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Heartworms – Frequently Asked Questions

Heartworm disease is a common disease in dogs, cats, and ferrets that is preventable and treatable (if caught early). Heartworms is a serious disease, and can lead to death in your dog or cat. While there is a lot of information out there about heartworms, you should know the main facts to help you dispel any myths, and to help make any big decisions concerning current and/or future family pets.


Here are the down and dirty facts you should know about Heartworms:


What are heartworms?

Heartworms are long, thin parasitic roundworms that infect a variety of mammals. There are several forms of these worms, and some are not found in the United States. When we talk about heartworms, we are referring to the D. immitis species of the worm.

How do our pets get heartworms?

Mosquitos. Those tiny, annoying, flying bugs that return every spring and summer to ruin our evenings are the culprits for infecting and spreading heartworms in our pets. They feed on an infected animal (which can include wildlife such as coyotes, wolves, foxes, bears, etc.), and the heartworms in their larvae stage grow inside the mosquito until it bites your pet. It is through the bite that the heartworm infects the animal, and grows to full maturation. Areas with higher mosquito infestations have a higher risk of infection for our pets, making it even more important here in Florida to give our pets heartworm preventatives.


Is heartworm detection/diagnosis immediate?

No, heartworms are undetectable until they have finished maturing. Because of this, it can take 6-7 months before modern vet tests detect that your pet has been infected. However, they can live for years and reproduce inside the animal. If an animal is infected, but goes untreated, the chances of a full recovery are lower, and severe complications can arise. The earlier the detection, the earlier the treatment can be administered. The earlier the treatment, the better their chance is for a successful recovery.


How do heartworms harm your pet?

In non-clinical terms, they clog/strangle the internal organs such as the heart and lungs, until the animal dies. Especially for dogs, since the worms reproduce and take up to 7 years to die, the dog’s heart and lungs will fill to capacity with the worms. For dogs, this all leads to a cardiovascular collapse, and the only way to save the animal at this severe stage of the disease, is surgery. That is if you catch it in time, and very few dogs survive the surgery. Symptoms vary between dogs and cats, and early detection symptoms are hard to diagnose.

Early signs of heartworms in dogs: a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss.

For cats, the signs vary wildly. They can be very subtle or very extreme, and this is because the worm life cycle is drastically different for cats.

Early signs of heartworms in cats: coughing, asthma-like attacks, periodic vomiting, lack of appetite, or weight loss, difficulty walking, fainting or seizures, or fluid accumulation in the abdomen. In extreme cases, the only symptom can be a sudden collapse of the cat, or sudden death.


Is treatment for a heartworm positive dog the same as a cat?

No. While both animals can become infected, the worms live and infect differently. Heartworms thrive in dogs, maturing and reproducing, choking the pulmonary organs and surrounding areas. In a cat, the worms cannot survive to the reproductive stage. So, while an infected dog could have 30 or more worms inside their system, a cat will usually have 6 or less. More importantly, for dogs there is a treatment to follow that can end in a successful recovery if caught and treated early. However, currently there is no treatment for a cat that is diagnosed as heartworm positive. This makes heartworm prevention medicine the best, and only, course of keeping your feline friend happy and heartworm-free.


Can my other pets get heartworms from a heartworm positive animal?

No, remember heartworms are only transferable by a mosquito bite. They cannot be passed on between animals. The biggest issue is the strangulation and eventual death of your pet if they get infected and go untreated.


Can humans get Heartworms?

It is very, very rare for a human to catch heartworms, but they can. Again, it is ONLY from a mosquito bite, not from an infected animal. According to PetMD, the heartworm cannot complete its life cycle inside of humans. In the rarest of cases they manage to migrate to the lungs and leave a small lesion, which is then detectable. Heartworm infection in humans is so rare it is not a concern, however if you do worry, your best protection is to protect yourself from mosquito bites.


Is it safe to adopt a pet with heartworms?

Absolutely. Again, they cannot pass those heartworms on to any humans or other animals, the threat is to that animal alone. A shelter will inform you if the animal is heartworm positive, but keep in mind not all shelters have the financial means to treat the animal. More and more animals arrive heartworm positive, which makes treatment very expensive for a shelter as each animal must be treated separately. If you want to adopt an animal that is heartworm positive, one thing to keep in mind is that it can be an expensive treatment, and for dogs especially, they will need a commitment of your time and patience while they are being treated. When treating a dog for heartworm it is imperative to restrict their exercise and movement. Exercise increases the heartworm activity and damage to their lungs and heart. The American Heartworm Society has a 5-stage diagnosis and treatment explanation, and is a reputable source of knowledge.

The Animal League is one shelter that does heartworm treatment for their animals if they are found to be heartworm positive. They will let you know if the dog or cat you are looking at is positive, and if they are in the middle of treatment. If they are not yet, they will let you know when they are scheduled to start their treatment. They will sit down with you and work out a plan if they are being treated at the shelter or at home with you. If you are adopting a heartworm positive cat, they will discuss how to care for your new pet as there is no current treatment for them.


What is the best way to prevent heartworms?

The best and only way to prevent heartworms is prevention. Currently, all heartworm prevention is a monthly medication, usually in a chewable tablet. They need to be prescribed by a vet, if you find a heartworm prevention that can be bought without a vet’s consent, DO NOT ADMINISTER to your animal. This will not be an official heartworm preventative, and you could seriously harm your pet. The Animal League Wellness Center offers Heartworm testing and disease treatment, and carries preventative medication. Make your wellness care appointment today, your pet’s life depends on it.


Cover model: Vans, a Yorkie/wire fox terrier blend, rescued by The Animal League. Van was not heartworm positive but was a Have-A-Heart Fundraiser pet. His slightly higher adoption fees helped treat heartworm positive dogs rescued by The Animal League.


For more information on heartworms, please talk with your vet. Read more at an official medical source online:

American Heartworm Society


The CDC (Center for Disease Control)