Dear readers,

A recent UrbanAnimal column focused on heartworm in dogs and its prevalence, prevention and cure. A small mention was included about heartworm in cats that concluded it's not a real concern, especially to those of us in southern Ontario.

A friend of mine, now living in Texas, contacted me to let me know heartworm prevention is just as important for cats as it is for dogs in her part of the world.

Keeping in mind that pets are now travelling more frequently across the border between the U.S. and Canada, I did more research into heartworm in cats and, although the number of infected cats in Ontario is extremely low compared with dogs, it's a subject all cat owners should know about.

According to Ontario Veterinary Medical Association (OVMA), "On average, one to three cats in Ontario (each year) are diagnosed with heartworm."

That's a small number, isn't it?

But the OVMA goes on to say, "Because of the range of signs that can be seen with heartworm disease, it's a much more difficult disease to diagnose in cats than in dogs whose signs are restricted more or less to the heart and lungs."

Symptoms in cats can include coughing, difficulty breathing, vomiting, anorexia, lethargy and weight loss.

How many cats are infected, but haven't been diagnosed?

And since mosquitoes breed prolifically in hot, humid weather - as we've been experiencing this summer - there will surely be an increase in the number of mosquitoes carrying heartworm from one infected pet to the next.

With an increase in cross-border adoptions, which often originate in the southern U.S. where heartworm is rampant, and destined for southern Ontario, how many of these southern pets will be carrying heartworm along with their adoption papers?

I'm not implying we're surrounded by heartworm-carrying mosquitoes at the present time, but you can see how conditions are slowly evolving and, if the pattern doesn't change, veterinarians in more northern climates may soon be more adamant when recommending heartworm prevention for cats.

Even cats that aren't allowed outside the house are at risk. According to the OVMA, up to one-third of infected cats are kept strictly indoors. All it takes is one infected mosquito.

Cats tend to resist heartworm, however, and if they do become infected, they are more able to live with it, which is a good thing since there are no approved methods for treating heartworm in cats as there are for dogs.

Heartworms can live for up to three years in cats and unless symptoms are causing complications, a veterinarian may decide to avoid any treatment and allow the heartworms to live out their lives in the cat while monitoring for symptoms every six months or so. If symptoms are beginning to show, a medication to reduce inflammation may be recommended. More advanced signs may require oxygen therapy and intravenous fluids.

Heartworm in cats can be prevented with products such as Heartgard and Revolution, but it's important to remember cats and dogs can't share these products. They are formulated specifically to suit each species and a blood test must be performed prior to administration of preventive products.

If you need more information, consult with your veterinarian.