Anaplasmosis

TL;DR. Anaplasmosis is a common tick-borne bacterial infection in dogs and cats that targets blood cells, causing symptoms like fever, lethargy, lameness, and bleeding tendencies, but it typically responds rapidly to appropriate antibiotic therapy.

Ticks in grassy environments pose a transmission risk for anaplasmosis.

What is it?

Anaplasmosis is a common tick-borne infectious disease that affects both dogs and cats. It is caused by microscopic, intracellular bacteria belonging to the genus Anaplasma. Because these organisms live inside the host's blood cells, they are highly specialized pathogens that can disrupt vital bodily systems, primarily the hematopoietic (blood-forming) and immune systems.

There are two primary species of Anaplasma that infect pets:

1. Anaplasma phagocytophilum: This bacterium causes canine granulocytotropic anaplasmosis. It specifically targets granulocytes, which are a category of white blood cells (primarily neutrophils) crucial for fighting off infections.
2. Anaplasma platys: This bacterium causes canine thrombocytotropic anaplasmosis, also known as canine infectious cyclic thrombocytopenia. It targets platelets, the cell fragments responsible for blood clotting.

When an infected tick bites a pet, the bacteria enter the bloodstream and invade these specific target cells. Once inside, they multiply and cause cellular dysfunction, leading to a range of clinical signs from mild, unnoticeable infections to severe bleeding disorders and joint pain.

Causes & risk factors

The primary route of transmission for anaplasmosis is through the bite of an infected tick. Anaplasma phagocytophilum is primarily transmitted by Ixodes species ticks (commonly known as blacklegged ticks or deer ticks). The risk of infection is highest in geographic areas where these ticks are endemic and during seasons when ticks are most active.

While dogs are the most frequently diagnosed patients, cats can also contract the disease. In feline patients, tick-control products are vital for prevention. Additionally, because the bacteria reside in the bloodstream, transmission can occur via blood transfusions. Therefore, cats and dogs used as blood donors in endemic regions must undergo rigorous screening.

There are no documented breed predispositions for anaplasmosis; any dog or cat exposed to infected ticks can contract the disease. However, pets that spend significant time outdoors in wooded or grassy areas are at a much higher risk. Furthermore, co-infection with other tick-borne pathogens, such as Ehrlichia canis, is common and can significantly worsen the severity and duration of the illness. As noted in a leading veterinary internal medicine reference:

"Anemia and thrombocytopenia in dogs experimentally infected with either A. platys and/or E. canis were more persistent in the co-infected dogs."

Signs to watch for

The clinical signs of anaplasmosis can vary widely. Many pets remain subclinical, meaning they carry the bacteria but show no outward signs of illness. When clinical disease does develop, it typically manifests during the acute phase of infection.

Common Signs

• Fever: A sudden, high body temperature is one of the most frequent signs.
• Inappetence: A complete loss of appetite or reluctance to eat.
• Lethargy: Marked sluggishness, weakness, or depression.
• Lameness and Stiffness: Reluctance to move, a stiff gait, or shifting lameness caused by joint pain and inflammation.
• Thrombocytopenia: A drop in blood platelet counts, which is a hallmark finding on blood tests.

Occasional Signs

• Anemia: A low red blood cell count, leading to pale gums and weakness.
• Bleeding tendencies: This includes nosebleeds (epistaxis), bleeding gums (gingival bleeding), blood in the stool (melena), and the formation of blood pools under the skin (hematomas).
• Bruising: Tiny pinpoint red spots on the gums or skin (petechiae) or larger purple bruises (ecchymoses).
• Joint swelling (Polyarthritis): Multiple swollen, painful joints.
• Enlarged organs: Swelling of the lymph nodes (lymphadenopathy) or enlargement of the liver and spleen (hepatosplenomegaly).
• Gastrointestinal upset: Vomiting and diarrhea.
• Respiratory signs: Coughing or difficult breathing.
• Eye inflammation: Inflammation of the inner structures of the eye (uveitis) or bleeding within the retina (retinal hemorrhage).

Rare Signs

• Ataxia: Loss of coordination, wobbliness, or stumbling.
• Seizures: Abnormal electrical activity in the brain, leading to convulsions.

Petechiae on the gums can indicate a low platelet count caused by anaplasmosis.

How vets diagnose it

Diagnosing anaplasmosis can be challenging because many healthy pets living in tick-endemic areas carry antibodies to the bacteria without actively being sick. Your vet will perform a comprehensive physical examination and recommend a suite of diagnostic tests to confirm active infection.

• Complete Blood Count (CBC): This is a fundamental first step. The CBC allows your vet to evaluate red blood cells, white blood cells, and platelets. It often reveals thrombocytopenia (low platelets) and sometimes hemolytic anemia or changes in white blood cell counts. In some cases, the vet can actually see the Anaplasma organisms (called morulae) inside the neutrophils under a microscope.
• Synovial Fluid Evaluation: If your pet is showing signs of severe joint pain or lameness, your vet may perform a joint tap to analyze the fluid. This helps confirm whether joint inflammation (polyarthritis) is present.
• Serologic Testing (IFA or ELISA): These tests detect antibodies produced by the pet's immune system in response to the bacteria. However, because exposure rates are high and antibodies can persist long after the infection has cleared, a positive antibody test alone does not prove active clinical disease.
• Polymerase Chain Reaction (PCR) Assay: This is the gold standard for diagnosis. A PCR test detects the actual DNA of the bacteria in the blood, bone marrow, or splenic aspirates. It is highly sensitive and can confirm active infection even in the early stages before antibodies have fully developed.

As a leading veterinary internal medicine reference explains:

"A. phagocytophilum have subclinical infections, most infected dogs only have an acute phase, exposure rates in endemic areas are high, and the disease syndromes associated with infection have multiple other causes. Thus antibody test results and polymerase chain reaction (PCR) assay results alone cannot be used to prove clinical disease associated with A. phagocytophilum infection."

Therefore, your vet will correlate positive test results with your pet's clinical symptoms and response to therapy to make a definitive diagnosis.

Microscopic evaluation of blood smears helps veterinarians identify intracellular pathogens.

Treatment options

Fortunately, anaplasmosis is highly treatable. The primary goal of therapy is to eliminate the bacteria from the bloodstream and target cells.

First-Line Antibiotic Therapy

The standard treatment for anaplasmosis involves a course of tetracycline antibiotics.

• Doxycycline: This is the most commonly prescribed antibiotic for tick-borne infections in veterinary medicine. It penetrates tissues and cells exceptionally well, directly targeting the intracellular bacteria.
• Tetracycline: Another antibiotic in the same class that may be used as an alternative.

These medications are typically administered orally for several weeks. It is crucial to complete the entire prescribed course of antibiotics, even if your pet seems completely recovered within the first few days, to ensure the infection is fully cleared.

Prognosis

The prognosis for pets diagnosed with anaplasmosis is excellent. Most dogs and cats respond remarkably fast to antibiotic therapy, often showing noticeable improvement in their fever, energy levels, and appetite within 24 to 48 hours of starting treatment.

While the acute phase can be dramatic, long-term complications are rare if the infection is caught and treated early. However, because some pets can develop persistent subclinical infections, monitoring blood counts (especially platelet levels) after treatment is completed is a standard recommendation to ensure long-term recovery.

Prevention

Preventing anaplasmosis relies entirely on minimizing your pet's exposure to ticks.

• Tick-Control Products: Use veterinarian-approved acaricidal products (topical treatments, oral chews, or collars) year-round. This is the single most effective way to protect both dogs and cats.
• Environmental Management: Keep grass mowed short, clear brush from your yard, and avoid walking your pet in dense undergrowth or tall grass where ticks thrive.
• Daily Tick Checks: Thoroughly check your pet's skin and coat for ticks after outdoor activities, paying close attention to the ears, neck, underarms, and between the toes. Promptly remove any ticks you find.
• Screening Blood Donors: If your pet is a blood donor, regular screening via PCR or serology is essential to prevent transmitting the bacteria to vulnerable patients.

When to call your vet

You should contact your veterinarian if your pet shows any signs of lethargy, unexplained limping, joint stiffness, or a sudden loss of appetite, especially if you live in a tick-endemic area or have recently found a tick on your pet.

Seek immediate emergency veterinary care if your pet exhibits any of the following red-flag symptoms:

• Uncontrolled bleeding (such as nosebleeds or bleeding gums)
• Severe breathing difficulties or rapid, labored breathing
• Widespread bruising or pinpoint red spots on the gums or skin
• Seizures or sudden loss of coordination
• Extreme weakness or collapse

Sources

• Internal Medicine, 5th Edition, pages 1360, 1361, 1362, 1363.

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