Borreliosis (Lyme Disease)

Chapter 18 Borreliosis (Lyme Disease)

Lyme borreliosis is a polysystemic, tickborne disease caused by the spirochete Borrelia burgdorferi. The disease has been associated with polyarthritis in dogs, cattle, horses, and humans. Infection is widespread in the United States, and is endemic in the northeastern coastal states and the upper Midwest. Infection also occurs worldwide and is prevalent in areas of Europe. Borreliosis is transmitted to animals and people by deer ticks.


Lyme borreliosis in dogs and humans is caused by at least 6 subspecies of the Borrelia burgdorferi sensu lato complex. The strain that primarily causes borreliosis in North America is Borrelia burgdorferi senso stricto. These eubacteria are spiral-shaped, flagellated, gram-negative spirochetes that are related to Leptospira, except they do not survive as free-living organisms outside of the host.

B. burgdorferi is easy to isolate from vector ticks but not from clinically affected patients. The organisms are microaerophilic and have special growth requirements. The outer membrane of the spirochete can undergo antigenic variation during the course of infection, which enables the organism to evade the host’s immune response and cause persistent infection. Antigenic variation may limit the effectiveness of vaccines.

Dogs in endemic areas are commonly co-infected with other tickborne agents, especially Anaplasma phagocytophila (see Chapter 17), and mixed infections may contribute to the pathogenesis and severity of disease in some cases.


Dogs are infected through the bite of an infected tick. The primary vectors of Lyme borreliosis are Ixodes spp. ticks, also called black-legged or deer ticks. These hard ticks are small (2-3 mm) 3-host ticks that have a 2-year life cycle with larval, nymph, and adult stages.


Most dogs develop persistent subclinical infection that may lifelong. Seroconversion occurs within 3 to 6 weeks after exposure. Clinical disease develops in only 5% of infected dogs, depending on age, immune status, strain of Borrelia, and dose of exposure (number of ticks). In experimental infections, clinical signs develop 2 to 5 months after tick exposure.


Consider borreliosis in dogs from endemic areas with typical clinical signs, especially if there is a history of exposure to a wooded environment or tick-infested area. The diagnosis depends on finding the organism or antibodies directed against the organism. Serologic testing provides a presumptive diagnosis; however, in endemic areas many healthy dogs have been exposed and are seropositive, leading to a tendency to over-diagnose the disease. Definitive diagnosis requires identification of the Borrelia spirochetes by culture or polymerase chain reaction (PCR) assay, but these are not routinely available to the clinician.

In endemic areas, the differential diagnosis is challenging because other doxycycline-responsive tickborne infectious diseases are often prevalent as well, many of which cause clinical signs that overlap with borreliosis; such as infections caused by Anaplasma, Ehrlichia, Rickettsia, and Bartonella (see Chapters 17 and 19). Lyme borreliosis also is difficult to distinguish from immune-mediated polyarthritis (see Chapter 124).

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Borreliosis (Lyme Disease)

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