Recombinant expression and use in serology of a specific fragment from the Cowdria ruminantium MAP1 protein

Abstract

The major antigenic protein (MAPI) of #Cowdria ruminantium# was screened for immunogenic regions by expression of overlapping recombinant DNA clones of the gene encoding the MAP1 protein. Two regions, designated MAP1-A and MAP1-B, were recognized by all antisera to 9 different isolates of #C. ruminantium#. MAP1 -A contained one or more epitopes responsible for false-positive reactions with #Ehrlichia antisera# in several serological tests for cowdriosis. Cross-reactivity with MAP1-B was limited to antisera to #Ehrlichia chaffeensis# and #Ehrlichia canis#. Antisera to #Ehrlichia# species that infect ruminants (#E. bovis, E. ovina, and E. phagocytophila#) did not recognize MAP1-B. The sensitivity of an indirect ELISA based on MAP1-B was found to be excellent, since all sera from animals experimentally infected with #C. ruminantium# (64 out of 64) reacted with MAP1-B. Validation of this ELISA was carried out with field sera obtained from sheep raised in heartwater-free areas in Zimbabwe and from several Caribbean islands. Only 9 out of II I samples from Zimbabwe, and 1 out of 58 samples from the Caribbean islands, which were considered to be false positives by immunoblot or indirect ELISA, reacted with MAP1-B. Thus, the ELISA based on MAP1-B is at present the most specific and sensitive serological test for cowdriosis