Heartworm Disease |
| Heartworm Disease |
Heartworm Disease has been diagnosed in all 50 states and world wide.
Heartworms are transmitted from one animal to another by the mosquito. Both dogs and cats are at risk for this disease. If your pet was infected last mosquito season, evidence of the disease may now be detected. Dogs may be treated for heartworm disease and the earlier the better. Cats can not be treated. Please see the part about cats at the end of this report or click here.
These worms are about the diameter of thin spaghetti and normally live free floating in the right ventricle of the heart and nearby blood vessels. Your vet will run or send in to a lab blood from your pet to be tested and/or do X-rays to diagnose this disease. Commonly used antigen blood test will work only when the worms are sexually mature. About 6 months after entering the animal. Female worms must be present for accurate test results.
Puppies should be started on a heartworm preventive by 8 weeks of age depending on the product being used. They than should be tested at 7 months of age. Adult dogs should be tested on a regular basis. If the pet is on a preventive year round, testing is done every 2-3 years. If you live in a hight risk area you'll want to test every year and KEEP the animal on a preventative year round. If dose's are missed or depending on your geographical area some of the winter months skipped entirely, than testing should be once a year. The presence of heartworm is difficult to detect in cats with a blood test alone. Often times preventive medication is started with out testing unless signs of infection are noticed. For a cat, one worm can cause sudden death or sudden acute respiratory signs that are indistinguishable from asthma without a medical work up. It was thought that dogs got heartworm more than cats. I think this view may be changing as we are learning that perhaps many cat heartworm infected patients were overlooked due to the disease not showing the same common signs and symptoms as in dogs. Cats tend to die quicker from this disease due to the size of their vessels and the inability to handle a heaver load of worms circulating through the system. In cats the infection can act like other cat diseases, therefore overlooked. This is truly a shame as too many cats have not been given the preventive in the first place because so many people thought that cats didn't usually get heartworm disease. But still, the detection in cats is difficult and the tests are not 100% reliable, YET.
Where dose heartworm disease come from?
The first documentation of heartworm was in 1874. It was in the Western Journal of Medicine and the article was written about a canine. It wasn't until the early 1900's the first documentation was written on a feline. These worms have been around for a long time. No one knows for sure where they evolved originally. Both dogs and cats are susceptible to being infected. But for some reason, cats are less susceptible to heartworm harboring mosquito.
As people acquired more pets especially dogs, the disease has accelerated. As pet owners started traveling more with pets, heartworm disease has spread. The pet was taken into an infected area and thus becoming infected themselves. The worm was brought back home to an area that was at the time not infested with heartworm. Heartworm disease has now been diagnosed in all 50 states in the USA as well as worldwide. Cats as of yet have not been found to be big factors in spreading the disease. Unfortunately this could change as we learn more about the disease.
Are your pets at Risk for heartworm disease?
Dogs are the preferred host for this parasite. Some other animals that can become infected are the: cat, ferret, horse, bear, fox, wolf, coyote, bobcat, muskrat, raccoon, otter, tiger, jaguar, lion, orangutan, sea lion gibbon, and MAN
This can be kinda confusing so just stick with me while we make sense of this.
The life cycle consist of 4 molts to mature into an adult worm. While in the mosquito the first two molts take place. The 3rd and 4th happen in the body of the host (your pet). First the mosquito bites and draws blood from an infected animal. It sucks up microfilaria in the blood. In 14 days or so the microfilaria goes through 2 molts. (depending on the environment's temperature). At this point they change from an L1 to an L2 and then to an L3 (3rd stage of development of the larva). As L3 the larva has gone into the mosquito's salivary glands. At the next meal for the mosquito the larva burrow into the victim through the bite wound.
Once in the animal the development continues. It will take at least 6-7 months to go through the last two molts. At this time it becomes sexually mature. As said earlier the worm needs to be sexually mature and at least one female present to be detected by a heartworm test. Within the next 15 days the L3 larva will molt and change to L4. This can happen as early as 2-5 days after the mosquito bite. L4 to L5 (the second molt) occurs within the next 2 months. At L5 the worm is now considered a juvenile adult. It works it's way through the tissues of the animal all the way to the heart. All this could happen as early as 70 days after becoming infected. The majority of L5 arrive in the heart by the 90th day. Here is where they live. Now at home they grow quickly in size. Their life expectancy is 5 to 7 years. After the worm gets home (in the heart) sexual maturity is about three months later. The worm is still growing. The females grow up to 14 inches and the males are generally shorter. The females start passing microfilaria into the blood. Once the worm is an adult it will continue to produce young for many years.
Signs of Heartworm Disease in Dogs.
At first there aren't any visible signs. Blood test will not show anything. It will take up to the final molt of the worm (L5). The larvae arrive in the right ventricle and blood vessels that are close by. The arteries now have worms living in them and the lining is being damaged. Inflammation of the arteries and other inflammation occur due to the body's response in trying to heal itself. After time the changes that are undergone could show up on x-rays. Certain characteristics of heartworm disease are typical. The vessels become tortured and dilated. Blood clots and aneurysms are common side effects. Complete blockages of small blood vessels can occur. The blood needs to re-route itself to arteries that do not have worms. With complete and partial blockages of vessels fluid starts to accumulate around them and in the lungs. The results, loss of lung tissue. This reduces the lungs to oxygenate the blood for the body. With inflammation, blood vessel obstruction, and fluid accumulation, coughing is the results. Secondary to the increase in lung inflammation (pulmonary eosinophilic granulomatosis) there could be nose bleeds, shortness of breath and pneumonia may occur
As more and more worms continue to arrive in the heart to join up with the mature ones already living there the animals reactions become more significant and the signs get worse. More vessels and surrounding lung tissue are damaged. Less blood flows through the lungs. Blood pressure increases in the right side of the heart and Vena Cava. More accumulation of fluid in the lungs. The end result, heart failure. The severity depends greatly on the number of worms and the animals reaction to them. The weakened heart muscle results in rhythm abnormalities, accumulation of fluid in the lungs (pulmonary edema) and exercise intolerance.
In time the immune system works at a higher rate putting extra proteins (antibodies) into the system. They can settle out in various organs in the body, eye, kidney, blood vessels, and joints. This causes more inflammation and tissue damage and more pain.
The most severe heartworm infestation of adult heartworms (around 100 and more) is called Vena Cava Syndrome. Almost complete blockage of all blood flow. Often times there are no signs of heart disease. The animal will just collapse, with death being within 1 to 2 days. There is severe shock and red blood cell destruction. The only chance for survival is surgery. The veterinarian must remove the worms from the heart through the jugular vein. If enough worms are removed and some blood flow is re-establish there is a chance for the animal to survive. There is not a guarantee on this and many patients die in spite of the surgical procedure.
Testing for Heartworm Disease in Dogs.
If you suspect your pet to have heartworms see your vet immediately. A complete medical history will be taken and a thorough physical exam. Blood will be drawn and a test run. If your pet is positive for the disease more test need to be ran to evaluate the severity of the disease and the impact that it has on your dog. X-rays will be taken, a complete blood count (CBC), chemistry profile to evaluate the organs functioning capacity, and urinalysis. The animal will be rated as to risk to decide the method of treatment that is best. The disease is rated in stages. The stages being:
Stage 1 Lowest Risk being young healthy dogs with minimal heartworm disease showing on x-rays and all the other test are normal.
Stage 2 Moderately Affected Dogs some coughing, some difficulty breathing, changes are seen on the x-rays, blood work reveals some kidney damage, liver damage, or both.
Stage 3 Severely Affected Dogs the animal has weight loss, coughing, difficult breathing, more damage visible on x-rays, blood work shows some kidney damage, liver damage, or both.
Stage 4 Vena Cava Syndrome the dog is collapsing and in shock, the dog is dying.
Treatment for Dogs with Heartworm Disease.
This is very a complicated issue. There are many factors that go into the answer to this question. We must eliminate the worms from the dogs system. The treatment will vary from dog to dog. The animals general state of health, the number of worms present, the dogs reaction to their presence, how the dog will handle the side effects due to the medication and the effects of the dead worms in the circulatory system will all play a major role in the treatment your veterinarian will pick for the animal. There is a treatment protocol for this and the best medication will be chosen. Keep in mind, there is no way to predict how each animal will react to heartworm treatment.
Some animals will need to be stabilized before heartworm treatment can begin. 3rd stage patients may require jugular vein surgery before other steps of parasite removal are considered.
The elimination of the heartworm parasite is a two step process. The adult worm and the microfilaria need to be eliminated separately. There is not a medication that will kill both of them. First the adults need to be treated, then the microfilaria and migrating larvae.
Treating the adult worm usually has the most serious side effects. The dead worms get lodged in the lung arteries and block even more blood vessels. The inflammation is increased because of decomposing worms in the vessels. As the worms destruction occur, this releases foreign substances into the dog's circulation and are eliminated from the body by the immune system. Generally more inflammation and swelling will occur during this time. Most clinic or hospitals will keep the dog while the treatment is being done so they can monitor them closely as the treatment is very hard on the animal. Side effects from the medication can take up to 2 weeks to appear. It is very important to keep the animal very quiet. Follow all of your veterinarians instructions. Do not hesitate to call with any questions. This is a very serious disease and you will need to know all you can to help your pet to get through this and try to repair its body.
Sometimes a second set of treatments may be required to kill the L5 and young female adult heartworms. Usually about 1 month after the first treatments the microfilaria are then treated for elimination. Approximately 4 months after the first treatment the animal is retested for heartworm. This determines if a second treatment is needed. Once heartworm disease is eliminated a preventative medication will be prescribed to help keep your pet from getting this horrible disease again.
Another factor to consider is that an animal can act as a source for future additional infesting mosquito bites, so over time unprotected dogs can develop a large number of adult worms in the heart. Also, some animals develop something similar to an allergy to the worms, or to the microfilaria, which results in the Occult Heartworm Disease infections and can cause varying signs similar to allergies. This more elusive kind of infestation occurs most often in the cat. Cats seem to harbor only small numbers of adult worms, the worms are usually males only, microfilaria are rarely found in circulation, and signs of heartworm disease infection can present as an allergic condition similar to asthma. It is not uncommon for infected cats to suddenly die from the effects of just a few worms. The worms that happen to make the normal migration to the heart can cause many problems since the cats heart and vessels are much much smaller than most dogs. The adult worm reach a shorter adult length of 5 - 8 inches versus 14 inches in the dog. Other feature not unusual in cats is single sex heartworm infections. This means that no microfilaria can be produced which make identification of the disease more difficult. These single sex infections are commonly male worms only in the cats that are positive
There are differences with this disease between cats and dogs. First let me explain, cats are not a natural host for the hearworm. Thats good news to a point. But this isn't saying that it wont or cant be found in cats. It is just less common for them to become infected with the heartworm disease. Aberrant migration of the larval worms die before they can mature in the cat. The worms that do reach adulthood live a shorter life in a cat as apposed to dogs. The lifespan being, 2-3 years in the cat versus 7 years in a dog. We have learned that male cats are more susceptible to getting heartwrom disease than female. Cats with heartworm disease are more likely to be between 3-6 years of age.
Felines have an activated immune system that readily helps them fight off heartworms. The signs of an infestation are quite different than what we see in dogs. Circulating microfilaria is rarely ever seen in cats. This is because the cat's immune system removes them too quickly. Even one worm could be a medical emergency. It is most often beneficial to let the worm die naturally rather than risking treatment. Even at this rate severe reactions may occur as the adult worm dies.
Common Signs
Lung disease associated with respiratory stress, gagging and or vomiting, loss of appetite, weight loss, lethargy. Feline asthma is often times thought to be the problem. Many times clinical signs are not apparent and the cat dies suddenly. If clinical signs are present, they often do not reflect pulmonary disease. It only may take a few worms in the lungs to lead to death. As with dogs, sudden death may occur. Loss of coordination, seizures, collapse or blood from the nostrils could indicate a lung obstruction.
Diagnosing Feline Heartworm Disease
Feline heartworm disease diagnosis may be a challenging one. Most cats with heartworm disease have the male worms. Therefore there are only a few adult worms. Antigen test show a higher incidence of false negatives. Filter test are unreliable as there usually isn't microfilaria or very small amounts and may not always be found. X-rays may show some interstitial lung pattern, enlarged lobar pulmonary arteries, and occasionally right sided heart enlargement. Lab analysis of the blood may show a transient eosinophilia during the early stages of infection and may be absent thereafter. The best way to test for heartworm in cats is with an antibody-based Elisa.
Treatment of Feline Heartworm Disease
The same heartworm adulticide therapy used in dogs may be used in cats but it is extremely dangerous to do so. There may not be a choice, however, depending on the degree of illness from the heartworm disease. Approximately one third of cats receiving heartworm adulticide therapy will experience life-threatening embolic complications when the worms die suddenly. One month of cage confinement is typically recommended to control circulatory effort after adulticide treatment.
In general, if the cat does not appear sick, the American Heartworm Society recommends attempting to wait out the worm's 2-3 year life span and simply monitor chest radiographs every 6 months or so. Since the major signs of disease in the cat are due to inflammation and immune stimulation, a medication such as prednisone can be used to control symptoms.
Prevention. click here to buy Heartgard products.
WHEN TO START GIVING HEARTWORM PREVENTIVE EACH YEAR?
Obviously the answer to this question is regional. Indeed it may be simplest to just use preventive medications all year round. There is more to transmission than just the presence of mosquitoes; it must also be warm enough to allow the development of microfilariae to infective L3’s. A simple formula involves counting the degrees above 57 degrees F reached each day. Each degree is called a “heartworm development unit” and when 234 heartworm development units have accumulated within a 30-day period, conditions have been reached to allow the transmission of L3 heartworm to new hosts. A monthly heartworm pill or chewable must be given at the end of a month in which 234-heartworm development units has accumulated.
When 30 days pass and 234 heartworm development have not accumulated, mosquitoes will die having reached the end of their natural lives before any microfilariae they carry can develop to L3’s. Monthly heartworm disease preventive needs not be given after a month under these conditions.
When daily heartworm disease preventive is used, things are a little trickier. In order to work, DEC must already have been started by the time transmission becomes possible. This involves a bit of prediction based on past weather patterns in the area in question.
If all this sounds complicated, it is. In addition, most of us have better things to do besides monitoring average weather temperatures. It may be simpler to use the product all year round or just go by the recommendations of a practicing veterinarian in the region in question.
Product List
Ivermectin (Heartgard30, Heartgard Plus &
Iverheart Plus)
Selamectin (Revolution)
Milbemycin Oxime (Interceptor and Sentinel)
Moxidectin (ProHeart and ProHeart 6)
Diethylcarbamazine (Filaribits)
To see a Product list comparison chart Click Here
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Heartworm Disease
