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Babesiosis in Dogs

Babesiosis is the diseased state caused by the protozoal (single celled) parasites of the genus Babesia. Infection in a dog may occur by tick transmission, direct transmission via blood transfer from dog bites, blood transfusions, or transplacental transmission. The most common mode of transmission is by tick bite, as the Babesia parasite uses the tick as a reservoir to reach host mammals. The incubation period averages about two weeks, but symptoms may remain mild and some cases are not diagnosed for months to years. Piroplasms infect and replicate in the red blood cells, resulting in both direct and immune-mediated hemolytic anemia, where the red blood cells (RBCs) are broken down through hemolysis (destruction) and hemoglobin is released into the body. This release of hemoglobin can lead to jaundice, and to anemia when the body cannot produce enough new red blood cells to replace the ones being destroyed. Immune-mediated hemolytic anemia is likely to be more clinically important than parasite-induced RBC destruction, since the severity of the condition does not depend on the degree of parasitemia.

Dogs that spend a lot of time outdoors, especially in wooded areas, at at an increased risk for tick bites and for contracting this parasite. This is especially true in the summer months, from May through September, when tick populations are highest. Being vigilant about tick prevention and removal is the best method for avoiding the onset of Babesiosis.

• B. canis — A large (4–7 µm) piroplasm that infects dogs, B. canis is distributed worldwide, and there are 3 subspecies based on genetic, biologic, and geographic data. B. canis vogeli has been reported in the U.S., Africa, Asia, and Australia. B. canis rossi is the most virulent and is present in Africa. B. canis canis has been reported in Europe.
• Recent studies have identified at least three genetically distinct small (2–5 µm) piroplasms that can infect dogs.
• B. gibsoni — small piroplasm that infects dogs; worldwide distribution; emerging disease in the U.S.
• B. conradae — small piroplasm that infects dogs; only reported in California
• Theileria annae (Spanish dog piroplasm) — small piroplasm that infects dogs; reported in Spain and other parts of Europe
• Babesia sp. (Coco) — large piroplasm identified in dogs with a surgically removed spleen, and immune suppressed dogs in the U.S.

Symptoms and Types

• Lack of energy
• Lack of appetite
• Pale gums
• Fever
• Enlarged abdomen
• Colored urine
• Yellow or orange skin
• Weight loss
• Discolored stool

Causes

• Background history of tick attachment
• Immune suppression may cause clinical signs and increased parasitemia (parasite infection in the blood) in chronically infected dogs
• History of a recent dog-bite wound
• Recent blood transfusion

Diagnosis

You will need to give a thorough history of your dog's health, including a background history of symptoms, and possible incidents that might have precipitated this condition. Your veterinarian will perform a complete physical exam on your dog. A blood chemical profile, a complete blood count, a urinalysis and an electrolyte panel will be conducted.

Your veterinarian may use a Wright’s stain to stain a blood sample for microscopic examination, since this will allow for your doctor to distinguish blood cells, making an infection of the blood more readily apparent. Immunofluorescent antibody (IFA) tests for antibodies in the serum that react with Babesia organisms may also be performed. Cross-reactive antibodies can prevent the differentiation of species and subspecies. However, some infected animals, particularly young dogs, may have no detectable antibodies.

PCR (polymerase chain reaction) tests for the presence of Babesia DNA in a biological sample can differentiate subspecies and species and are more sensitive than microscopy.