Mosquitoes and Heartworm

Pet Tales
by  Barry B. Burtis D.V.M.

The Buzz of Spring

They have been here for over 30 million years. Obviously, they are pretty successful at what they do. They are equipped with some very powerful, very impressive sensors to track their prey. They can detect carbon dioxide and lactic acid up to 100 feet away. Mammals and birds, of course, release carbon dioxide when they breathe. Their visual detectors pick up movement. These detectors are especially accurate if the colour of the moving object contrasts with its background. When close enough they have heat sensors that can make birds and mammals an easy target.

There are over 2700 different species of them around the world. They carry many types of diseases caused by bacteria, parasites or viruses. These diseases include malaria, yellow fever, encephalitis and dengue fever. Have you guessed who they are yet?  Of course, it's of the mosquito that I speak.

Living in our part of the world, for the past few months we have been able to forget about them. However, with the return of spring they are back in the picture. An old saying advises that it is wise to know your enemy.  Therefore, a review of some mosquito facts may be in order.

The word mosquito is Spanish for little fly. In North America, they have been called by this name since the late 1500's. Europeans called them gnats. Mosquitoes are members of the fly family of insects. Accordingly, they have 3 body parts - head, thorax and abdomen. The head has the sensors and biting apparatus. Only the female mosquito has the long feeding tube, called the proboscis, and therefore it is only she who can bite.

The female mosquito lays her eggs in water.  It may be large pools of water or small puddles. Stagnant or slow moving water is preferred. In most species, the female deposits the eggs singly or in clumps on the surface of the water. The length of time required to complete the life cycle, from egg to adult, varies depending on environmental conditions and the species of mosquito.  Most eggs, in proper conditions can survive over winter and hatch in the spring. Eggs hatch into the larva stage of the life cycle The next stage in their life is called the pupa and both larva and pupa stages are spent entirely in water. The pupa changes into an adult and leaves the water as a free flying insect.

After emerging as an adult, one of the first things it does is seek a mate. With its short mouth parts, a male mosquito feeds on plant nectar and will live only a few days after mating. The female after mating must ingest a blood meal before she can lay her eggs.  Here is where the story can get serious for our pets (and for ourselves in the case of diseases that affect humans).

 If the source of that blood meal happens to be a dog or a wild canine who is infected with heartworm a bad chain of events can be about to begin. The female mosquito in drawing up enough blood to fill the digestive organs in her abdomen will take in some microfilaria.


Microfilaria are the immature stage of the heartworm parasite that is living in the infected animal's heart. These microfilaria have been released by the adult female worm into the animal's circulating blood. They travel where the blood travels. They can enter the body of the mosquito as she feeds. In the mosquito, the microfilaria go through a maturing step and are now able to infect another susceptible animal.

The female mosquito, after eating, may now go about her egg laying. However, unlike the male who has quite a brief life, the female will continue to live anywhere from many days to weeks. Now, remember she must have another blood meal before she can lay again. Her next victim may be a canine (or feline) who is not infected with heartworm. But, it won't take long to change that. She begins to bite her next victim  by inserting her proboscis through the skin. Saliva with proteins to prevent the blood from clotting are injected, as she takes in more blood. At the same time some of those microfilaria from her last meal can be passed on to the next host. If this happens, the heartworm parasite has just  successfully used the mosquito to infect a new animal.  It may take a few weeks or a few months, depending on where the bite occurs, but eventually that infective stage of the microfilaria will reach the animals heart and develop into an adult.

When you hear that familiar buzz of spring, make sure your pet is not going to become such a victim. Yes, you can try and reduce the risk of exposure to mosquitoes. Eliminate pools of water in your yard that may increase the population of mosquitoes.  Avoid taking your dog into mosquito areas at dawn or dusk when they are most likely to be bitten. Ask your veterinarian about mosquito repellants that can be used safely on animals. But let's be real, they have been around for 30 million years, you're not going to wipe them out as a risk with these measures. Don't take any chances. Make sure your pet receives medication that will stop and kill that migrating microfilaria, if it is bitten by a mosquito carrying the disease. If only we could stop all the life-threatening diseases that mosquitoes spread by such a simple measure, the world would be a much healthier place. Protect your pet against heartworm, in our region, beginning the first week in June.