The canine vector-borne disease timeline: how it works in practice
With the growing awareness of tick-borne disease among veterinarians and dog owners, screening and prevention protocols are commonplace in many veterinary hospitals across the US. However, the details of pathogen transmission times after tick attachment, how soon after infection antibodies may be detected in point-of-care tests, and when to expect clinical signs if they occur, are often unclear.
Vector-borne pathogens like Anaplasma spp., Ehrlichia spp., and Borrelia burgdorferi are subject to a variety of transmission modifying factors, such as pathogen species, host species, and the status of specific host immunity against the agent. The site of infection in the tick is also important, as transmission is facilitated if the pathogen lives in the salivary glands of the tick, as in the case with Anaplasma spp. In contrast, B. burgdorferi lives in the midgut of the tick and must undergo a change in outer surface protein (Osp) expression from OspA to OspC before moving to the tick salivary glands and then into the mammalian host after tick attachment occurs, thereby slowing transmission. Anaplasma spp. and Ehrlichia spp. are transmitted within 24 hours of tick attachment and B. burgdorferi is transmitted from about 24–53 hours after tick attachment (Kidd and Breitschwerdt, 2003).
After transmission, the time for infected dogs to become antibody-positive is pathogen-dependent. Anaplasma spp. seropositivity occurs first, at 2–3 weeks post-infection, followed by Ehrlichia spp. at 3–4 weeks post-infection, and then B. burgdorferi at approximately 4–6 weeks post-infection. In the case of B. burgdorferi, some antibody test platforms produce positive results in uninfected but recently vaccinated dogs, so test results must be interpreted together with vaccination history (Little, 2009). Antibody test results are unaffected by the administration of antimicrobial treatments such as doxycycline (Sainz et al., 2015). The duration of antibody-positive status after infection with any of the three tick-borne pathogens can be months to years, posing potential problems for test interpretation when subsequent tests are performed (Little, 2009).
Clinical signs of infection with Anaplasma phagocytophilum or Ehrlichia spp. can include fever, lethargy, bleeding diatheses due to platelet destruction, and/or lameness. While not all infections produce clinical signs, effects can occur as early as 1–3 weeks after tick attachment. Since this could be before seroconversion is detectable by antibody screening tests (Little, 2010), if clinical signs and CBC parameters are suggestive of tick-borne disease, presumptive treatment with doxycycline and follow up with further antibody tests in 1–2 weeks is an appropriate course of action in practice. Lyme disease, the clinical manifestation of B. burgdorferi infection, is often subclinical, but can cause immune complex-related joint disease and/or glomerulonephropathy. Lyme disease is unusual in that it has no acute phase; one experimental infection study reported that the incubation period for clinical arthropathy was median 68 days (Straubinger et al., 1998).
An understanding of tick-borne disease transmission times and how antibody screening test results relate to pathogen transmission and the appearance of clinical signs are important case management tools wherever canine tick-borne disease occurs.
Annette Litster, BVSc PhD FANZCVS (Feline Medicine) MMedSci (Clinical Epidemiology)
Senior Veterinary Specialist
Zoetis, US Companion Animal Division, Veterinary Specialty Operations
Kidd, L., & Breitschwerdt, E. (2003). Transmission times and prevention of tick-borne diseases in dogs. Compendium 25(10), 742-751.
Little S. (2009). Anaplasmosis and Ehrlichiosis—Clinical characteristics of infection webinar FAQs. https://idexxlearningcenter.idexx.com/idexx/resources/library/media_edu/archived_webinars/faqs/Anaplasmosis_and_Ehrlichiosis_Webinar_FAQs.pdf (accessed April 7, 2017).
Little S. (2010). Ehrlichiosis and anaplasmosis in dogs and cats. Veterinary Clinics of North America Small Animal Practice 40, 1121-1140.
Sainz, Á., Roura, X., Miró, G., Estrada-Peña, A., Kohn, B., Harrus, S., & Solano-Gallego, L. (2015). Guideline for veterinary practitioners on canine ehrlichiosis and anaplasmosis in Europe. Parasites and Vectors 8, 75. doi: 10.1186/s13071-015-0649-0.
Straubinger, RK., Straubinger, AF., Summers, BA., Jacobson, RH., & Erb, HN. (1998). Clinical manifestations, pathogenesis, and effect of antibiotic treatment on Lyme borreliosis in dogs. Wiener Klinische Wochenschrift 110(24), 874-81.
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