Your Dog and Heartworm

Heartworm (Dirofilaria immitis) in dogs is a severe disease which can cause long term harm to your pet. Heartworms are a parasite which have been around for over a century. These bloodsuckers love warm geographic areas however they can be found almost anywhere in the nation. This video is not pretty but says it all when it comes to understanding heartworm:

How Heartworms Work

These parasites dwell in the circulatory system. They can not only affect pets but they can also cause elephantiasis in humans via a relative parasite of the heartworm called Wucheria bancroff. Dogs however, seem to be the favored host, but heartworm can also be found in cats.

The adult worms are about seven to ten inches long and are very thin. The female can produce these as microfilariae. These “baby” heartworms travel in the blood until they are picked up and swallowed by a mosquito during its bite.

Once inside the mosquito, the microfilariae start growing and travel up to the mouth of the insect. This cycle can take up to two weeks. From here they move to a new host when bitten by the mosquito. The microfilariae remain at the site of injection for three to four months while they further develop.

The last part of this cycle is for the adult worms to travel to the heart by entering small blood vessels. It takes another two to three months for the parasite to reach full maturity in the pets heart

Clinical Signs of Heartworm Disease:

sick puppyClinical signs of heartworm disease cam be determined by the amount of worms that are present, their location, the length of time in the host, and the vulnerability of the host. Early infections will most likely stay asymptomatic. With older infections or a larger number of worms that are present, abnormalities are more likely to be detected.

The changes that happen are due in large part to some type of allergic reaction between the parasite and it’s host. Since most worms are found in the right ventricle of the heart and the pulmonary artery, the clinical signs are often those of heart failure and or lung collapse.

Dogs can initially show signs of heartworm disease by coughing, loss of energy, drop in body weight, and a dull coat. As the disease gets worse, coughing can become more severe, intermittently with blood, breathing becomes more labored and exhaustion is constant.

Fluid retention can cause the pets abdomen to swell (ascites) as the muscles contract causing a skeleton like appearance. Impaired circulation also causes the body to break down which effects other organs, like the liver and kidneys, and they will start to depreciate. If untreated, this disease is often fatal.


The best way of detecting heartworm in a dog is by finding the microfilariae (baby heartworms) in the blood. The fastest test is simply to examine a fresh blood smear under the microscope.

Occasionally, there are other reasons, a dog can have active heartworms living in the heart and lungs but not have microfilariae in the blood. If the veterinarian suspects heartworms, he may take a few blood samples over a time period to try to show microfilariae. An X-ray of the chest is also taken in this case. This disease can cause positive radiographic changes which cam be sufficient in order to help diagnosis heartworm in spite of negative blood samples.

Treatment for Heartworms:

Heartworm treatmentTreatment for heartworm can be either medical or surgical, No therapy ought to be started before conditions such as heart failure, congestion, liver disease, kidney disease, and coexisting infections are under control.

Cost is a major factor that should not be overlooked. Lab tests, X-rays, hospitalization, drugs, or even surgery can cost a considerable amount. It is very important for a dog owner to completely understand the risk and expenses of treating heartworms prior to starting heartworm treatment.

The administration of an arsenic compound into the blood stream (intravenous) is one of the Medical treatments that can be considered. This is typically administered twice a day for two days. This is the only effective drug currently offered. Laboratory work must be done before treatment is started in order to evaluate the condition of the pets’ organs and minimize risk. This treatment has been proven highly effective in killing adult heartworms.

The worms are trapped inside the circulatory system, so once they are destroyed they cannot be eliminated from the body. As the heartworms dies from the arsenical treatment, they disintegrate and are carried into the lungs. The lungs then absorb the worm remains. This can cause coughing, fever, and loss of appetite. This can occur seven to fourteen days after the final arsenical injection. It is very important that pets are kept as quiet as possible for three to four weeks following the treatment.

The removal of the worms surgically may be the only option for some dogs. Dogs with severe heart and lung changes would fall into this category in which arsenical therapy would be too dangerous.

Regardless of the means used to remove the adult worms, a follow-up drug must be given after recovery to destroy the microfilariae in the blood. These young worms will ultimately die, but this can take several months. Throughout this time the dog can be a source of infection to other dogs. Re-infection is also possible if the microfilariae are not eliminated. Several drugs are effective in removing microfilariae and each veterinarian has his or her own preference.

Prevention Is The Best Cure:

Considering that Heartworm is a severe disease, and difficult to treat, it would be much heartworm testbetter to try and prevent it. Drugs are available which, if administered properly during the mosquito season, are effective in preventing heartworms from developing in the dog.

Mosquito control can help in protecting your pet. Tips like screening outdoor pens or keeping dogs indoors as much as possible can be helpful. Some veterinarians like to treat dogs once even twice a year with the intravenous arsenical in areas where there are high concentrations of pets with heartworm.

An annual or bi-annual blood test should be scheduled in prevalent areas. This will often detect infections before the onset of clinical signs. These cases typically have the best reaction to treatment as damage to organs is small.

Since a dog with heartworm can be a cause of infection to other dogs, diagnosis and treatment are an vital part of control and prevention. Continual upgrading of diagnosis, treatment, and control is the reward of this work. Without owner awareness and concern, however, the disease will continue to flourish.