Hepatozoonosis in a dog
Sarah Eide and Julie Piccione, DVM, MS, DACVP
An 11-month-old Bloodhound dog presented to an east Texas veterinary clinic with a 2-week history of lethargy, painfulness, and losing muscle mass. Vital signs included a temperature of 104°F, pulse 160 bpm, pink mucous membranes, and capillary refill time of more than two seconds. The fecal exam indicated a severe hookworm infestation. An in-house CBC indicated a slight anemia, but an error message prevented the clinic from obtaining an accurate WBC count. The veterinarian forwarded the CBC to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL).
The Advia 120 hematology analyzer was able to report a WBC count of 160.0 K/µL (reference interval 6.0 – 17.5 K/µL). While performing a microscopic exam of the peripheral blood smear, rare gamonts were noted within WBCs (Figure 1).
Figure 1. One of several rare gamonts noted in WBC.
These gamonts were consistent with Hepatozoon spp. Hepatozoon spp. are protozoal parasites in the same family as Babesia and Plasmodium spp. There are two species present in the United States – H. canis, also known as Old World Hepatozoon, and H. americanum, or New World Hepatozoon. The ticks responsible for transmission are Amblyomma maculatum, the Gulf Coast tick (transmits H. americanum) and Rhipicephalus sanguineous, the Brown Dog Tick (transmits H. canis).
H. americanum causes severe illness, including muscle wasting, lethargy, mild anemia, and fever. Conversely, H. canis can be found incidentally when examining a dog for something totally unrelated.
On CBC findings, extremely elevated WBC counts are seen with rare parasitemia (less than 0.1% of circulating WBCs). This is a tick-borne disease, however it is not the tick bite that transmits the organism. The animal becomes infected after ingesting the tick while grooming or eating a carcass of a tick infested animal, such as a rabbit. This disease is found most commonly in hunting dogs, rural dogs, and dogs that are mainly outdoor animals.
There is a PCR test available, however finding the organisms on a peripheral blood smear may be accomplished by careful scrutiny and preparing a WBC buffy coat smear.
In the past, many of these infected dogs were euthanized. There are reports of an effective treatment protocol that must be maintained for the dog’s life, but allows the pet to live a relatively normal existence.
For more information about this case, contact Sarah Eide, clinical pathology assistant section head, or Dr. Julie Piccione, clinical pathology section head. To learn more about TVMDL’s test offerings and services, visit tvmdl.tamu.edu or call 1.888.646.5623.