Mosquitoes are responsible for one of the most deadly internal canine parasites — heartworms. When a mosquito bites a dog, it can infect it with adolescent heartworms. Within six or seven months, the new adult heartworms root themselves in the heart and blood vessels of the lungs and grow as long as eleven inches.

All dogs should be protected from heartworm before mosquito season and until a month or two after the season is over. In some areas, treatment is necessary all year. Indoor dogs that go out in the morning and evening are especially at risk because mosquitoes are most active during these times.

The heart must pump extra blood to handle the extra worm population blocking the blood flow of oxygen to other tissues. There may be no signs of heartworm, but severe cases may present with persistent coughing, lethargy, shortness of breath, weakness, fainting, heart failure, or sudden death.

Early Prevention

Preventing heartworm is the best defense against this deadly disease. Two oral medications — ivermectin and milbemycin — given once a month immediately kill any microscopic heartworm larvae.

As a precaution in regions with high mosquito populations, give your dog coenzyme Q10 as well as antioxidants. These supplements are helpful when there may be damage to the heart, but they are not preventatives for infection. Another way to reduce mosquito bites and your dog's risk of contracting heartworm is to feed him a raw diet. The ingredients may repel mosquitoes.

When your dog goes outside in the early morning or evening, rub a solution of one drop of eucalyptus oil mixed with a cup of water over his face. You can also reduce the risk of mosquito bites by eliminating standing water on your property, maintaining a clean outdoor environment, and by avoiding large bodies of water.

Diagnosing Heartworm

Your veterinarian will use a series of blood tests to check for proteins from heartworms. An ultrasound of the heart and X-rays will reveal the actual worms and the extent of the damage to the heart. Your veterinarian may also run a blood panel to determine if there is any liver or kidney damage.

The veterinarian evaluates the results and determines the level of severity. Sometimes a dog shows no signs of heartworm disease. In minimal cases, dogs may show no symptoms of illness or may cough occasionally or be tired after exercising. Moderately affected dogs have mild anemia and some protein in the urine, while severely affected dogs have difficulty breathing, a persistent cough, weight loss, more severe anemia, and urinary protein loss. In the worst cases, death is imminent and dogs can only be saved by surgically removing the adult heartworms. However, this surgery carries extreme risk because the dog may be too weak to survive the procedure.


In serious cases, treating heartworm infection isn't simple or safe. Harsh arsenic-based drugs may be needed to kill adult heartworms. While herbs such as rosemary, thyme, mint, sage, clove, garlic, hawthorn berry, milk thistle extract, and dried cranberry have been used to treat heartworms, these may be helpful only in the early stages of the disease.

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