Canine Heartworm Disease

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Canine Heartworm Disease Canine heartworm disease is a potentially life threatening disease that is transmitted by an infected mosquito. Although it can affect other animals as well, even humans, it is most commonly seen in the dog.

What is canine heartworm disease?	Canine heartworm disease occurs when a dog is bitten by an infected mosquito, which transmits the worm larvae to the blood of the dog. The worms eventually mature and move through the vein system into the right side of the animal's heart. They may also extend into the pulmonary vein system and the veins of the liver. Consequently, the worms can cause loss of lung function, liver failure, and cardiac failure.

What are the symptoms of heartworms?	Unfortunately, most infected dogs don't show symptoms for quite some time. The most common signs are a coughing, intolerance to exercise, weight loss, tiredness, and shortness of breath. As the disease progresses, the dog may have an inverted pear shape, due to the ribs becoming prominent and the chest starting to bulge. The dog may also have labored breathing at rest. When the disease is advanced, congestive heart failure can result.

What breeds are most prone to heartworms?	Heartworms occur without regard to breed, since they are spread by mosquitoes. However, some breeds are more sensitive to heartworm treatments than others, and may require further testing or a different type of medication. For example, Ivermectin used to kill heartworm larvae has been known to cause shock and death in some Collies and Collie mixes.

What causes heartworms?	Heartworms are caused by an infected mosquito. The infected mosquito bites the dog, causing the larvae of the parasite (Dirofilaria immitis) to be deposited in the skin. These larvae eventually turn into worms in three to four months, make their way into a vein, and eventually move into the heart. Heartworms can reach lengths of four to twelve inches and can live up to 5 years in a dog's heart. If both sexes of worms are present, a female can reproduce up to 5000 offspring in a day.These offspring (microfilaria) must go into another host (e.g. the mosquito) to continue their life cycle. However, they can live in the bloodstream of an untreated dog for up to 3 years. Once the mosquito bites a dog with the microfilaria in its bloodstream, the microfilaria develop into infective larvae in the mosquito. When the mosquito bites another dog, the process begins all over again.

Can anything be done to prevent heartworm disease?	Several drugs are currently available to prevent heartworm disease and are available through your veterinarian. Since the medication used depends on many factors, including your dog's current health status, sensitivity to medications, and whether your dog currently has heartworm disease, it is recommended that your dog be tested for heartworms before starting a prevention program. Southern and coastal areas where mosquitoes may be a year round problem may require that you start a heartworm preventative when your dog is a puppy and continue giving the medication throughout its life. If you live in an area where mosquitoes are only a seasonal problem, your veterinarian may recommend starting the preventative a month before mosquito season and two months after the first frost. To prevent your dog from being bit by mosquitoes, you may also want to keep them indoors in the late afternoon and evenings when mosquitoes are feeding. Stagnant water should also be avoided since it can provide ideal conditions for mosquitoes to breed. The three most common drugs used for heartworm prevention are: Diethylcarbamazine (DEC) used in Filaribits, Carbam and Nemacide tablets Dog must be microfilaria free. Otherwise shock or death can occur. Effective against infective larvae before they mature Very safe Must be given daily since passes through bloodstream Missing a day can make your pet susceptible Interceptor (milbemycin oxime) Dog must be microfilaria free. Otherwise shock or death can occur. Effective against infective larvae before they mature Given once a month Safe to use in Collies and Collie mixes Ivermectin (Heartguard-30) Testing required before use Given once a month Effective against infective larvae and microfilaria Adverse reactions have occurred in Collies and Collie mixes

How are heartworms treated?	Treatment for heartworms should always start with a careful evaluation by your veterinarian. If your dog is healthy enough for heartworm treatment, your veterinarian will probably administer a drug intravenously (thiacetarsamide) which kills the adult heartworms. They dog's body must be given time to recover from the treatment and absorb the dead worms (usually 3 to 6 weeks), at which time a drug (Ivermectin or Levamisole) to kill the worm larvae (microfilaria) may be given. In some cases if the dog is too ill to take the treatment, the worms may have to be removed surgically. In all cases, close supervision by your veterinarian is necessary due to complications or adverse drug reactions that may arise. As they say, an ounce of prevention is worth a pound of cure. The best thing to do is to remember to give your pet a heartworm preventative as indicated by your veterinarian.