Association of Vectorial Infectious Diseases with Immune-Mediated Anemia in the Dog: 40 Cases
Immune-mediated anemia (IMA) in the dog is usually identified as primary (i.e., idiopathic), because etiology is not known in most cases. Infectious diseases, especially those with vectorial transmission, are frequently quoted as probable causes of IMA. The purpose of this study is to evaluate the incidence of vectorial infectious diseases, particularly tick-transmitted diseases, among potential causes of IMA.
Forty French dogs were included between September 2005 and April 2007. Inclusion criteria were the existence of an anemia (hemoglobin < 12 g/dL), and the identification of the immune origin of this anemia: positive direct Coombs' test (DCT) (threshold of 1/8) and/or in-saline agglutination and/or marked spherocytosis. The following analyses were performed: complete hemogram, DCT at 37°C (N = 35) and at 4°C (N = 17), antinuclear antibodies (N = 6) and myelogram in case of persistent nonregenerative anemia (N = 12). For each dog, presence of or exposure to several tick-transmitted pathogens was evaluated: Ehrlichia canis (serology and PCR), Anaplasma phagocytophilum (serology and PCR), Rickettsia spp. (PCR), Bartonella spp. (PCR) and Babesia spp. (blood smears). Exposure to the following infectious agents was assessed in accordance with diagnostic suspicion: Leishmania infantum, Leptospira interrogans, Borrelia burgdorferi and Neospora caninum. Moreover, diagnostic imaging and biochemical analyses were performed if anomalies were detected during physical examination.
Anemia was generally moderate to severe, and nonregenerative in 16 cases. Thrombocytopenia was present in 22 dogs, and leukocytosis in 21 dogs. Direct identification and serology allowed identification of vectorial infectious diseases in 11 cases (27,5%): 7 babesiosis, 4 monocytic ehrlichiosis, 1 granulocytic anaplasmosis and 1 leishmaniosis (2 cases of co-infections: babesiosis and monocytic ehrlichiosis, monocytic ehrlichiosis and granulocytic anaplasmosis). No pathogen was identified using myelogram. All PCR assays were negative. Antinuclear antibodies were positive in 2 cases. Leptospirosis was identified in 2 cases and non-infectious disease in 3 last cases (hemangiosarcoma, malignant histiocytosis and bullous pemphigoid). No concomitant affection was identified in 24 dogs (60%).
This study confirms the predominance of idiopathic immune anemia and the relevance of the direct Coombs' test for their diagnostic. Unlike others, who find that neoplasia is the most common cause of secondary IMA, this study shows that infectious disease, especially tick-transmitted disease, is the first type of concomitant affection with IMA. Geographical location could be one of the explanations. Nevertheless, routine assays to evaluate exposure to vectorial diseases are useful for treatment. This study also points out the complementarity of direct and indirect diagnostic techniques for infectious origin, especially in cases of early anti-infectious treatments.