Guest Post - Ticks & Lyme Disease in Your Dog
We have asked Dr. Rich Montminy of MacDonald Veterinary Services to tell us all about Lyme Disease and whether our dogs can get Lyme Disease and, if so, how will they be affected and treated.
Types of Ticks Found in New Hampshire
Of the nearly 900 species of ticks, there are four that represent the largest threat to our pets here in New Hampshire: the American Dog Tick (Dermacenter variabilis), the Brown Dog Tick (Rhipicephalus sanguineus), the Blacklegged Tick (Ixodes scapularis) and the Lone Star Tick (Amblyomma americanum). Of these ticks, the Blacklegged Tick (also called the “Deer Tick”) is the most well known, but ALL can carry tick-borne disease. These diseases affect not only dogs but are also seen in cats and present a significant health risk for humans. Ticks are second only to mosquitoes in number of diseases they carry.
Life Cycle of a Tick
The life cycle of the tick includes 4 distinct stages: egg, larvae, nymph and adult.
An adult female tick, after taking a blood meal, will lay her eggs off of the host. Some females can lay up to 5,000 eggs in less than one week! The eggs are coated in a secretion that prevents them from drying out and allows them to survive in the environment for many weeks.
What hatches from the egg is a 6-legged larvae (approximately the size of a grain of sand). Though not a full-grown tick, it will still find a host and take a blood meal. In fact, every stage of development needs a fresh blood meal to proceed to the next stage. (As such, these ticks are called “Three-host” ticks, because they must find a host 3 separate times. The hosts are usually different individual animals, but could, theoretically, be the same animal multiple times.)
After a blood meal, the larvae will drop off the host and molt to an 8-legged nymph (approximately the size of a poppy seed, which is why ticks in this stage are often called “seed ticks.”).
Again, this stage will find a host from which it can feed so it can molt one final time to the 8-legged adult (approximately the size of an apple seed when not engorged). All molts take place off of the host.
The interval from hatching of the egg to becoming an adult can be up to three years, particularly if the climate is cool or there is no host from which to take a blood meal. Each stage of development can last months between feeding if there is no host immediately available. Many ticks seem to prefer to feed on dogs, but WILL feed from another host if necessary, so beware trying to eliminate a tick infestation by removing dogs from the environment! Most ticks need to be outdoors to complete the life cycle, but the Brown Dog tick is an exception in that it can complete the cycle completely indoors. (Another good reason to use effective tick prevention YEAR-ROUND!)Ticks are not born with disease; to pass disease to a dog, cat, or human, they must first acquire the disease from either of their first two hosts. As an example, the white-footed deer mouse, NOT the deer themselves, is the main reservoir for Lyme disease! A tick would need to use this mouse as a host before it can pass Lyme disease to one of it's later hosts. (Many people believe that because Blacklegged Ticks are called Deer Ticks, the deer must carry the Lyme Disease. This is not true; the deer are simply the most common host for the Blacklegged Tick.)
Finding a Host
Ticks do not jump like a flea, fly like an insect, or drop from above like a spider. Rather, they find their host by behavior called “questing”. This involves perching on the end of a branch or tall grass, and waiting for a suitable host to pass. They cling to their perch with their 2nd, 3rd and 4th pairs of legs while they stretch out their first pair of legs. When the host comes near enough, they will grab on with the first set of legs and then make their way down the hair shaft to the skin. Remember that ticks like to “seek higher ground.” This means when they are on their perch they will go as high as possible to better position themselves to ambush a potential host, and once on the host they will climb toward the armpits, groin or head where the skin is thinner and attachment is easier.
Of all the tick-borne diseases, Borreliosis (Lyme disease) is the most well-known. Borrelia burgdorferi is a bacteria which is carried only by the Deer Tick. The bacteria is transmitted to your pet when the tick bites the skin to ingest a blood meal. Many factors play a role in the time of transmission, but generally, 48 hours of attachment is required for transmission to occur. Nymph stage ticks are more likely to pass disease than adults. This may be because the nymph's small size make early detection, and therefore prompt removal, more difficult.
Symptoms of Lyme Disease in Your Dog
Clinical signs can be very nonspecific (fever, malaise, decreased appetite), but symptoms for which Lyme disease is best known are musculoskeletal in nature: stiffness, joint swelling, lameness and generalized pain. These signs can be seen with many other diseases and are often mistaken for osteoarthritis. Rarely, Lyme disease can also affect the kidneys. It is estimated that only 5-10% of animals infected with Lyme disease show ever show clinical signs. Dogs test positive on our in-house Lyme antibody test 3 weeks after infective bite, but symptoms are not seen for 2-5 months!
Diagnosing Lyme Disease in Your Dog
Index of suspicion for clinical infection may be based on presence of ticks, clinical signs, and response to treatment. Laboratory testing is available but does not always indicate active infection. Most current in-house heartworm screening tests will also screen for presence of antibody to Lyme disease. If your pet is antibody (+), it indicates only that your pet has been exposed to the Borrelia organism and has mounted its own immune response. A positive antibody test does NOT necessarily mean your dog has a current, active infection. As such, not every animal that is antibody (+) needs to be treated; the decision to treat is based on presence of clinical signs, whether or not the dog has been Ab (+) in the past, and results of other laboratory testing.
When warranted, treatment consists of a four-week course of antibiotics, usually doxycycline. Analgesics are used as necessary for pain and special medications are employed when kidney involvement is confirmed. Most animals show improvement within 4 days of starting antibiotics. Unfortunately, antibiotics rarely completely clear the organism from the bloodstream. The spirochete will persist in low numbers, causing a chronic antigenic simulation that will continuously stimulate antibody production and likely cause your dog to show up as antibody positive for years.
Vaccinating for Lyme Disease
There is a vaccination for Lyme disease that can reduce the odds of your pet acquiring the disease, but no vaccine is 100% effective. Thus, preventative measures should also include limiting your pet's exposure to ticks, daily removal of any ticks found on your pet, and using effective tick control year-round!!!!
If your dog is antibody (+) for Lyme disease you will need to determine whether or not you wish to administer the Lyme vaccine. The antibodies your pet has naturally developed may not provide protective immunity. On the other hand, studies have not clearly shown that vaccinating such a patient decreases likelihood of re-infection. In short, continuing to vaccinate will not harm your pet, but a benefit is not guaranteed. Here at MacDonald Veterinary Services we recommend continuing the vaccinations citing possible increased protection and a lack of contraindications, but we always tailor all vaccination protocols to the individual patient. Your veterinarian will help you make the best choice for your pet.
About the Author: Dr. Montminy attended Mississippi State University for both undergraduate and veterinary school, he graduated in 1998. He's been practicing veterinary medicine since graduation. Dr. Montminy enjoys outdoor activities and rooting for the New England Patriots.