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AHS HEARTWORM HOTLINE
Wolbachia and Heartworm:
Why Doxycycline Is Needed
in Heartworm Treatment
Andy Moorhead, DVM, MS, PhD
University of Georgia College of Veterinary Medicine
AHS HEARTWORM HOTLINE
The treatment of adult heartworm (Dirofilaria
immitis) infection in dogs has changed significantly
since the days when veterinarians' only option
was injectable thiacetarsamide sodium. First, the
introduction of melarsomine dihydrochloride in the
mid-1990s revolutionized the treatment of adult
heartworm infection by providing superior efficacy
via intramuscular administration.
1
The next great
leap forward in heartworm treatment came with
the discovery that some filarial worms harbor a
type of bacteria, Wolbachia, and that elimination
of these bacteria proved beneficial to the animal
and reduced the complications of disease.
2
This article explains why Wolbachia are
important in the pathogenesis of heartworm
disease and why eliminating them through
the use of doxycycline is so important to the
treatment of the heartworm-infected animal.
WHAT ARE WOLBACHIA AND
WHY ARE THEY IMPORTANT
TO THE HEARTWORM?
Wolbachia bacteria are related to Rickettsia, which
are intracellular bacterial parasites that live within
certain invertebrates, including some flies and
nematodes.
3
Wolbachia are bacterial symbionts. As
endosymbionts, Wolbachia bacteria require the host
organism, the heartworm, to survive; equally, the
heartworm requires Wolbachia for its survival.
4
The exact function of Wolbachia in heartworms
is unknown.
5
It has been hypothesized that the
presence of these bacteria may aid in energy
metabolism.
6
Populations of Wolbachia, which are
present in all heartworm life stages, expand between
the third-stage infectious larvae (L3) and fourth-
stage larvae (L4). For this reason, it is hypothesized
that preventing the expansion of the Wolbachia
population will prevent heartworm development.
7
shutterstock.com/otsphoto
The Heartworm Hotline column is presented in partnership
between Today's Veterinary Practice and the American
Heartworm Society ( heartwormsociety.org ). The goal
of the column is to communicate practical and timely
information on prevention, diagnosis, and treatment of
heartworm disease, as well
as highlight current topics
related to heartworm
research and findings
in veterinary medicine.
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