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Can Canine Heartworm Disease Be Succesfully Treated?

Canine heartworm disease [also called dirofilariasis (dir-oh-filla-RYE-uh-sis) is a serious and potentially fatal disease of dogs.

What Is Heartworm Disease?

Long white worms, technically known as Dirofilaria immitis (dir-oh-fill-AY-riah im-MIGHT-iss), are the cause. Adult worms, which reach a length of 6 to 14 inches, live in the right side of the heart in the adjacent large blood vessels. A dog (and occasionally cats) may have several hundred of them in its system, although the number is usually much less.


Occasionally canine heartworms are found in other animals such as foxes, skunks, horses, and cats. In a few isolated instances they have been reported in people as small disturbances in the lungs, having little or no effect on the person’s health. Such cases are considered biological oddities.


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What Happens in Heartworm Infection?

Large accumulations of adult worms impair circulation of the blood, which can result in serious damage to the heart, lungs, liver, and kidneys. The important thing for pet owners to remember is that a great deal of damage can occur before any outward signs of heartworm disease are noticed. Although a dog (and especially cats) can lead a nearly normal, healthy life with a few heartworms in its’ system, in advanced stages the disease may cause its victim to have difficulty breathing, cough, tire easily, become listless, lose weight or faint. If not detected and controlled with proper treatment, the disease can lead to congestive heart failure and death.


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How Does a Dog or Cat Get Heartworm?

Heartworm infection is spread by mosquitoes. When a mosquito bites an infected pet, it takes up blood which may contain microscopic immature forms of heartworms called microfilariae. The microfilariae incubate in the mosquito for about two weeks, during which they become infective larvae. Then, when the mosquito bites another animal, the infective larvae infect it as well. The infective larvae migrate through the tissues of the body for about three months, then enter the heart where they reach adult size in another three months. The mosquito is the only natural agent of transmission for canine heartworms. As you might expect, heartworm infection is more common in areas where mosquitoes are numerous, and outdoor dogs constantly exposed to mosquitoes are the most frequent victims.


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How Is Heartworm Disease Detected?

The only way to detect heartworm disease in its early states in through a blood test. A veterinarian, using relatively simple diagnostic procedures, can usually detect antibodies against the heartworms. Nowadays, most infections are “occult”, and therefore the tiny heartworm microfilariae is not seen. In some cases however, microfilariae can be detected even during a routine CBC. But occasionally, an infected dog will have adult heartworms but no microfilariae. Chest x-rays, echocardiogram as well as other laboratory tests may be needed to fully define that state of a heartworm infection.


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Can Heartworm Infected Dogs Be Treated?

Most dogs can be successfully treated for heartworms. Early detection is optimal, but even later stages are treatable. The adult worms are killed with an arsenical drug given through a series of carefully administered injections. A few days after treatment, the worms die and are carried by the bloodstream to the lungs where they may lodge in small blood vessels. They then decompose and are absorbed by the body over a period of several months.


There is always some risk involved in treating a dog with heartworms. However, fatalities resulting from treatment are rare among dogs that are otherwise in good general health. The patient should be given a thorough physical and laboratory examination prior to treatment, and any other problems that might cause complications should be corrected before heartworm treatment begins. Following treatment, complete rest is needed to prevent lung damage from the dead and decomposed worms.


Excitement and exercise should be avoided for a period of time, followed by gradual return to normal activity. After all adult heartworms are eliminated, another drug must be given to rid the bloodstream of microfilariae, which are not affected by the drug used to kill adult heartworms.


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Can Heartworm Disease Be Prevented?

The best way to prevent infection is to keep your dog healthy by minimizing drug and vaccine exposure, feeding a proper diet (fresh food in moderation and variety) and homeopathic care. Minimize mosquito bites by using topical essential oil sprays (or similar non-toxic products).


Your veterinarian may recommend a low dose of a drug that keeps the infective larvae from developing into adult worms. This drug is recommended for year round use. When my clients choose to use a monthly heartworm preventative, they often only give it during the higher risk seasons. This depends on the weather in your part of the country.


Monthly heartworm “preventatives” are actually early treatment of disease (remember it is always better to prevent disease than to have to treat it). When a dog takes this drug (usually Heartgard or Interceptor) any microfilariae that have been transmitted by a prior mosquito bite are killed (hence the monthly administration though there is good evidence that the so-called “throwback period” is actually 6-8 weeks). Understanding how the drugs work is very helpful in there proper use.


Like most animal health problems, canine heartworm disease still holds mysteries that veterinarians and other scientists are trying to solve. But adequate treatment and preventative procedures have been developed, and the conscientious dog owner, cooperating closely with his veterinarian, can keep his pet free from this disease.


Heartworm disease is very preventable but potentially difficult and dangerous to treat. As always, prevention through holistic care is the best answer.


 NB: Although there is no proven natural prevention for heartworm disease, these low dose medications are usually very safe and effective. However, I do advise mindful use of any drug. I assess every patient individually as some pets are very sensitive to this and other drugs.


Here is the current FAQ from the American Heartworm Society:


Here are their full guidelines for vets:

Please note: The information provided here is intended to supplement the recommendations of your veterinarian. Do not disregard veterinary advice or delay treatment based on information on this site. Nothing can replace a complete history and physical examination performed by your veterinarian. -Dr. Jeff