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Monmouth, Maine 04259
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 1980s. Media exposure of this infection virtually exploded, leaving most of the general public with some basic knowledge and a great deal of misconception. We hope to straighten out some of the myths surrounding at least the canine version of the Lyme disease infection.
Human Lyme Disease vs. Canine Lyme Disease
The first lesson about the Lyme disease infection is that 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, 80% of humans will develop a rash and/or flu-like symptoms. (Note that less than 30% of human Lyme patients actually recall a rash or tick bite. If you think you may have Lyme disease, do not postpone treatment based on recollection of tick bite or rash.)
In the next few weeks, joint pain ensues with 15% of people developing 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. Weeks to months after infection, about 60% of people will experience intermittent attacks of arthritis and 5% will develop chronic neurologic manifestations. In humans, Lyme disease presents with the potential for serious long-term illness. In dogs, Lyme disease does not begin to manifest for weeks to months after infection at which point signs of arthritis are noticed. Sometimes there is a fever. In dogs, heart and neurologic issues are exceedingly rare. The symptoms of canine Lyme disease respond rapidly to an inexpensive course of proper antibiotics.
In dogs, the 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 stimulus). It is important not to discount Lyme disease in dogs completely lest one overlook an easily eliminated cause of chronic joint disease, especially in dogs in the Northeastern U.S.
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 U.S. is the deer tick, Ixodes scapularis. The female tick lays a clump of approximately 2000 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 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 larva can get infected at this point.
The larva 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 to 5 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 on the range of the deer, there are often plenty of dogs or humans for the tick to attack. The adult ticks mate on this 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 2-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 can regurgitate assorted enzymes that keep the blood flow liquid and smooth. It is during this regurgitation process that the Lyme spirochete is brought up from the tick's midgut to its mouthparts.
This process 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 several effective tick control products available, including: the Preventic® collar, Advantix®, Frontline®, and Revolution®. All of these products either kill the tick or cause it to drop off prior to the 48-hour deadline.
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. There are several subspecies of Borrelia burgdorferi in different parts of the world so Lyme disease is not unique to the U.S. In the mammal's body, the spirochete is especially adept at binding to connective tissue. While reading additional material on this organism, you will encounter references to the spirochete's surface proteins called Osps (Osp stands for outer surface protein). Different Osps are expressed depending on whether the spirochete is attached to the tick midgut (OspA), the mammal's connective tissue (OspC), or whether the tick is in an early or late stage of mammal infection (Osps E and F respectively). By modifying its Osps, the spirochete is able to 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 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 host's immune system can't even find the organism, how are we supposed to detect it?
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 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 active infection from those that have been exposed and are not sick from their exposure?
• Vaccine has been available for Lyme disease for a decade or more. 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 these problems has come about only recently in the form of the C6 test. This is an immunological test for antibody against the C6 peptide, a unique section of the one of the Borrelia burgdorferi surface antigens. 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 (the IDEXX Snap-4 Dx test), which can be run in most veterinary hospitals with results in approximately 10 minutes.
This still does not address distinguishing active infection from exposure. In order to determine whether to treat for Lyme disease, further testing is recommended to assess actual antibody titers to the Lyme organism. A blood test sent off to an out-of-clinic laboratory can give more definitive results. Dogs can test 4Dx positive within to 3 to 5 weeks of infection. They often stay positive for over a year, even after treatment.
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 2 to 4 week course of doxycylcine, a medication that is inexpensive and has limited side effects potential. Amoxicillin is another effective alternative, also inexpensive and with minimal side effects. If Lyme disease is a consideration, many veterinarians simply prescribe the medication. 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 are all share responsive to doxycycline so a simple course of medication actually covers several types of infection. Eradication 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.
Some dogs are in fact harmed by the long-term 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. 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. This group of dogs may require medication for their kidney disease.
Recently an especially sensitive test has been developed for the detection of minute quantities of blood proteins in the urine. This test, called the Erd test, is so sensitive that its use is not yet determined (i.e., at what point is albumin loss in the kidney significant and under what circumstances might some albumin loss be normal and expected?).
Vaccination: Yes or No?
Vaccine prevents infection in dogs vaccinated before any exposure to Lyme spirochetes. This means it is only helpful for dogs not yet exposed, such as puppies and dogs from non-endemic areas traveling to endemic areas. Annual boosters continue the vaccine-based immunity. There are two types of vaccine available; one is the killed whole spirochete vaccine (LymeVax by Fort Dodge and Lyme Galaxy by Schering) where intact dead spirochetes are 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 may lead to vaccine reaction. The other type of vaccine is felt to be superior in preventive reactions and that is the recombinant vaccine (Merial’s Recombitek Lyme and Intervet's ProLyme). 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 bacteria. The bacteria produce large amounts of OspA, which are collected and used in the vaccine so that the entire Lyme spirochete is not used; only the OspA protein is used.
Argument Against Vaccination
Lyme disease in the dog is an infection for which over 90% of infected dogs will never get sick and the 5% to 10% that do get sick can be easily treated with a safe inexpensive course of antibiotics. This situation would seem to indicate that vaccination is simply not worth the expense.
As for the kidney disease that can occur in some individuals with long-term antigen exposure, we do not know what Borrelia antigens are involved in the immune stimulation that causes this condition. It might be that the same antigens used in the vaccines are involved, in which case vaccination might be just as hazardous as actual infection. Even OspA, the same antigen of the recombinant vaccine, has been implicated in chronic human disease.
Argument for Vaccination
We vaccinate ourselves for the flu (an infection that is for most people more of an unpleasant nuisance than a life-threatening event) and think nothing of it. Vaccination is about prevention of infection; just because an illness is not life-threatening does not mean that we should not prevent it with vaccine. Further, in a non-endemic area, Lyme disease is not going to be a cause of arthritis that most veterinarians will consider. Treatment is only simple if one thinks to perform the treatment, but in an area where there is little Lyme disease, this treatment may easily be omitted. Why not just prevent the infection outright from the beginning if the dog is going to travel to a tick endemic area?
If we allow our dogs to readily become infected with the Lyme organism, do they not become a potential source for human infection (through their ticks)? We try to minimize the deer and mice in our vicinity and we want to keep company with the family dog, but who wants a reservoir of Lyme spirochete in their home?
As for the kidney disease, we do not know what spirochete antigens are implicated in this condition. The recombinant vaccine exposes the patient only to one spirochete antigen (OspA) and prevents the introduction of the spirochete into the mammal's body. Vaccination, at least with the recombinant vaccine, may prevent this syndrome.
When it comes to prevention, there is nothing controversial about tick control. It is crucial in Lyme endemic areas to use tick-controlling products.
Below are a group of Deer ticks, showing just how small they can be, and because of that, how difficult they can be to find on your animal: