Photo by Karen James
Hepatozoonosis is a parasitic infection of dogs primarily caused by either Hepatozoon canis or Hepatozoon americanum. The illness is difficult to treat and can be fatal in dogs showing symptoms. Both forms are transmitted from ticks and are debilitating. Without treatment, chronic wasting begins in either form, which usually ends with death within 12 months.
Species of Hepatozoon are protozoans, which are a different kind of infectious organism than bacteria or viruses. Like ameba, protozoans are single-celled parasites that live in the environment. Although both species cause hepatozoonosis, the disease and recommended treatment are different.
People cannot be infected by these protozoa.
Transmission and Infection
Ticks get infected by feeding from a host, and then transmit Hepatozoon protozoans to dogs when the dog ingests them. This is not a disease in which ticks biting the dog make it sick. The tick becomes infected with protozoans after it has a blood meal from an infected animal. This can occur by eating birds or rodents with infected ticks attached, or eating a tick on themselves. Infection does not occur because of a tick bite, and dogs are not infectious to each other.
Hepatozoon protozoans develop to a certain life stage in the tick to allow for infection of another animal. Dogs must eat the infected tick in order to become infected.
Concurrent infection, debilitating disease, immunosuppressant drugs, and young age increase a dog’s chances of becoming infected and having symptoms.
Symptoms of Infection
H. canis and H. americanum have different symptoms, ticks, life cycles, and prevalence. H. americanum comes from dogs eating Gulf Coast ticks, and the brown dog tick conveys H. canis. Many dogs have mild symptoms, or none.
When a dog is infected with H. canis, the protozoans reproduce and develop primarily in organs associated with blood storage (e.g. spleen) or the immune system (e.g. bone marrow, lymph nodes). You may see your dog not wanting to move around, and he may have fever, pale gums and skin, and enlarged lymph nodes. Many infected dogs do not have symptoms. Disease tends to be less severe than with H. americanum. Young dogs less than 18 months of age are most frequently affected by H. canis.
H. americanum protozoans tend to be a far more severe disease that reproduces and develops in muscles, including the heart. Cysts — thick, protective capsules — can form around the organisms, resulting in life-long infections. A dog’s immune system tends to respond more strongly to these protozoans compared to H. canis, leading to severe reactions. The infection can result in symptoms such as pain in the muscle, bone, and/or joints. Infected dogs may limp or be unable to walk, seem painful when touched, run a fever, and lose weight.
A veterinarian will need to examine the dog to note all the physical abnormalities. Blood can be drawn to check immune cells, blood cells, and to make sure the internal organs are working properly. X-rays may help determine the extent of damage and rule out other diseases. Hepatozoonosis can sometimes be diagnosed by blood tests. Examining blood under the microscope can also be helpful for diagnosis. In many cases, a biopsy needs to be taken from infected muscle and examined by a pathologist to determine which protozoan is responsible for the infection.
Treatment is difficult in dogs showing symptoms. Sadly, many dogs cannot be cured. Dogs infected with Hepatozoon organisms can be treated with medications that will decrease the severity of the symptoms, but return of symptoms is common. It’s more difficult to control symptoms in H. americanum than H. canis. Pain medications, blood transfusions, and nutritional or fluid support such as intravenous fluids, syringe feeding, and high calorie diets may be needed for dogs with severe symptoms.
Remember, treatment will not cure your dog, but can make him more comfortable and give him a higher quality of life.
No vaccines are available for hepatozoonosis. The best method for prevention is aggressive, year round tick prevention, as well as keeping your dog from hunting and eating wild rodents or birds (often easier said than done). Treat the yard for ticks if it does not freeze in your climate. Remove ticks quickly from your dog to keep him from eating them.