Comparison of subcutaneous versus intranasal immunization of male koalas (Phascolarctos cinereus) for induction of mucosal and systemic immunity against Chlamydia pecorum

Abstract

Chlamydia pecorum infections are debilitating in the koala, contributing significantly to morbidity and mortality, with current antibiotic treatments having minimal success and adversely affecting gut microflora. This, combined with the sometimes-asymptomatic nature of the infection, suggests that an efficacious anti-chlamydial vaccine is required to control chlamydial infections in the koala. To date vaccination studies have focused primarily on female koalas, however, given the physiological differences between male and female reproductive tracts, we tested the efficacy of a vaccine in 12 captive male koalas. We evaluated the potential of both subcutaneous and intranasal vaccine delivery to elicit mucosal immunity in male koalas. Our results showed that both intranasal and subcutaneous delivery of a vaccine consisting of C. pecorum major outer membrane protein (MOMP) and the adjuvant immunostimulating complex (ISC) induced significant immune responses in male koalas. Subcutaneous immunization elicited stronger cell-mediated responses in peripheral blood lymphocytes (PBL), and greater plasma antibody levels whereas the intranasal immunization elicited stronger humoral responses in urogenital tract (UGT) secretions. This is the first time a Chlamydia vaccine has been tested in the male koala and the first assessment of a mucosal vaccination route in this species. Our results suggest that vaccination of male koalas can elicit mucosal immunity and could contribute to the long-term survivability of wild populations of the koala.