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.