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What state has the most heartworms in dogs?


Heartworms are common in dogs throughout the United States (cats can have them, too). They are among the most damaging parasites in dogs but they are almost 100 percent preventable. Heartworms are transmitted by mosquitoes and, once mature, they live in the heart and large blood vessels of the lungs. Adult heartworms can measure over one foot in length. View the heartworm disease infection rate forecast for your local area at

How will heartworms affect my dog?

The heartworm larvae deposited by the feeding mosquito eventually migrate to the chambers of the heart or into the vessels of the lungs. Once in the heart, the worms can affect blood flow throughout the body. Heartworm infection can affect many different organs of the dog—heart, lungs, kidneys, and liver, for example—so symptoms may be varied. Most commonly though, signs of heart or lung disease are present. A veterinarian may suspect that a dog has been infected if an active animal tires easily or shows shortness of breath or coughing. Early in the disease, dogs are often asymptomatic. Signs are often progressive over weeks to months and untreated, heartworm infection can be fatal.

Testing for heartworm infection

Blood tests are most commonly used to diagnose heartworm infection in dogs. An in-house screening test run by your veterinarian may be followed by a confirmatory blood test sent to an outside lab. Other tests frequently employed in determining the extent and severity of heartwom infection in a dog include blood tests of kidney and liver function, x-rays of the chest and an ultrasound (sonogram) of the heart. Once infection is confirmed, your veterinarian will discuss the most appropriate treatment for your pet.

How do I prevent my dog from getting heartworms?

Heartworms have been found in dogs in all 50 states so all dogs are at risk, even those animals that primarily live indoors. Fortunately, with medication, heartworm infection is almost always preventable.

Ask your veterinarian about heartworm prevention. Preventive treatment should begin at 6 or 8 weeks of age in puppies and after tests have been conducted in older dogs to determine if your dog has already been infected. An annual blood test should be run to confirm the dog continues to be negative for heartworms. If your dog does have heartworms, your veterinarian can advise you about treatment options.

Can humans contract heartworm disease?

Isolated and rare cases of human infection have been reported, however, the heartworm is generally not considered a risk to human health and direct transmission of heartworm from dogs to humans is not possible.

For veterinary professionals, more detailed information on heartworms can be found at

Did you know?

  • If left untreated, heartworm disease can result in your dog’s death.
  • Heartworms can grow to 16 inches in length and there can be as many as 250 heartworms in a dog’s vital organs.
  • Your dog can have no symptoms until heartworms are well-established.
  • Almost 300,000 dogs in the U.S. are infected with heartworms each year.
  • It is difficult, especially for your dog, to treat heartworms once established. It is much easier and less expensive to prevent heartworms than to treat them.
  • Other kinds of worms that dogs can get include hookworms, roundworms, tapeworms, and whipworms.

Learn More about Specific Parasites

Ask Your Veterinarian

Heartworm Prevention

Preventive treatment should begin at 6 or 8 weeks of age in puppies and after tests have been conducted in older dogs to determine if your dog has already been infected. If your dog does have heartworms, your veterinarian can advise you about treatment options.

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What is Heartworm Disease and How Does it Spread?

mosquito biology

Dirofilaria immitis, commonly referred to as heartworm, is a parasitic roundworm that infects a variety of mammals. Heartworm is found throughout the world and has been reported in all states in the U.S. The natural host for heartworms is dogs but heartworms may also live in cats, ferrets, and humans. Infection in dogs can lead to heartworm disease, a serious condition that may result in death. Cats are an atypical host since most worms in cats don’t survive to the adult stage. If cats become infected, however, they may develop serious health problems. Although isolated human infections have been reported, heartworm is not currently recognized as a human health problem.

Hosts for heartworm include domestic dogs, wolves, foxes, and raccoons. Heartworm is spread by mosquitoes that bite an infected host and then pass the parasite to another host during a blood meal. Aedes, Anopheles, and Mansonia species of mosquito are all capable of transmitting heartworm. Humans and other mammals are accidental hosts and cannot play a role in spreading heartworm as the worms do not produce the microfilariae necessary for transmission. Heartworms are only spread by the bite of a mosquito and cannot be passed directly from one dog to another. And people cannot get heartworms from their pets.

Symptoms of Heartworm Disease in Dogs
  • It takes about seven months for the parasite to develop into an adult heartworm once a dog is bitten by an infected mosquito. So, initially, dogs will show little to no symptoms.
  • As infection persists, dogs may experience a persistent cough, fatigue, decreased appetite, and weight loss.
  • Heavy worm burden can stop blood flow to the heart and cause a condition called caval syndrome, which leads to heart failure.
Treatment and Prevention of Heartworm Disease in Dogs
  • Both topical and intravenous drugs exist to treat heartworms. The specific treatment plan will depend on severity and stage of the disease.
  • For dogs that develop caval syndrome, surgical removal is the only treatment option.
  • Without proper treatment or surgical removal, most dogs will die from heartworm disease.
  • Fortunately, there are FDA-approved products to prevent heartworms in dogs. Most are given monthly and require a veterinarian’s prescription.

Heartworms in Cats


Though cats are not as susceptible to infection as the worms don’t thrive as well in their bodies, they are still at risk for the disease. In cats, heartworms don’t live as long and rarely mature into adult worms. Signs of heartworm may be hard to detect and include coughing, wheezing, periodic vomiting, or weight loss. Unfortunately, there is no approved drug treatment for heartworm in cats and the goal is to stabilize the cat through long-term treatment. There are, however, FDA-approved products for the prevention of heartworms in cats.

Meet the Heartworm

Adult heartworms grow to 12 inches in length and have the appearance of cooked spaghetti. Heartworms have a lifespan of five to seven years and an infected dog may have anywhere from 1 to 250 worms.

Heartworm Life Cycle


Controlling Aedes, Anopheles, Culex, and Mansonia Mosquito Species and Heartworms

An Integrated Mosquito Management (IMM) program is essential to helping prevent mosquito bites and transmission of serious vector diseases to both humans and pets. As part of an effective IMM program, VDCI recommends a 4-pronged approach to target all phases of the mosquito’s life cycle.

Community understanding of how to properly eliminate mosquito breeding habitat and take personal protective measures is critical. Furthermore, distribution of educational pieces is important for treating symptoms and aids public health officials in identifying disease problem areas.

2: Surveillance

In order to understand the risk and address the threat appropriately, it is critical to determine the mosquito distribution, density, and species composition throughout the target area. Surveillance will also provide direct evidence of an increased transmission risk of a disease.

When mosquito larvae are detected in an area, trained and experienced ground crews reduce breeding habitat when possible, then preferentially apply Bacillus thuringiensis var israelensis (Bti) to remaining areas of standing water, stagnant pools, and water-holding containers. Aerial and ground application of larvicide via ULV equipment can provide control in hard to reach container habitats.

VDCI recommends the deployment of two-person teams to conduct targeted ULV applications combined with residual “barrier” applications via backpack applicators to mosquito harborage areas near homes and other structures. In addition, when the disease risk warrants it, truck and aerial ULV applications should be utilized to reduce the adult mosquito population. When combined with our larvicide efforts, these methods have proven highly effective at significantly reducing local populations of the target mosquitoes.

VDCI is a company built on the foundations of public health, ethics, professionalism, and technical expertise. We establish vector management programs that are based on an understanding of the underlying vector’s ecology and rooted in the current science of environmentally sound control measures.

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