Effects of phenol on card-agglutination and complement-fixation tests for bovine anaplasmosis

Effects of adding phenol to sera used for the card-agglutination test (CAT) and for the micro-complement-fixation test (CFT) for bovine anaplasmosis were studied. Sera were obtained from 14 recently infected cattle, 17 cattle vaccinated with a killed anaplasmosis vaccine, 5 cattle in the carrier phase of the disease, and 45 cattle of unknown anaplasmosis status. Aliquots of sera were tested with and without phenol (0.25% final concentration). Phenol adversely affected the CAT by causing false-negative results. The CAT reactions of nonphenolized sera from recently infected cattle were all positive 4 weeks after inoculation, whereas CAT reactions of phenolized sera were not all positive until 10 weeks after inoculation. Nine non-phenolized sera from vaccinated cattle that were CAT-positive were CAT-negative after being phenolized. Phenolized sera from carrier cattle and from cattle of unknown anaplasmosis status were less reactive on the CAT than were nonphenolized sera. Effects of phenol on the CFT were not so obvious. Although phenol had little effect on end-titer results, it eliminated most prozones that cause false-negative CFT results at the 1:5 dilution. Without phenol, 30 of 215 sera would have been CFT-negative at this dilution because of prozones; with phenol, 6 would have been CFT-negative.