Ehrlichiosis in Cats

Ehrlichiosis in felines is believed to be a tick-born disease caused by one of several intracellular organisms known as rickettsial. Belonging to the genus, Ehrlichia, the primary causative agents to cause ehrlichiosis in cats are Ehrlichia risticii (E. risticii) and Ehrlichia canis  (E. canis ). The organisms act like parasites, entering and infecting eukaryotic cells, eventually destroying the cell. Ehrlichiosis is present in geographical regions that support tick life including the United States, France, and warmer regions of the world. Over 50 cases of ehrlichiosis in cats have been proven with accurate diagnoses completed through a PCR test capable of detecting the Ehrlichia polymerase chain reaction.

Ehrlichiosis in cats is a rare disease that is believed to be transmitted by the blood-feeding parasite, the tick. Ehrlichiosis disease is caused by rickettsial organisms that are microscopic in size and attack the various cells of the feline body. Rickettsial organisms act differently than bacterial or viral infections, as they enter the cell, destroying said cell from the inside. The mass cell destruction causes clinical signs of swollen joints, pale gums and breathing difficulties in cats. If the feline’s condition is not properly diagnosed and treated, ehrlichiosis could progress to a life-threatening condition. 

Felines with Ehrlichiosis have variable symptoms including dyspnea or coughing, edema of the limbs and reluctance to walk. The cat may develop a stiffness to her body, become depressed and anorexic, reluctant to eat. Clinical signs cat owner may note at home, which indicate an ehrlichiosis infection include: 

• Inner eye inflammation 
• Eye discharge 
• Swollen joints 
• Enlarged lymph nodes
• Difficulty breathing 
• Pale mucous membranes 
• Anemia 
• Fever 
• Diarrhea 
• Vomiting 
• Anorexia 
• Weight loss 
• Depression 
• Lethargy 
• Tendency to bleed

Ehrlichiosis contraction in cats is not well understood, but ticks have been identified as the most probable link to this uncommon disease. Ticks acquire the ehrlichiosis organism by feeding on infected hosts. The organism remains in the tick host throughout the external parasite’s life stages. The tick can then transmit the intracellular organism to the feline when they feed on its blood. It is estimated that the Ehrlichia spp. can be transmitted within three to six hours upon tick attachment, therefore, an infected tick may not infect the feline if said parasite is removed prior to three hours’ time. Left attached, the tick transmits the Ehrlichia organism, which enter the cat’s platelets, granulocytes and mononuclear leukocytes, multiplying and progressively destroying the cells.

The Ehrlichia polymerase chain reaction test, or PCR, is the only test capable of detecting the presence of the rickettsial parasite, confirming the diagnosis of ehrlichiosis in cat. However, as ehrlichiosis is a rare disease in cats, a differential diagnosis is completed prior to PCR testing. 

Blood Work

Low platelet counts, low white blood cell counts and increased protein levels in the blood are common abnormalities found in feline ehrlichiosis. Tests include:

• CBC: Complete blood cell count 
• Biochemical profile 
• Platelet count 

Blood Smear

On occasion, the organisms can be found residing within the cell under microscopic view. 

Radiographs

X-rays often reveal an enlarged liver or spleen, the two organs that house affected cells. 

Bone Marrow Aspirate 

A fine needle biopsy of the cat’s bone marrow can detect the overall health of the cells and cell count within the house of production. 

Serological Testing 

The cat’s immune system may react to the parasite by creating antibodies against it, which would be present in the blood serum. 

Ehrlichiosis in cats may be treated as an inpatient or outpatient procedure, depending on the feline’s current state. In acute infections, the feline will likely be prescribed antibiotic therapy as antimicrobial medication is an effective treatment for ehrlichiosis. If the feline is severely ill, the doctor may admit her to hospital care, administering intravenous fluid therapy and transfusions of blood in the incidence of severe anemia. Commonly, the veterinarian prescribes antibiotics of the tetracycline drug family including minocycline, oxytetracycline, tetracycline or doxycycline. 

Clinical improvement is reported for most cats following antibiotic therapy of imidocarb dipropionate, doxycycline and/or tetracycline. The prognosis for ehrlichiosis in cats is especially positive for immunocompetent felines, but cats with weak immune systems may have a lesser prognosis. Follow-up appointments are to be expected in ehrlichiosis cases in felines as the veterinarian will want to note your cat’s progress and reaction to the drugs. 

Arthropod vectors (ticks) should be controlled in your cat’s environment to prevent reoccurrence through use of a topical anti-parasitic drug. If your cat was or will be a blood donor, she should be screened for the ehrlichiosis organism before making a contribution.