New Heartworm Information

Posted with permission of Mary Straus of dogware.com

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 reaction during heartworm treatment.

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

From VeterinaryPartner.com:

"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."

From Auburn State University School of Veterinary Medicine:

"Wolbachia are intracellular bacteria that infect numerous species of filarial worms including heartworms. Many contend that these friendly inhabitants (endosymbionts) play a role in the pathogenesis of diseases caused by heartworms and other filarids. Contention is that host immune responses directed at Wolbachia can actually go awry and enhance the disease process in heartworm infections. Some also contend that elimination of Wolbachia spp. from heartworms may affect the survival of adult heartworms and may decrease the host's errant immunologic responses when adult worms are killed or die."

"Dirofilaria immitis [heartworms] the cause of heartworm disease in dogs and cats harbours an endosymbiont intracellular bacteria of the genus Wolbachia (a Rickettsia). Studies performed recently indicate that these bacteria may play an important role in the pathogenesis and immune response to filarial infection (Bandi et al, 2001)." This article goes on to say that Wolbachia may contribute to many of the side effects of heartworm disease, including inflammation, kidney disease, lung problems and allergic reactions.

"Furthermore, preliminary data from our laboratory indicates that antibiotic treatment before adulticide therapy in dogs with heartworm disease leads to a decrease in pro-inflammatory cytokines, particularly IL-8."

At BioInfoBank:

This site has numerous other studies on human treatment, indicating that doxycycline, oxytetracycline (of which doxycycline is a derivative) and rifampicin (sometimes use in conjunction with doxycycline) are all effective against Wolbachia.

From National Academy of the Sciences:

"Bacterial relatives of Wolbachia include a number of agents that have arthropods as vectors and cause serious human diseases such as typhus, scrub typhus, erhlichiosis, and Rocky Mountain spotted fever. Studies of these bacteria require special containment facilities. In contrast, Wolbachia have so far been found only in invertebrates and are not known to cause mammalian disease."