Anaplasmosis in Cats

At a glance

About: Anaplasmosis is a tick-borne infection caused by the intracellular bacterium Anaplasma phagocytophilum which takes up residence in the white blood cells of cats and other warm-blooded mammals.

Transmission: Ticks spread the bacteria when they feed on an infected animal. Bacteria in the host blood are ingested and make their way to the salivary glands of the tick. From there into the next host when the tick feeds on a blood meal.

Symptoms: Cats are often asymptomatic to anaplasmosis. When symptoms do present, they include loss of appetite, fever, lethargy, and lameness.

Diagnosis: Baseline tests including complete physical examination and medical history, blood count, biochemical profile and urinalysis. Polymerase chain reaction (PCR) can diagnose infection.

Treatment: Mildly affected cats may require no treatment at all — antibiotics for symptomatic cats.


Formerly known as Ehrlichiosis, Anaplasmosis is a tick-borne disease spread by ticks of the Ixodes genus. It is caused by the intracellular bacterium Anaplasma phagocytophilum. As one can guess, an intracellular bacterium lives in certain cells, and A. phagocytophilum takes up residence in the white blood cells, specifically granulocytes. These cells are responsible for fighting infection.

Anaplasma phagocytophilum infects humans and a wide range of animals including cats and dogs and has been detected in the following countries; United States, Sweden, Finland, Poland, Switzerland, Germany, Italy, and Spain. In the United States, it is endemic in the upper Midwest, East, and Northeast regions as well as the western coastal regions. Infection occurs most often from spring to autumn. Cats who have had exposure to A. phagocytophilum may have a co-infection with other tick-borne pathogens.


A. phagocytophilum enter the tick gut when it feeds on the blood of an infected animal and from there, it migrates to the salivary glands and is secreted when the tick feeds on the next host. White-tailed deer, raccoon, white-footed mouse, and the grey squirrel are important reservoirs of the disease. The tick must feed for 24 hours or more for transmission to occur. Cats who roam outdoors in rural areas are at the greatest risk of infection.

Blood transfusion can also transmit infection.

Clinical signs

It can take 1-2 weeks for symptoms to develop after a bite. Most infections are subclinical, or mind and non-specific, which may include the following:

Less common symptoms of anaplasmosis include gastrointestinal disturbances such as vomiting and diarrhea and neurological signs.


Your veterinarian will perform a complete physical examination of your cat and thorough medical history from you, including the onset of symptoms.

Diagnostic tests:

  • Baseline tests including complete blood count, biochemical profile and urinalysis may reveal a decreased white blood cell count.
  • Blood smears can reveal morulae (microcolonies of anaplasma) in circulating white blood cells.
  • A polymerase chain reaction is the most effective diagnostic test for anaplasmosis, which detects A. phagocytophilum DNA.


Anaplasmosis is a largely self-limiting infection, and your veterinarian may suggest a wait and see approach in cats who appear to be well.

Tetracycline (usually doxycycline) antibiotics administered twice a day are the treatment for anaplasmosis. Most cats will improve within 24-48 hours.

Anti-inflammatory medication to relieve joint pain.


Re-infection can occur in animals who have had anaplasmosis. The most effective way to prevent anaplasmosis is with strict tick control.

Check cats who roam outdoors every day, start at the head and work your way towards the rear. Remove any ticks you find and be careful not to leave the head behind.

Can I get anaplasmosis from my cat?

Direct infection can’t occur from cats to people, people become infected the same way as cats, via the bite of a tick.


  • Julia Wilson, 'Cat World' Founder

    Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio

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