What is Heartworm Disease?
Heartworm disease is a serious condition that can have a huge impact on the health of your pet. Heartworms can lead to severe lung disease, heart failure and damage to other internal organs. While heartworm disease most frequently affects dogs, it can also appear in cats and smaller house pets like ferrets.
The disease is caused by a parasitic worm called Dirofilaria immitis, which is spread by the bite of an infected mosquito. One of the main carriers of the disease is the Asian Tiger mosquito (Aedes Albopictus), which you can learn more about here. These parasites can live in the heart, lungs and major blood vessels of the infected animal.
Where Is Heartworm Disease Most Common?
Heartworm disease is most prevalent in the coastal areas along the Atlantic and the Gulf of Mexico. Hosts carrying the disease can also be found along the Mississippi River and its tributaries. Any region with a large mosquito population will likely see a rise in heartworm disease, though it has been reported in all 50 states, Puerto Rico and the U.S. Virgin Islands.
Heartworm Life Cycle
The domesticated dog and some wild canines are typical hosts for heartworms. Other mammals such as cats and ferrets can also serve as hosts, but this occurs much less frequently.
The process starts with a mosquito drawing blood from an infected host. The mosquito draws in heartworm eggs (microfilariae) with the host’s blood. The mosquito then acts as a theoretical incubator as the microfilariae cycles through three larva stages of development. Larva stages take anywhere from 10 to 14 days, depending upon environmental conditions such as temperature.
In the third development stage, the larva migrates to the mouth of the mosquitoes where they become infective. When the mosquito takes a blood meal, larva enter the host through the puncture wounds from the mosquito bite. Larva then travel through the host tissue and will eventually enter the bloodstream, where they develop into juvenile worms. After another 4 to 5 months, they develop into adult worms and take up residence in various blood vessels, the host’s lungs or the heart. They then breed and begin the life cycle all over again.
An adult heartworm can live inside a dog for 5 to 7 years. Males can reach lengths of 4 to 6 inches while females reach 10 to 12 inches in length.
Symptoms and Diagnosis of Heartworm Disease
There are several factors regarding the severity of heartworm disease and the ability to recognize symptoms. These include the number of worms infecting the dog, how long the dog has been infected and how the dog’s immune system is responding to the infection.
There are 4 classes of heartworm disease, each with varying symptoms and side effects.
Class 1: No symptoms or mild symptoms such as an occasional cough.
Class 2: Mild or moderate symptoms such as an occasional cough, tiredness after moderate activity, decreased appetite and abnormal breathing patterns.
Class 3: Persistent cough, abnormal heart rhythm and breathing patterns, decrease in appetite and tiredness after moderate activity.
Class 4: Caval Syndrome, severe lethargy and weakness. There are so many worms that the blood flowing back to the heart is physically blocked. At this stage the disease is life-threatening and the surgical removal of the worms is the only form of treatment.
If heartworm disease is suspected, visit your veterinarian immediately to have your pet tested.
Testing for Heartworm Disease
A veterinarian can use several different procedures to test your pet for heartworm. A blood test can be done for specific proteins (antigens) released by adult female heartworms. This test can detect an infection by one or more adult female heartworms. The earliest that this test can be performed is 5 to 6 months after the dog may have been bitten by an infected mosquito.
Another blood test detects the presence of microfilariae (heartworm eggs) in the bloodstream. The test can indicate that adult heartworms are present and are breeding and producing the microfilariae. Heartworms would need to be present for 6 to 7 months for this test to be effective.
A dog that tests positive for heartworm infection may require additional testing, such as x-rays and a urinalysis to determine how much damage has occurred and what the best form of treatment will be.
When Should I Test my Dog for Heartworm?
All dogs should be tested annually for heartworm infection. This can be done during a routine veterinary visit.
Reference the following tips for when you should vaccinate your pet for preventative measures:
- Puppies under 7 months of age can be started on a heartworm preventative medication without a heartworm test (it takes 6-7 months for the heartworm to reach maturity). They should be tested 6 months from starting the medication and then again after 6 months to ensure they are heartworm free.
- Adult dogs and puppies over 7 months should be tested before starting any heartworm medication, then again in 6 months followed by annual testing.
Annual testing is recommended and necessary even when dogs are on heartworm preventative medication to ensure that the treatments are working.
Treating Heartworm Disease
If the worst case happens and your pet is infected with heartworms, the good news is that most infected pets can be successfully treated. Your veterinarian will develop a treatment plan customized for your pet to kill any adult and immature worms while keeping the side effects to a minimum.
Treatment usually involves administering medication to kill any circulating microfilariae and a series of injections to kill any adult or juvenile worms. In some cases, oral medications may be used instead of the injections. In the most severe cases, surgery may be required to remove adult heartworms from the animal.
All treatments should be done by a veterinarian who is trained and knowledgeable about heartworm disease. After treatment, your pet will require restful home care and observation.
Heartworm Prevention Medication
Fortunately, the prevention of heartworm disease is relatively easy, safe and less expensive than treatment. Consult with your veterinarian to determine the best heartworm preventative medication for your pet. Many medications also offer protection against other intestinal parasites. Several medications, including Advantage Multi, Revolution and Sentinel work to control fleas as well.
Heartworm medications are usually in the form of a pill, a chewable treat or a topical solution that is administered monthly. Year round treatment is recommended for the best protection and you should continue to treat for heartworms every year to ensure that the preventative treatments are working.
Other Preventive Measures
As the old saying goes, an ounce of prevention is worth a pound of cure. You can significantly reduce your pets’ chance of obtaining heartworm disease by reducing their exposure to the carrier of the disease: mosquitoes. Follow a good mosquito management protocol by eliminating mosquito breeding habitats around your home and implementing a good mosquito control program with scheduled spraying and other control methods. You can learn more about mosquito control here.
You can also provide your dog personal protection against mosquitoes with K9 Advantix II. K9 Advantix II is a broad-spectrum topical treatment that provides wider protection to dogs against, fleas, ticks, mosquitoes, lice, and biting flies.
Benefits of preventative treatment against mosquitoes:
- Easy to apply on a monthly basis
- Repels and kills lice, ticks, biting flies, fleas and mosquitoes
- Kills all stages of fleas and prevents development of fleas, their eggs, larva and pupae
- Kills fleas with 12 hours and kills infesting fleas within 2 hours
- Waterproof
- No prescription required
- Registered and approved by United States Environmental Protection Agency
Be sure to note that K9 Advantix II can only be used on dogs and puppies over 4 pounds and over 7 weeks of age. NOT FOR USE ON CATS.
If your dog spends a lot of time outside you should consider a dog bed that is impregnated with Permethrin which will repel fleas, tick, mosquitoes and other biting pests.
Cats and Heartworm Disease
While heartworm disease is most common in dogs, cats can also suffer from this ailment. Cats aren’t the usual host for heartworms and most worms present in cats do not survive to adulthood. Cats with adult worms typically only have 1 to 3 worms and most cats have no adult worms at all. The average lifespan of an adult heartworm in a cat is typically only 2 to 4 years long.
As with dogs, the main transmitter of the disease is an infected mosquito. Both indoor and outdoor cats are at risk.
The symptoms for heartworm disease in cats can be difficult to diagnose or they can be extreme. Some cats may not present any symptoms at all, while some cats are able to rid themselves of the disease on their own. Respiratory distress is the most common sign that a cat has parasites and is referred to as Heartworm Associated Respiratory Disease (HARD). HARD usually occurs 3 to 4 months after a cat is bitten by a mosquito and the immature worms arrive in the heart and lung arteries, where the worms die. This causes issues such as trouble breathing, increased respiratory rates and coughing. Other symptoms include vomiting, lack of appetite and weight loss. An infected cat may have difficulty walking and could experience seizures.
Detecting Heartworm Disease in Cats
Heartworm infection in cats is harder to detect than in dogs. The veterinarian will utilize similar testing for antigens and antibodies to detect the presence of worms or their larvae. Tests such as an x-ray or ultra-sound can also confirm the presence of an infection.
There is no FDA-approved treatment for heartworm disease in cats, but most symptoms can be managed with medications.
Prevention is critical to keep your cat heartworm free. There are both topical and oral medications for cats which can be given monthly under a veterinarian’s prescription. Like with dogs, year-round care is the best course of action.
Testing is more difficult for cats but it is recommended to test before any preventative medications are prescribed. For more information on heartworm in cats, be sure to consult with your veterinarian.
Additional Information about Heartworm Disease
- Always consult with your veterinarian.
- Prevent Heartworm in Pets
- Heartworm Prevention in Your Pet
- American Heartworm Society