Update on Canine and Feline Blood Donor Screening for Blood-Borne Pathogens

Wardrop, K.J.; Birkenheuer, A.; Blais, M.C.; Callan, M.B.; Kohn, B.; Lappin, M.R.; Sykes, J.

Anaplasma spp. A. phagocytophilum and A. platys are the causative agents of canine granulocytic anaplasmosis and infectious canine cyclic thrombocytopenia, respectively. Transmission of A. phagocytophilum occurs via Ixodes scapularis and Ixodes pacificus ticks in the United States. Widespread subclinical infections followed by pathogen clearance appear common in both humans and dogs. A further pathway for transmission is via infected blood, either experimentally or by blood transfusion. 3 In human medicine, several reports of transfusion-transmission of A. phagocytophilum via different blood products (non-leukoreduced/leukoreduced RBCs, leukoreduced platelets) and also transfusiontransmitted granulocytic anaplasmosis have been documented. 4,5 Widespread subclinical infections followed by pathogen clearance appear common in both humans and dogs, and in immunocompromised or elderly people such infections can cause severe disease. Donation screening or inactivation by pathogen reduction tech-nologies is considered in human medicine. 5 Anaplasmosis occurred in a splenectomized dog on chemotherapy after a packed RBC transfusion; both the donor and recipient tested positive by PCR (Kohn unpublished data). PCR positive dogs can be seronegative and can have clinical and hematologic variables within reference intervals. 6, 7 Antibodies to Anaplasma species can be detected using IFA assays, automated fluorescencebased systems, a point-of-care lateral flow ELISA assay, a or laboratory-based ELISA assays. b,7,8 Serologic cross-reactivity among Anaplasma species occurs in some assays, but not all ( Table 3 ). The seroprevalence (IFA or ELISA) is high in endemic areas (up to 50%) and antibody titers may persist for several months or even years. 6, 9 The extent to which A. phagocytophilum can persist in tissues and contribute to chronic disease manifestations in humans and dogs currently is unknown. In 1 study, treatment of experimentally infected dogs with prednisolone up to 6 months after infection was followed by development of positive PCR results for the organism, and in some dogs, thrombocytopenia and reappearance of morulae on blood smears. 10 In another study, dogs infected with A. phagocytophilum by exposure to wild-caught Ixodes scapularis ticks were PCR positive for at least 12 weeks. 7 In light of the above information, the panel recommends that optimal standards are to screen donors using both serology and PCR, and dogs that test positive with 1 or both assays should be excluded. Exclusion of all seropositive dogs might limit the donor pool in endemic areas (see comments in Table 1 ).