Abstract
Vaccination strategies provide a crucial tool for managements of disease risks in wildlife, but have been utilized mostly for domestic species. However, a significant body of work has now been published describing the successful development of an anti-chlamydial vaccine for the koala Phascolarctos cinereus, Goldfuss, 1817. As such, vaccinations against these infections in the koala, can provide important insights into the use of vaccines for wildlife. Chlamydia infections in the koala have been intensively studied for over 30 years. Infections cause severe disease states, such as kerato-conjunctivitis (blindness) and reproductive tract disease (infertility), and/or mortality; and are contributing significantly to population declines. We aim to use the plethora of data available from koala chlamydial studies as a template to propose a roadmap for the development of vaccines for other wildlife species, especially in this era of antibiotic resistance. As such we have outlined the important steps that have led to significant milestones resulting in the successful development of a vaccine against an infectious disease in a non-domestic species. We hope to thus provide, not only a timely review on Chlamydia vaccines in koalas, but also an important conservation and management roadmap to help guide future researchers that are considering the development of a vaccine for a wild species.
Highlights
Optimization of the antigenic propertiesOne of the major decisions in the development of vaccines is the choice of antigen. Chlamydial studies in the mouse model had previously shown that the chlamydial major outer membrane protein (MOMP) was a major component of the chlamydial surface, highly immunogenic and could provide a level of immunity against live challenge (Brunham and Rey-Ladino 2005)
In the past two decades there has been an increase in the emergence of infectious diseases in wildlife
Evaluation of a novel one-dose adjuvant (Tri-Adj). The results of these initial C. pecorum vaccine trials had shown that a vaccine consisting of 3rMOMP (A, F and G) proteins combined with ISC adjuvant, given sub-cutaneously as a three-dose vaccination schedule, was: 1) safe to administer to both healthy and clinically diseased koalas; 2) led to the development of specific humoral and cell-mediated immune responses, and 3) elicited a therapeutic effect on animals already infected (Nyari et al 2019)
Summary
One of the major decisions in the development of vaccines is the choice of antigen. Chlamydial studies in the mouse model had previously shown that the chlamydial MOMP was a major component of the chlamydial surface, highly immunogenic and could provide a level of immunity against live challenge (Brunham and Rey-Ladino 2005). There was evidence that a single MOMP genotype could produce cross-reacting antibodies against other MOMP proteins (Kollipara et al 2012), the degree of cross-reactivity achievable throughout different locations was obviously essential for developing an optimal Chlamydia vaccine capable of producing widespread protective immunity. Despite the diversity seen between strains of koala C. pecorum, rMOMP was chosen by Kollipara et al (2012) as the vaccinating antigen and evaluated in a series of trials. The single ‘G’ variant of rMOMP was used (Kollipara et al 2012), but subsequently a multiple subunit vaccine containing a combination of rMOMPs e.g. A, F and G (the most prevalent variants found in circulation in wild koalas) was evaluated. Kollipara et al (2013b) assessed the cross-protective ability of three C. pecorum rMOMP genotypes (A, F and G), combined with ISC adjuvant, in a vaccine trial of healthy, captive female koalas. A formulation of three rMOMPs (3rMOMP) A, F and G, was selected for downstream evaluations
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