A LYME DISEASE PRIMER
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 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 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 larva can get infected at this point.
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 requires a minimum of 48 hours which means
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 that 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 searchable by zip code showing the prevalence of Lyme disease in any U.S. area can be viewed at:
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 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:
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:
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.
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. Amoxicillin can also be used as an effective alternative. 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.
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 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. 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. For more information on glomerular disease, click here.
VACCINATION: YES OR NO?
The object of vaccination is to prevent 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 travelling to endemic areas. Annual boosters continue the vaccine-based immunity.
Vaccination against the Lyme organism remains controversial. We will present both sides of the argument and the pet owner can decide if they want to include vaccination in their Lyme prevention efforts.
Argument Against Vaccination
Argument For Vaccination
Again, when it comes to prevention, there is nothing controversial about tick control.
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:
Page last updated: 1/23/2016