Canine babesiosis was first described in South Africa in the late 1800's and was originally presumed to be a "biliary form" of canine distemper. Most researchers assume that this was actually a case of babesiosis caused by Babesia canis rossi. The first report of canine babesiosis in the United States was made in 1934 and is presumed to have been caused by Babesia canis vogeli. The first report a small Babesia infection in a dog was in 1968. The first case of endemic babesiosis caused by a small piroplasm was in 1979. Since 1991 the number of cases of babesiosis caused by small Babesia spp. in the US has increased dramatically.
ClassificationHistorically Babesia spp. have been named/distinguished based on the vertebrate host infected and on the size of the red blood cell stage of the parasite. More recent molecular investigations have determined that this approach can be misleading, and it is now well accepted that specific DNA testing is the most accurate way to characterize the organisms causing Babesia infections. The majority of cases of canine babesiosis caused by large Babesia spp. in the US have been due to B. canis vogeli. However, molecular testing has identified a novel large Babesia spp. and has not been performed on most cases babesiosis. Therefore it is possible that other existing B. canis subspecies or novel large Babesia spp. that can infect dogs exist in the US. The majority of cases of canine babesiosis caused by small Babesia spp. in the US have been due to B. gibsoni (Asian genotype). At the time of this writing, there are at least nine genetically unique piroplasma that have been identified in the blood of dogs
Clinical signs and laboratory abnormalities
The following observations will pertain primarily to babesiosis in the United States. Lethargy, weakness, anorexia, pale mucous membranes and poor body condition are the most common clinical signs that cause owners to bring their pet to the hospital. Fever, lymphadenomegaly, splenomegaly, jaundice and pigmenturia are less commonly identified signs. Despite severe thrombocytopenia in some cases, petechiae and ecchymoses seem to be rare with babesiosis. Other animals are brought in for testing due to increased owner awareness and pre-breeding screening tests. It is very important to remember that many chronically infected dogs have no detectable physical abnormalities. Babesia infection is sometimes recognized as an incidental finding or is only recognized after immune suppressive therapy or splenectomy. Thrombocytopenia, hyperglobulinemia and anemia are the most common laboratory abnormalities detected. The thrombocytopenia can range from mild to severe, and is absent in some cases. The degree of anemia is variable and may be absent. Some cases present with a PCV of < 10% and others present with a PCV >50%. Most cases have a regenerative anemia at the time of presentation. Hypoalbuminemia, hyperbilirubinemia and pigmenturia are less commonly identified laboratory abnormalities.