Anaplasma is a tick-borne bacterial infection that targets your dog’s blood cells, causing fever, lethargy, and a drop in platelet counts. Two species of the bacteria affect dogs: one invades white blood cells, and the other attacks platelets directly. Most dogs recover fully with a standard course of antibiotics, but the infection can become serious if it goes undiagnosed.
Two Types of Anaplasma in Dogs
The two bacterial species behind canine anaplasmosis work differently inside your dog’s body. Anaplasma phagocytophilum infects white blood cells, specifically a type called granulocytes. This form is sometimes called canine granulocytic anaplasmosis and is the more commonly diagnosed of the two. Anaplasma platys targets platelets, the cells responsible for blood clotting. This second form causes a condition known as canine cyclic thrombocytopenia, where platelet counts drop in waves, partially recovering before falling again roughly every two weeks.
Both species belong to the same family of bacteria as Ehrlichia, another tick-borne pathogen in dogs. Infections with either species tend to peak during summer months when ticks are most active.
How Dogs Get Infected
Black-legged ticks (also called deer ticks) are the primary carriers of A. phagocytophilum. These are the same ticks that transmit Lyme disease, which is why coinfections are common. In one study of ticks removed from dogs in Germany, about 19% carried A. phagocytophilum and nearly 29% carried Lyme-causing bacteria. Around 7% of those ticks carried both pathogens simultaneously.
A tick needs to stay attached for 24 to 48 hours before it can transmit the bacteria. This window is important because it means prompt tick removal after walks or outdoor time can prevent infection entirely. Dogs don’t spread anaplasmosis to other dogs or to people directly. The tick is always the intermediary.
Signs and Symptoms to Watch For
Symptoms typically appear one to two weeks after an infected tick bite. The most common signs include:
- Fever and chills
- Lethargy or unusual tiredness
- Loss of appetite and weight loss
- Muscle aches, which may show up as stiffness, limping, or reluctance to move
- Vomiting or diarrhea
Dogs infected with A. platys often remain asymptomatic, but when symptoms do appear they tend to reflect low platelet counts. You might notice nosebleeds, small spots of hemorrhage on the gums or whites of the eyes, or bruising on the skin. Swollen lymph nodes, eye discharge, and an enlarged spleen can also occur. Because platelet counts cycle up and down with this species, symptoms may seem to improve on their own before returning, which can make the infection easy to overlook.
Both forms of anaplasmosis cause a decline in platelet numbers. In severe or untreated cases, this can progress to bleeding problems, respiratory difficulty, or organ failure, though that level of severity is uncommon in otherwise healthy dogs.
How Anaplasmosis Is Diagnosed
Most veterinary clinics use a point-of-care blood test that screens for antibodies to Anaplasma alongside other tick-borne diseases like Lyme and Ehrlichia. This is often part of the annual heartworm screening your vet already runs. The test takes about 10 minutes and is a good first step, but it has limitations. Newer versions of this test detect antibodies in roughly 51% of dogs with confirmed A. phagocytophilum infection and about 64% of dogs with A. platys. That means a negative result doesn’t always rule out infection, especially early on before the dog has produced enough antibodies.
When clinical suspicion is high but the antibody test comes back negative, your vet may send blood out for PCR testing, which detects the bacteria’s genetic material directly. This is more sensitive during the early, active stage of infection. A basic blood count showing unusually low platelets in a dog with fever and tick exposure is also a strong clue that points toward anaplasmosis.
Treatment and Recovery
Anaplasmosis responds well to antibiotic therapy. The standard treatment is a course of doxycycline, typically given for about 28 days. Most dogs start to improve within 24 to 48 hours of beginning the medication, which can feel reassuring when your dog has been visibly unwell. The full course is important even after symptoms resolve, because stopping early can lead to incomplete clearance of the bacteria.
Dogs with severe thrombocytopenia (very low platelets) may need supportive care while the antibiotics take effect. This could include fluids or monitoring for signs of bleeding. In the vast majority of cases, dogs make a complete recovery with no lasting effects.
One complicating factor is that some dogs become subclinical carriers after treatment, meaning they test positive on antibody tests long after the active infection has cleared. A positive antibody result in a dog that feels perfectly fine doesn’t necessarily mean the infection is still active or needs retreatment. Your vet may recommend follow-up PCR testing to distinguish past exposure from ongoing infection.
Why Coinfection Matters
Because black-legged ticks carry multiple pathogens, a single tick bite can transmit more than one disease. Lyme disease is the most common coinfection alongside anaplasmosis. Dogs carrying both infections may show more pronounced symptoms or take longer to recover than dogs with either infection alone. This is one reason vets use combination screening tests that check for several tick-borne diseases at once. If your dog tests positive for Anaplasma, it’s worth confirming whether Lyme or Ehrlichia is also in the picture, since that can change the treatment plan.
Preventing Anaplasmosis
Tick prevention is the most effective way to protect your dog. Modern oral tick preventatives kill ticks within hours of attachment, well before the 24-to-48-hour transmission window. Topical treatments and tick collars also reduce risk significantly. The key is consistent, year-round use, since ticks can be active in milder winter weather too, particularly in temperate climates.
Daily tick checks after time spent in wooded or grassy areas add another layer of protection. Pay close attention to the ears, groin, armpits, and between the toes, where ticks tend to hide. If you find an attached tick, removing it promptly with fine-tipped tweezers reduces the chance of transmission. There is no vaccine for canine anaplasmosis, so prevention comes down to keeping ticks off your dog and catching them quickly when they do latch on.