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Genetic diversity of Chlamydia pecorum strains in wild koala locations across Australia and the implications for a recombinant C. pecorum major outer membrane protein based vaccine

Avinash Kollipara a, Adam Polkinghorne a, Charles Wan a, Pride Kanyoka a, Jon Hanger b, Joanne Loader b, John Callaghan c, Alicia Bell c, William Ellis d, Sean Fitzgibbon d, Alistar Melzer e, Kenneth Beagley a, Peter Timms a,*

a Institute of Health and Biomedical Innovation, Queensland University of Technology, 60 Musk Avenue, Kelvin Grove 4059, Australia

b Endeavour Veterinary Ecology Pty Ltd., 1695 Pumicestone Road, Toorbul 4510, Australia

c City of Gold Coast, City Planning, Nerang, Queensland 4211, Australia

d Sustainable Minerals Institute, The University of Queensland, St. Lucia, Queensland 4072, Australia

e Koala Research Centre of Central Queensland, Centre for Environmental Management, Building 361, Central Queensland University, Bruce Highway, Rockhampton, Queensland 4702, Australia

ABSTRACT

The long term survival of the koala (Phascolarctos cinereus) is at risk due to a range of threatening processes. A major contributing factor is disease caused by infection with Chlamydia pecorum, which has been detected in most mainland koala populations and is associated with ocular and genital tract infections. A critical aspect for the development of vaccines against koala chlamydial infections is a thorough understanding of the prevalence and strain diversity of C. pecorum infections across wild populations. In this study, we describe the largest survey (403 koalas from eight wild populations and three wildlife hospitals) examining the diversity of C. pecorum infections. 181 of the 403 koalas tested (45%) positive for C. pecorum by species-specific quantitative PCR with infection rates ranging from 20% to 61% in the eight wild populations sampled. The ompA gene, which encodes the chlamydial major outer membrane protein (MOMP), has been the major target of several chlamydial vaccines. Based on our analysis of the diversity of MOMP amino types in the infected koalas, we conclude that, (a) there exists significant diversity of C. pecorum strains in koalas, with 10 distinct, full length C. pecorum MOMP amino types identified in the 11 koala locations sampled, (b) despite this diversity, there are predicted T and B cell epitopes in both conserved as well as variable domains of MOMP which suggest cross-amino type immune responses, and (c) a recombinant MOMP-based vaccine consisting of MOMP ‘‘F’’ could potentially induce heterotypic protection against a range of C. pecorum strains.