Dog Heartworm
Heartworms are capable of causing severe disease and death in dogs. There is increasing evidence now that they
are also found in cats so the following information is relevant to cats as well. In areas where heartworm is endemic,
continuous medication (as a preventative) is necessary to prevent the establishment of heartworm and avoid
heartworm disease. It is better to prevent heartworm disease because the treatment is costly and somewhat
hazardous to the dog.
What is a heartworm
Heartworm (Dirofilaria immitis) is commonly found in the right chamber of the heart, the pulmonary artery (which is the main artery leaving the right chamber of the heart going into the lungs) and the vena cava (which is the main vein entering the right chamber collecting blood from the rest of the body). Heartworms are generally about 12-30cm long (up to 12 inches!).
Life cycle of the heartworm
It is important to understand the life cycle of the dog heartworm to prevent the disease from taking hold.
Mosquito (having bitten an infected dog picks up the baby heartworms – microfilaria) bites another ‘clean’ dog -> Heartworm larval stage 3 injected into dog -> migrates to heart of the dog and matures to adult heartworm (this takes about 6 months from infection) -> adult female heartworm lays live young (microfilaria) which circulates in the blood -> mosquito picks up microfilaria as it feeds on dog -> cycle starts again.
Dog heartworm symptoms
Symptoms of heartworm are the result of the maturing heartworm larvae and adult heartworms in the heart. The presence of the heartworm in the heart results in irritation of the heart and blood vessel walls causing thickening and blockage of blood flow. Sometimes heartworms can lodge in the liver blood vessels and result in liver failure. Heartworm symptoms in the dog can take years to show up. It usually starts of as a mild cough which most owners dismiss as unimportant but then gradually worsens to include symptoms like fatigue, more severe coughing and breathing difficulties. If left untreated, it will result in the eventual death of the animal. The more heartworms there are in the system the more severe the heartworm symptoms are. If the liver is involved, then other symptoms will include jaundice, loss of appetite and collapse.
Heartworm control
In general, you can tackle heartworm on 2 fronts – 1. mosquito control, AND 2. putting the dog on heartworm preventative medication.
Heartworm prevention for the dog
- Daily heartworm tablets – these are still around but are rapidly being replaced by the monthly heartworm tablets. Although I know collie breeders who still prefer to use daily tablets because there have been some reactions particular to the collie breed to the monthly preparations (in particular Heartgard).
- Monthly heartworm tablets.
First on the market was Heartgard (Ivermectin). Given as a monthly tablet, it is great in heartworm prevention although many collie breeders steer clear of it because of reactions to the drug in their breed opting for the daily heartworm tablets. Safe for use in puppies as young as 6 weeks. Recommended that before you put the dog on heartworm preventative that you take the dog into the vet for a heartworm test first. Comes in 3 sizes for dogs – in chewable tablets or just plain tablet form for dogs with beef allergies. Comes in 2 sizes for cats – in chewable tablets.
Now comes as Heartgard plus (Ivermectin/Pyrantel) for dogs which is given as a monthly tablet to prevent heartworm disease and with the added benefit of countering roundworms and hookworms.
Interceptor (milbemycin) is another heartworm preventative tablet that soon came into the market. It comes as a monthly flavored tablet and counters heartworm, roundworms, hookworms and whipworms. Comes in 3 sizes for dogs and cats – I find this a bit confusing because the packets say it can be used for dogs or cats of different weight ranges.
Sentinel (milbemycin/lufenuron) combines the heartworm preventative with flea control. Click here to read about Sentinel and flea control. Comes in a flavored tablet in 4 sizes for dogs for monthly consumption. Controls heartworm, roundworm, hookworm and whipworm.
To read about Revolution (selamectin) which is different from the above because it is a spot on treatment which protects against heartworm and counters fleas as well – click here.
My take on it :
- Cat owners – you can choose between Heartgard or Interceptor. I find the packaging for Interceptor confusing but if you don’t mind ‘sharing the stage’ with dogs, then it does the job just as well. Interceptor does not deal with tapeworms so a separate wormer is needed to deal with that. If you aren’t keen on giving tablets then Revolution is the go.
- Dog owners – you can choose any of the monthly tablets or Revolution (the spot on treatment) depending on your requirements. Monthly prevention of heartworm is the goal for all the above treatments. All the other side benefits eg hookworms, whipworms are secondary. Please note that NONE of the treatments above deal with tapeworms so you will still need to get a worming tablet for that. For collie owners, if you want to play it safe, then I say use Interceptor or Sentinel or use daily heartworm tablets.
Mosquito control in the environment
- aimed at general mosquito population control eg mosquito dunks in ponds (click here to buy) – these knock out the mosquito larvae in the water and are safe to use around fish.
- Don’t let pools of stagnant water collect where mosquitoes can breed.
- For other ideas on mosquito control, visit Gardeners Supply Co by clicking here.
Final Note : heartworm needs mosquitoes to be transmitted, so in areas where mosquitoes are not present, then heartworm prevention should not be required. Check with your local vet.
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