Heartworm Disease
Heartworm is a serious and potentially fatal disease of dogs and cats that is caused by worms that live in the right side of the heart and neighbouring blood vessels. Adult worms can grow up to 30cm in length.
How do dogs and cats become infected?
Heartworm is transmitted by mosquitoes. This means that even if your dog or cat never comes in contact with other animals, they can still have the parasite transmitted to them. A mosquito will bite an infected animal and pass immature worms (larvae or microfilaria) to your pet. The larvae then take six months to grow into adults, which live in the heart and neighbouring blood vessels. These adults then produce more larvae and the cycles continue.
How does it affect my pet?
With heavy infestations the worms obstruct normal blood flow through the heart and blood vessels. Changes can occur in the heart, lungs, liver and kidneys due to the interruption of blood flow. Signs you may notice include coughing, decrease exercise tolerance, difficulty breathing, weight loss and accumulation of fluid in the abdomen, giving your pet a pot-bellied appearance.
How can Heartworm be diagnosed?'If your dog has never been on preventative medication or it is not up to date, we may need to test for the presence of heartworm. If your dog shows no signs of heartworm disease your veterinarian may start your dog on a specific medication and then strongly recommend we test your dog in six months time. If your dog is showing signs of heartworm disease a blood test may be performed straight away. If the situation is more complex chest x-rays may be required to see how far the disease has progressed.
Treatment of heartworm positive animal
If you pet is positive to heartworm, treatment involves a course of injections and strict rest. This is fairly successful in dogs where the diagnosis has been made early, however there is always some risk in treating heartworm cases. Dogs can react badly to the drugs used to kill the worms and the dead worms floating in the flood can also block major blood vessels causing further serious problems.
Prevention
Heartworm disease is one disease where prevention is better and easier than cure. We recommend starting your pet on a preventative medication from 3 months of age. There are many different products on the market to prevent heartworm, all of which prevent larvae developing into adults.
A yearly injection (“Proheart SR-12”) is available for dogs. It lasts 12 months and can be given at the same time as your pets yearly vaccinations. Again a blood test is recommended if your pet is over six months of age and has not yet been on any preventative medication. Proheart injections are suitable to be given to dogs 12 weeks of age and over, this is repeated at 6 months of age, 15 months of age, then yearly for life. Proheart is safe for use in Ivermectin sensitive breeds eg. Collies.
Monthly treatments are available for both dogs and cats. They are available either as a tablet, a meaty chew or a spot-on formulation. Some products kill other parasites such as intestinal worms (“Sentinel”) or some intestinal worms and fleas (“Revolution” and Advocate”). Monthly treatments should be given on the same day every month and can be used in both dogs and cats. However many of these treatments cannot be used if your pet already has heartworm, as a serious reactions can occur. Therefore we may recommend a blood test for these products if your pet is older than six months and has not been on any prevention as yet. Some of these treatments are not recommended with certain breeds – ask us for more information.
Daily tablets are available from supermarkets and vets. If you are just starting out on prevention it is important you speak to your vet first as they can cause very serious reactions if your pet already has heartworm or if you miss a single dose. Therefore all pets going onto daily tablets must be tested for heartworm first.
BE WARNED Intestinal wormers are often called “Allwormers” but do not cover your pet against heartworm. Intestinal wormers are required every 3 months whilst heartworm prevention is generally monthly or yearly.