Evidence of Chlamydophila abortus vaccine strain 1B as a possible cause of ovine enzootic abortion

Abstract Chlamydophila abortus , the agent of ovine enzootic abortion (OEA), is a major cause of lamb mortality worldwide. Disease can be controlled through the use of vaccines based on the 1B temperature-sensitive mutant strain of C. abortus . This study investigated suspected OEA cases across Scotland for the presence of the 1B strain by analysis of recently identified unique point mutations (9). Thirty-five cases were C. abortus -positive and 14 came from vaccinated flocks. Analysis of single nucleotide polymorphisms by PCR-RFLP and sequence analysis revealed the presence of point mutations consistent with the presence of the 1B vaccine strain in 5 of these 14 samples. Quantitative real-time PCR revealed comparable numbers of genome copies of the 1B strain in infected placentas to those present following wild-type infection. This study is the first to demonstrate the presence of the 1B vaccine strain in the placentas of OEA cases and suggests a probable causal role in the disease.