Updated August 12, 2021
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?
Ticks are tiny bloodsucking parasites known to spread many blood-borne infections. Tick paralysis is caused by a toxin from the saliva of only certain species of Australian ticks. The map shows where they are found.
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®, and Credelio®. The regular use of these products is thought to give nearly 100% protection against ticks, although checking is still recommended.
But what, I hear you ask, about the side effects?
Simparica, Bravecto, NexGard & 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, and a puppy have a seizure after a first dose. Both dogs had other significant health issues, but I suspect the isoxazoline 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, NexGard, Bravecto & Credelio 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.
You can find the other methods listed in our page on canine ehrlichiosis. They generally work by preventing ticks attaching, and while less effective, are a lot better than nothing.
Dogs Not In Paralysis Tick Areas
For dogs with no history of seizures: consider carefully. Here you are using isoxazolines 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.
Valuable advice was provided by Dr Jakki Yeomans, a vet working in a paralysis tick area.
Have something to add? Comments are welcome below and will appear within 24 hours.
By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These articles are from a series regularly posted on email and Twitter. Subscribe via email here to never miss a story!