Tuesday, August 2, 2011

No place to hide

A few months ago I had the opportunity to visit with scientists at Research Associates Labs in Addison, Texas.  They told me about a new application of DNA detective work that, I believe, has some exciting uses in the pest control industry.  Last week I had the chance to catch up again with one of Research Associates' scientists, Dr. Kate Johnson, who was explaining the service to PMPs attending the first ever Bed Bug Academy of the Southwest sponsored by the Texas Pest Control Association. More about that meeting in a later post, but to see what Dr. Kate had to say, and how the process works, check out the video below.

This meeting was Research Associates' Labs first introduction to the pest control industry. Until recently, their focus was on providing molecular diagnostics tests to vets and zoos. The techniques that Dr. Kate describes  may seem like cutting edge stuff to us in pest control, but the technology is not especially new.  Using a technique known as real-time PCR, DNA collected on a swab can be rapidly amplified so that it can be detected by laboratory equipment, much like a stereo receiver amplifies otherwise inaudible radio waves.

The key to pest detection is finding a piece of DNA that is unique to the target organism you wish to detect.  Once this DNA fragment is identified, special primers can be selected that will amplify only the target DNA strands.  If the unique DNA is not present, nothing get amplified and detected. Research Associates Labs has taken the time to customize the technique to look specifically for human bed bug DNA.  Using sterile swabs, a PMP can walk into an account and quickly sample the likeliest locations in a room for bed bug DNA. Once received by the laboratory, its only a matter of a few hours to learn whether bed bugs have been present in a room.

There are a few limitations to the procedure and how to interpret the results.  First, you have to take a good sample from the right spots in a room.  Second, some chemicals, including pesticides, can interfere with the results.  But perhaps most importantly, the test cannot easily tell whether bed bugs are still active in a room.  Because bed bug DNA lasts a long time in an indoor environment, one cannot assume that a positive test didn't come from an infestation that was eliminated a year earlier, for example.

With time, I suspect we'll see the real value of DNA testing in detecting low level bed bug infestations in homes where visual inspections don't reveal bed bugs, but where a client insists that bites are occurring.  Given the expensive nature of expanding bed bug treatment into rooms beyond a bedroom, the technique might also be useful when initially inspecting and bidding an account to determine whether additional rooms in a home might need treatment. At $15 a pop, hotels might find the service a little pricey for regular use; however the technique might be useful in confirming a positive detection of bed bugs by a canine bed bug team doing routine hotel inspections.

With additional tests, the DNA technique could be most helpful in confirming the presence or likely absence of biting mites, fleas and bed bugs from those mystery bug clients we encounter so often.  While there's not yet a test for the several home-infesting species of biting mites, cat flea and scabies mite tests are currently available.  Pretty soon I predict that bed bugs, and perhaps all pests, will have no place to go, no place to hide.


James said...

One important thing to consider is that a negative test result would not confirm the absence of bed bugs. In working with PCR and testing for arthopod-borne diseases it is important to be using the right material.

For example, we test ticks for diseases, if we do not have access to the digestive track such as a sample that was only half of the tick remaining and no digestive track (this actually happened today), then the sample is not appropriate for testing, Even if the tick was carrying the pathogen, the test would most likely not yield a positive result.

I agree that PCR could be used to confirm the presence of bed bugs, but it would be incorrect to assume no bed bugs, or for that matter any other pest, was not present based upon a negative test result. That route is a slippery slope. Depending on how the sample is collected, it's likely possible that a bed bug just didn't come in contact with that surface. You couldn't sample 100% of the room.

I would be curious to learn more about what a test sample consists of and how they are collected.

Mike Merchant, PhD said...

Good point James. I tried to address when I discussed limitations of the technology, but I didn't expand on very well. It's crucial to take a good sample, and of course it doesn't change the old maxim: "its hard to prove a negative".