Hepatozoonosis in Dogs

What is Hepatozoonosis?

Hepatozoonosis in dogs is an infectious disease caused by a single-cell organism called a protozoan. There are two main types of Hepatozoonosis: Hepatozoon canis, carried by the Brown Dog tick, and Hepatozoon americanum, carried by Gulf Cost ticks.

A dog can become infected by swallowing a contaminated tick or by eating prey animals that are infected by ticks. Dogs that hunt or scavenge on outdoor prey or those that live in areas with high Brown Dog or Gulf Coast tick populations have a higher risk of exposure. In most cases, a dog will show symptoms 4 to 10 weeks after ingesting the tick.       

The disease occurs in the southeast and south-central United States, specifically Texas, Louisiana, Alabama, Georgia, Mississippi, Oklahoma, Tennessee, and Florida, where the Gulf Coast and Brown Dog ticks are more common.

Hepatozoonosis caused by H. Americanum can be debilitating and eventually fatal within a few months without treatment. Pet parents are not at risk because the disease cannot spread to humans.

Symptoms of Hepatozoonosis in Dogs

Infection with H. canis tends to be less severe, and since these organisms like to live in the immune system (lymph nodes and bone marrow) and blood storage organs (spleen) they tend to have symptoms of enlarged lymph nodes, pale gums, and lethargy. Some pets infected with H. canis have very mild or even unnoticeable symptoms.

With H. americanum infections, symptoms can become debilitating without treatment. Symptoms may include:

• Fever

• Lethargy

• Weight loss

• Muscle or bone pain

• Muscle loss

• Discharge from the eyes

Pet parents may first notice a reluctance to rise, a stiff gait when walking, and lethargy due to fever.  They may notice that the dog become hypersensitive to touch (hyperesthesia) and may scratch or self-mutilate. As the condition worsens, a dog may lose muscle.

Causes of Hepatozoonosis in Dogs

Unlike most tick-borne diseases, which are transmitted from a tick bite, hepatozoonosis is transmitted by swallowing an infected tick. Dogs can also acquire the infection by eating a tick-contaminated carcass of a wild animal. Recent studies have also shown that dogs can get the infection from eating a wild animal that has the infection, even if the dog does not eat a tick directly.

Fortunately, this disease cannot be transmitted from dog to dog.    

How Veterinarians Diagnose Hepatozoonosis in Dogs

Diagnosis of hepatozoonosis in dogs starts with a comprehensive history of the dog’s daily routine, geographic location, and recent tick exposure.  Other methods for diagnosis may include:

• Physical examination

• Complete blood count

• Blood chemistry analysis

• Urinalysis

• X-rays

• PCR testing

• Muscle biopsy

A veterinarian will look for anemia in the blood, and for high levels of a type of white blood cells called neutrophils. Rarely, the disease-causing protozoan can be seen in your pet’s blood sample. In x-rays, a vet will look for bone lesions. These tests are all used to rule out other conditions with similar symptoms, such as diskospondylitis, meningitis, canine distemper, and polyarthritis (as well as other tick-borne diseases in dogs).

Once these initial tests are done, your veterinarian will likely send out a PCR test to confirm infection. A PCR test looks for the protozoan’s DNA in a dog’s bloodstream. A biopsy of muscle tissue may be necessary to confirm the presence of the protozoan, as this is the primary location for the organism to live.

Treatment of Hepatozoonosis in Dogs

While there is no long-term cure for hepatozoonosis, treatments can help alleviate the symptoms and increase survival time. Treatments include hydration, assisted feeding of a high-calorie diet, and non-steroidal anti-inflammatories to reduce inflammation and pain medication. 

Anti-protozoa medication will likely be prescribed, which can increase lifespan and quality of life. Two  therapy options are commonly used. The most common therapy uses three medications, which together are referred to as TCP:

• T for trimethoprim-sulfadiazine (an antibiotic)

• C for clindamycin (also an antibiotic)

• P for pyrimethamine (an anti-parasitic)

Another therapy options utilizes ponazuril, an anti-parasitic that may be used alone.

Your veterinarian will likely recommend long-term treatment with decoquinate (an anti-parasiticide that can be mixed with food) twice daily for 2 years to reduce chances of symptoms returning.

This therapy does not clear the protozoa completely from the dog’s system, but it reduces their number to lower the inflammation and accompanying symptoms. Relapse of symptoms is likely as remission tends to only last 2-6 months after decoquinate is discontinued. Without treatment, the body becomes debilitated and the muscles waste away, which can lead to death within months. 

With H. canis infection, treatment generally consists of use of an anti-protozoal medication called imidocarb twice monthly for multiple months. Healthy dogs without additional diseases can potentially be cleared of the protozoan with consistent care.

Recovery and Management of Hepatozoonosis in Dogs

The triple combination therapy is commonly prescribed for 14 days. By this time, if the dog is responding to therapy, movement and activity should improve as pain recedes. Dogs have used decoquinate therapy for years, and the consensus is that the therapy increases survival time and good quality of life.  It is important to mention that dogs with hepatozoonosis cannot be cured, and management of the disease is a lifelong process.

Prevention of Hepatozoonosis in Dogs

The only effective way to prevent Hepatozoonosis is to prevent your dog from ingesting ticks.  There are many safe and effective tick treatments to ask your veterinarian about that can be administered every 1-3 months.

Other strategies include:

• Using year-round tick control on your dog in endemic areas

• Preventing your dog from eating prey animals outside where ticks are common

• Keeping your house and yard free of ticks (which may require professional pest control assistance)