According to the Handbook for Zoonotic Diseases of Companion Animals, ehrlichiosis refers to a group of diseases. The specific type of ehrlichiosis is named according to the host and type of white blood cell it affects. Canine granulocytic ehrlichiosis is caused by the pathogens Anaplasma phagocytophilum and Ehrlichia ewingii, affecting your dog's granulocytic white blood cells.
Granulocyte + Ehrlichiosis = Granulocytic Ehrlichiosis
A granulocyte is a white blood cell comprised of small granules containing proteins. This particular type of blood cell wards off bacterial infections, which is why a dog's granulocyte count increases if he's battling this particular infection. In the U.S., the bacterial infection ehrlichiosis is caused by one of three types of ehrlichia: Ehrlichia chaffeensis, Ehrlichia ewingii and Ehrlichia muris-like, with Ehrlichia ewingii targeting granulocytes. Though it doesn't carry the "ehrlichia" label, Anaplasma phagocytophilum also can cause granulocytic ehrlichiosis. Both types of bacteria are spread to dogs by ticks.
Coming From a Tick Near You
Contracting granulocytic ehrlichiosis can be as easy as a walk in the park for your dog -- all it takes is a run-in with the wrong kind of tick. If Duff lives in the Northeast or Upper Midwestern U.S., the black-legged tick carrying Anaplasma phagocytophilum can give him granulocytic ehrlichiosis; the Western black-legged trick can do the same thing in Northern California. The lone star tick, found in the south central and southeastern U.S., can transmit granulocytic ehrlichiosis to your dog by carrying Ehrlichia ewingii. Regardless of where he lives or what kind of tick he meets, Duff becomes infected with the disease in the same way: The tick jumps on your pup, feeds and transfers the bacteria to his granulocytes. The bacteria live on, multiplying and spreading through your dog's system.
Different Phases, Different Symptoms
Ehrlichiosis progresses in three phases in dogs: acute, subclinical and chronic. Common symptoms of granulocytic ehrlichiosis in the acute phase include fever, loss of appetite, weight loss and listlessness. Swollen joints, stiffness and hesitation to move are also signs of infection. The acute phase lasts one to three weeks and if left untreated, progresses to the subclinical stage. At this point, your pup will appear to return to his normal good health and remain there for months or even years. For certain dogs, such as one with a compromised immune system, the chronic phase can be life-threatening. In the chronic phase, weight loss and fever are common, particularly in severe cases.
Searching for Antibodies
Blood testing is important for diagnosing granulocytic ehrlichiosis; a positive test for antibodies against the bacteria confirms exposure to the pathogen, but doesn't confirm an infection is active. A negative test doesn't give an all-clear because Duff may be too sick to produce the antibodies or it's too soon after infection to detect the antibodies. Other tests may confirm diagnosis, and as Veterinary Partner notes, occasionally the offending organism can be seen on a blood smear. The antibiotics tetracycline and doxycycline are effective at treating granulocytic ehrlichiosis. Prior infection doesn't build immunity to this disease, so if Duff picks up this pathogen again, he'll need treatment again.
Keep it Clean
It takes 24 to 48 hours for an infected tick to pass the bacteria to its host. That means you can help decrease the odds your pup becomes infected by performing a thorough check of him after he's been outside. Look for and remove any attached ticks from Duff promptly to minimize any chance of infection. Using a topical acaricide vastly decreases his chance of getting a tick bite. Finally, keeping his outside environment free of brush and yard debris discourages ticks from taking up residence near your home.
- Iowa State University Center for Food Security and Health: Ehrlichiosis and Anaplasmosis: Zoonotic Species
- Journal of the American Veterinary Medical Association: Zoonosis Update: Ehrlichiosis and Related Infections
- Handbook for Zoonotic Diseases of Companion Animals; edited by Glenda Dvorak et al
- Companion Animal Parasite Council: Ehrlichia SPP and Anaplasma SPP
- Veterinary Partner: Ehrlichia Infection in Dogs
- Medline Plus: Granulocyte
- Centers for Disease Control: Ehrlichiosis