As most pet owners already know, heartworm treatment for cats and dogs is not the same. Never, under any circumstances, should you give your cat heartworm treatment that is designed for a dog or vice versa. Even though you may own both dogs and cats, you should always give them medicine that is designed for their species. No matter how you look at it, heartworm treatment is not easy. Your goal is to get rid of the heartworms, although there are several factors that you will need to consider. The first thing to do is take your cat to the vet, as he will be able to run tests to determine just how many heartworms your pet has. He can also find out how the worms are affecting your cat and if your cat can deal with any side effects that the treatment medicine may impose. Heartworms are a very serious condition, as the worms will feast on the vital areas around your cats heart.

Treatment can be serious as well, especially if something goes wrong. Veterinarians are trained to deal with heartworms though, in both cats and dogs. Even though you may be able to buy treatment medicine at your local department store, you should always consult with your vet before you give anything to your pet. Treating your cat for heartworms may indeed be no treatment at all, as cats are extremely difficult to treat. The dying worms have side effects as well, often times causing more than 1/3 of the treated cats to end up with serious problems. Dying worms can become lodged in the arteries of the heart, which are already inflamed due to the worms being there. When a lodged worm starts to decompose, it can lead to very serious problems. Pets that have a serious infestation with heartworms may need to spend some time at the hospital, to ensure that they are properly treated. Some cats may not be able to take a certain type of heartworm treatment medicine. Depending on the side affects and how the medicine affects the cat, some breeds may not be able to take some of the better medicines.

To determine the best treatment options for your cat, your vet will need to run several tests. Once the tests have concluded, your vet will be able to tell you the best options available for treatment. With all diseases, prevention is a lot better and safer than treatment. Be sure to talk to your vet and find out what heartworm prevention medication is the best to use. Your vet can tell you what you need to get, and how to use it. This way, you can prevent your pet from getting heartworms and the serious side effects and life threatening issues that go along with them.

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Heartworm (Dirofilaria immitis is a Parasitism roundworm that is spread from host (biology) to host through the bites of mosquito s. The heartworm is a type of nematode a small thread-like worm, that causes filariasis The definitive host is the dog but it can also infect cat , wolf coyote , fox s and other animals, such as ferret , sea lion and even, under very rare circumstances, human .http://www.heartwormsociety.org/pet-owner-resources/faqs.html The parasite is commonly called "heartworm"; however, that is a misnomer because the adults actually reside in the pulmonary arterial system (lung arteries) for the most part, and the primary effect on the health of the animal is a manifestation of damage to the lung vessels and tissues.lt;/ref> Occasionally, adult heartworms migrate to the right heart and even the great veins in heavy infections. Heartworm infection may result in serious disease for the host.

Distribution

Although at one time confined to the southern United States heartworm has now spread to nearly all locations where its Vector (epidemiology) the mosquito, is found. Transmission of the parasite occurs in all of the United States (cases have even been reported in Alaska , and the warmer regions of Canada The highest infection rates are found within 150 miles of the coast from Texas to New Jersey and along the Mississippi River and its major tributary lt;/ref> It has also been found in South America lt;/ref> southern Europe lt;/ref> Southeast Asia lt;/ref> the Middle East lt;/ref> Australia Korea, and Japan

Course of infection

File Microfilaria.jpg (as seen at 400× magnification)]] Heartworms go through several Developmental biology before they become adults infecting the pulmonary artery of the host animal. The worms require the mosquito as an intermediate stage to complete their life cycles. The rate of development in the mosquito is temperature-dependent, requiring about two weeks of temperature at or above 27°C (80°F). Below a threshold temperature of 14°C (57°F), development cannot occur, and the cycle will be halted.lt;/ref> As a result, transmission is limited to warm months, and duration of the transmission season varies geographically. The period between the initial infection when the dog is bitten by a mosquito and the maturation of the worms into adults living in the heart takes six to seven months in dogs and is known as the "prepatent period". After infection, the third-stage larva heartworms (L₃) deposited by the mosquito grow for a week or two and molt to the fourth larval stage (L₄) under the skin at the site of the mosquito bite. Then, they migrate to the muscle of the chest and abdomen and 45 to 60 days after infection, molt to the fifth stage (L₅, immature adult). Between 75 and 120 days after infection, these immature heartworms then enter the bloodstream and are carried through the heart to reside in the pulmonary artery. Over the next three to four months, they increase greatly in size. The female adult worm is about 30 cm in length, and the male is about 23 cm, with a coiled tail.lt;/ref> By seven months after infection, the adult worms have mated and the females begin giving birth to live young, called microfilaria . The microfilariae circulate in the bloodstream for as long as two years, waiting for the next stage in their life cycles in the gut of a bloodsucking mosquito. When ingested by a mosquito, the microfilariae undergo a series of ecdysis to the infective third larval stage, and then migrate to the salivary glands of the mosquito, where they wait to infect another host. The incubation period required to reach the stage where the microfilariae become transmittable to another host can be as little as two weeks or as long as six weeks, depending on the warmth of the climate, and the larval life cycle ceases entirely if the ambient temperature drops below 14°C (57°F).

Hosts

Hosts of Dirofilaria immitisinclude: * Dog * Cat * Wolf * Coyote * Fox * Ferret * Sea lion * African leopard (Panthera pardus pardus)lt;ref>Mazzariol S., Cassini R., Voltan L., Aresu L. & di Regalbono A. F. (2010). "Heartworm (Dirofilaria immitis infection in a leopard (Panthera pardus pardus housed in a zoological park in north-eastern Italy". [[Parasites & Vectors]]3 25. * Human (rare) * Beaver

Clinical signs of infection

Dogs show no indication of heartworm infection during the six-month prepatent period prior to the worms maturation, and current diagnostic tests for the presence of microfilaria or antigen cannot detect prepatent infections. Rarely, migrating heartworm larvae get "lost" and end up in unusual sites, such as the eye, brain, or an artery in the leg, which results in unusual symptoms such as blindness, seizure and lameness But normally, until the larvae mature and congregate inside the heart, they produce no symptoms or signs of illness. Many dogs will show little or no sign of infection even after the worms become adults. These animals usually have only a light infection and live a fairly sedentary lifestyle. However, active dogs and those with heavier infections may show the classic signs of heartworm disease. Early signs include a cough, especially on exercise and early exhaustion upon exercise. In the most advanced cases where many adult worms have built up in the heart without treatment, signs progress to severe weight loss, fainting coughing up blood and, finally, congestive heart failure.

Role of ''Wolbachia''

[[Wolbachia]] pipientisis an intracellular bacterium that is an endosymbiont of Dirofilaria immitis All heartworms are thought to be infected with Wolbachiato some degree. Research indicates the inflammation occurring at the die-off of adult heartworms or larvae is in part due to the release of Wolbachiabacteria or protein into the tissues. This may be particularly significant in cats, in which the disease seems to be more related to larval death than living adult heartworms (see below). Treating heartworm-positive animals with an antibiotic such as doxycycline to remove Wolbachiamay prove to be beneficial, but further studies are necessary.lt;/ref>

Diagnosis

Three methods can be used for the diagnosis: Microfilarial detection was accomplished most commonly in the past by the microscopic identification of microfilariae on a Blood film above the buffy coat in a microhematocrit tube (or capillary tube , using the http://www.heartwormsociety.org/veterinary-resources/canine-guidelines.html#3 modified Knott test], or after millipore filtration. The accuracy of these tests, typically used for routine screening or diagnosis of heartworm infection, is improved by multiple testing. The modified Knott test and millipore filtration are more sensitive because they concentrate microfilariae, improving the chance of diagnosis. The direct smear technique allows examination of larval motion, helping in the distinction of [[Dirofilaria immitis]]from Acanthocheilonema reconditum This distinction is important because the presence of the latter parasite does not require expensive and potentially harmful therapy. However, the potential for amicrofilaremic infections is 5-67%. The number of circulating microfilariae does not correlate with the number of adult heartworms, so is not an indicator of disease severity. [[Antigen test]]ing in most practices, has supplanted or supplemented microfilarial detection. Combining the microfilaria and adult antigen test is most useful in dogs receiving diethylcarbamazine or no preventative (as macrolides as for example ivermectin or moxidectin typically render the dog amicrofilaremic). Up to 1% of infected dogs are microfilaria-positive and antigen-negative. [[Immunodiagnostics]] (ELISA Lateral flow test rapid immunomigration techniques) to detect heartworm antigen in the hosts blood are now regularly used. The weakness of these tests is they only detect the antigens released from the adult female worms reproductive tract so will produce negative results during the first five to eight months of infection. The Sensitivity and specificity Specificity of these tests is close to 100%, and the Sensitivity and specificity Sensitivity is more than 80%.lt;/ref> A recent study demonstrated a sensitivity of only 64% for infections of only one female worm, but improved with increasing female worm burden (85%, 88%, and 89% for two, three and four female worms, respectively). Specificity in this study was 97%. Type I and type II errors test results can be due to low worm counts, immature infections and all male infections. [[Radiography|X-rays]] re used to evaluate the amount of lung damage caused by the presence of heartworms.

Treatment

If an animal is diagnosed with heartworms, treatment may be indicated. Before the worms can be treated, however, the dog must be evaluated for heart, liver, and kidney function to evaluate the risks of treatment. Usually, the adult worms are killed with an arsenic based compound. The currently approved drug in the US, melarsomine dihydrochloride is marketed under the brand name Immiticide lt;/ref> It has a greater efficiency and fewer side effects than previously used drug (thiacetarsamide sodium sold as Caparsolate which makes it a safer alternative for dogs with late-stage infections. After treatment, the dog must rest (restricted exercise) for several weeks so as to give its body sufficient time to absorb the dead worms without ill effect. Otherwise, when the dog is under exertion, dead worms may break loose and travel to the lungs, potentially causing respiratory failure and death. According to the American Heartworm Society, use of aspirin in dogs infected with heartworms is no longer recommended due to a lack of evidence of clinical benefit and may be contraindicated. It had previously been recommended for its effects on platelet adhesion and reduction of vascular damage caused by the heartworms. The course of treatment is not completed until several weeks later, when the microfilariae are dealt with in a separate course of treatment. Once heartworm tests are negative, the treatment is considered a success. Surgical removal of the adult heartworms as a treatment also may be indicated, especially in advanced cases with substantial heart involvement.lt;/ref> Long-term monthly administration of ivermectin year-round at three times the dose normally used for heartworm prevention (see "Heartworm Prevention ) will eventually kill adult heartworms. However, this is not the treatment of choice for removal of adult heartworms for two reasons. First, this treatment is not as effective as melarsamine. More importantly, adult heartworms do not begin to die until 18 months of treatment have elapsed, which is not acceptable for dogs with high-volume infections. Long-term treatment over a year with doxycycline daily and Heartguard Plus has been shown to be effective in early heartworm patients which are asymptomatic.

Prevention

Prevention of heartworm infection can be obtained through a number of veterinary drugs. The drugs approved for use in the US are ivermectin (sold under the brand names Heartgard Iverhart and several other generic versions), milbemycin (Interceptor Flavor Tabs and Sentinel Flavor Tabs and moxidectin (ProHeart) administered as pills or chewable tablets. Moxidectin is also available in both a six-month and 12-month, sustained-release injections, ProHeart 6 or ProHeart 12 administered by veterinarians. The injectable form of moxidectin was taken off the market in the United States due to safety concerns in 2004, but the FDA returned a newly formulated ProHeart 6 to the market in 2008. ProHeart 6 remains on the market in many other countries, including Canada and Japan. Its sister product, ProHeart 12 is used extensively in Australia and Asia as a 12-month injectable preventive. Topical treatments are available, as well. Advantage Multi (imidacloprid + moxidectin) Topical Solution, uses moxidectin for control and prevention of Toxocaridae , hookworm , heartworms, and whipworm , as well as imidacloprid to kill adult flea . Selamectin (revolution (pet medicine) is a topical preventive likewise administered monthly; it also controls flea , tick , and mite . Preventive drugs are highly effective, and when regularly administered, will protect more than 99% of dogs and cats from heartworm. Most compromises in protection result from failure to properly administer the drugs during seasonal transmission periods. In regions where the temperature is consistently above 14°C (57°F) year-round, a continuous prevention schedule is recommended. Lapses of up to four months between doses of ivermectin-based products still provides 95% protection from adult worms. This period is called the reach-back effect.lt;/ref> Annual heartworm testing is highly recommended for pet owners who choose to use minimal dosing schedules. Heartworm prevention for cats is available as ivermectin (Heartgard for Cats), milbemycin (Interceptor), or the topical selamectin (Revolution for Cats) and Advantage Multi (imidacloprid + moxidectin) topical solution.

Feline heartworm disease

While dogs are a natural host for D. immitis cats are an atypical host. Because of this, differences between canine and feline heartworm diseases are significant. The majority of heartworm larvae do not survive in cats, so unlike in dogs, a typical infection in cats is two to five worms. The lifespan of heartworms is considerably shorter in cats, only two to three years, and most infections in cats do not have circulating microfilariae. Cats are also more likely to have aberrant migration of heartworm larvae, resulting in infections in the brain or body cavities.lt;/ref> The infection rate in cats is 1-5% of that in dogs in endemic (epidemiology) areas.lt;/ref> Both indoor and outdoor cats are infected. The mosquito vector is known to enter homes.lt;/ref>

Pathology

The vascular disease in cats that occurs when the L₅ larvae invade the pulmonary arteries is more severe than in dogs. A syndrome related to this inflammatory reaction has been identified in cats: heartworm-associated respiratory disease (HARD). HARD can occur three to four months after the initial infection, and is caused by the presence of the L₅ larvae in the vessels. The subsequent inflammation of the pulmonary vasculature and lungs can be easily misdiagnosed as feline asthma or allergic bronchitis.lt;/ref> Obstruction of pulmonary arteries due to Embolism from dying worms is more likely to be fatal in cats than dogs because of less collateral circulation and fewer vessels.lt;/ref>

Signs and symptoms

Acute heartworm disease in cats can result in shock (circulatory) vomiting, diarrhea, fainting, and sudden death. Chronic infection can cause loss of appetite, weight loss, lethargy, exercise intolerance, coughing, and difficulty breathing. The signs of HARD can persist even after complete elimination of the heartworm infection.

Diagnosis

Diagnosis of heartworm infection in cats is problematic. Like in dogs, a positive ELISA test for heartworm antigen is a very strong indication of infection. However, the likelihood of a positive antigen test depends on the number of adult female worms present. If there are only male worms, the test will be negative. Even with female worms, an antigen test will usually only become positive seven to eight months after infection. Therefore, a cat may have significant clinical signs long before the development of a positive test. HARD can be found in cats that never develop adult heartworms and therefore never have a positive antigen test. An antibody test is also available for feline heartworm infection. It will be positive in the event of exposure to D. immitis so a cat that has successfully eliminated an infection may still be positive for up to three months. The antibody test is more sensitive than the antigen test, but it does not provide direct evidence of adult infection.lt;/ref> It can, however, be considered specific for diagnosing previous larval infections, and therefore fairly specific for HARD. Radiography of the chest of a heartworm-infected cat may show an increased width of the pulmonary arteries and focal or diffuse opacities in the lungs. Echocardiography is a fairly sensitive test in cats. Adult heartworms appear as double-lined hyperechoic structures within the heart or pulmonary arteries.lt;/ref>

Treatment and prevention

Arsenic compounds have been used for heartworm adulticide treatment in cats, as well as dogs, but seem more likely to cause pulmonary reactions. A significant number of cats develop pulmonary embolism a few days after treatment. The effects of melarsomine are poorly studied in cats. Due to a lack of studies showing a clear benefit of treatment and the short lifespan of heartworms in cats, adulticide therapy is not recommended, and no drugs are approved in the US for use in cats. Treatment typically consists of putting the cat on a monthly heartworm preventive and a short-term corticosteroid Surgery has also been used successfully to remove adult worms. Three drugs are approved for use in cats in the US: ivermectin, milbemycin, and selamectin. The prognosis for feline heartworm disease is guarded.

Human health considerations

The dog heartworm is of negligible public health risk, because it is unusual for humans to become infected. Additionally, human infections usually are of little or no consequence, although rarely an infected human may show signs of respiratory disease. In most cases, however, the heartworm dies shortly after arriving in the human lung, and a nodule, known as a granuloma forms around the dead worm as it is being killed and absorbed. If an infected person happens to have a chest X-ray following granuloma formation, the nodule may be large enough to resemble lung cancer on the X-ray and require a biopsy for a pathologic assessment. This may well be the most significant medical consequence of human infection by the dog heartworm. At one time, the dog heartworm was thought to infect the human eye, with most cases reported from the southeastern United States. However, these cases are now thought to be caused by a closely related parasite of raccoon , [[Dirofilaria tenuis]] Several hundred cases of subcutaneous infections in humans have been reported in Europe, but these are almost always caused by another closely related parasite, [[Dirofilaria repens]] rather than the dog heartworm.

References

External links

* Traversa D., Cesare A. Di & Conboy G. (2010). "Canine and feline cardiopulmonary parasitic nematodes in Europe: emerging and underestimated". [[Parasites & Vectors]]3 62.

American Heartworm Society

* http://www.heartwormsociety.org American Heartworm Society] Founded in 1974, the American Heartworm Society is internationally recognized as the definitive authority with respect to heartworm disease in dogs and cats.

Resources

* http://www.veterinarypartner.com/Content.plx?A595 Preventing Heartworm Infection in Dogs] (VeterinaryPartner.com) * http://www.metapathogen.com/heartworm/ Overview and main concepts of Dirofilaria immitis(heartworm) infection] (MetaPathogen.com) * http://www.moxidectinfacts.com Moxidectin Facts, Usage, and Safety Information] * http://www.vetmed.auburn.edu/distance/cardio/page1.html Feline Heartworm Disease] (from Auburn University) * http://cal.vet.upenn.edu/merial/hrtworm/hw_top.htm Heartworm Topics] (from the University of Pennsylvania) * http://edis.ifas.ufl.edu/MG100 Mosquito-borne Dog Heartworm Disease] (University of Florida Extension Bulletin) * http://www.avma.org/animal_health/brochures/heartworm/heartworm_brochure.asp What You Should Know About Heartworm Disease] (from the American Veterinary Medical Association) * http://www.vmth.ucdavis.edu/cardio/cases/case27/case27.htm Case Study of Canine Heartworm Disease] (from the University of California, Davis) * http://www.vmth.ucdavis.edu/cardio/cases/case31/case31.htm Case Study of Feline Heartworm Disease] (from the University of California, Davis) * http://www.vmth.ucdavis.edu/cardio/cases/case33/case33.htm Case Study of Canine Heartworm Disease] (from the University of California, Davis) * http://www.drsfostersmith.com/general.cfm?gid262 Heartworm Prevention Resources for Dog Owners] (from Drs. Foster & Smiths Veterinary Staff) * http://www.heartwormmedicinefordogs.net/ Heart Worm Medicine for Dogs] * http://www.petvetkamu.com/articles_files/heartworm.htm Heartworm in Europe] (From Clinica Veterinaria Pet Vet Kamu)

Pet owners

* http://www.heartwormsociety.org/article_17.html What Is Heartworm?] * http://www.heartwormsociety.org/article_14.html Frequently Asked Questions] * http://www.heartwormsociety.org/article_11.html Heartworm Disease in Dogs] * http://www.heartwormsociety.org/article_16.html Heartworm Disease in Cats] * http://www.tibetanmastiff.net/Heartworm.html Seasonal Timing Schedule for Heartworm Prevention] * http://www.heartwormprevention.net Heartworm Prevention In Dogs] * http://dogs-corner.blogspot.com/2009/09/dealing-with-your-dog-heartworm.html Dealing with Your Dog Heartworm]

Veterinarians

* http://www.heartwormsociety.org/article_48.html Guidelines for the Diagnosis, Prevention and Management of Heartworm (Dirofilaria immitis) Infection in Dogs] * http://www.heartwormsociety.org/article_47.html Guidelines for the Diagnosis, Prevention and Management of Heartworm (Dirofilaria immitis) Infection in Cats] Category Parasites Category Dog diseases Category Cat diseases Category Veterinary helminthology Category Zoonoses