Lyme disease

Lyme disease is caused by an organism called Borrelia burgdorferi. This organism is well known to cause serious disease in humans. It also affects dogs, but the symptoms are different than the ones seen in humans. In dogs, Borrelia burgdorferi causes fever, chronic joint disease, and Lyme nephritis. Nephritis 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. It can lead to serious kidney disease. The symptoms of Lyme disease do not appear for weeks to months after infection.

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 United States is the deer tick, Ixodes scapularis. The female tick lays approximately 2,000 eggs in the spring. A small six-legged larva hatches and attaches to a host. Since the larva is small, it typically can only reach a small host, usually a 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 Borrelia organism infects the host.

A dog with symptoms of Lyme disease 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. 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?

The solution to some of these problems has come about in the form of the “Quant C6 Antibody test.” This is an immunological test for antibodies against the “C6 peptide,” a very unique section of the Borrelia burgdorferi 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.

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

In areas where Lyme disease is common, testing is typically done as part of the annual wellness visit along with heartworm testing (4DX test). 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 of Lyme disease consists of a four-week course of the antibiotic doxycycline or minocycline. Oral amoxicillin or injectable cefovecin (Convenia®) can also be used as effective alternatives.

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.

A particularly serious complication of Borrelia burgdorferi infection is Lyme nephritis. 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 immunosuppressive 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.

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 need tick prevention and vaccination should be considered for additional protection.

In summary, it is important to vaccinate your dogs for Lyme disease. It is equally important to use a flea and tick preventative year-round.

Linda Lewiston, DVM