Heartworm is a parasitic roundworm that is transmitted to certain animals (dogs, cats, ferrets and coyotes, for example) only through the bite of an infected mosquito. An uninfected mosquito can bite an already-infected animal and then spread it to other animals it subsequently bites.

It takes seven months from the bite for the heartworm to reach the adult stage in its victim. It lodges in the heart, lungs and respiratory blood vessels where it reproduces. It can grow up to 12 inches and live for five to seven years in your dog.

There are no symptoms of infestation in the early stages. As the heartworm grows and reproduces, the dog may cough and be short of breath. Weight loss becomes evident. If left untreated, an unpleasant death will occur.

On his website, www.avlanimalhospital.com, Hemet veterinarian Clay Johnson calls Idyllwild a “hotbed” of heartworm disease. While the incidence in Riverside County is not considered severe, you do take a risk if you leave your dog unprotected.

In the last three years, ARF and Sadie’s Clinic have been aware of several Idyllwild dogs testing positive and requiring the harsh but life-saving treatment.

A simple blood test can tell in 10 minutes if your dog is infected. That test costs about $35 and determines the presence of adult heartworms. However, there is a separate test that checks for the larvae or microfilariae.

Treatment for positive test results involves an arsenic-based drug which requires the animal to be kept quiet during and for a few months after the series of injections. As they die off, the heartworms break into pieces that can block pulmonary vessels and cause death. It’s a costly procedure, as much as $1,000, and dangerous for your pet.

For prevention, a monthly dose of the drug Ivermectin kills the heartworm larvae before they grow and reproduce. The dose depends on the weight of the dog and can begin as early as six weeks. The cost at Sadie’s Clinic is from $18 to $28 for a six-month supply.

Some Collies and other related breeds have a gene which makes them sensitive to Ivermectin. These dogs can safely take Interceptor, a brand of heartworm prevention that does not use Ivermectin.

If you decide not to follow a preventative regimen, it is recommended that you have your dog tested every six months.

Many Idyllwild residents give heartworm prevention every month, even during the winter when supposedly there are no mosquitoes present.

But there are folks who think it’s best to give their animals a break from the medication. Some holistically minded vets support this stance, saying that you’re safe giving the preventive every six weeks or even every other month.

One website I checked, www.dogs4dogs.com, said it was okay to skip doses after the temperature has remained below 57 degrees for 35 to 45 days.

If you’re meticulous about keeping such important health information on your calendar, it seems safe to give the drug at regular intervals other than monthly. But it doesn’t seem probable that many of us are going to chart daily outside temperatures during the winter months.

The usual recommendation to give a consistent dose monthly is more likely to be remembered by most people. It’s all about routine and what’s best for your dog’s welfare.

Do the research before you make a decision. Discuss it with your vet. And consider the risks to your family pets.

More helpful information can be found at www.heartwormsociety.

Note: Last month, the manufacturers of the heartworm prevention Iverhart Plus recalled six lots because potency failed to meet stability specifications. The numbers are 120076, 120086, 120856, 120202, 120196, 120844.