Ehrlichiosis in Cats

What is Ehrlichiosis in Cats?

Ehrlichiosis is a rare, poorly understood tick-borne disease that affects the blood cells of cats. Ehrlichia, the bacteria that causes ehrlichiosis, is a Rickettsial disease. These are typified by bacteria that only live inside other cells, causing disease in dogs, cats, and humans. The disease in cats is called feline mononuclear ehrlichiosis.

It is unclear which ticks transmit Ehrlichia to cats, but most likely they are similar to the brown dog tick that transmits a similar condition in dogs. These ticks become infected by feeding on diseased hosts. Ticks require multiple hosts throughout their life cycle, including rodents, white-tailed deer, dogs, and cats.

Ehrlichia can be transmitted to cats as quickly as three hours after a tick becomes attached. Bacteria enter the cat through the bite wound and saliva. Once in the bloodstream, the Ehrlichia bacteria infects and reproduces in the cat’s white blood cells, spreading through tissues. This can create problems with white blood cells, red blood cells, and platelets, and cause disease in organs throughout the body.

While dogs with ehrlichiosis experience three stages of the disease, this does not appear to occur in cats. They may have co-infections with other viruses and tick-borne diseases, which will lead to worsening clinical signs. 

Symptoms of Ehrlichiosis in Cats

Symptoms of feline mononuclear ehrlichiosis vary greatly. Common symptoms include:

• Fever

• Lethargy

• Decreased appetite

• Pale mucous membranes (gums)

• Bruising and bleeding

• Vomiting

• Diarrhea

• Joint pain

• Uveitis (inflammation in the eye)

• Enlarged lymph nodes

• Weight loss

• Difficulty breathing

• Enlarged spleen, which may make the abdomen appear enlarged

• Nervous system issues (meningitis, brain bleeds)

Causes of Ehrlichiosis in Cats

A tick acquires ehrlichiosis after feeding on an infected host. Most ticks that cause tick-borne disease require three hosts throughout their life to reproduce and complete their life cycle. These hosts include rodents, rabbits, deer, foxes, dogs, and cats. Once a tick is infected, it transmits the disease to cats through a bite as it feeds on the cat’s blood. The bacteria appear in the bloodstream and white blood cells a few weeks after the tick feeds.

How Veterinarians Diagnose Ehrlichiosis in Cats

Veterinarians may suspect a tick-borne disease, such as ehrlichiosis, based on clinical history and symptoms. However, because ehrlichiosis is extremely rare, other causes for clinical signs should be thoroughly evaluated. Blood work plays a major role in diagnosing ehrlichiosis, as well as side effects and complications. Diagnostic tests include:

• Blood chemistry

• Complete blood count: Cats with ehrlichiosis commonly have low platelets, anemia, and increased monocytes (a certain white blood cell).

• Blood smear: Ehrlichia organisms may be visualized in white blood cells, but it is rare to find them in the peripheral blood.

• Serology and PCR assays: For Ehrlichia, these tests can be used for definitive diagnosis but may cross-react with other rickettsial species, causing the possibility for false positives and negatives.

• X-rays: These may be taken to rule out fractures or other causes of joint pain.

Treatment of Ehrlichiosis in Cats

Doxycycline is the treatment of choice for cats with confirmed or suspected feline mononuclear ehrlichiosis. Most cats respond rapidly, within days. Cats are treated for suspected ehrlichiosis for at least 28 days.

Owners should use caution when using doxycycline in cats. In tablet form, it can cause esophageal strictures— narrowing scar-like formations in the esophagus—if it gets stuck. Many veterinarians use liquid doxycycline or follow the tablet with a good amount of water.

If your cat does not respond appropriately, other diagnoses should be considered, or different antibiotics like tetracycline or imidocarb may be prescribed.

During acute illness, depending on the severity of clinical signs, cats may require supportive care, including:

• Intravenous fluid therapy

• Nutritional support

• Pain management

• Blood transfusions

Recovery and Management of Ehrlichiosis in Cats

Overall, the prognosis for cats with feline mononuclear ehrlichiosis is good. Cats should show signs of initial improvement over three days, but complete recovery may take longer based on the severity of the disease.

Antibiotics are usually administered for a full month, sometimes longer. While most cats respond favorably, some do not recover and die or are euthanized due to the disease. Common long-term complications include chronic arthritis, ocular issues, anemia, and side effects from blood transfusions.

Veterinarians may recommend rechecking bloodwork to ensure complete removal of the organism 1-2 months after treatment. If the results are still positive and the cat is still symptomatic, a second round of antibiotics may be required.

Prevention of Ehrlichiosis in Cats

There is no vaccine to prevent ehrlichiosis in dogs or cats. Tick avoidance and prevention is critical to ensure the safety of pets. There are a variety of tick preventives on the market, and your veterinarian can help you make the best choice for your pet.

Be sure to check your pet for ticks and remove any you find. Ehrlichia is zoonotic, which means it can infect humans. It’s important to note that cats cannot transmit Ehrlichia directly to their owners; an infected tick would need to bite a human. But dogs and cats can bring unattached ticks in from outside. Ensure that your cat is up to date on tick prevention, and check your cat for ticks whenever they come in from outside.