. For example, in our testing of a botanical-based topical repellent, over 200min of protection against Culex quinquefasciatus was achieved but no protection against Aedes aegypti was recorded.

I couldn’t find any reference to the mosquito species used for the lab testing of the Kite™ Mosquito Patch but I’d suspect that they probably used Aedes aegypti.

Does the product repel or protect?

This is a tricky one. What is an effective repellent? One that stops some mosquitoes biting or one that stops ALL mosquitoes biting? Given that it only takes one mosquito bite for the transmission of a pathogen, I believe that a repellent should provide protection from all bites. This is why most published reports contain information on “complete protection time” of candidate repellents. This represents the duration of protection provided by a repellent. It is interesting to note that once a candidate repellent has failed this test (i.e. mosquitoes are actively biting) there may be still be over 80% reduction in the number of mosquitoes landing on treated forearms compared to untreated controls.

A repellent that only reduces the number of bites won’t necessarily prevent disease.

When will we know if the Kite™ Mosquito Patch works?

As the developers state on their fundraising page, field work is to be conducted in Uganda. It will be interesting to see the results. They will certainly have a great funding base to work from. In their promotional video they state they’re testing in the “toughest proving ground there is”. It is true that Uganda has a high rate of malaria. It will be great to see a well designed project that investigates the role of the new repellent device in reducing disease risks. I hope they include other strategies as well including bed nets and insecticides as well to determine what works best.

If they really want to test the Kite™ Mosquito Patch with regard to protecting against mosquito bites, they are welcome to get in touch with me. Some of my study sites have huge populations of the saltmarsh mosquito Aedes vigilax. If the repellent patch works in those situations, it really will be a game changer!

Webb_mosquitoesIn summary, I would like to remain optimistic about the Kite™ Mosquito Patch. Despite all the technology at our finger tips, the burden of mosquito-borne disease internationally remains a significant health problem. Along with a range of strategies, new mosquito repellents will definitely play an important role in reducing public health risks internationally.

I’ll look forward to reading about the results of the Uganda field tests in the months ahead!

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