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Lyme Disease

 

A LYME DISEASE PRIMER

Borrelia burgdorferi spirochete

The Borrelia burgdorferi spirochete: the agent of Lyme disease
(Photocredit: CDC Public Health Image Library)

Dear Tick or Black Legged Tick

The deer tick, Ixodes scapularis: the main carrier of the Borrelia burgdorferi
(Photo credit: Public Domain Graphic, Agricultural Research Service, USDA)

 

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 really occur until the late 1980’s. 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 both 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 with this article.

 

HUMAN LYME DISEASE VS. CANINE LYME DISEASE

The first lesson to be learned about the 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 the dog completely lest one overlook an easily eliminated cause of chronic joint disease especially in dogs of the Northeast U.S.

The infected dog’s most likely serious long term potential is “glomerular disease.” This is a type of kidney damage that occurs when the immune system is stimulated over a very long time by a infectious organism (or other immune stimulus) in hiding. This is a much more insidious problem for which special testing is needed (see later).

Erythema migrans: The characteristic
skin rash shown by humans shortly
after
Borrelia burgdorferi infection.
Dogs only rarely exhibit a similar
rash with Lyme disease.

(Photocredit: CDC Public Health Image Library)


After exposure to the Lyme organism, 90% of humans will ultimately
develop symptoms but only about 5% of dogs will experience disease.

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 Northeast U.S. is the deer tick, Ixodes scapularis. The female tick lays a clump of approximately 2000 eggs in the spring. A very small six-legged larva hatches and attaches to a host as soon as it is able. Since the larva is very 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 blood. The tick won't get sick but it will carry the Lyme organism with it throughout its life.

Three stages of the deer tick:
The larva (bottom right)
nymph (second from right)
and adult female (left)

(Photocredit: CDC Public Domain Image)

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 host or may approach larger game such as a dog or human. The nymph feeds 3-5 days and when it is full it drops off, 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 lays her eggs in the spring for the two-year cycle to begin again.

The feeding tick is basically a blood-sucker. It must keep its host’s blood from clotting in order to continue sucking so it is able to regurgitate assorted enzymes to keep the blood flow liquid and smooth. It is during this regurgitation process that the Lyme spirochete is brought up from the tick’s mid-gut to its mouthparts.

 

This process of transmitting Borrelia burgdorferi from tick to new
mammal host requires a minimum of 48 hours which means
that if the tick is removed within 48 hours of attachment,
the spirochete cannot be transmitted and the host will not get the disease.

 

Tick control on the host is an effective means of infection prevention. 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 prior to the 48 hour deadline.

For a chart specifying and comparing the details of these tick prevention products, click here.

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 prefers to feed on reptiles rather than mammals.. Reptile blood has natural anti-Borrelia factors which kill the Lyme spirochete and prevent further transmission.

A color coded map where you can click on your state and county to determine Lyme disease risk:

https://petdiseasealerts.org/forecast-map/#/

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


Public Health Microbiologist

(Photocredit: CDC Public Health Image Library)

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 one is doing additional reading on this organism, one will encounter references to the spirochete’s surface proteins called “Osp’s” (“Osp” stands for “outer surface protein”). Different Osp’s 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 Osp’s, the spirochete is able to change its presentation to the mammalian host’s immune system thus escaping immune destruction. In addition to changing Osp’s, the spirochete can change its shape into at least 3 different forms and is able to hide within cellular folds. (The Lyme spirochete is a master of disguise and camouflage.)


This presents an enormous diagnostic challenge:
 if the ACTUAL HOST'S immune system can’t even find the organism, how are WE supposed to detect it?

 

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 detection of antibodies against the Osp’s. Here are the problems encountered with this method:

  • 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 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 generate 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 antibody against the “C6 peptide,” a very unique section of the one 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. Vaccine does not contain the C6 peptide so vaccinated dogs will not test positive. Dogs with other infections will not erroneously test positive. Further, this test is simple enough to be available as an in-house test kit which 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 so as 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 ones 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 2-4 week course of doxycycline, or its cousin minocycline. Oral amoxicillin or injectable cefovecin (Convenia®) can also be used as an effective alternatives. If Lyme disease is a consideration, many veterinarians simply prescribe the medication. Obvious improvement is seen within 48 hours. Further, most tick-borne infections capable of causing joint pain, fever, and signs similar to Lyme disease generally all share doxycycline responsiveness so a simple course of medication actually 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.” 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% of dogs infected with Borrelia burgdorferi never get sick, some infected dogs are in fact 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 which 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 the these patients while their disease is still treatable. For more information on glomerular disease, click here.

 

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

 

There are presently several types of vaccine that have been marketed and all of them are effective:

Ft Dodge lymevax

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.

 

Merial Lyme Vaccine
(original graphic by marvistavet.com)

 

SHOULD HEALTHY DOGS TESTING POSITIVE STILL GET VACCINATED?

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

 

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

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 much organism the dog has to deal with. Vaccination will minimize the quantity of organism in the dog's body by preventing the entry of new organisms.

Argument Against Vaccination

  • The idea that more organism = 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 so as to reduce the load of organism and reduce the chance of vaccination. 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.

Again, when it comes to prevention, there is nothing controversial about tick control.
It is crucial in Lyme endemic areas to use tick controlling products.

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

ADDITIONAL LINKS ON LYME DISEASE:

www.cdc.gov/lyme/index.html

www.avma.org/public/PetCare/Pages/lyme-disease.aspx?utm_source=facebook&utm_medium=socmed&utm_campaign=gen

Page last updated: 6/2/2022