Wolbachia and Their Role in Heartworm Disease and Treatment

By Dr. Susan Muller Esneault

Filed Under: Dogs, Diseases, Parasites

Does your dog have heartworms or Dirofilaria immitis? There is a long list of complications that may occur as a result of heartworm disease or in the treatment thereof. New research has shown that a gram-negative intracellular bacterium by the name of Wolbachia may be responsible for many of these complications and side-effects.

Wolbachia is a member of the family Rickettsiales. This bacterium does not live outside of its host and is actually transmitted vertically from adult female heartworms to their offspring, termed microfilaria. A symbiotic relationship is believed to exist between the heartworm and the bacteria. The Wolbachia infect all stages of the heartworm life cycle and is believed to be necessary for the development, reproduction, and the long-term survival of the parasite

A direct relationship has been shown between the inflammation associated with heartworm disease and the presence of Wolbachia within the microfilaria. A pet infected with heartworms is protected from the Wolbachia bacteria as long as the heartworm itself remains alive and well. When that heartworm dies, from natural causes or heartworm treatment, the Wolbachia bacteria are released and severe inflammatory complications may result.

Following the death of an adult heartworm, the Wolbachia bacteria are released into the bloodstream and body tissues in massive numbers. The presence of these bacteria causes severe inflammation in the pulmonary artery endothelium which in turn may result in the formation of thrombi and interstitial inflammation. Proteins found on the Wolbachia have also been shown to activate proinflammatory cytokines, thereby causing an increase in the inflammatory response by the host.

Studies have shown that treatment with tetracycline 30 days prior to adulticide heartworm treatment will be lethal to some of the adult D. immitis, suppress microfilaria production, and when given following heartworm treatment, may decrease the post treatment inflammation associated with the destruction of the parasite.

References:

Bonagura, John and David Twedt, Editors. Kirk’s Current Veterinary Therapy XIV. Saunders/Elsevier. 2009. P. 841.

Todd-Jenkins, Karen. “The Role of Wolbachia in Heartworm Disease.” Veterinary Forum. October 2007. Pp. 28-29.

Topics: bacteria, dirofilaria immitis, heartworms, wolbachia

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