Hepatozoonosis (Tick-Borne Disease) in Dogs

Key Takeaways

Hepatozoonosis is a tick-borne protozoal infection in dogs. 

• Dogs are exposed to the parasite when they ingest infected ticks, either directly or by consuming tick-infested prey animals.

• Canine hepatozoonosis is rarely diagnosed.

• Dogs who frequently get ticks have a higher chance of infection.

• Symptoms of infection include pale gums, limping, inability to walk, and pain. 

• Diagnostics include blood work, x-rays, and in some cases a muscle biopsy

• Hepatozoonosis is prevented by minimizing exposure to ticks and opportunities to eat tick-infested prey

A Closer Look: What is Hepatozoonosis in Dogs?

Unlike other types of tick-borne illness, hepatozoonosis is caused by exposure to the protozoan species Hepatozoon americanum or Hepatozoon canis. The infection is not transmitted by tick bites; dogs are only exposed when they eat infected ticks. Infection caused by H. americanum is more severe than H. canis. Some dogs may not present with symptoms at all. Some cases lead to death.  Not all infected dogs develop symptoms.

Risk Factors

Hepatozoonosis is of grave concern since it is a debilitating and potentially fatal disease that is spread by ticks. If a dog is not exposed to ticks or does not eat tick-infested prey then there is little cause for concern.

The geographic range of the disease is limited to areas with large populations of the Brown Dog Tick and Gulf Coast Tick. This is currently primarily the Atlantic coast, Southeast, California, and the Pacific Northwest in the US. Dogs exposed to ticks in these regions are at risk for this rarely diagnosed but debilitating and potentially fatal disease.

Dogs who are maintained on veterinarian-approved tick control products are unlikely to contract hepatozoonosis. It is important to note that Hepatozoonosis is not caused by a tick bite and cannot be passed from dog to dog or dog to human.

Possible Causes

Hepatozoonosis results from ingestion of an infected tick or other prey-like animals (i.e. rodents or birds) that have infected ticks on them or in their tissues.

Main Symptoms

The main symptoms differ between the two types of protozoa. 

Gulf Coast Ticks become infected with H. americanum and the symptoms that present are as follows:

• Muscle pain • Bone/Joint pain • Lameness • Painful reaction to being touched • Weight loss

The Brown Dog Tick becomes infected with H. canis and the symptoms that present are as follows:

• Pale gums • Limited mobility • Enlarged lymph nodes

Hepatozoonosis may also cause: 

• Joint swelling • Diarrhea • Jaundice • Nasal discharge • Paralysis

Testing and Diagnosis

Dogs with symptoms consistent with hepatozoonosis typically undergo bloodwork and x-rays. The organism that causes hepatozoonosis is visible on blood smears examined under a microscope. PCR assays and muscle biopsies are additional specific diagnostic tests. A confirmed diagnosis of hepatozoonosis may not be made until a necropsy is performed on a deceased dog.

Steps to Recovery

Symptoms and pain are managed by the use of medications, anti-inflammatories for fever and pain, intravenous (IV) fluids, syringe feeding, blood transfusions, and high calorie diets. Antiprotozoal medications are given to eliminate the infection. 

Complete cure for hepatozoonosis is rare. The duration of treatment varies depending on the species of protozoan. Most patients do not fully clear the infection, and the goal of therapy is the reduction of clinical signs and to increase the quality of life.

Prevention

Hepatozoonosis is not contagious and cannot spread from dog to dog or dog to human. It is acquired from the ingestion of an infected tick or ingestion of a prey-like animal that has an infected tick on it. Since Hepatozoonosis is acquired through the ingestion of infected ticks, the disease can be prevented by the use of veterinarian approved tick control products as well as treating the yard for ticks. Daily inspection of dogs for ticks and prompt removal are additional preventive strategies for minimizing the likelihood of tick consumption.

Is Hepatozoonosis Common in Dogs?

Hepatozoonosis is more common in dogs that reside in areas that have a higher population of Brown Dog Ticks or Gulf Coast Ticks, as well as dogs that consume tick-infested prey in those regions.

Typical Treatment

Typical treatment consists of antiprotozoal medications, pain management, high calorie diets, blood transfusions and nutritional/ fluid support either by syringe feeding or IV fluids.