Mild winters, the northern migration of tick populations and the emergence of more frequent vector-borne zoonotic diseases
left the editors of DVM Newsmagazine with questions.
We found answers from noted expert Dr. Edward Breitschwerdt, professor of medicine and infectious diseases at North Carolina
State University College of Veterinary Medicine and an adjunct associate professor of medicine at Duke University Medical
Center. Also, Breitschwerdt co-supervises NCSU's Vector-transmitted Disease Diagnostic Laboratory and remains a principal
investigator for the Intracellular Pathogens Research Laboratory. His research emphasis is on the role of vector-transmitted
pathogens as a cause of disease in animals and humans.
DVM: The Midwest and North Atlantic regions have experienced very mild winter conditions this year. What risks does that pose
for vector-transmitted diseases?
Dr. Breitschwerdt: It is clear that climatic variations contribute to the expansion and contraction of tick populations in various geographic
regions. Using Amblyomma americanum as an example, it appears that this tick has moved northward during the past decade. This movement is probably facilitated
by expansion in deer populations throughout the eastern United States and the trend of warmer winters. Factors other than annual temperature also seem to influence the patterns of tick transmission for some pathogens such as
Rickettsia rickettsii, the organism that causes Rocky Mountain Spotted Fever (RMSF) in dogs and people. There seems to be a 10-year cycle of activity
relative to peaks in the incidence of RMSF in people; the reason for this cyclic pattern remains unknown.
Unfortunately, despite the fact that dogs are excellent sentinels for many vector-borne organisms, demographic data for vector-borne
diseases is frequently not available for dogs.
DVM: In your estimation, what is the most important emerging companion-animal, vector-borne disease threat? Why?
Dr. Breitschwerdt: Babesia gibsoni in dogs and Cytauxazoon felis in cats are perhaps near the top of the list. The range of C. felis transmission appears to be expanding to include most
of the southeastern and central United States. As for B. gibsoni, transmission by bites during dog fights appears to represent the most likely means of transmission among Pit Bull Terriers
in the United States; however, we are now seeing B. gibsoni-infected dogs that have not been associated with either a Pit Bull Terrier or a fight. Although unproven, this suggests that
the brown dog tick, Rhipacephalus sangineus, or other vectors may now be contributing to the transmission of B. gibsoni in the United States.
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Research from our laboratory and others suggests that vector-transmitted infectious diseases B. gibsoni and Leishmania infantum have been inadvertently introduced onto the North American continent by dog transport from endemic regions of the world.
Many companion-animal infectious disease and public-health veterinarians share a serious concern about the rapid transport
of vector-borne organisms throughout the world via infected dogs.
DVM: Could you address the role of Bartonella as a cause of chronic infection?
Dr. Breitschwerdt: The genus Bartonella, which at the time consisted of two known species, was essentially "rediscovered" in the early 1990s as a result of the HIV
epidemic. Currently, the genus is comprised of at least 20 species and subspecies, which are vector-transmitted, fastidious,
gram-negative bacteria that are highly adapted to one or more mammalian reservoir hosts.
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