The “Seasonal” Versus “All-Year-Round” Heartworm Prevention Debate

As we enter the Fall, the debate about whether all year round treatment with a heartworm preventative is absolutley necessary – or whether seasonal protection is still ok, depending on where you live, is sure to become a hot topic once more.

From many posts in forums online that I have seen, it certainly seems to me that many owners feel that the advice from Vets and from the American Heartworm Society about giving preventative treatments for heartworm all year round, is somehow a sort of ‘conspiracy’, fuelled by the drug companies making the medicines, to ensure that owners are paying out for twelve months of the year, instead of just during the warmer months.

I read a forum post from a Veterinary Technician working in Michigan who stated that she would definitely not be stopping the medications for her dogs during the winter because it just isn’t safe to do so. She reported that:-

“most people that stop their heartworm prevention in the fall about 50% of their dogs show up positive in the spring”

A Simple Misunderstanding Could Result In Your Dog Becoming Infected With Heartworm

Many people do not realise how the preventative medicines work and are running the risk of their dog becoming infected because they feel that the weather has turned cooler, the mosquitoes are gone, therefore they can stop the preventative. Wrong!

healthy dogUnfortunately, it doesn’t work that way. The preventative, does not protect your dog for the month ahead, it works to kill the microfilariae or tiny larvae which have infected your pet during the month since you last gave the dose of medication.

So, thinking in November that the weather is so cool now and that there are no skeeters around, does not mean it is safe to stop giving the monthly medicine if the previous month was warm and there were skeeters around. This is because doing so, will mean that if your dog has picked up any larvae during the warmer, preceding month, these will not be killed and your dog will go on to develop heartworm disease as these larvae grow into adults.

This is one of the main reasons why the AHS advocates all year round treatment. It ensures that the chance of your dog getting infected are reduced to an absolute minimum.

A Persuasive Argument For Prevention

What About The Cost Implications?

Saving the cost of monthly heartworm treatments through the winter months may seem like a good idea. This can be especially true if you have several dogs. However, if prevention is stopped,

  1. Your dog will need a heartworm test before preventative medication can be resumed. This is liable to cost at least $30 per dog.
  2. If the preventative also protected against other internal parasites such as roundworms and hookworms and helped to control fleas, you are still going to have to pay for a medication to deal with these – even if you do not continue with the preventatives.
  3. If you stop the prevention and later find that your dog had become infected with microfilariae in the preceding month and gone on to develop heartworm disease, you are facing a huge bill to deal with a full-blown infection using Immiticide which is a painful process for the dog and an expensive one for the owner.

So, to sum up, Vets and the AHS advocating all-year-round preventative treatment isn’t a scam, or scaremongering or even a way to extract more of your hard-earned money, it is the only sure way to give your dog the best possible protection from contracting potentially fatal heartworm disease.


The “Seasonal” Versus “All-Year-Round” Heartworm Prevention Debate — 2 Comments

  1. Can my dog have another round of heartworm injections if he still has heart worms? He still seems sick and coughing even after the treatment was a few months ago

    • It is normal for your dog to have another heartworm test about four months after treatment. This will ascertain whether all the worms have been killed (although it is possible in very rare cases for a positive result even though the worms are all gone). If your dog is not due for this check up in the very near future, it would be a good idea to take him back to the vet to get the cause of the coughing checked out – it may be something unrelated but which still needs treatment. In answer to your initial question, yes it is possible for your dog to have another round of treatment for heartworm if the first round has not been completely successful and your vet will be able to discuss the options with you. All the best and do let us know how your dog gets on Tiese.