It seems we jumped from winter to almost summer here in Regina, and with the sunny weather we know that the ticks have emerged and sadly the next pests on the list are mosquitoes! Aside from being pesky, mosquitoes are also a concern when it comes to disease transmission. One of the diseases we worry about in relation to mosquitoes is heartworm infection. Dirofilaria immitis is the scientific name of the parasitic worm that causes heartworm disease. Dogs and cats have the parasite transmitted to them when they are bitten by an infected mosquito. Mosquitoes as we know, are masters at finding their way inside our homes, which means that both outdoor as well as indoor pets are susceptible to potential infection. Many animals infected by heartworm can remain asymptomatic for long periods of time (even years!). Unfortunately when they do begin to show clinical signs, the damage the parasite has already caused is usually significant and may even result in death of the animal. Adult heartworms can grow to be 15 to 30 cm in length and they live in the heart and the major vessels supplying the lungs. While a clinical heartworm infection in dogs can be treated, the damage that has already been done to the heart and associated vessels is not reversible. Also, there are many potential serious side effects and complications that can occur with the medications that need to be used to treat a dog with an active infection (note: drugs used to treat an infection are different than preventative medications). At this time, there is not a labelled medication even available to treat adult heartworm infection in cats! The moral of the story is...prevention is key!
Heartworm infection is endemic in the United States and Hawaii. In Canada so far, heartworm disease has been found in B.C., Manitoba, Ontario and Quebec. We know that since Saskatchewan is surrounded by other endemic provinces, it will only be a matter of time until our province is on the list as well. In addition, the number of pet owners travelling out of province with their pets and adopting animals from other countries around the globe, only continues to increase. This means that we can also be bringing infected pets back into Saskatchewan and potentially indirectly spreading disease to other animals.
At Wascana Animal Hospital, our veterinarians recommend that if you are travelling with your pet to a heartworm endemic area that your pet be on a heartworm preventative medication. There are both oral as well as topical products available for heartworm prevention and both are given monthly. If your dog has never been on a heartworm preventative medication before, a heartworm test is needed before starting the medication. This is a simple blood test that at Wascana Animal Hospital, we can run in our hospital lab for fast, convenient results. Also, if your animal has travelled to an endemic area previously without being on a preventative, our veterinarians recommend that you have your pet tested because many animals can appear asymptomatic. Heartworm testing in cats is more complicated, but preventative medications are still available for cats.
The American Heartworm Society recommends that animals living in heartworm prevalent areas of the country be tested annually. Pet owners who routinely give their dogs heartworm preventative medication may wonder why the annual testing is necessary. The reason we still recommend annual testing is because while the preventative medications are very effective, drug efficacy may not always be 100% in every animal. Also, some owners may forget to give the medication on time or may miss a dose towards the end of mosquito season. Let's also not forget that some pets can be very sneaky and may have appeared to have swallowed their medication but may go behind the furniture or outside and spit it out, or perhaps if a topical product was used it was not applied correctly or allowed time to dry and became washed or rubbed off. Both of these potential scenarios could result in your pet being unprotected for a whole month's worth of heartworm-infected mosquito bites!
Next time you are in to see us, ask one of our veterinarians to discuss the risk of heartworm infection for your pet based on their lifestyle. Your veterinarian will be then be able to determine if a preventative medication is indicated, as well as how often your pet should be tested.