Chapter One-Page3
Chapter One
Microfiliaria and Wolbachia
Adult heartworms may live five to seven years and, during this time, the female produces millions of offspring called microfilaria. These microfilariae live mainly in the small vessels of the bloodstream. Many pathogenic filarial worms are also infected by Wolbachia pipientis, an intracellular, gram-negative rickettsial bacterium, in an endosymbiotic relationship. The role of Wolbachia which live intracellularly within the filarid parasite, is not completely understood but it is thought that these organisms assist the metabolism of the worm and may even assist in keeping the host’s immune system from attacking the heartworms. However, these bacteria have been implicated in the pathogenesis of filarial diseases, possibly through endotoxin production (MERCK Manual, 2016)4 and the severe inflammation they cause when adult heartworms die.
For veterinarians, the most important aspect of Wolbachia is its symbiotic relationship with D immitis. This bacterium is necessary for normal maturation, reproduction, and infectivity of the heartworm.
Wolbachia and D immitis – A Symbiotic Relationship
Studies have demonstrated that a primary surface protein of Wolbachia (WSP) induces a specific IgG antibody response in hosts infected by D immitis. For veterinarians, the most important aspect of Wolbachia is its symbiotic relationship with D immitis. This bacterium is necessary for normal maturation, reproduction, and infectivity of the heartworm. If Wolbachia are eradicated from inside the heartworm, the heartworm gradually dies, after first becoming sterile. This can be accomplished with doxycycline therapy (MERCK Manual, 2016)4.
We will discuss in depth in a later module how the heartworm infection, once established in the vessels and lungs, may be considered curable, yet the pathology of the disease cannot be reversed in most cases.
4 http://www.merckvetmanual.com/mvm/circulatory_system/heartworm_disease/overview_of_heartworm_disease.html accessed October 16, 2016.