Heartworm Treatment

Important new information regarding treatment of heartworm.

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By Mary Straus

For some time, biologists have been aware of and studied an organism called Wolbachia that lives symbiotically inside heartworms. But recently, study of this microscopic creature has given researchers new ideas about how to combat its host (the heartworm) to benefit its host, the dog.

Wolbachia is a genus of rickettsial organisms, a microorganism positioned somewhere between viruses and true bacteria. Like viruses, they grow only in living cells, but like bacteria, they are vulnerable to antibiotics. Bacteria in the Rickettsia genus are carried as intracellular parasites inside a number of what we have always thought of as tiny parasites (such as ticks, fleas, and lice). Rocky Mountain spotted fever is a disease caused by a rickettsial organism carried inside ticks.

Recent studies indicate some of the adverse effects of both heartworm infection and heartworm treatment, including inflammation, embolism, and allergic reaction, may actually be due to the presence of Wolbachia inside the heartworms, in addition to the heartworms themselves. Researchers have learned that treating a heartworm-infected dog 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 reaction during heartworm treatment.

The takeaway message? Any dog that is currently infected with heartworms should be treated with doxycycline for 30 days. If the infected dog will be treated with Immiticide (fast-kill method), it is best to give the doxycycline prior to beginning Immiticide treatment. This should make the treatment much safer, by greatly reducing the potential for embolism and allergic reaction to the death of the worms. There may also be benefit in continuing to give doxycycline during treatment.

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 researchers do not know for certain at this time. To be safe, it may be best to give doxycycline for 30 days to any dogs that have completed heartworm treatment in the past, to clear any possible remaining Wolbachia.

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. For updates, see www.dogaware.com/heartworm.html.

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Mary Straus has been a regular contributor to Whole Dog Journal since 2006. Mary first became interested in dog training and behavior in the 1980s. In 1997, Mary attended a seminar on wolf behavior at Wolf Park in Indiana. There, she was introduced to clicker training for the first time, and began to consider the question of how we feed our dogs after watching the wolves eat whole deer carcasses. Mary maintains and operates her own site, DogAware.com, which offers information and research on canine nutrition and health. DogAware.com has been created to help make people more "aware" of how to make the best decisions for their dogs. It's designed for people who like to ask questions and understand the reasoning behind decisions, rather than just being told what to do.  Mary has spent years doing research for people whose dogs have health problems, or who just want to learn how to feed them a better diet. Over this time, she has learned a great deal about dog nutrition and health, including the role of diet, supplements and nutraceuticals.  In 2007, she was asked by The Ivy Group to contribute to The Healthy Dog Cookbook. She previously also wrote a column for Dog World.

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