Dogs

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Lifecycle

  Clinical signs

Unfortunately there are no early signs. As the disease slowly progresses, the dog may show symptoms - coughing, decreased appetite, tiredness, loss of endurance during exercise, weight-loss, a bot belly and, in advanced stages, liver and heart failure. The worms interfere with the ability of the heart to pump blood. Clots can form and shower the lungs. The body reacts to the worms causing further damage especially to the lungs as well as the vessels. Heartworm can be half a metre long.

Diagnosis

Diagnosis is via blood tests that usually can be done in the veterinary clinic while you wait. There are two types of tests. Recently new "snap-type" tests have been produced that look for antigens(protein) produced by the adult heartworm. A negative result definitely means your dog is free of adult heartworm. If we obtain a positive result we then run the second (and older) type of test that looks for microfilariae (this test is 100 % accurate if positive however false-negatives are common as not all heartworm infections produce offspring). We do this test to double-check the first one and to decide on the type of treatment we need to undertake. Unfortunately, because heartworm has a long lifecycle, a second set of testing should be carried out 6 months after commencement of the preventive medication. We don't stress this in Melbourne but it is essential in high-risk areas.

Treatment

Treatment of adult heartworm is based on the stage of the disease. The aim of the treatment is to kill the adult heartworm however many dogs are too sick to handle the drugs needed to do this. They have to be treated for weeks to months on drugs designed to prevent clotting and the body's reaction to the worms. Once the dog is stable the adult worms can be killed chemically. A month later the microfilariae are killed off using another drug. Some dogs die in treatment and the success rate of killing all the worms is not 100 %. During treatment the dog must be kept quiet and can be very sick. For that reason we prefer to prevent heartworm rather than have to try to treat it.

Prevention

There are four groups of drugs available to prevent heartworm.

Diethylcarbamazine citrate or DEC is found in all the daily tablets. It's cheaper than the monthly tablets but must be given every single day. Once the dog is over 6 months if 2 tablets are missed in a row the dog must be retested before another tablet can be given.

DEC given to an infected dog can be fatal.

There are three different types of monthly tablets, Heartgard, Interceptor (Sentinal is Interceptor with Program to control fleas) and Proheart. They are roughly three times the price of daily medication. Monthly tablets should be given on the same day each month. If a tablet is missed then the next month should be given. Your dog should be retested after 6 months. Treating an infected dog with monthly medication is not recommended but will not be fatal.

The third medication is Revolution. This is a spot-on that also controls fleas, ear mites and sarcoptic mange. It is easy to apply and water fast in 2 hours, however is the most expensive of the treatments available. Recent price reductions has made Revolution's cost close to a combination of a monthly tablet and a flea control spot-on like Frontline or Advantage. The same protocol applies to Revolution as the monthly tablets.

A once yearly injection to prevent heartworm came on the market late 2000. This injection prevents infection often a long period of time by a new slow release technology. It is suitable for dogs over 6 months of age so we recommend you start you pet on tablets and change over when you pack runs out or at your dog's first yearly vaccination. This injection is ideal for owners who need or want the convenience without remembering tablets. Costs are approximately equal to a year's supply of monthly tablets.

Pups under six months of age cannot have adult heartworm and do not need to be tested to be placed on preventive medication. If you decide on daily tablets they should be started as soon as the pup is weaned. Monthly tablets (and Revolution) kill over a larger period of time but are still best started as soon as possible, and at least by 4 months of age. While not essential in Melbourne a blood test is recommended after 6 months of medication to ensure your dog was not biten by an infected mosquito prior to the start of medication.

Dogs over 6 months of age must be tested and found free of heartworm prior to starting prevention. A second test after 6 months on medication is recommended.

One mosquito bite can cause heartworm infection. As parts of Melbourne have low incidence it is up to you, the owner, if you wish to take the risk of your dog being infected with heartworm, or wish to give preventative medication. However if your dog is outdoors in Doncaster , Blackburn Lakes area or into Greensborough, and all the surrounding areas, we recommend you should give prevention. Of course in other parts of Australia such as Sydney and further north prevention must be given. In Darwin , for instance, the incidence of heartworm in unprotected dogs is close to 100 %. Remember heartworm disease can be fatal. Treatment is also far more expensive than prevention, not completely successful and your dog can die from complications (caused by the worms starting to decompose in the arteries).

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