Heartworm in Dogs: What You Should Know
Heartworm in dogs is a potentially fatal parasite exclusively spread by mosquitos, which pick up larval heartworms, known as microfilaria, transferring them in the circulation of affected animals.
Although dogs and other canids such as foxes, wolves, and coyotes are believed to be the main heartworm hosts, these parasites can also harm other domestic animals.
Heartworm illness is a dangerous disorder that may have long-term consequences for your pet’s health, even if it is effectively treated. The good news is that heartworm illness is avoidable, so if you’re well-informed and on top of your pup-parenting game, you can rest easy (or at least easier).
Keep reading to find out everything you need to know about canine heartworm disease, including symptoms, treatments and prevention.
Table of Contents
- What Causes Heartworm Disease?
- What Is the Life Cycle of the Heartworm?
- Where Is Heartworm Disease Found?
- How Is Heartworm Disease Spread?
- What Do Heartworms Do to the Dog?
- How Is Heartworm Disease Diagnosed?
- How Is Heartworm Disease Treated?
- Are Any Other Treatments Necessary?
- Recovery and Management of Heartworm Disease in Dogs
- Recovery and Management of Heartworm Disease in Dogs
- How Can I Prevent My Dog from Getting Heartworms?
- The Takeaway
- Nutrition Strength Cardio Support for Dogs
Check out our Nutrition Strength Cardio Support for Dogs here.
What Causes Heartworm Disease?
Also known as dirofilariasis, heartworm illness is a dangerous and sometimes deadly infection. Dirofilaria immitis, a blood-borne parasite, causes it.
Adult heartworms are found in infected dogs’ hearts, pulmonary arteries, and nearby major blood vessels. Worms may sometimes be detected in other sections of the circulatory system.
Female mature heartworms are 6 to 14″ (15 to 36 cm) in length and 1/8″ broad (3 mm). Males are around half the size of females. When a dog is diagnosed, he or she may have up to 300 worms.
Adult heartworms have a lifespan of a maximum of five years. Females create millions of microfilaria throughout this time, primarily found in tiny bloodstream channels.
What Is the Life Cycle of the Heartworm?
The heartworm has a convoluted life cycle. The parasite needs the mosquito as an intermediary host before it can complete its life cycle in the dog. The mosquito is a vital part of the heartworm life cycle. Heartworms may be transmitted by up to 30 different mosquito species.
When a female mosquito bites an infected dog and consumes the microfilariae during a blood meal, the life cycle starts. The microfilariae grow further in the mosquito’s stomach for 10 to 30 days before entering its mouthparts.
They are infective larvae at this stage and may complete their development when they enter a dog. When the mosquito bites the dog, the infective larvae enter the dog’s body.
Within 6 to 7 months, these infective larvae migrate into the circulation and proceed to the heart and nearby blood arteries, growing to adults, mating, and spawning microfilariae.
Where Is Heartworm Disease Found?
Canine heartworm disease occurs worldwide. It was initially restricted to the south and southeast of the United States. The majority of recorded cases continue to be within 150 miles of the Gulf of Mexico and Atlantic Ocean coasts and along the Mississippi River and its tributaries.
The illness, however, is expanding and may now be found in most parts of the United States, including California, Oregon and Washington.
In Canada, the illness is a concern in mosquito-infested locations, such as around lakes and coasts in several provinces. The southern Great Lakes have the highest number of Canadian instances.
The prevalence of heartworm infection is affected by mosquito type, climate and the existence of reservoir animals.
When mosquitoes are actively feeding, the risk of infection is highest. Temperatures over 50°F (10°C) are often required.
How Is Heartworm Disease Spread?
The illness is not transmitted directly from dog to dog because transmission needs the mosquito as an intermediary host. Therefore, the disease’s spread correlates with mosquito season, which may extend all year in many regions of the United States.
The number of affected canines and the mosquito season’s duration is closely connected to heartworm disease prevalence in any particular location.
What Do Heartworms Do to the Dog?
It often takes many years for dogs to exhibit clinical indications of illness. As a result, the condition is mainly detected in dogs aged two to eight years.
As microfilariae take 5 to 7 months to grow into adult heartworms after infection, the illness is uncommon in dogs under one year old. Unfortunately, the disease has typically progressed significantly by the time clinical symptoms appear.
There may be no indications of sickness in the early stages. As the worms increase and develop, symptoms become more severe as the condition advances. Infections are classified into four types:
- Class one has no signs or perhaps a faint cough.
- Class two symptoms include modest activity intolerance and a persistent cough.
- Class three will result in increased exercise intolerance, irregular lung sounds, a weak pulse, syncope (fainting caused by the reduced blood supply to the brain), decreased appetite, weight loss and ascites (swollen belly due to heart failure).
- Class four is the caval syndrome. It is a potentially fatal cardiovascular collapse characterized by laborious breathing, pale gums and black coffee-colored urine, which leads to organ failure and death.
Adult Heartworms
Adult heartworms in dogs cause illness by blocking the heart and main blood arteries that branch from it, including the pulmonary artery. They also interfere with the function of cardiac valves.
Blood supply to various body organs is diminished when the major blood arteries get clogged, notably blood flow to the lungs, liver and kidneys. These organs may fail due to reduced blood flow and oxygen supply.
The severity of heartworm illness is determined by the number of mature worms present, their location, the amount of time the worms have been in the dog and the degree of impairment to the heart, lungs, liver and kidneys.
A quiet, dry cough, shortness of breath, weakness, listlessness and lack of stamina are heartworm infections’ most prominent clinical indications.
These symptoms are most visible after activity, when some dogs may faint or become confused. Your veterinarian may discover aberrant lung and heart sounds when listening to the chest using a stethoscope.
Congestive heart failure may cause the belly and legs to enlarge due to fluid collection in severe instances. Weight loss, poor health and anemia may also be present. Dogs with severe infections may die abruptly during exercise or excitement.
Microfilariae (Immature Heartworms)
Microfilariae circulate throughout the body but are primarily found in tiny blood arteries. Because microfilariae are nearly the same width as small vessels, they may obstruct blood flow.
The cells nourished by these vessels are subsequently deprived of the nutrients and oxygen that the blood typically provides. Microfilariae mainly cause damage to the lungs and liver.
Coughing is induced by the destruction of lung tissue. Cirrhosis of the liver develops due to liver damage, producing jaundice, anemia, and widespread weakness. Toxins may build in the body if the kidneys are compromised.
How Is Heartworm Disease Diagnosed?
Heartworm disease should be checked on dogs 7 months and older at least once a year. If the dog fails to take a preventative dosage, he should be examined more often. Testing is usually performed at the patient’s bedside in the hospital and takes just a tiny quantity of blood.
Antigen-based testing is the most commonly used approach for detecting heartworm disease. Antigens are proteins located only on an organism’s surface that are used to identify the presence of that organism in a sample.
The antigens being tested for in this situation are generated by the female adult heartworm. If the test is positive, the dog is infected.
A blood smear is another procedure that may be conducted to look for circulating microfilariae.
Once a diagnosis has been made, your veterinarian may prescribe further tests to determine the severity of the illness and the degree of risk associated with treatment.
Standard tests are chest radiographs, ECGs, blood pressure, cardiac enzyme assessment (NT-proBNP), echocardiograms, blood work, and urine testing.
Class I dogs are at the lowest risk for treatment, whereas Class IV dogs are often diagnosed with caval syndrome and are at the most significant threat.
This signifies that the worm load is high, and the worms prevent blood from leaving the heart. These canines are dying and must have the worms surgically removed (typically by a specialist) to extend their life.
How Is Heartworm Disease Treated?
There is considerable danger in treating dogs with heartworms. However, deaths are uncommon. Previously, the medicine used to treat heartworms had high quantities of arsenic, and severe side effects were common.
A new drug with fewer side effects is now available, enabling more than 95 percent of dogs with heartworms to be successfully treated.
Many dogs are already infected with heartworms before they are diagnosed. This indicates that the heartworms have been present for a long enough period to cause significant harm to the heart, lungs, blood vessels, kidneys and liver.
Rarely, instances may be so advanced that treating organ damage and keeping the dog comfortable is preferable to risking the detrimental consequences of eradicating the heartworms.
Dogs in this condition will most likely die within a few weeks or months. Your veterinarian will advise you on the best course of therapy for dogs with advanced heartworm disease.
Adult heartworms are killed with this treatment. Melarsomine is an injectable heartworm medication for dogs used to kill adult heartworms.
It eliminates adult heartworms in the heart and its surrounding arteries. This drug is delivered in a series of injections.
The specific injection schedule will be decided by your veterinarian depending on your dog’s health. Most dogs are given the first shot, then a 30-day rest period and then two further injections 24 hours apart.
Many dogs will also be given an antibiotic (doxycycline) to prevent infection with the bacteria (Wolbachia) that live in the heartworm.
Following the therapy, complete rest is required. Adult worms die after a few days and begin to deteriorate. They are taken to the lungs when they break up, where they lodge in the tiny blood vessels and are subsequently reabsorbed by the body.
This resorption may take from weeks to months, and these pieces of dead heartworms are responsible for most post-treatment problems. This may be a difficult time. Therefore the dog must be kept as quiet as possible and not permitted to exercise for one month after the last injection of heartworm therapy.
The first week following the injections is essential since the worms die during this time. Many highly infected dogs have a cough for seven to eight weeks after the therapy. If your cough is severe, contact your veterinarian to discuss the most appropriate option of heartworm treatment for dogs.
Suppose the dog develops an intense response weeks after the first treatment. In that case, prompt treatment is critical, albeit such reactions are uncommon.
Notify your veterinarian if your dog has loss of appetite, shortness of breath, severe coughing, blood coughing, fever or sadness.
Anti-inflammatories, antibiotics, cage rest, supportive treatment and intravenous fluids are typically successful in these circumstances.
Treatment to Eradicate Microfilaria
Your dog should be given medicine to fight microfilariae and prevent the body from developing adult heartworms. Your dog may need to remain in the hospital to monitor the day this drug is given, before or after the adult heartworm injections. After treatment, your dog will be put on heartworm prevention.
Newer heartworm treatment regimens include several medicines to destroy the microfilariae. Your veterinarian will choose the appropriate dosage and delivery time based on your dog’s condition.
Are Any Other Treatments Necessary?
Before heartworm therapy, dogs with severe heartworm illness may need antibiotics, pain relievers, special diets, diuretics to eliminate fluid build-up in the lungs and / or pharmaceuticals to enhance heart function.
Even when the heartworms are eradicated, some dogs may need ongoing therapy for heart failure. This includes diuretics, heart drugs such as ACE inhibitors, beta-blockers, cardiac glycosides and specific low-salt diets.
Recovery and Management of Heartworm Disease in Dogs
Treatment for heartworm disease is not without risks. Dogs undergoing heartworm treatment, as previously noted, may have anaphylaxis (shock), emboli (clots), and abrupt death, not to mention the likelihood of an abscess (pocket of pus) forming at the site of melarsomine injection and mental anguish from months of activity restriction.
Dogs may also face long-term health issues resulting from worm damage to their heart and lungs. Scarring and inflammation (swelling) caused by the worms make it difficult for blood to be pushed through the heart and lungs. Even with adequate therapy, right-sided heart failure may occur.
The severity of the condition will influence the prognosis and the sooner the disease is detected and treated, the better the prognosis.
Unfortunately, dogs with heartworm disease do not develop immunity and are in danger of re-infection in the future. As a result, year-round prevention is essential for your dog’s health.
How Can I Prevent My Dog from Getting Heartworms?
The best method to treat your dog is to prevent the condition from occurring in the first place by using year-round heartworm prevention for dogs.
The good news is that there are several kinds and forms of heartworm prevention available on the market and they are all reasonably priced.
There are pills, topicals, and even injectable forms that may give protection for 1 to 12 months. Some solutions combine flea and tick management to provide your dog a more complete preventative profile.
All products are intended to destroy the L3 and / or L4 heartworm larvae. Some of them are designed to cleanse the circulatory system of circulating microfilariae.
Suppose your dog tests positive for heartworm illness. It is critical to clarify the precise prophylactic required while treating it since just a handful should be given to reduce additional issues.
Consult your veterinarian to determine the best prevention method for your dog’s lifestyle and budget. Limiting your dog’s exposure to mosquitoes can also assist, although this is practically difficult in certain areas. Remember that heartworm illness can be caused by only one infected mosquito.
The Takeaway
Heartworm illness is a severe problem that needs prompt medical intervention for your sick dog. Nonetheless, the best therapy is effective heartworm prevention.
Routine heartworm testing is necessary, even for dogs on year-round prevention, to ensure that the medicine is effective. While heartworm therapy is usually effective, your dog may get infected due to vomiting the pill or rubbing away the topical treatment.
Is your dog displaying signs of heartworm disease? Remember that the sooner we diagnose a heartworm infection, the better our chances of saving his life. Your dog will appreciate your efforts to keep them healthy, protected and free of several abnormalities.
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Image source: Wikimedia / Meg Sanchez.
