Do Popular Dog Tick Treatments Cause Seizures?

There’s a new health scare in dogs and cats. Four common flea and tick treatments are being linked with nervous system disorders like muscle tremors, twitching, unsteadiness and even seizures.

Most of the discussion so far has been from the USA, but Australians have a unique perspective on this. The drugs we’re talking about are the best chance we’ve ever had to end the greatest fear of many pet owners: tick paralysis.

Tick paralysis? If like me, you live outside a tick area this might surprise you.

What Is Tick Paralysis?

Adapted from Roberts FHS (1970) Australian Ticks. Yeerongpilly QLD by TAGS Inc, Bill Conroy & Norbert Fischer [Attribution], via Wikimedia Commons

Main article: Tick paralysis in dogs & cats

Ticks are tiny bloodsucking parasites known to spread many blood-borne infections. The most famous of these is Lyme Disease, but there are also several important animal diseases here in Australia. Tick paralysis, however, is not caused by an infection, but by a toxin from the saliva of only certain ticks.

The map is only a guide but you can see that around half of Australian pet dogs and cats live near a tick area. Many more will travel into an affected region in their lifetime.

Signs Of Tick Paralysis In Dogs

A few days after attachment, an animal starts to develop some or all of the following signs:

  • Change in the voice
  • Weakness e.g. difficulty climbing stairs
  • Stumbling and ‘drunken’ hind legs
  • Rapid, shallow breathing

Without treatment, paralysis spreads throughout the body to eventually cause death by failure of swallowing and respiration. It’s vital to see a vet as soon as the first signs appear.

Prevention Of Tick Paralysis

In tick areas, prevention of paralysis is by a combination of:

  1. Daily searching for ticks
  2. The use of tick repellents and tick killers
brown dog ticks

Searching is difficult, and rarely 100% successful. Just look at the size of ticks before they feed and you can see why. Success is improved by keeping long coats clipped short.

Tick prevention options are found at our review of flea and tick treatments for dogs. However, it’s not as simple as it looks. The products that rely on being put on the outside of the animal (Frontline®, Advantix® and Seresto®) aren’t thought by most vets to be reliable enough, and are easily disturbed by bathing.

It’s the newer tablet-based Isoxazoline products that are the real game changers. Currently, these are Nexgard®, Bravecto® and Simparica®, with Credelio® to come. The regular use of these products is thought to give nearly 100% protection against ticks, although checking is still recommended.

Why I Use Simparica

Of the three isoxazolines currently available, I use and recommend Simparica for dogs. Here’s why:

  1. Simparica kills fleas and ticks faster than Nexgard at the end of each month
  2. Simparica kills fleas and ticks faster than Bravecto at the end of each 90 day period
  3. Side effects seem less common, but this is only my personal view

The second point shouldn’t be a surprise. An ultra-long-acting product like Bravecto is likely to be weaker than a similar product given more often. However, I’m splitting hairs. Any of these three drugs is better than anything else currently available for ticks.

But what, I hear you ask, about the side effects?

Simparica & Seizures

Seizures in dogs are common, but it does appear that the risk increases when using Nexgard, Bravecto and Simparica. The only question is by how much. This is where life gets complicated.

The US Food and Drug Administration has issued the following public notice:

  • Isoxazoline products have been associated with neurologic adverse reactions, including muscle tremors, ataxia, and seizures in some dogs and cats
  • Although most dogs and cats haven’t had neurologic adverse reactions, seizures may occur in animals without a prior history
  • The FDA considers products in the isoxazoline class to be safe and effective for dogs and cats but is providing this information so that pet owners and veterinarians can take it into consideration when choosing flea and tick products for their pets

Personally, I have seen one dog develop intermittent twitches for two weeks after the second dose of Simparica, and a puppy have a seizure after a first dose. Both dogs had other significant health issues, but I suspect the Simparica was at least partly responsible.

So when do we use these drugs? There are two groups of dogs to consider:

Dogs In Paralysis Tick Areas

For dogs with no history of seizures: use. The risk and consequences of tick paralysis are much higher than the risk of side effects. Other alternative drugs are likely to offer poorer protection.

For dogs with a history of seizures: consider carefully. Simparica may not increase the number of seizures, but the risk is real. Whether you use it will depend on how likely it is that your dog will get a tick and your confidence in other methods of prevention.

Dogs Not In Paralysis Tick Areas

For dogs with no history of seizures: consider carefully. Here you are using Simparica for the prevention of fleas and mites only. Personally, I consider it to be so far ahead of the rest that the low risk of seizures is easily justified by better results. I use it on both my dogs but you are welcome to do otherwise.

For dogs with a history of seizures: don’t use. Other products exist which can give nearly the same results. An exception might be for dogs with demodex mites, for which there is no good alternative to isoxazolines.

If a dog does have a seizure while on these drugs, it does not appear to be a disaster. These dogs are likely to be the ones who were always prone to seizures, and should go back to having none or very few once the medication is stopped.

The Cause vs Correlation Issue

We will never know how many of the dogs reported to have twitching or seizures would have started having them regardless. This is hard to say to an owner placed in such a situation, and of course I can never be certain. For a view of a similar debate with a different issue, visit our page called Does Bravecto Kill Dogs?

But the reality is that all drugs do have side effects. Vets are often guilty of not talking about them just because it’s such a can of worms. Without wanting to sound complacent, the reality is that everything has a potential downside. It’s up to vets and manufacturers to supply the information so you can make the best informed decision for your dog.

If you live in a tick area, or travel to one, please use these products if you can. Used correctly, they save countless lives. Vets in tick paralysis areas are seeing a big reduction in the number of cases being treated now that the oral treatments have arrived. That’s fewer prolonged stays in vet hospitals and fewer deaths.

Related: Treatment Of Seizures In Dogs | Causes Of Tremors & Twitching

Valuable advice was provided by Dr Jakki Yeomans, a vet working in a paralysis tick area.

By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These blogs are from a series regularly posted on email and Twitter. Subscribe via email here to never miss a story!
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