Hepatozoonosis in Cats

Unlike most tick-borne diseases, hepatozoonosis is not transmitted through a tick bite but through the carnivore ingesting an infected tick. The parasite invades and resides in organs and muscle tissue of the carnivorous host animal, where it divides and ruptures cells, and enter the bloodstream. Once in the bloodstream, it can be taken up by a biting tick, infecting the tick, and repeating the cycle. Hepatozoonosis can cause damage to tissue in cats resulting in symptoms, and has been associated with immune system suppression.

Hepatozoonosis is caused by the protozoan organism, Hepatozoon, that is carried by ticks. The disease affects wild and domestic carnivores but is not as common in cats as other carnivores, or possibly, it is not commonly detected as often in cats as they usually are asymptomatic when infected with Hepatozoon parasites.

Most cats infected with hepatozoonosis parasites are asymptomatic. When symptoms do occur, the cat is often found to have another condition present that may also account for symptoms. This makes understanding hepatozoonosis disease difficult as symptoms may be from damage to tissues by the tick-borne parasite infecting the cat, or from other conditions acquired due to impaired immune system functioning. Symptoms of hepatozoonosis that may occur include:

• Lethargy
• Weakness
• Fever
• Swollen lymph nodes
• Anemia
• Thrombocytopenia (abnormal blood clotting)
• Presence of virus or immune system disease

Hepatozoonosis is caused by a Hepatozoon parasite that infects blood-sucking arthropods (most commonly ticks). Unlike in most disease transmissions involving ticks, hepatozoonosis is not transferred by the tick biting the animal, but occurs when a carnivorous host animal (domestic or wild) ingests a tick infected with the Hepatozoon parasite. Another mode of transmission occurs when the parasite crosses the placenta of an infected pregnant carnivore. 

Two types of parasite have been found in cats H. canis is the hepatozoonosis parasite most frequently found in dogs, but can also infect cats. H. felis hepatozoonosis the predominant species found infecting cats. This disease is most commonly found in tropical locations. Countries reporting cases include, India, South Africa, Nigeria, USA, Brazil, Israel, Spain, France and Portugal.

Outdoor cats, which are more prone to ticks that may be carrying the disease, are more at risk for infection than indoor cats. Once an animal has been infected the parasite invades tissues and divides and ruptures cells, which may result in symptoms of hepatozoonosis and associated immune system disorders.

Because hepatozoonosis is usually asymptomatic in cats, the majority of infections go undetected. When discovered it is usually incidental to diagnosis or treatment for another condition. 

Diagnosis of hepatozoonosis can be very difficult due to its association with immunosuppression and the presence of other conditions that coincide with hepatozoonosis infection. Your veterinarian will perform a physical examination and conduct blood and urine tests to determine the presence of other conditions that may account for symptoms, or be present in conjunction with hepatozoonosis. Your vet will want to know if your pet has been to an area where hepatozoonosis in ticks has been reported. 

If hepatozoonosis is suspected, a definitive diagnosis of hepatozoonosis in cats can be determined through discovering: 

• parasite gametes in blood smears
• parasite meronts in muscle
• parasite DNA in blood and tissue samples. 

These methods are not always conclusive as gametes, meronts, and DNA of the hepatozoonosis parasite in cats are infrequent and can be difficult to detect.

Treatment will consist of medications to counteract the parasite, however these medications have limited success and recurrence of infection may occur. A variety of antiparasitic medications have been employed to treat hepatozoonosis infection with varying success. Ongoing treatment and intervention by your veterinarian may be required. 

In addition, any symptoms and secondary conditions present will need to be treated. Supportive care will be provided as required. 

Your veterinarian will also need to treat any other disease or viral infections that may be present due to hepatozoonosis infections correlation with suppressed immune system functioning. 

Preventative treatment against the presence of blood sucking pests is the best method of protecting your pet from hepatozoonosis. 

Your cat may need to be monitored long term for recurrence of hepatozoonosis, as a complete cure is not always achievable and lifelong treatment with anti-parasitic medications may be required This infection is not known to be a risk to humans. Keeping pets indoors and preventing exposure to ticks and other blood-sucking insects is the most effective way of preventing hepatozoonosis.