Ehrlichia ruminantium major antigenic protein gene (map1) variants are not geographically constrained and show no evidence of having evolved under positive selection pressure

Abstract

In a search for tools to distinguish antigenic variants of Ehrlichia ruminantium, we sequenced the major antigenic protein genes (map1 genes) of 21 different isolates and found that the sequence polymorphisms were too great to permit the design of probes which could be used as markers for immunogenicity. Phylogenetic comparison of the 21 deduced MAP1 sequences plus another 9 sequences which had been previously published did not reveal any geographic clustering among the isolates. Maximum likelihood analysis of codon and amino acid changes over the phylogeny provided no statistical evidence that the gene is under positive selection pressure, suggesting that it may not be important for the evasion of host immune responses.

FIG. 1

All MAP1 hypervariable regions for isolates in which differences occur. At the bottom of the figure, asterisks denote identical amino acids, colons denote strong amino acid similarity, and periods denote weak amino acid similarity.

FIG. 2

ML tree with bootstrap values of MAP1 sequences from 30 isolates of E. ruminantium. Two names on one branch indicate identical amino acid sequences. Notations in parentheses indicate geographical origins: WA, Western Africa; EA, Eastern Africa; SA, Southern Africa; and Car, Caribbean (French Antilles).