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Vet Talk

There’s a Test For That Tick! But Is There a Need?
June 6, 2016 (published) | June 6, 2016 (revised)
J. Scott Weese, DVM, DACVIM

questing tick Dryden

Some diagnostic tests that are available are more of a situation of a test looking for a market rather than filling a clinical need for additional information. That complicates matters since providing new information isn’t necessarily useful if we don’t know what to do with it. In some situations, it can even lead to bad decisions.

Increased awareness of tick-borne diseases is spawning a market for tick testing. If people find ticks on themselves or their pets, they can submit the ticks for testing. In some regions, public health agencies do (and pay for) the testing. In others, it’s user-pay.

The question is “what does the test result tell us, and what do we do based on the results?” That’s the key. If testing leads to useful information or appropriate action, it’s good. If it confuses the situation, leads to no action or leads to inappropriate action, it’s bad. Tick testing can cover all of those, depending on how it’s applied.

Some government agencies test ticks to better understand what tick-borne infections may be in the area, and to determine how commonly ticks are infected. That does not impact the management of the person or pet from which the tick came. Rather, it’s used at the population level to get more information and guide various programs and response. That’s useful, as long as people realize what the testing is for and the individual results aren’t going to change what happens to them.

Sometimes, tick testing results are taken as an indication that infection is present or likely, and that treatment is required. That’s not useful, and if anything is probably harmful. For example, for Lyme disease to develop, the following has to happen (also check out the latest OAHN infographic on Lyme Disease in dogs in Ontario):

  • a tick has to attach
  • it has to be the right type of tick
  • that tick has to be infected with Borrelia burgdorferi (the bacterium that causes Lyme disease)
  • it has to feed for at least 24-48 hours to transmit the bacterium
  • the bacterium has to enter the body
  • the bacterium has to evade the immune system
  • disease has to develop.

Testing the tick can answer points 1-3, but not the rest.

This leads me back to testing.  An over-the-counter test is now available in Canada for testing ticks for the presence of B. burgdorferi. If the test is accurate (a big if, since I’m not aware of any published data), the usefulness is as discussed above, i.e. potentially useful to understand the population and if an individual has been potentially exposed (but not necessarily infected). However, it’s bound to be misused.

As reported by the CBC,  “The Public Health Agency of Canada does not recommend testing of ticks for infection to decide whether to treat someone for Lyme disease, but said the test may have a role to play in disease prevention if it prompts people to seek medical attention.” The question is, does this test actually change much?

If the tick is positive, what does that mean?

  • It means there was the potential for exposure, if the tick was attached for long enough. That doesn’t mean disease will occur. It means that if the individual develops signs consistent with Lyme disease, they should go to a physician (or bring their dog to a vet), and mention the Lyme test result. However, the same should apply to anyone who has (or has a pet with) signs consistent with Lyme disease if they have recently had a tick exposure, even without knowing the tick’s Borrelia status.

If the tick was negative…

  • That means the individual is at low risk of Lyme disease from that tick. It doesn’t mean no risk, unless the test is 100% accurate, which is unlikely, nor does it rule out potential exposure via other ticks that weren’t found and tested (particularly on a furry dog which makes them tough to find).

If I had the test available, would I test a tick I found on myself or my dog? Probably, out of interest and to get a better understanding of Borrelia in the area. The problem is, not everyone will approach the test that way. Unfortunately, it’s bound to lead to an “OMG THE TICK WAS POSITIVE. GIVE ME DRUGS… NOW!!!”

That’s bad.


Republished with permission from Worms and Germs Blog


 
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