Dirofilaria immitis is commonly referred to as “heartworm” because the adult resides in the pulmonary arterial system for the most part and the primary effect of this infection on the health of its host is a manifestation of damage to the lung vessels and tissues. Occasionally, when the surrounding conditions are right, adult heartworms can migrate to the right heart and the great veins to cause heavy infections. Heartworm infection normally results in serious diseases for the host.

Transmission of the Parasitic Roundworm

The mode of transmission of the heartworm disease is relatively simple and it occurs in the same way that many of diseases affecting humans work. Basically, when a mosquito carrying infective heartworm larvae bites a dog, it transmits the infection. Once in the host, the larvae grow and develop, migrating in the body of the host over a period of time that can span several months. By the end of this period, the larvae would have become sexually mature male and female worms that principally reside in the heart, lungs and the associated blood vessels. As the adults go on to mate, the females release their offspring called microfilariae, which are released into the blood stream.

The presence of the offspring of the worm can be detected in the blood in the pre-patent period, which occurs about 6 to 7 months after the infective larvae from the mosquito were first introduced in the host dog. When fully grown, the male heartworms are normally between 4 to 6 inches in length while the females grow to become 10-12 inches when fully grown. After an infection, it takes about a year for the larvae to become fully grown adults.

Distribution of the Heartworm Disease

Canine heartworm infection is widely distributed throughout the United States. It can be found in dogs native to all 50 states. All dogs, irrespective of factors such as age, sex and habitat, are susceptible to heartworm infection. Statistically, the highest infection rates in dogs was observed within 150 miles of the Atlantic and Gulf coasts along the Mississippi River and its major tributaries. This basically leads to the conclusion that regions that have environmental, mosquito population and dog population factors have a higher local incidence of heartworm infection.

For regions where heartworm disease is common, infections have been diagnosed in dogs as young as one year of age. Between the ages of 3 and 8 years, dogs tend to be particularly susceptible. However, although there are differences in frequency of infection for various groups of dogs, all dogs in all regions are at risk of this parasitic infection. This is one of the primary reasons why if you have a dog, you need to place it on prevention programs and have your dog frequently examined by a veterinarian.

Clinical Signs and Symptoms of Heartworm Infection

The heartworm disease may cause a combination of medical conditions including dysfunction of the lungs and organs such as the heart, liver and kidneys. Unfortunately, the disease often begins with barely detectable signs resulting from a chronic infection and a combination of physiologic changes. As a matter of fact, dogs with a low number of adult worms in their body that are not exercised strenuously may never have apparent signs of the disease.

However, because in most dogs, the heart and lungs are the primary organs affected by the roundworm, the heartworm disease often shows varying degrees of clinical signs post the early stages of infection including cough for the mild form of the disease, exercise intolerance and abnormal lung sounds for the moderate form of the disease and hepatomegaly, ascites and abnormal heart sounds in more severe cases.

Diagnosis of the Heartworm Disease

The diagnosis of the canine heartworm disease in dogs and the other potential hosts requires:

1. An accurate patient history
2. The recognition of varied clinical sign
3. The accurate use of several diagnostic procedures that may include:
- Blood or serological testing
- Microfilarial detection and differentiation
- Physical examination and clinical laboratory tests
- Angiography and ultrasound
- In the worst cases, necropsy (examination after death)

Heartworm Treatment for Dogs

Heartworm treatment for dogs can be done in a number of different ways depending on the severity of the infection and some other factors. The good news is that with modern technology, most dogs infected with heartworm can be successfully treated. The goal of any heartworm treatment for dogs is to primarily kill the adult worms with an adulticide and the microfilariae with a microfilaricide. For this initial treatment method, it is absolutely vital that the treatment is accomplished with a minimum of harmful effects from drugs and a tolerable degree of complications. Heartworm treatment for dogs showing no signs or mild signs of the disease have a higher success rate. Patients with evidence of the more severe forms of the heartworm infection can be successfully treated but the possibility of complications and mortality is greater.

1. Adult heartworm therapy

There is currently one drug approved by the FDA for use in dogs for the treatment of adult heartworms. This drug is an organic arsenical compound typically administered at a local facility. Melarsomine dihydrochloride demonstrates a higher level of effectiveness and safety than any other adult heartworm treatment previously used and evaluated. It is administered by deep intramuscular injection into the lumbar muscles.

2. Elimination of the microfilariae

The most effective drugs for the elimination of the microfilariae are the macrocyclic lactone anthelminticsm including milbemycin oxime, moxidectin and ivermectin. These drugs are the active ingredients in commonly used heartworm preventives. Generally, it is recommended that microfilariae positive dogs treated with these macrocyclic lactones be hospitalized for at least 8 hours following treatment. This is important because the host needs to be placed under constant observation for signs of potential complications resulting from the use of the drug.

Over the years, heartworm disease in dogs has been reported in all 50 states of the U.S. The first published description of heartworm in dogs in the United States appeared more than 100 years ago in The Western Journal of Medicine and Surgery. Since then, naturally acquired heartworm infection in cats and dogs has been identified worldwide as a significant and serious clinical problem. Despite improved diagnostic methods, effective preventives and increasing awareness among veterinary professionals and pet owners, till date, cases of heartworm infection continue to appear in pets around the world.

How Heartworm Disease Happens

Adult female heartworms are biologically programmed to release their young, called microfilariae, into an animal’s bloodstream. Mosquitoes that become infected with microfilariae while taking blood from the infected animal can pass on the microfilariae mature to the infective larval stage through mosquito bites. Once the infective larvae enter through the bite wound, it then takes about 6 months for the infective larvae to mature into adult worms. In dogs, which are the principal hosts for the parasites, the worms may live for up to 7 years. Microfilariae cannot mature into adult heartworms without first passing through a mosquito.

The Clinical Heartworm Symptoms In Dogs

The clinical heartworm symptoms in dogs are not normally recognized in the early stages of the disease. This is because the number of heartworms in an animal tends to accumulate gradually over a period of months, sometimes years and after repeated mosquito bites. This basically means that recently infected dogs may exhibit no heartworm symptoms in dogs. For heavily infected dogs, things might be a little different and they may show several clinical signs of the disease, including a mild, persistent cough, reluctance to move or exercise, fatigue after only moderate exercise, reduced appetite and weight loss.

In some ways, clinical signs of the heartworm disease tend to be very similar to those of heart failure. The host may experience a mild cough, tiring on exercise and possibly fainting. Nose bleeds, congestion in the lungs, fluid development into the abdomen and the classic tiring on exercise are also common heartworm symptoms in dogs. Fortunately, these days, with testing that’s available, it is possible to detect heartworm infections before the disease gets to the point of getting to clinical signs.

In summary..

The heartworm symptoms in dogs can be very similar to any of those of heart failure. Ascites fluid in the abdomen, coughing, fluid in the chest, nosebleed because of the way the blood is affected by part of the heartworm and collapsing are all signs of this potentially fatal disease that affects dogs and to a large extent cats, If you see any of these signs develop in your pet at home, you need to visit a veterinary professional for assistance. Because the heartworm disease affects the lungs and the heart of the host, it can result in a number of serous medical conditions and it is extremely important that you put your pet in the prevention of heartworm disease. For instance, heartworms are transmitted by mosquito bites so letting your pet go out early in the morning or in the evening certainly is an opportunity for infestation.

Heartworm infection in apparently healthy animals is usually detected via blood tests for a heartworm substance called an antigen. It may also occasionally be detected through ultrasound or x-ray images of the heart and lungs. This method of diagnosis is usually only used on animals already known to be heavily infected.

Preventives

While treatment of heartworm disease in dogs is usually successful, prevention of the disease is much safer and more economical. To prevent the occurrence of heartworm infection in your pet, you can choose from a variety of preventive options including daily or monthly tablets and chewables, monthly topicals or a six-month injectable product. The products available today for the prevention of heartworm infection in dogs are extremely effective and when administered properly on a timely schedule, heartworm infection can be effectively and successfully prevented.

For the purpose of prevention heartworm infection, The American Heartworm Society is now recommending year-round prevention, even in the seasonal areas. The reason for this lies in the fact that medicine for the prevention of this fatal disease should be given properly by the pet owner. In addition, most monthly heartworm preventives have activity against intestinal parasites. Many of these same intestinal parasites that infect dogs can also infect people. Last but not least, before starting a preventive program, all dogs that could possibly be infected with mature heartworms should be tested.

Useful Drugs for the Prevention of Heartworm Infection

1. Macrocyclic Lactone

Macrocyclic lactones are highly effective parasiticides. They are extensively used in the prevention of heartworm infections. Their primary benefits lie in their safety and ease of administration. Macrocyclic lactones also have additional intestinal parasite and external parasite activity.

2. Ivermectin

Ivermectin was the first in a family of drugs to be approved for preventing heartworm infection. An infection with larvae as long as two months prior to the use of ivermectin will be blocked from development by this drug so it is a potent cocktail.

3. Milbemycin

Milbemycin oxime by Novartis has benefits, which are similar to ivermectin. It is a good product for the prevention and potential treatment of heartworm infections.

Diagnosis of Heartworm Infection in Dogs

The diagnosis of heartworm disease depends on a number of factors including:

1. A good patient history. This is one of the reasons why if you are a pet owner, it should have a personal veterinary professional.

2. The recognition of the clinical signs that often vary.

3. The use of the appropriate diagnostic procedures including serological testing, microfilarial detection, physical examination and clinical laboratory tests and sometimes necropsy.

Some of the primary symptoms of heartworms are loss of appetite and weight loss, the outward appearance of an animal, lethargic behavior, and more. While any of these could be a temporary sign of an otherwise minor problem, each is a primary symptom of heartworms and should not be ignored. When any of these symptoms are observed action should be taken as soon as possible.

Loss of weight is one of the many symptoms of heartworms in pets. Always keep an eye on how much your pet eats daily, and take note of any loss of appetite or loss of weight. Weight loss can be a symptom of many things, however it is one of the primary symptoms of heartworms, and when noticed it should be addressed immediately.

Aside from loss of weight, an animal’s outward appearance may change obviously. Any sign of the ribs becoming more protruded or if the chest seems to have become more prominent or bulged should be noted. Take care too to notice if the animal appears to have trouble breathing. These are each potential early signs of heartworms and should be observed by a licensed veterinarian.

Some animals can be lazy of course, and lounging around the house or on a favorite piece of furniture may not be cause for alarm, however most enjoy a good run with their owner or a nice game of fetch. If a general disinterest in these types of activities is noticed when the animal typically participates eagerly, or if the animal appears to tire easily, this should be discussed with a veterinarian.

Animals cough for a variety of reasons just as people do. Just as with people, an animal’s cough can be an indicator of nothing more than having ingested something improper or too quickly, however it can also provide clues to a bigger problem and is an early indicator of heartworms. Pay close attention if an animal begins to cough frequently. A soft but deep sounding cough is an early symptom of heartworms and should not be taken lightly or overlooked.

More symptoms including vomiting and diarrhea, bloody stool, jaundice, poor coat condition, and blindness. Any of these should sound the alarm and a trip to a trusted veterinary clinic should follow quickly.

While heartworms are most prominent in dogs, other animals are vulnerable, and even people can become infected! It is critical to recognize heartworm symptoms as quickly as possible and seek treatment immediately.

They are very similar to more common illnesses and maladies. Owners and even vets sometimes don’t pay much attention to what appears to be run of the mill problems. To make matters worse, once he starts showing signs of sickness, he’s already very very ill.

Common symptoms in the beginning are vomiting, diarrhea, breathing problems including wheezing, and coughing. They can progress to an enlarged rib cage (which grows wider to encompass the enlarged heart and lungs), bloody stools, and loss of appetite. All these symptoms are similar to those caused by more common diseases and not always recognized by owners or even vets.

They more frequently than not look like the common cold or an allergy. Even your vet may not immediately think of heart worm when you bring him in for a check up.

Outdoor dogs are more likely to become infected with heartworm because heartworm is transmitted by infected mosquitoes and, of course, mosquitoes are more likely to be found outside. However, since these pests can all too easily get into our homes, it’s not unheard of indoor dogs to become victims to the disease as well. And, because these same dogs don’t go out often, owners tend to ignore the symptoms and never think about heartworm when the coughing and wheezing starts.

Even tiny dogs can be in danger, whether they seldom go outdoors. Don’t assume that just because your little Maltese never leaves the house that his coughing or diarrhea can’t be serious. Small dogs run a higher risk of mortality, too, if heartworm is left untreated because the worms can grow to about a foot long without regard to the size of the dog or the size of his heart.

Even though prevention is the key, that doesn’t mean that your dog is immune to the disease just because he received his heartworm medication on time. Even the best medications on the market won’t guarantee that your dog will be able to ward off the effects of an infected mosquito.

One of the major reasons symptoms tend to be ignored is because the dog has received heartworm medication and there is an assumption after that that the dog must be coming down with something else; he couldn’t possibly have heartworm. This assumption can cause your dog’s demise.

No matter what type of pill you or vet chooses for your pet, the ingredients will most likely include either selamectin or ivermectin. Many vets recommend that these pills should be given in addition to the usual topical treatments, especially in known areas of high infestation – regardless of how much time your dog might spend outside.

It might take some trial and error to find the perfect pill for your individual pet. In families with multiple dogs, there’s a good chance that each dog might need or do well with one particular brand vs. What his housemates take.

Years ago, the first type of pill came on the market – once which needed to be administered daily. Any dog owner knows how difficult it is to get a pill into his beloved pet, so researchers finally developed a monthly pill. Of course, this comes with risks because the level of medicine – which is tantamount to poison for the worms – can cause problems in these dosage levels.

Dogs who do take a monthly heartworm pills for dogs frequently experience some toxic side effects which can range from a simple nuisance to life threatening heart palpitations and seizures. The real problem here is that poisons tend to build up in the body and they don’t always cause an immediate reaction.

For pooches who need the pills but do everything possible to avoid them, there are some beef flavored alternatives that even the most fussy are usually more than happy to gobble up when asked to.

Whatever you do, never give your dog any type of heartworm medication without consulting with your vet and getting explicit instructions and a prescribed course of action. Because of the inherent levels of toxicity involved with these preparations, you don’t want to cause problems unnecessarily. Don’t try buying these online “without a prescription” and don’t buy generic brands you aren’t familiar with.

One pill may be too much for many dogs. Take for example a toy poodle and a Huskey. It only stands to reason that the poodle would need a lower dose than the Huskey, and therefore, giving the poodle the same pill could quickly cause disastrous side effects. Don’t self prescribe!

Heartworm is delivered by a simple mosquito bite. In geographic areas near water, it’s common to have these diseased mosquitoes all over. The assumption is that all mosquitoes carry the potentially fatal larvae that turn into the troublesome worms once they enter the dog’s bloodstream and grow uncontrollably.

The safest, but by no means easiest, method is to move your family to South Dakota where there are no known cases of heartworm in cats or dogs. If that seems out of the question, the next most effective option is simply to keep mosquitoes away from your dog. Considering we can’t even keep mosquitoes away from us most of the time, this is no easy task. However, we can be very diligent in applying ointments to our pets just as we apply them to ourselves. One trick that seems to work wonders is garlic. Bugs hate garlic, but dogs love it! Add some chopped garlic to each meal – he’ll be happy and healthy.

Healthy, active dogs have a better chance of warding off the disease even they are bitten. A strong heart and circulation, along with a healthy immune system will prevent the worms from causing any damage; they won’t be able to grow, and they won’t be able to take up residence in the vital organs like hearts and lungs.

Monthly prescription medication is the real key. It must be applied diligently – on time, in the right amount, in the right place. One tiny mistake could put your dog at risk. The medications are simple to apply actually and all you need to do is break open a capsule and squeeze it onto the back of his neck, in an area he can’t reach to lick or scratch. It sinks into the skin and enters the bloodstream immediately.

Many of these preventive medicines prevent not only heartworm but fleas, ticks, their larvae, and other types of worms.

Even though prevention is important, commonly prescribed, and in many states almost mandatory for your dog’s health, many dogs suffer serious adverse effects. These medications are strong and if applied to an ill, old, or weak dog, you could be causing some serious side effects such as seizures, paralysis or even coma. The problem is that these don’t happen right away all the time; poisons frequently build up silently in the body and it could months to tell your pet is experiencing some adverse side effects.

Preventive medicines have been around for quite some time and even though they aren’t 100% effective, they indeed do a remarkable job at keeping our pets safe, especially in areas known for high levels of infected mosquito infestations. Monthly treatments involve topical ointments that are usually rubbed onto the back of your dog’s neck where he can’t lick it off, and/or pills that can be taken daily or monthly.

Most medicines are multi-functional, meaning, they work on more than just heartworms. Depending on the medicine it could also be used to prevent roundworms, hookworms, and/or tapeworms, along with being able to kill eggs and larvae and perhaps even ticks.

Don’t think that keeping your dog indoors is preventive medicine! Mosquitoes are notorious for going where they aren’t welcome, and our homes aren’t immune from harboring at least one or two of these pesky critters. And that’s all you need to get your dog infected.

Depending on your vet, he may also recommend giving your dogs pills in addition to using the topical ointments. In areas that are near water – where mosquitoes thrive – he may want your dog to be doubly protected. Do as he suggests, but make certain you don’t overmedicate or buy substitute prescriptions that may be cheaper without checking with your vet first.

If your dog has been diagnosed with heartworm, you will now need to give him the heartworm medications that are to cure/treat, rather than prevent. Once your dog has been diagnosed with heartworm, he’s already very sick, and these medications can make him worse. Some dogs have no side effects, others succumb to the side effects. Much like chemotherapy in human cancer patients, these medicines are poisons meant to kill the invading worms and larvae, frequently making the patient sicker before things get better.

It’s difficult to get a true reading on how effective these drugs can be because frequently the deaths caused by the drugs are recorded as “death by heartworm” instead of the real culprit. If your vet suggests that you begin an aggressive treatment schedule, you need to have a serious discussion with him about possible side effects – especially in your pet – vs. What would happen with no medical intervention.

The symptoms can mask other illnesses or they can be so general that most pet owners may not pay much attention to them. To compound the already serious problem of your dog being infected, symptoms don’t usually occur until your pet’s life is in danger.

The most common symptoms include coughing, vomiting, lethargy, difficulty breathing even when resting, weight loss, and a protruding rib cage. As the disease progresses undetected and untreated, these symptoms will progress in their severity to the point that either there is no doubt what is wrong with your pet, or the animal collapses and dies without ever being properly diagnosed.

Dog heartworm symptoms can sometimes look like a cold and even when taken to the vet, he may not immediately think of anything more serious than a cold or even an allergy.

Even though heartworm is more prevalent with dogs who spend a considerable amount of time outdoors, in climates rife with mosquitoes, it’s not unheard of for indoor dogs to be infected as well. We all know that pesky mosquitoes can easily make their way indoors and all it takes is one bite from one infected mosquito and any dog can be immediately infected.

Smaller dogs are in even worse danger, and their symptoms should always be closely monitored. A cough or bout of diarrhea in a 3 pound teacup Chihuahua can be fatal with or without the added dangers of heartworm. Since heartworms can easily reach about 12 inches long, and dogs can be infected with many at once, smaller dogs have a higher death rate simply because owners and vets alike tend to ignore the coughs and general symptoms until it’s too late.

Since prevention is so aggressively touted and highly recommended, many vets and pet owners simply assume that because they have given their dog the appropriate medication as prescribed, nothing can happen and the dog won’t – or can’t – be infected with heartworm.

This just isn’t true. Even dogs who receive their heart worming medicine as regularly scheduled still are not immune to heart worm. Unfortunately, all it takes is one powerful mosquito bite that is infected with the worm, and the dog can become infected with or without the medication at work in his system.