Anaplasmosis in dogs ranges from completely silent to life-threatening, but most cases fall on the milder end and respond well to treatment. The mortality rate in the U.S. is estimated at 7% to 10%, with deaths typically linked to complications like kidney failure, blood clotting disorders, or seizures rather than the infection alone. Roughly 40% of symptomatic cases require hospitalization, so while this isn’t a disease to brush off, the vast majority of dogs recover fully with prompt antibiotic therapy.
Two Types of Canine Anaplasmosis
Anaplasmosis isn’t a single disease. Two different bacteria cause it, and they attack different blood cells. The more common and more studied form, canine granulocytic anaplasmosis, is caused by a bacterium that infects white blood cells called neutrophils. It’s transmitted primarily by the black-legged tick (the same tick that carries Lyme disease). The second form, canine cyclic thrombocytopenia, targets platelets and is spread by the brown dog tick.
Both forms are often subclinical, meaning many infected dogs never show symptoms at all. When symptoms do appear, the two types look similar: fever, swollen lymph nodes, an enlarged spleen, and a tendency to bleed or bruise. The key difference is that granulocytic anaplasmosis frequently causes joint pain and lameness, and cyclic thrombocytopenia produces a distinctive pattern where platelet counts rise and fall on a one- to two-week cycle.
What Symptoms Look Like
After a tick bite, symptoms typically appear within about seven days. The hallmark of the acute phase is a sudden onset of lethargy, which shows up in nearly all symptomatic dogs. More than 75% also lose their appetite. Over half experience musculoskeletal pain, which can look like reluctance to move, stiffness, limping, or general weakness. Fever is common, and some dogs lose noticeable weight.
On blood work, the most consistent finding is a drop in platelet count (thrombocytopenia), reported in up to 95% of naturally infected dogs. Platelet counts can plunge dramatically, sometimes falling as low as 5,000 cells per microliter when the normal range starts around 175,000. Mild anemia and changes in white blood cell counts are also common. Liver enzyme levels often rise, reflecting inflammation in the liver or spleen.
When It Becomes Dangerous
About 30% of hospitalized cases develop life-threatening complications, including severe sepsis, shock, and respiratory distress. The dogs most at risk of dying tend to have multiple problems stacking up at once: uncontrolled bleeding from clotting disorders, kidney failure, heart enlargement, or neurological crises like seizures and coma. Dogs with severe anemia may need blood transfusions.
Age, immune status, and the presence of other illnesses all influence how hard anaplasmosis hits. A young, otherwise healthy dog that gets diagnosed early has excellent odds. An older dog with compromised immunity or an underlying condition faces a steeper climb. The infection itself is rarely what kills; it’s the cascade of organ damage that follows when the immune system is overwhelmed.
Coinfection With Lyme and Other Tick Diseases
Because the same black-legged tick transmits both anaplasmosis and Lyme disease, coinfection is common, especially in the northeastern and upper midwestern United States. Dogs carrying both pathogens at once tend to be sicker than those with either infection alone. The clinical signs of the two diseases overlap heavily (fever, lethargy, joint pain, appetite loss), which can make diagnosis tricky without blood testing. Other tick-borne organisms, including Ehrlichia species, can also be present simultaneously and add to the severity.
Treatment and Recovery
The standard treatment is a 28-day course of the antibiotic doxycycline. This same drug is effective against Lyme disease and ehrlichiosis, which is convenient when coinfections are suspected. Most dogs start to improve within 24 to 48 hours of beginning the antibiotic, and that rapid turnaround is one of the clearest signs that the diagnosis was correct.
Shorter courses of antibiotics have been tried, but studies show they’re more likely to fail at fully clearing the bacteria. Completing the full four weeks matters. Dogs with severe anemia or debility at the time of diagnosis typically need to be hospitalized for supportive care, including fluids and potentially blood transfusions, before they stabilize.
Can Dogs Become Carriers?
One concern for dog owners is whether the infection lingers after treatment. Dogs naturally produce antibodies that peak about three to four weeks after a tick bite and gradually decline over seven to eight months. A positive antibody test months after treatment doesn’t necessarily mean the dog is still infected; it may simply reflect the immune system’s memory of the encounter. However, not all infections are completely cleared, and some dogs may carry the bacteria at low levels without showing symptoms. Whether this subclinical carrier state leads to long-term problems is still not fully understood, but relapse is possible, particularly if the immune system becomes suppressed later in life.
Where the Risk Is Highest
Anaplasmosis cases in dogs are concentrated in the same regions where Lyme disease thrives. The highest and fastest-growing rates of positive test results between 2013 and 2019 were in New England, Pennsylvania, and the upper Midwest (particularly northern Wisconsin and Minnesota). Positive trends extended as far south as Virginia and Kentucky in the East, and into North Dakota and Iowa in the Midwest. Smaller pockets of increasing risk appeared in northern California, southern Oregon, and parts of Texas.
The geographic spread is expanding. If you live in or travel with your dog to any of these regions, year-round tick prevention is the most effective way to reduce the risk. Ticks need to feed for at least 24 to 48 hours to transmit most pathogens, so daily tick checks after outdoor activity and prompt removal remain a practical first line of defense.