Hepatozoonosis (Tick-Borne Parasitic Protozoan Disease) in Cats

Summary

Feline hepatozoonosis is an uncommon disease caused by several different parasitic species of Hepatozoon protozoa, most commonly Hepatozoon felis. H. felis is presumed to be transmitted by ticks, similar to other Hepatozoon species.

It is extremely rare for Hepatozoon infection to cause symptoms in cats. Cats are usually diagnosed as an incidental finding when their blood is examined for other reasons. There is a possible connection between hepatozoonosis and immunosuppression, so follow-up with a veterinarian is recommended.

Most cats diagnosed with hepatozoonosis have other underlying conditions. Due to this, it is difficult to say whether a cat’s symptoms are caused by hepatozoonosis or another condition. Associated symptoms include fever and enlarged lymph nodes. Cats diagnosed with this condition may also have anemia (low red blood cell count).

In other words, a positive finding of Hepatazoon is presumed to be noteworthy but does not conclusively explain any symptoms at all. Diagnosis typically involves a blood smear to identify the parasitic organisms within the feline immune cells. In some cases, testing for parasitic DNA may be performed to confirm the species of organism present.

Treatment is usually only recommended for cats with symptoms. Definitive treatment protocols have not been established for this condition due to its rarity. Anti-protozoal medications may be effective if the presence of protozoans is confirmed. Feline hepatozoonosis can be prevented by year round maintenance of vet-approved flea and tick control. Always consult a vet before selecting preventative external parasite control. Hepatozoon may be contagious to other cats.

Risk Factors

Hepatozoonosis occurs commonly in many parts of the world, including Africa, Asia, North America and Europe. Hepatozoonosis is rarely diagnosed and is usually an incidental finding. As such, this condition is not an emergency, so pet owners should not be highly concerned about this disease. Cats displaying associated symptoms may have an underlying condition, so follow up with a vet is recommended.

Possible Causes

Most cases of hepatozoonosis in cats are caused by the presence of parasitic protozoa in the host’s bloodstream. Specifically, the species Hepatozoon felis, Hepatozoon canis, and Hepatozoon silvestris have been reported in cats.

Little is known about the transmission of Hepatozoon felis, but it is presumed to behave similarly to the more extensively studied species Hepatozoon canis. H. canis infection occurs when a dog eats an infected tick, usually from licking or chewing a tick embedded in the skin. H. felis has been identified in ticks, however a link between tick exposure and H. felis infection has not been fully established.

Main Symptoms

As noted above, hepatozoonosis in cats does not conclusively cause symptoms in and of itself. 

Associated symptoms include:

• Lethargy • Fever • Weakness • Enlarged lymph nodes (lymphadenopathy) • Blood clotting abnormalities

Detailed Characterization

Cats diagnosed with hepatozoonosis may become anemic, but this, like the associated symptoms already listed, may be caused by other underlying conditions and not the parasitic protozoan species itself.

Infection with H. felis may indicate immunosuppression, so cats diagnosed with the disease should be tested for feline immunodeficiency virus and other potential conditions as symptoms indicate.

Testing and Diagnosis

Cats are usually diagnosed with hepatozoonosis when their blood is examined for other reasons. The parasite is visible under a microscope in the immune cells of the bloodstream.

Diagnostic tests indicated for cats experiencing symptoms associated with hepatozoonosis include: 

• Blood tests: Routine blood tests like a complete blood count and biochemistry profile may show changes associated with hepatozoonosis, but these abnormalities are not specific to the condition. Routine screening tests for feline leukemia virus and feline immunodeficiency virus (FeLV/FIV) also provide information on the state of the cat’s immune system. 

• Molecular testing: A blood sample may be tested for the parasite’s DNA specifically to confirm a diagnosis. 

• Muscle biopsy: A sample of muscle tissue is collected and submitted for analysis. Hepatozoon may create parasitic cysts in the muscle, which can be seen under the microscope. 

Treatment protocols have not been extensively studied in cats and treatment is not always indicated. There have been reports of successful combination treatment with anti-protozoal and antibiotic medications

Steps to Recovery

Since little is known about feline hepatozoonosis, the prognosis is undefined. However, it is unlikely to cause symptoms and is expected to have a favorable outcome as long as any underlying associated conditions are treated effectively.

Prevention

Hepatozoon felis is thought to be contagious to other cats, and may be transmitted by ticks, similar to H. canis. H. canis is contagious to dogs and wild canine species. The most effective prevention method is limiting tick exposure and consistent adherence to vet-approved external parasite control. Always consult a vet before choosing an external pesticide, as there are many products on the market whose safety and efficacy have not been proven.

Is Hepatozoonsis Common in Cats?

Hepatozoonosis is expected to be common in areas where the parasite has been found, including Asia, Africa, North America and Europe, but is rarely diagnosed.

Typical Treatment

• Benign neglect - Anti-protozoal medications - Antibiotics