Jul 14 2015

Should I Worry About Heartworm?

We hear about heartworm in the media – especially if we watch programming from the US.  But do we need to worry about it in southern Alberta? The short answer is no – unless you are travelling, you don’t need to worry too much about heartworm.  The long answer follows:

Heartworm disease or dirofilariasis can be a serious and potentially fatal disease. It is caused by a blood-borne parasite known as Dirofilaria immitis.  It is a disease that occurs worldwide but some geographic areas will have higher rates of infection while others have virtually none.  Southern Alberta is not be considered to be an endemic area of infection (it is not found regularly here).

The life cycle of heartworm is a complicated one and takes months to complete even under the most ideal conditions. It is not a disease that is transmitted from dog to dog. It requires an intermediate host, the mosquito, to help complete its development.  In order for the parasite to establish itself in an area, there are specific conditions that must be met:

  • Types of mosquitoes capable of carrying larval heartworms must be present (there are 30+).
  • The weather must be warm enough for enough days to allow heartworm larval development within the mosquito (a minimum of 14oC for a number of weeks) to become infective to dogs/cats.
  • There must be infected dogs or coyotes in the area.
  • There must be vulnerable host dogs in the area.

When these conditions come together, an area becomes endemic for heartworm disease.  This is important as our temperature is the greatest limiting factor for completion of the lifecycle.  A baby heartworm (microfilaria -L1) needs to first be ingested by the right mosquito, then needs to develop into an adolecent heartworm (L3 microfilaria) capable of infecting a dog.  This process takes a few weeks and anytime the environmental temperature drops below 14oC/57oF the lavae in the mosquito dies and no heartworms can be transmitted.  So our cooler temperatures don’t allow for the lifecycle to be carried through – which is why we are not considered an endemic area for heartworm.

The disease is more of a concern when people travel with their pets to endemic areas.  The disease was once limited to the south and southeast regions of the USA, however, the disease in spreading and now found in most regions in the US.  In Canada, it’s considered problematic along waterways and coastlines with the greatest number of cases occurring around the southern Great Lakes.  If travelling to known endemic areas it would be recommended to have your dog on a preventive medication to avoid becoming infected with the disease.  There are several prescription products that would be available from your veterinarian.

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