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.

Culture. Positive blood culture results indicate the presence of cultivable bacteria in the blood. Although transient bacteremia can occur in healthy animals after disruption of mucosal barriers, transfusion of blood from animals with transient bacteremia has not been documented to cause disease in a recipient. Therefore, routine blood culture generally is not indicated for screening potential blood donors, with rare exceptions (see Bartonella section). In transfusion medicine, routine Serum Antigen Tests. Assays that detect antigens of several blood-borne pathogens in whole blood or serum are commercially available. Dirofilaria immitis (dogs and cats) and feline leukemia virus (FeLV) antigen tests are used most frequently for donor screening and health assessment. Point-of-care tests are available for both organisms, and the potential for inaccurate results from operator error is small. Molecular Assays. Because the immune system generally clears nonviable microbes quickly, amplification of specific microbial nucleic acids using assays like polymerase chain reaction (PCR) generally indicates the presence of viable microbes, provided laboratory quality assurance is high. These techniques can provide high analytic sensitivity and specificity and the potential to rapidly test for more than 1 pathogen. Disadvantages include the current lack of point-of-care nucleic acidbased assays in veterinary medicine; lack of standardization of assays among laboratories, which results in variable sensitivities and specificities; lack of assay availability for some infectious agents; and expense. Also, high analytical sensitivity of a PCR assay does not necessarily imply high clinical sensitivity. In other words, an assay may detect minute quantities of DNA in the laboratory but have poor sensitivity for detection of a pathogen in a blood specimen. Most PCR assays utilize 10-200 lL of blood, and animals can receive over 10,000 times that volume during a transfusion. Although most molecular assays have high analytical sensitivity, these assays cannot amplify microbes that are not in the specimen collected; thus, false negative results can occur with some agents found in very low quantities in the bloodstream, such as Ehrlichia canis and feline immunodeficiency virus (FIV).