After a tick bite, Borrelia burgdorferi disseminates by active movement of the bacteria through the tissue. Therefore, even early infections require full dose antibiotic to penetrate all tissues in adequate concentrations to be bactericidal to the organism.
There is no universally effective antibiotic for treating Lyme borreliosis. The choice of medication used and the dosage prescribed will vary for different individuals based on multiple factors. These include age, weight, gastrointestinal function, blood levels achieved, and patient tolerance.
- Tetracyclines, including doxycycline (treatment of choice) and minocycline, are bacteriostatic unless given in high doses.
- Penicillins are bactericidal. Amoxicillin has been shown to be more effective than oral penicillin V. Because of its short half-life and need for high levels, amoxicillin is usually administered along with probenecid.
- Cephalosporins of the third generation have been shown to be effective in penicillin and tetracycline failures. The third generation cephalosporin ceftriaxon is able to cross the blood-brain-barrier.
Duration of treatment
The spirochete has a very long generation time (12 to 24 hours in vitro and possibly much longer in living systems) and may have periods of dormancy, during which antibiotics will not kill the organism. Therefore, treatment has to be continued for a long time.
It has been observed for humans that symptoms will flare in cycles every four weeks. It is thought that this represents the organism's cell cycle, with the growth phase occurring once per month. As antibiotics will only kill bacteria during their growth phase, therapy is designed to brake at least one whole generation cycle. This is why the minimum treatment duration should be at least four weeks (also for dogs).
If antibiotics are effective, over time these flares will lessen in severity and duration. But a persistent infection with Borrelia even after antibiotic therapy is commonly reported in dogs.
Measurements to prevent Lyme borreliosis should be based on three columns:
- daily tick checks; since it takes about 24 to 48 hours until borrelia reach the host skin after a tick bite had occurred, daily tick checks can dramatically reduce the risk of infection.
- application of tick-killing or -repelling substances; many products are available, which can be applied to the dog’s skin (spot-on) or are incorporated into collars. These products reduce tick infestation significantly and therefore limit the risk of infection with Borrelia burgdorferi.
- vaccination; vaccines consisting of complete killed B. burgdorferi, so called bacterins, have been available for several years. Although there are a few immediate adverse reactions to this vaccine in dogs, it is undesirable to have multiple components in the vaccine that are not involved in protection from infection and that have the potential to induce a delayed adverse response.
A vaccine for dogs based on the outer surface protein A (OspA) has been commercially available since 1996. OspA is expressed by Borrelia in unfed ticks. For the transfer to the salivary gland of the tick via the gut wall OspA is down regulated and OspC is expressed. Anti-OspA antibodies induced by vaccination and ingested by feeding ticks attach to OspA on the spirochetes, and thus prevent adhesion of the bacteria to the gut wall - preventing migration within the tick. Thus, passage of Borrelia to the salivary gland is halted. But sufficient amounts of anti-OspA antibodies have to be present in the peripheral blood of the host at the time of tick feeding to be effective. This, and the missing refreshment of the vaccination due to the fact that no natural pathogen contact takes place, are resulting in the necessity of a quite frequent revaccination program. Furthermore slight variations of OspA can cause protective failure of the antibodies, and for Europe, cross-reactivity between the Borrelia genospecies is necessary and so far has only been demonstrated in studies (using recombinant OspA) to exist in minor amount. Finally the serological diagnosis of the disease in dogs is made difficult by vaccination.
A combined OspA/OspC subunit vaccine has also been evaluated. In experimental challenge studies, these vaccines appear to protect from spirochetemia and clinical signs (polyarthritis) relative to unvaccinated control dogs. The vaccines are recommended for use in endemic areas but, as they are based on B. burgdorferi sensu stricto from the USA, they might not cross-protect against other Borrelia species. Various canine vaccines are available worldwide of which 4 are from the USA, three from Germany/France and one available in the Czech Republic.
A vaccine for the prevention of human Lyme disease based on recombinant outer-surface protein specific to B. burgdorferi has been launched in 1998, but was withdrawn from the market in 2002.
- Appel MJG: Lyme disease in dogs. Comp. Cont Educ Pract Vet. 2002, 24 (Suppl.), 19-23
- Shaw SE, Day MJ, Birtles RJ, et al.: Tick-borne infectious diseases of dogs. Trends Parasitol. 2001, 17, 74-80
- Straubinger RK, Dharma Rao T, Davidson E, et al.: Protection against tick-transmitted Lyme disease in dogs vaccinated with a multiantigenic vaccine. Vaccine 2002, 20, 181-93