Heartworm Treatment

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Recent research has led to the discovery of a parasite called Wolbachia that lives symbiotically inside heartworms. Studies indicate that this parasite contributes to the adverse effects of both heartworm infection and heartworm treatment, including
inflammation, embolism, and allergic reaction. Treatment with doxycycline for 30 days to kill the Wolbachia parasite weakens the heartworms and makes them unable to reproduce and greatly reduces the chance of adverse reactions during heartworm treatment. Any dog that currently has heartworms should be treated with doxycycline for 30 days. If the dog will be treated with Immiticide (fast-kill method), it is best to treat with doxycycline prior to beginning Immiticide treatment, as this should make the treatment much safer by greatly reducing the potential for embolism and allergic reactions to the death of the worms. If anyone has dogs currently undergoing treatment with Immiticide, I would, however, still give doxycycline, as even concurrent treatment may have some benefit.

Doxycycline should also be given to dogs that are being treated with monthly Heartgard (slow kill method) or any type of alternative heartworm treatment method, as it will weaken the heartworms, prevent them from reproducing, and reduce the chance of adverse effects
caused by the heartworm infection itself, and by the worms dying.

It appears unlikely that the Wolbachia parasite persists in the body after the heartworms have been cleared, though we do not know for certain at this time. To be safe, it may be best to treat any dogs that have completed heartworm treatment in the past with doxycycline for 30 days in order to clear any possible remaining Wolbachia.

I was unable to find any information on the recommended dosage of doxycycline in dogs. Because Wolbachia is a rickettsial organism, similar to those that cause tick disease, it may be advisable to use the higher dose of doxycycline that is recommended for treatment of tick disease, which is 10 mg/kg twice a day.

Veterinarians may contact Merial, the manufacturer of Immiticide, for more information on this topic, if needed.

Here is some additional information on the topic that I was able to find, though most of it is highly technical and still in preliminary stages of research:

http://www.veterinarypartner.com/Content.plx?P=A&A=610
"Wolbachia is a genus of rickettsial organisms (sort of like bacteria, but not exactly). They live inside the adult heartworm. These organisms seem to be protective or beneficial to heartworms and treating the dog with the antibiotic doxycycline seems to sterilize female heartworms (meaning they cannot reproduce). Wolbachia is also thought to be involved in the embolism and shock that result when heartworms die. The role of this organism is still being investigated. If your veterinarian wants to pre-treat your heartworm positive dog with doxycycline, it may be because of concerns regarding this organism. As new information emerges, we will post here."