Heartworm disease is a very significant problem in our part of the United States. It is spread by mosquitoes and not from animal to animal. With our proximity to the Missouri River and its’ tributaries, our pets are at great risk of contracting this life-threatening disease.

As the name implies, after being bit by an infective mosquito, the parasite Dirofilaria immitis, migrates and develops in the heart and lungs of our pets. The worms can be several inches in length and about the same thickness as heavy fishing line. With time, hundreds of worms can be present in one animal.        Click here for a diagram of the Heartworm life cycle

The presence of so many worms obviously causes great stress on the heart and lungs, making it difficult for an affected animal to breathe and function normally. The greatest cause of death is from chronic heart and lung failure and eventual cardiac arrest.

Once an animal is bitten by a mosquito, the larvae of the heartworm, (called a microfilaria),begins to migrate through the skin and eventually into the blood stream. It then moves into the heart and lungs where it begins to mature and reproduce. New microfilariae are then released back into the bloodstream, where they are ingested by another mosquito, and the cycle begins all over again.

It takes roughly 6-7 months from the time an animal is bitten by a mosquito until mature worms begin to reproduce within the heart. Our in-house blood tests detect a special protein that is released from an adult, pregnant, female worm. Therefore, it can take 6-7 months for an animal to test positive for heartworm disease.

The good news is that this devastating disease is very preventable. There are several good products available. The average cost to have an animal on year-round preventative is about $4 a month (depending on weight) plus an annual blood test (less than $20). The average cost of treating heartworm disease can be $300-$400 and has potential for side effects. Most dogs begin preventative at 4-6 months of age (testing need not be done first on a dog 6 months of age or younger).

Why do we need to test so often? There are several reasons—the first is for safety. There are potentially life-threatening reactions that can occur if preventative is given to an already heartworm-positive animal. The second is to ensure that the preventatives are working (most companies will pay for the cost of treatment if an animal becomes infected while on preventative). Lastly, we routinely test for other diseases at the same time (and at no extra charge) such as Lyme’s Disease and Ehrlichiosis (tick-borne diseases that have no preventatives).

Because of the long life cycle (remember, it can take almost 7 months for a blood test to become positive) and the high numbers of infective mosquitoes in our area, we very strongly recommend yearly protection. All of the preventatives on the market work by eliminating the larval stages in the body, which can persist several months beyond the traditional “mosquito season”.  A dog that is bitten in July still has larvae migrating through the skin and blood until November or December, long after the last mosquito is seen in the environment.

Because of the potential side effects and the necessity for blood tests, ALL HEARTWORM PREVENTATIVES ARE BY PRESCRIPTION ONLY! Do not trust any product at the store that claims to prevent heartworm disease. It is at the very least ineffective, and potentially dangerous (if not deadly).

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