Dirofilaria immitis and Dipetalonema reconditum
Heartworm has become established across much of the world. The life cycle of this parasite requires just two hosts; the dog and the intermediary host, the mosquito.

Infection occurs when a mosquito carrying developed larvae bites a dog; the mosquito acquires its infection by biting an infected dog.
Heartworm infestation in the dog can be controlled by using chemicals in a prophylatic regime, that is as a preventative against larvae developing in the dog. A number of chemicals are available to achieve this, and manufacturers do monitor the success rate of their products.
Diethylcarbamazine is readily available but must be administered daily to achieved the desired control as the active ingredient is excreted 24 hours are ingestion. A number of brand names are available.
Ivermectin and milbemycin are effective if used on a monthly or 30 day basis. The monthly preparations are restricted in availablity so consult your Veterinary Surgeon about supply. These compounds are more expensive but of course not as many tablets are used per dog per year.
The use of these chemicals does not stop mosquitoes biting someone else’s infected dog, the chemicals, by maintaining a constant low dose level in your own dog’s body, prevents the infective agent developing into an adult heartworm.
Heartworm disease, the manifestation of adult heartworms in the bloodstream and close lying tissues, is possible but extremely risky. The location of the worm in delicate tissues requires very careful administration of highly toxic compounds but in a regime that will kill the worm rather than harm the host. The further complication is the actual eradication of the dead adult heartworm, which have been reported at lengths of 30cm plus. If the dead heartworm is actually lodged in the artery or other major bloodvessel it will be free to circulate and so could act like a blood clot obstructing flow as well as becoming toxic in its own right as it decomposes.
Left untreated there is a chance that heartworm will not dramatically affect the lifestyle of a dog, take the dog population in Papua New Guinea for example. Studies there reveal that over 90% of the population there has adult heartworm infection – there is still an active dog population! However, there is a grave chance that a dog’s life could be shortened or the quality of life deteriorated. There is no way you can predict when the adult heartworm population in a dog will die from natural causes and so present the same types of problems as when the worms are destroyed under treatment.