Tick-Borne Diseases in Dogs Lyme, Anaplasmosis, Ehrlichiosis, and Rocky Mountain Spotted Fever

Infections transmitted by ticks are "increasingly recognized as important causes of disease in North American dogs" (TVP 2015), and the pool of pathogens keeps growing — "the geographic range of many of these pathogens has expanded, and several novel infections have been identified" (TVP 2015), according to a 2015 review in Today's Veterinary Practice. The Companion Animal Parasite Council reports that "continued expansion of heartworm, Lyme Disease and other tick-borne diseases throughout the United States" (CAPC 2023) is ongoing, that "ticks and mosquitoes remain the principal transmitters of pet and human vector-borne diseases" (CAPC 2023), and that "The risks of contracting Lyme, anaplasmosis, ehrlichiosis and heartworm diseases are increasing" (CAPC 2023).

See also: The Disease Landscape for human clinical presentations of these same pathogens.

The four canine tick-borne infections that dominate the veterinary literature in the United States are Lyme disease, anaplasmosis, ehrlichiosis, and Rocky Mountain spotted fever (RMSF). A 2016 CDC clinical guideline states that "Dogs are frequently exposed to ticks and are susceptible to infections with many of the same tickborne rickettsial pathogens as humans, including R. rickettsii, E. chaffeensis, E. ewingii, and A. phagocytophilum" (CDC 2016). A 2009 review in Topics in Companion Animal Medicine characterizes the relative weight of these illnesses: "The most burdensome of the tick-borne infections for dogs are ehrlichiosis and babesiosis, and for cats, cytauxzoonosis (a form of babesiosis)" (TopCompanionAnimMed 2009). Lyme disease has nonetheless received the most public attention, since "canine disease was first reported in the early 1980s" (TopCompanionAnimMed 2009).

Each disease has a characteristic pathogen, vector, and geography. Borrelia burgdorferi — the Lyme disease bacterium — "is the causative agent of Lyme disease in dogs and humans in the United States. Transmitted by Ixodes ticks, infection is most common in the Northeast, Midwest, and West Coast states" (TVP 2015) (black-legged and deer ticks are Ixodes scapularis and I. pacificus, respectively). The same review notes that "geographic expansion of the I scapularis / B burgdorferi maintenance cycle has resulted in increasing reports of disease in new regions, including the Great Lakes states, Mid-Atlantic states, southern Appalachia, and southern Canada" (TVP 2015). Anaplasma phagocytophilum — the anaplasmosis bacterium — is also transmitted by Ixodes ticks; "A phagocytophilum infections are most prevalent in the Northeast and upper Midwest" (TVP 2015). A separate Anaplasma species, A. platys, travels via the brown dog tick: "A platys infection is seen throughout the U.S. but is most common in south central states, such as Texas and Oklahoma, likely due to higher populations of R sanguineus" (TVP 2015). And "Several different Ehrlichia species can infect dogs in the U.S., including E canis, E ewingii, E chaffeensis, Panola Mountain Ehrlichia species, and E muris" (TVP 2015).

The same review frames RMSF as "Rocky Mountain spotted fever—caused by Rickettsia rickettsii —is considered one of the most serious tick-borne diseases in the Americas due to its high fatality rate and rapid onset" (TVP 2015). In the southwestern United States and northern Mexico, the brown dog tick (Rhipicephalus sanguineus) drives human RMSF outbreaks through zoonotic transmission from infected dogs; a 2022 HHS Tick-Borne Disease Working Group subcommittee report described the mechanism:

"Canine vaccines against Rickettsia rickettsii could have considerable impact at mitigating large outbreaks or epidemic levels of RMSF that have been identified in the southwestern United States and northern Mexico during the past two decades. In these settings, cases of human disease result from zoonotic infections in dogs and massive populations of brown dog ticks (Rhipicephalus sanguineus). A canine vaccine against the pathogen could have targeted impact in these unique but highly relevant circumstances." — HHS, 2022. Disease Prevention and Tr...

Beyond this core four, dogs can be infected with additional Ixodes-transmitted organisms. The 2018 ACVIM Consensus Update on Lyme borreliosis in dogs and cats notes that "Other organisms transmitted by I. scapularis and potentially associated with clinical illness in humans, dogs, and cats (some agents) include Anaplasma phagocytophilum, Ehrlichia muris, tickborne encephalitis (Powassan) virus, F. tularensis, and possibly Bartonella spp." (ACVIM 2018) — and that "These infections can mimic LB and if coinfections occur, may be associated with increased morbidity" (ACVIM 2018). The same consensus document opens with a framing observation that captures why the disease landscape has shifted:

"Over the past decade, since the first ACVIM Small Animal Lyme Consensus Statement was written, a broader understanding of the large number of Borrelia species that exist, the variability of strains of Borrelia burgdorferi sensu stricto (Bb), and the diversity of other pathogens carried by Ixodes and other ticks has been gained. The geographic distribution of infected ticks has expanded because of bird migration, suburban sprawl, and climate changes. Additional diagnostic tests are available to help rule out coinfections and other causes of clinical signs potentially attributable to Lyme borreliosis (LB), help differentiate vaccinal from natural acute or chronic exposure anti-Bb antibodies, and follow those antibodies that may wane post-treatment. Guidelines are offered for management of nonclinical nonproteinuric Bb-seropositive dogs and those with suspected clinical Lyme arthritis, Lyme nephritis, or both. Prevention updates include discussion of acaricide products provided as collars, topicals, or chewables that may facilitate owner compliance as well as new vaccination updates." — ACVIM, 2018. ACVIM Consensus Update on...

Signs of Tick-Borne Illness in a Dog

Clinical presentation varies substantially by pathogen, and dogs can be infected without showing any signs at all. What follows is how each of the four diseases tends to look in the exam room.

Dogs infected with Lyme disease may develop lameness, joint swelling, and fever, while anaplasmosis typically causes fever, lethargy, and low platelet counts—though clinical presentation varies widely and some infections remain asymptomatic. Dog Tick Disease Symptoms covers the full range of clinical signs and diagnostic indicators for each pathogen.

Ehrlichiosis and Rocky Mountain spotted fever present with overlapping acute signs—fever, lethargy, and bleeding abnormalities—though some species associations and chronic sequelae differ between them. See Dog Tick Disease Symptoms for detailed clinical presentation and diagnostic interpretation.

Two patterns cut across all four diseases. First, per the Today's Veterinary Practice review, "Co-infection with bacterial and protozoal agents is frequent and can be responsible for apparent doxycycline treatment failure in some patients" (TVP 2015). Second, rickettsial and ehrlichial infections track between species — the CDC guideline observes that "Infections with R. rickettsii and Ehrlichia species have been observed concurrently in humans and their pet dogs. Recognition of a dog’s death from RMSF has even prompted recognition and appropriate treatment of RMSF in the sick owner" (CDC 2016).

See also: Dog Tick Disease Family Risk Indicator on how a dog's infection signals family exposure risk.

How Quickly Symptoms Appear After a Bite

The honest answer is that the timeline varies dramatically by pathogen — from days for RMSF to months or never for Lyme disease — and that many infected dogs never develop clinical signs at all.

RMSF moves fastest. The same review describes RMSF presentation in dogs: "Clinical signs include rapid onset of fever, lethargy, and anorexia. Thrombocytopenia is often present, and some dogs may develop bleeding diatheses. Neurologic complications occur frequently" (TVP 2015). It continues: "Prompt, aggressive treatment can result in a rapid response, with resolution of clinical signs within a few days" (TVP 2015).

Lyme disease moves slowest, when it moves at all. The same review notes that for canine Lyme, "Clinical disease, when present, usually develops several months after infection, and serologic testing is the preferred means of diagnosis" (TVP 2015). It goes on: "However, most seropositive dogs do not appear to develop clinical signs" (TVP 2015). The 2018 ACVIM consensus statement frames the same observation at the exposure level — "LB is established in geographical areas in North America and Europe, and is spreading" (ACVIM 2018), but "most dogs that are exposed seroconvert, but do not develop clinical illness" (ACVIM 2018).

The 2007 CAES handbook gives concrete numbers for a Lyme-endemic area: "Most dogs (47-73% of unvaccinated animals) in a Lyme disease endemic area will eventually become infected" (CAES 2007) based on positive serology, yet only "about 5% will develop disease each year" (CAES 2007).

See also: Canine Lyme Disease Vaccine.

Anaplasmosis and ehrlichiosis fall between these extremes. For anaplasmosis, the Today's Veterinary Practice review notes that "many dogs may be clinically normal despite current infection" (TVP 2015). For ehrlichiosis, the same review observes that "Some animals that become chronically infected with E canis can develop pancytopenia, neurologic disease, bleeding diatheses, or ocular abnormalities" (TVP 2015), but "Many dogs, however, exhibit subclinical Ehrlichia species infections" (TVP 2015).

The practical implication is that "time since bite" alone does not tell you whether a dog is sick. A dog bitten last week that looks fine may be incubating RMSF; a dog bitten last summer that seroconverted to Borrelia burgdorferi may live a normal life and never need antibiotics. The 2018 ACVIM consensus recommends that clinicians "screen all healthy dogs that live in, live near, or travel to Bb-endemic areas in North America for Bb antibodies" (ACVIM 2018). For acute illness after a known tick exposure, the Today's Veterinary Practice review describes the standard treatment approach:

"Treatment of choice for common bacterial tick-borne disease agents is doxycycline. Recommended regimens vary according to the specific target agents, but doxycycline at 10 mg/kg PO Q 24 H for 28 days is effective against B burgdorferi, Anaplasma species, Ehrlichia species, and R rickettsii." — TVP, 2015. Parasitology Expertise fr...

The same review adds that "Clinical improvement is typically evident within the first week of therapy" (TVP 2015) — a diagnostic signal in its own right.

Sources

    Not medical advice. See a healthcare provider for medical decisions. Medical Disclaimer