By Teresa Garden, DVM
Canine Ehrlichiosis is a worldwide tick-borne disease caused by the rickettsial organism Ehrlichia canis.
Ehrlichia lives and multiplies inside ticks. Rhipicephalus sanguineus is the tick that transmits Ehrlichia to dogs. Other hosts for the disease include wild canids and cats. These ticks love warm climates but are considered nonseasonal. Ticks are tough and tolerant to adverse environmental conditions. They are adaptable to a variety of habitats and can travel with their host animal across broad geographic ranges. Rhipicephalus is the only species of tick that will infest human dwellings. Therefore, they are found indoors and outdoors. They are cold intolerant and must get indoors in order to survive winters in North America.
Therefore, ticks constitute a year-round risk to dogs and cats.
Ticks have three life stages-larval, nymph, and adult. Ticks use an ambush strategy to get on your dog. They do not jump onto pets out of trees. They climb onto weeds, grasses, bushes, or other leafy vegetation. They wait for the dog to brush against the plant. When the dog does, the tick will release from the vegetation and crawl onto the dog. Adult ticks are commonly found in and around the ears and toes. Larval and nymph forms of the tick are distributed along the back and neck of dogs. Adult ticks feed for 5 to 21 days. Ticks reproduce at an alarming rate. They drop off the dog and lay up to 4000 eggs per clutch in cracks and crevices along floors, behind dog cages, and even in ceilings. The eggs hatch in 20 to 30 days. Larvae and nymphs feed for 3 to 11 days. Even unfed, larvae, nymphs, and adults can survive for up to 8, 6, and 19 months respectively.
A tick “bite” is not really a bite at all. It is much more traumatic-more like a chain saw assaulting your dog’s skin. Ticks have mouthparts that cut, penetrate, and anchor to the tissue. The mouthparts have cutting edges and hook-like barbs which lacerate and saw through tissue. Ticks not only suck blood, they “spit”. Their spit is a cement-like substance secreted from the tick’s salivary glands which helps Ehrlichia to evade the dog’s immune system and helps the pathogen to proliferate and invade. The longer the mouthparts remain attached to the dog the greater the likelihood an infective dose of pathogen can be transmitted. Ehrlichia canis transmission time is less than 18 to 24 hours. Ticks require blood meals to survive, grow, and develop into the next life stage and to reproduce. The volume of ingested blood in a female tick may range from a half to 2 ccs or more. Males will ingest a smaller volume.
Ehrlichiosis disease can be acute or chronic or subclinical. Dogs may or may not show symptoms and spontaneous resolution may occur. Clinical signs are vague and similar to many other conditions. Symptoms to watch for are fever, lethargy, weight loss, swollen joints, limping, enlarged lymph nodes, and petechiae (bruising spots on skin and gums). Neurological signs such as seizures, ataxia, paresis, and tremors can be seen. The disease may be more severe in puppies, immunosuppressed dogs, and German Shepherds who are predisposed.
The diagnosis of the disease is based on a history of ticks or exposure to ticks coupled with clinical signs consistent with Ehrlichiosis. Blood tests are performed and may show decreased platelets, white blood cells, and red blood cells. Liver enzymes are increased and albumin is decreased. A positive antibody test will confirm current or prior disease.
Antibodies are in circulation for multiple years to protect the body against future infections. Your pet may remain positive for 2 years to life. Urine tests will show decreased concentration and the presence of protein. Active infections are treated with Doxycycline antibiotic for 4 to 6 weeks. Blood tests are monitored to look for improvement and we monitor for resolution of clinical symptoms. At Animal Health & Healing, we will also prescribe immune system boosters to help treat Ehrlichiosis.
Prevention options have much improved over the years. Newer products on the market kill ticks quickly before they can transmit disease. Nexguard or Simparica are available as easy to administer monthly chews. These are isoxazoline compounds that work as neurotoxins resulting in convulsions and death of fleas and ticks. They target receptors specifically unique to fleas and ticks while sparing the dog. I consider the monthly chews safer than topicals. Topicals can be licked off, washed off, or contaminate people’s skin. In September 2018 the media reported neurological abnormalities observed in some dogs taking these isoxazoline products. The FDA maintains at present the drugs safe for most animals. Additional research is needed to further clarify the nature and prevalence of these neurologic events. l, personally, try to avoid using them in dogs with neurological disease such as epilepsy or brain masses. In a perfect world it is best to avoid ticks. However, as we all know, the world is far from perfect.
Dr. Teresa Garden is chief veterinarian/owner of Animal Health & Healing, a full-service holistic and conventional veterinary practice in the Maplewood/Richmond Heights area. 314-781-1738. www.AnimalHealthandHealing.com.