What is heartworm disease and what causes it?
Heartworm disease can results in severe lung disease, heart failure, other organ damage, and death in pets, mainly dogs and cats. It is caused by a parasitic worm called Dirofilaria immitis. The worms are spread through the bite of a mosquito. The worms are called “heartworms” because the adults live in the heart, lungs, and associated blood vessels of an infected animal.
In the United States, heartworm disease is most commonly found along the Atlantic and Gulf coasts from the Gulf of Mexico to New Jersey and along the Mississippi River and its major tributaries, but it has been reported in dogs in all 50 states.
In an infected dog, adult female heartworms release their offspring, called microfilariae, into the dog’s bloodstream. When a mosquito bites the infected dog, the mosquito becomes infected with the microfilariae. Over the next 10 to 14 days and under the right environmental conditions, the microfilariae become infective larvae while living inside the mosquito. Microfilariae must pass through a mosquito to become infective larvae. When the infected mosquito bites another dog, the mosquito spreads the infective larvae to the dog through the bite wound. In the newly infected dog, it takes about 6 to 7 months for the infective larvae to mature into adult heartworms. The adult heartworms mate and the females release their offspring into the dog’s bloodstream, completing the lifecycle.
The earliest that the heartworms can be detected in a dog’s bloodstream is about 5 months after it is bitten by an infected mosquito via an antigen test.
Heartworm disease is not contagious, meaning that a dog cannot catch the disease from being near an infected dog. Heartworm disease is only spread through the bite of a mosquito.
Annual testing of all dogs on heartworm prevention is recommended. Talk to your dog’s veterinarian about the best time for your dog’s annual heartworm test.
What are the symptoms which indicate your dog might have heartworms?
The severity of heartworm disease is related to how many worms are living inside the dog (the worm burden), how long the dog has been infected, and how the dog’s body is responding to the presence of the heartworms. The dog’s activity level also plays a role in the severity of the disease and in when symptoms are first seen.
- Mild symptoms such as an occasional cough.
- Mild to moderate symptoms such as an occasional cough and tiredness after moderate activity.
- More severe symptoms such as a sickly appearance, a persistent cough, and tiredness after mild activity. Trouble breathing and signs of heart failure are common.
When there is heavy worm burden such that blood flowing back to the heart is physically blocked by a large mass of worms. it causes caval syndrome. Caval syndrome is life-threatening and quick surgical removal of the heartworms is the only treatment option. The surgery is risky, and even with surgery, most dogs with caval syndrome die.
Not all dogs with heartworm disease develop caval syndrome. However, if left untreated, heartworm disease will progress and damage the dog’s heart, lungs, liver, and kidneys, eventually causing death.
Prevention is better than cure
Many products are FDA-approved to prevent heartworms in dogs. All require a veterinarian’s prescription. Most products are given monthly, either as a topical liquid applied on the skin or as an oral tablet. Both chewable and non-chewable oral tablets are available. Some heartworm preventives contain other ingredients that are effective against certain intestinal worms (such as roundworms and hookworms) and other parasites (such as fleas, ticks, and ear mites).
Melarsomine dihydrochloride (available under the trade names Immiticide and Diroban) is an arsenic-containing drug that is FDA-approved to kill adult heartworms in dogs.
Another drug, Advantage Multi for Dogs (imidacloprid and moxidectin), is FDA-approved to get rid of microfilariae in the dog’s bloodstream. Advantage Multi for Dogs is a topical solution applied to the dog’s skin
Year-round prevention is best! Talk to your dog’s veterinarian to decide which preventive is best for your dog.
The American Heartworm Society advocates to Think 12. Give dogs 12 months of heartworm prevention and get them tested for heartworms every 12 months.