Ticks & Lyme Disease: The Importance of Repellency

Consider these 2 common scenarios*:

Radar, a 5-year-old, neutered male Labrador retriever, is presented to a suburban Maine veterinary hospital for lethargy characterized by a lack of interest in walks to his local park. Radar is currently on oral flea and tick prevention.

On examination, Radar appears quiet, alert, and responsive and has a mild fever (103.1°F). Swelling and tenderness is noted in both carpi. Routine blood work (CBC, serum chemistry, urinalysis) is unremarkable, but a blue dot on Radar’s SNAP 4Dx test is consistent with infection and seroconversion to Borrelia burgdorferi. Further confirmatory diagnostics and treatment are discussed with the owner, who is distressed by the realization that Radar was not completely protected against Lyme disease as she had believed.

Ruby, a 3-year-old, spayed Labrador retriever, is presented to the same hospital for an annual examination and yearly diagnostics. Ruby is a neighbor of Radar’s and frequents all the same parks he does. She is currently healthy and receives oral flea and tick prevention.

Ruby’s examination is unremarkable. Her routine SNAP 4Dx test also shows a blue dot indicating infection and seroconversion to B burgdorferi. Long-term monitoring is discussed with the owner, who is frustrated that her apparently healthy and supposedly protected dog should require such measures.

Oral tick preventives require a blood meal to have an effect. Only when attached and feeding is the tick exposed to the ectoparasiticide, which then kills the tick over time. However, this same attachment required to kill the tick simultaneously stimulates B burgdorferi to mobilize from the tick’s midgut to its salivary glands, therefore giving B burgdorferi the opportunity to infect the host.²

Most oral tick preventives rely on speed-of-kill claims to protect dogs from B burgdorferi transmission during the necessary blood meal; however, the minimum transmission time for this and other tick-borne pathogens has yet to be established and is still debated.^2,3 A recent rodent model found B burgdorferi transmission to occur as early as 12 hours after attachment as compared with the 24- to 48-hour transmission time typically cited.^2,4 Factors such as coinfection with other tick-borne pathogens, simultaneous feeding by multiple B burgdorferi-infected nymphs, and B burgdorferi strain differences have all been suggested to shorten transmission time and increase infectivity.^3-5 Furthermore, ticks whose feedings are interrupted on one host can finish feeding on another, therefore requiring less attachment time on the second host to transmit pathogens.⁶

Lastly, preventing tick bites is also important in the prevention of other tick-borne diseases such as anaplasmosis and ehrlichiosis, which are likewise transmitted during a blood meal and can transmit in as quickly as a few hours of attachment.^1,7

The blue dots on Radar and Ruby’s tests represent apparent failure of effective tick control. Protecting dogs from tick-borne disease such as Lyme borreliosis requires blocking the transmission of the pathogen. Products that repel and kill ticks on contact reduce the likelihood of a blood meal and the risk for transmission of pathogens like B burgdorferi.²