Persistence of Anaplasma ovis infection and conservation of the msp-2 and msp-3 multigene families within the genus Anaplasma

Goats which have recovered from acute Anaplasma ovis infection remain serop ositive, although infected erythrocytes cannot be detected by microscopic e xamination Persistence of A. ovis 17 to 21 months following experimental in fection was demonstrated by PCR detection of the msp-5 gene. Quantitative a nalysis of persistent rickettsemia over time showed that all levels were be low the limit of microscopic detection and ranged from a low of 10(2) organ isms/ml to peaks of 10(6) organisms/ml. Two patterns of persistent ricketts emia were observed: the first was characterized by cyclic fluctuations at 6 - to 9-week intervals, similar to the pattern described for A. marginale-in fected cattle, while in the second pattern, repetitive cycles did not occur and the rickettsemia levels were relatively constant. The msp-2 and msp-3 multigene families. which provide the genetic capacity for outer membrane p rotein antigenic variation during persistent A. marginale rickettsemia, wer e identified in the A. ovis genome by Southern blot analysis, and expressio n of an MSP-2 homologue was confirmed by using immunoblots.