Borrelia burgdorfi

This spirochete is the agent of Lyme disease. Photo by CDC

The Deer Tick

Ixodes scapularis is the main carrier of the Borrelia burgdorferi. Photo by USDA.

Erythema Migrans in a Human Patient

This is the characteristic skin rash shown by humans shortly after Borrelia burgdorferi infection. Dogs only rarely exhibit a similar rash with Lyme disease. Photo by CDC.

Three States of the Deer Tick

The larva (bottom right), nymph (bottom left), and adult female (top). Photo by CDC

While the infection we know today as Lyme disease (named for the Connecticut town of Lyme) has been around for at least a century, public awareness and confusion did not occur until the late 1980s. Media exposure of this infection virtually exploded, leaving most of the general public with some basic knowledge and concern about this infection as it pertains to themselves as well as to their dogs. The canine experience of Lyme disease is very different from the human infection and we hope to sort out confusion here.

Human Lyme Disease vs. Canine Lyme Disease

The first lesson to be learned about Lyme disease infection is that, as mentioned, it manifests completely differently in man’s best friend compared with the human experience. After being bitten by a tick that has transmitted Borrelia burgdorferi, 90% of humans will develop a rash and flu-like symptoms. In the next few weeks, for 60% of people, joint pain ensues with 15% of people developing actual neurologic abnormalities associated with Lyme disease and 5% of people developing a heart rhythm disturbance called “A-V block.” At this same point in the infection timeline, dogs have yet to develop any symptoms at all and 95% of infected dogs never will. In humans, Lyme disease presents with the potential for serious long-term illness while this is a possibility for only a small number of dogs.

When canine illness does occur, it does not begin to manifest for weeks to months after infection at which point arthritis signs are noticed.

Sometimes there is a fever. Most canine Lyme patients will respond rapidly to a simple course of proper antibiotics but there will be some unlucky dogs that develop an associated kidney disease so some related screening tests will be recommended for dogs testing positive. Heart and neurologic issues are exceedingly rare.

The Borrelia burgdorferi organism is fairly well suited to live in the canine body without causing trouble. Most exposed dogs harbor the organism uneventfully. Still, it is important not to discount Lyme disease in dogs completely lest you overlook an easily eliminated cause of chronic joint disease, especially in dogs of the Northeast U.S.

The infected dog’s most serious long-term potential regards glomerular disease. This is a type of kidney damage that occurs when the immune system is stimulated over a long time by a latent infectious organism or other immune stimuli in hiding. This is a much more insidious problem for which specific testing is needed (see below).

The Tick and Its Control

An organism that serves to transport and deliver an infectious organism from one host to another is called a vector. The vector of Lyme disease in the Northeastern United States is the deer tick, Ixodes scapularis. The female tick lays a clump of approximately 2,000 eggs in the spring. A small six-legged larva hatches and attaches to a host as soon as it is able. Since the larva is small, it typically can only reach a small host, usually a white-footed mouse.

If the mouse is carrying the Lyme disease spirochete, the baby tick will become infected when it drinks the mouse's blood. The tick won't get sick but it will carry the Lyme organism with it throughout its life.

When the larva is full of blood, it will drop off the host and lie dormant until the following spring, about a year later. At this point, the larva molts and becomes a nymph. The nymph is a bit larger and may select another mouse as a host or may approach a larger game such as a dog or human. The nymph feeds for three to five days and when it is full it drops off and remains dormant until late summer. It then molts into an adult tick. When the nymph is feeding, it may infect its host with the Lyme spirochete. If the nymph was not already infected from its larval stage, it may become infected now during its spring feeding.

The adult tick seeks a larger host, hence its name the deer tick; however, with man encroaching upon the range of the deer, there are often plenty of dogs or humans for the tick to attack. The adult ticks mate on their new host, feed, and transmit the Lyme spirochete if they are carrying it. The male tick remains attached through the winter but the female, once engorged with the host’s blood, drops off, hides under leaves and other debris through the winter, and in spring lays her eggs for the two-year cycle to begin again.

Tick control on the host is an effective means of preventing infection. There are numerous effective tick control products available in assorted formats including chewable treats, collars, and topical spot-on treatments. All of these products either kill the tick or cause it to drop off before the 48-hour deadline.

On the west coast of the United States, there is far less Lyme disease than in the east, although the northern coast of California is considered to have moderate risk. This is because the Lyme vector in these areas is primarily Ixodes pacificus, a tick whose nymphal and larval stages strongly prefer to feed on reptiles rather than mammals. Reptile blood has natural anti-Borrelia factors that kill the Lyme spirochete and prevent further transmission.

There are several subspecies of Borrelia burgdorferi in different parts of the world, so Lyme disease is not unique to the United States.

Borrelia burgdorferi: The Spirochete and Its Detection

The spirochete that causes Lyme disease cannot live outside the body of a host. It must live within either a mammal or a tick.

In the mammal’s body, the spirochete is especially adept at binding to connective tissue. If you are doing additional reading on this organism, you will encounter references to the spirochete’s surface proteins called Osp (Osp stands for outer surface protein). Different Osps are expressed depending on whether the spirochete is attached to the tick midgut (OspA, OspB, and OspD) or the mammal’s connective tissue (OspC). By modifying its Osps, the spirochete can change its presentation to the mammalian host’s immune system thus escaping immune destruction. In addition to changing Osps, the spirochete can change its presentation to the mammalian host’s immune system, thus escaping immune destruction. In addition to changing Osps, the spirochete can change its shape into at least three different forms and can hide within cellular folds. The Lyme spirochete is a master of disguise and camouflage.

Antibody Levels

A dog with symptoms of Lyme disease ideally should have a test to confirm or rule out Lyme disease. Since it is almost impossible to culture the Lyme spirochete, efforts have centered on the detection of antibodies against the Osps. The problems encountered with this method are:

• In a Lyme endemic area, as many as 90% of the dogs will have antibodies against the Lyme spirochete. Most exposed dogs never get sick but almost all of them will develop antibodies and these antibodies persist for years. 
• How do we tell the dogs that have an active infection from those that have been exposed and are not sick from their exposure? (In other words, is our sick dog sick because of his Lyme disease infection, or is the Lyme infection incidental and he's sick from something else?).
• Vaccine has been available for Lyme disease for decades. How do we distinguish antibodies generated by the vaccine from those generated by natural infection?
• How do we distinguish antibodies generated by similar organisms (Leptospira, for example, or harmless other Borrelia species)?

The solution to some of these problems has come about in the form of the “C6 Antibody test.” This is an immunological test for antibodies against the “C6 peptide,” a very unique section of the Borrelia burgdorgeri surface antigens. It is only displayed by the organism after transmission into the mammal host's body.

As the spirochete changes its configuration to escape the host's immune system, the C6 peptide remains constant and always detectable. The vaccine does not contain the C6 peptide so vaccinated dogs will not test positive. Dogs with other infections will not erroneously test positive. Furthermore, this test is simple enough to be available as an in-house test kit that can be run in most veterinary hospitals, with results in approximately 10 minutes.

This still does not address distinguishing active infection from exposure. Dogs will test C6 positive within 3-5 weeks of infection. They stay positive for over a year. Putting together a clinical diagnosis based on the test results and symptoms of the pet remains in the realm of the veterinarian in charge.

Testing Apparently Healthy Dogs

The American College of Veterinary Internal Medicine Consensus Statement on Lyme disease recommends testing any dog living in or recently visiting a Lyme endemic area for C6 antibodies. In areas where Lyme disease is common, this is typically done as part of the annual wellness visit along with heartworm testing.  The idea is to identify infected dogs and then screen them for urinary protein loss to catch the diagnosis of Lyme Nephritis early. Since dogs do not generally get sick from their Lyme Borrelia infection, most experts do not recommend treating dogs for Lyme disease simply because they are positive for C6 antibodies but owners should be aware of the potential for Lyme disease symptoms in the future.

Treatment and Its Goals

Which of these dogs get sick and which do not? Does the dog with joint pain, fever, and a positive C6 test need medication? This is where the news is particularly good.

Treatment of Lyme disease utilizes a two to four-week course of doxycycline or its cousin minocycline.  Oral amoxicillin or injectable cefovecin (Convenia®) can also be used as effective alternatives.

If Lyme disease is a consideration, many veterinarians simply prescribe the medication. An obvious improvement is seen within 48 hours. Furthermore, most tick-borne infections capable of causing joint pain, fever, and signs similar to Lyme disease generally all respond to doxycycline so a simple course of medication covers several types of infection.

Complete elimination of the Lyme spirochete is not a reasonable expectation with treatment; the organism is simply too good at hiding. The goal instead is to bring the patient into what is called a premunitive state, or when the immune system is in a protective mode. This is the state that 90% of infected dogs achieve when they get infected but never get ill: the organism is in their bodies latently but is not causing active infection or disease.

Glomerular Disease (Lyme Nephritis)

It is important to discuss a particularly serious complication of Borrelia burgdorferi infection: Lyme nephritis. While this occurs in a small portion of infected dogs, the consequences to the kidneys are frequently severe. While, as noted, a good 90 percent of dogs infected with Borrelia burgdorferi never get sick, some infected dogs are harmed by the long-time presence of an infectious organism in their bodies. The immune system is constantly active in its attempt to remove the invading spirochete, and over the years these complexes of antibodies may deposit in the kidney and cause damage that can be severe. This group of dogs will likely require medication for their kidney disease: antibiotics, treatments to reduce protein loss in urine, and potentially immune suppressive therapy.  It has been recommended that dogs with positive Borrelia burgdorferi antibody levels be regularly screened for significant protein loss in their urine with a test called a “urine protein to creatinine ratio” so as not to miss these patients while their disease is still treatable. 

Vaccination: Lyme Disease Vaccination

The object of vaccination is to prevent infection in dogs vaccinated before any exposure to Lyme spirochetes. A series of two vaccines is given with one dose 2-4 weeks apart followed by annual boosters. Some experts recommend a 6-month booster before going to the annual booster schedule. Dogs living or visiting Lyme areas will definitely need tick prevention and vaccination should be considered for additional protection.

Virtually all the vaccines act by blocking OspA. Basically the tick drinks in the vaccinated host's blood full of anti-OspA antibodies. The Borrelia organism needs OspA to effectively move into the tick's mouth parts for transmission to the host but with the tick's belly full of OspA antibodies, OspA is blocked and the spirochete is quarantined inside the tick.

Some vaccines also include OspC which is expressed.

Several types of vaccines have been marketed and all of them are effective:

Killed Whole Bacterin
The killed whole spirochete vaccine uses intact dead spirochetes injected into the host. By using the entire spirochete, the host is exposed to parts of the organism that are not useful in immunization and has more potential to lead to vaccine reactions.

Recombinant OspA Vaccine
The next type of vaccine is felt to be superior in preventing reactions and that is the recombinant vaccine against OspA. This vaccine generates antibodies specifically against OspA, the surface protein the spirochete uses to attach to its tick host. When the tick bites and sucks blood full of Anti-OspA antibodies, the spirochete’s migration sequence is blocked and the spirochete is prevented from even exiting the tick. The vaccine utilizes DNA for OspA cloned into a harmless virus so that the entire Lyme spirochete is not used; only the OspA DNA is used.

OspA and OspC Vaccine
The third type of vaccine targets both OspA as above but also OspC. OspC is the surface protein the Borrelia organism expresses inside the dog. The idea is that the OspC antibodies target Borrelia organisms that make it inside the dog's body, theoretically providing enhanced protection.

Recombinant OspA plus Chimerized OspC Vaccine
This vaccine has all the advantages of the OspA attack as well as the advantages of recombinant technology. Taking things a step further is the Chimerized OspC portion. The idea here is that Borrelia burgdorferi expresses OspC in the dog's body and generating antibodies against OspC enables the immune system to find the organism where ever it is hiding. The problem is that OspC is not one protein; there are many forms of OspC. The chimerized OspC used in the vaccine takes pieces from seven different versions of OspC and binds them into an amalgamation. In this way, the immune system can be directed against multiple versions of OspC rather than only one.

Should Healthy Dogs Testing Positive Still Get Vaccinated?

Prevention of Lyme disease in the dog is based on the following principles: Vaccination, Education, and Tick control. Hopefully, we have covered all of this in this article.

This is a controversial subject and every veterinarian will have a perspective. Here are the pros and cons:

Argument For Vaccination

• Vaccines work by preventing new Borrelia organisms from entering the host. Whether or not a given dog develops actual symptoms of Lyme disease (nephritis in particular) will depend on how many organisms the dog has to deal with. Vaccination will minimize the number of organisms in the dog's body by preventing the entry of new organisms.

Argument Against Vaccination

• The idea that more organisms = more chance of disease is still theoretical.
• Unnecessary vaccine, especially if a "whole cell" vaccine is used, increases the chance of vaccination reaction.
• Some experts feel a 2-week course of antibiotics should be given to a positive dog before vaccination to reduce the load of organisms and reduce the chance of vaccination reaction. This practice is not likely to have side effects but any medication has that potential.

Dogs that are Lyme positive and sick (including having urinary protein loss) should not be vaccinated for Lyme disease.

Lyme disease is a regional problem. For more guidance regarding this infection in your area, or areas where you will be traveling, see your veterinarian.

Additional Links

CDC

AVMA