Anaplasmosis in Dogs

What is anaplasmosis?

Anaplasmosis is a tick-borne disease caused by the infectious bacterial organism Anaplasma phagocytophilum. It is transmitted by the bite of infected deer ticks (also known as black-legged ticks) and western black-legged ticks. Anaplasmosis has been reported worldwide in many animal species.

What are the clinical signs of anaplasmosis?

Most infected dogs have symptoms for one to seven days, but some have only minor symptoms, while others have no symptoms at all. 

Signs of infection with A. phagocytophilum often include:

• Fever
• Lethargy
• Lameness
• Joint pain
• Anorexia (lack of appetite)

Less common clinical signs may include:

• Vomiting
• Diarrhea
• Coughing
• Labored breathing
• Neurological signs such as seizures (rare)

Dogs with anaplasmosis often have many of the same symptoms as those with Lyme disease, and infection with both agents (co-infection) is not uncommon. Lyme disease and anaplasmosis are commonly found in the same geographic location and are transmitted by the same tick species.

How is anaplasmosis diagnosed?

Your veterinarian can perform tests to diagnose exposure or infection.

• A special in-clinic test can detect exposure to A. phagocytophilum.
• Laboratory tests can help determine if an active infection is present, including enzyme-linked immunosorbent assay (ELISA), indirect fluorescent antibody (IFA), and polymerase chain reaction (PCR).
• Microscopic examination of a blood sample may occasionally detect the organism during the peak phase of infection.

What is the treatment for anaplasmosis?

The most common treatment for anaplasmosis in dogs is administration of the antibiotic doxycycline. Other antibiotics that can be used include tetracycline, minocycline, and chloramphenicol. This treatment is the same as that for other tick-borne infections, including ehrlichiosis and Lyme disease. Infected dogs are often treated for two to four weeks; the longer course of antibiotics is often given when the dog is co-infected with Lyme disease.

What is the prognosis?

In most cases, symptoms improve rapidly with treatment. Dogs are usually noticeably better within 24 to 48 hours after treatment begins, and the prognosis for clinical recovery is excellent.

Although most dogs clinically improve, it can be difficult to determine whether the organism has been eliminated from the body. Some dogs stop producing antibodies after treatment, which may indicate that the organism has been cleared. However, even after a dog has recovered, blood tests may remain positive for exposure to A. phagocytophilum. A positive test result does not necessarily mean that the dog still has an active infection, so a second course of antibiotics is generally not recommended simply to obtain a negative blood test.

What if my dog tests positive but isn’t sick?

Dogs may have antibodies to A. phagocytophilum without showing any signs of illness. Dogs living in areas where anaplasmosis or Lyme disease are common are frequently exposed to A. phagocytophilum and may have a positive antibody test result even though they appear healthy. Research has shown that some healthy dogs remain infected with A. phagocytophilum for long periods without becoming ill. It is not known whether these dogs will eventually develop disease.

Research suggests that anaplasmosis is usually an acute (sudden) illness in dogs that develops one to two weeks after an infected tick bite. If your dog has tested positive, your veterinarian may recommend running additional tests, including a physical examination and a complete blood count (CBC) that may detect signs of active infection like fever, low platelet count, or may detect the organism in the blood.

Treatment is generally not recommended for dogs that test positive but have no other signs of infection because the screening tests only indicate exposure to the organism, not an active infection. Antibiotic treatment can resolve clinical signs, but it is still uncertain whether antibiotics can completely eliminate the organism from the body. If antibiotics were used to treat every dog that tests positive, it would increase the risk of antibiotic resistance developing, which can reduce future treatment effectiveness. 

How can I prevent my dog from getting anaplasmosis?

The key to prevention is limiting your dog’s exposure to ticks. Ticks are found in grassy, wooded, and sandy areas. They find their way onto an animal by climbing to the top of a leaf, blade of grass, or short tree (especially cedar trees), where they wait until their sensors detect an approaching animal on which to crawl or drop. Keeping animals away from thick underbrush reduces their exposure to ticks. Keep your dog on trails when walking near wooded or tall grass areas.

Ticks must feed for at least 24 hours before they can transmit A. phagocytophilum to a pet, so medications that kill ticks in under 24 hours can help prevent the disease. Ask your veterinarian what tick preventative options are best for your dog.

Can I get anaplasmosis from my dog?

Anaplasmosis is a zoonotic disease, meaning it can infect both animals and humans. However, it is not spread directly from dogs to people, or from one animal to another. Instead, infection occurs through the bite of an infected tick. If your dog is diagnosed with anaplasmosis, take strict tick-control measures because infected ticks may be present in your environment and could transmit the disease to humans.