When I lived and practiced in southern Virginia, ticks were a HUGE problem. The region was (and still is) so infested that I had to keep my own dogs on two separate forms of tick control throughout the most problematical months of the year. I took tick prevention seriously in large part because of ehrlichiosis.
Dogs get this disease after being bitten by a tick carrying certain types of Ehrlichia bacteria (usually E. canis and E. ewingii) that cause the immune system to attack and destroy the body’s own platelets, cells important to normal blood clot formation.
Dogs with ehrlichiosis typically develop some combination of
- lymph node enlargement
- abnormal bruising and bleeding<
- chronic eye inflammation
- neurologic abnormalities
Diagnosing ehrlichiosis is not always straightforward. Many dogs are bitten by Ehrlichia infected ticks without becoming noticeably ill, and the most commonly used diagnostic blood tests only determine whether or not a dog has been exposed to one or two Ehrlichia species. Therefore, both false positive and false negative results are not uncommon. Also, some dogs can develop clinical signs attributable to ehrlichiosis long after being bitten by an infected tick, so an apparent lack of recent tick exposure doesn’t rule out the disease as a cause of a dog’s symptoms.
I have had to resort to what I euphemistically call a doxycycline response test in cases where I suspect but can’t definitively prove that ehrlichiosis is to blame for a dog’s illness. Most of the time, dogs with ehrlichiosis respond very quickly (within a day or two) once they begin treatment with the antibiotic doxycyline. More severe cases may also require blood transfusions or immunosuppressive medications to control the body’s assault on its platelets.
There might be some good news on the horizon when it comes to ehrlichiosis prevention. A group of scientists have determined that an attenuated strain of E. canis could possibly be used as a vaccine in dogs. In this preliminary study, 12 beagles were divided into three groups. Group 1 received two doses of the potential vaccine, Group 2 received one dose, and Group 3 received no vaccine. All 12 dogs were then injected with a disease-causing strain of E. canis. All four of the Group 3 dogs developed severe ehrlichiosis, while three of the eight vaccinated dogs developed only a mild, transient fever.
A commercially available vaccine for canine ehrlichiosis is still a long way off, but I, for one, would welcome the addition to the veterinary armamentarium. In the meantime, do what you can to protect your dogs from this potentially devastating disease by being vigilant about using an effective tick control product (or two complementary products — under a veterinarian’s supervision) whenever ticks are active in the environment.
Dr. Jennifer Coates
Evaluation of an attenuated strain of Ehrlichia canis as a vaccine for canine monocytic ehrlichiosis. Rudoler N, Baneth G, Eyal O, van Straten M, Harrus S. Vaccine. 2012 Dec 17;31(1):226-33.