Vector-transmitted diseases in companion animals: Trends, risks, controls
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.
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.