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Guest Column: What dog owners need to know about mosquitoes and heartworm

By Jayna Karpinski-Costa–
By now everyone has been told to drain standing water to prevent mosquito breeding and hopefully lower the incidence of the diseases they transmit.

There are about 23 species of mosquitoes in the Sacramento area and at least two of them are notorious for carrying West Nile Virus (WNV). Culex pipiens and Culex tarsalis. You have all heard of the 7 Ds? Drain, Dawn/Dusk/Dress, Defend, Door, District. See

Let’s add another D! DOGS. Yes, DOGS.

Just as Culex mosquitoes transmit WNV to people, Aedes sierrensis, the Western tree hole mosquito (common in our area), transmits heartworm disease to dogs (and other species).

The Western tree hole mosquito is just that. Lives in tree holes. Citrus Heights has one of the densest tree canopies in the valley. All those trees. All those tree holes – where branches come together and make Vs in the limbs. Tree holes that hold water. Water that helps mosquitoes develop. Tree holes that cannot be drained!!!

The dog heartworm is another D. Dirofilaria immitis. The worms are 5-12 inches long and look like strands of spaghetti. They can live 5-7 years in your dog.

The adults live primarily in the heart, lungs and great vessels. They produce offspring called microfilaria. The microfilaria circulate through the bloodstream damaging the tissues (kidneys, liver, etc) and continuing to grow into adults that get lodged in the heart, lungs and great vessels where they mate and make more microfilaria.

A mosquito bites an infected dog, taking in some microfilaria which will develop a little in the mosquito gut, then move into the mosquito mouth parts and then infect the next dog that the mosquito bites with microfilaria that then circulate until they are adults. It takes about 6 months for the larvae from the mosquito to develop into an adult worm in the dog.

How do you know if your dog has heartworm? It requires a simple blood test performed by your veterinarian often right in the clinic. In the early stages of the disease, a dog may not have any symptoms at all – the microfilaria are circulating.

As the disease progresses a dog might show a mild cough or fatigue after mild exercise. As the larvae mature, the dog may show anemia, decreased appetite, weight loss and eventually heart failure.

Helpful websites are:,, and

We cannot drain all the tree holes in our neighborhood. The really good news is that there are many products available through your veterinarian that are safe and effective to prevent heartworm disease. They should be given all year (due to the long development cycle after the mosquito bites).

I have heard people say that prevention is too expensive! Consider this: Treatment is hard on the pet and hard on the wallet. It can cost over $1,000 to diagnose, treat and hospitalize your dog. Treatment requires injections, prescriptions, 6-12 months of cage rest (to prevent the dead worms from becoming an embolus).

We brush and floss to prevent dental disease. We vaccinate to prevent a variety of disease. We use seat belts, condoms, anti-slip flooring, anti-this and anti-that. Why not save your pet from a devastating disease with a simple monthly cookie? There’s even a 6-month injection!

Jayna Karpinski-Costa
Jayna Karpinski-Costa

Your dog depends on you to keep him/her safe.

Dr. Jayna Karpinski-Costa is a veterinarian currently serving on the Board of Trustees of the Sacramento-Yolo Mosquito & Vector Control District representing Citrus Heights

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