Every spring, veterinarians begin asking pet owners whether they have done or will do any travelling during the summer months. Part of the reasoning behind asking this question is to assess the pet's risk for contracting heartworm disease. This parasite infestation is easy to prevent but very difficult to treat. As always, we'd much prefer to prevent this horrendous and complicated disease.

Heartworm disease is the infestation by a worm that develops in the bloodstream of the dog and eventually matures to the adult form that lives in the vessels of the lungs and in the heart. For obvious reasons, this infestation can be a serious health threat to the patient.

This parasite is transmitted through a mosquito bite during hot weather in some areas of North America. These geographical areas of concern (known as endemic areas) tend to be hot and humid during an extended period of time in the summer months. Such areas identified in Canada are parts of Southern Manitoba, Southern Ontario, and the Okanagan Valley in B.C. The Eastern & Southern States are endemic for heartworm disease as well (highest risk in Southeastern states such as Florida!) These places are considered to have risk for the transmission of the heartworm parasite (Dirofilaria immitis).

Prevention of this parasite is quite simple! There are several products now available to choose from. We will mention three of them here.

1. Interceptor® - This is a pill that is given once each month during the summer months to cover the period of possible exposure. The dog has to have a heartworm test (simple, quick blood test) before starting this medication unless he/she is under 5 months of age. This medication also treats the dog for intestinal worms every month.

The advantage of using Interceptor® (once/month pill) is that is treats the dog for other internal parasites monthly. Another product called Sentinel® is a combination of Intercepter and Program (a flea preventative) and is handy for dealing with fleas, worms and heartworm prevention.

The advantages of using Revolution® are as follows. It is the only product available that is also approved for use in cats and it is very effective against fleas in both species! (In cats it also kills intestinal parasites and ear mites.) We don't have to test for heartworm in order to use this product and it can be used just once whenever it is needed -- if for example you only plan to visit the Okanagan for a couple of weeks, one dose of Revolution would do it.

Even when heartworm testing is not absolutely necessary for a veterinarian to prescribe one of the above medications, it is still recommended at regular intervals (every 3 years, for example). The only way we'll ever know if heartworm incidence is changing in our area is to test our dogs with some regularity. The frequency of testing recommended will depend on each individual's risk of exposure.

Heartworm is a complicated parasite. As far as we can tell at this point, Vancouver Island is not a geographical area of concern with regards to the transmission of this worm via mosquitoes. However, we are all keeping our eyes and ears open for any changes that may occur. Considering climate changes that are occurring, heartworm disease may become a larger risk in more and more areas of North America and elsewhere over time.