Veterinary Science - Theses
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ItemAn investigation of two significant infectious diseases in populations of Victorian koalas (Phascolarctos cinereus)( 2017)The koala (Phascolarctos cinereus), an iconic Australian marsupial, is considered a vulnerable species in parts of Australia due to recent rapid population declines. The role of infectious diseases in population declines in northern koalas (New South Wales (NSW) and Queensland populations) has been highly studied. Chlamydia pecorum and koala retrovirus (KoRV) have both been given considerable attention. C. pecorum in koalas is associated with infertility and blindness through infection of the urogenital tract and conjunctiva, respectively. The prevalence of C. pecorum in northern koalas is as high as 87%. Different genotypes of KoRV have been identified in northern koalas. KoRV-A has been identified in all northern koalas tested to date. KoRV-B appears to be less prevalent but has been implicated as a cause of neoplasia. Molecular testing of C. pecorum and KoRV prevalence in Victoria, a southern population of koalas, has been limited. No genotyping studies have been undertaken on either organism in Victorian koalas. This thesis conducted an extensive survey of Victorian koalas across seven separate regions to establish a prevalence estimate for both C. pecorum and KoRV. A genotyping study for each pathogen was also completed. The estimated prevalence of C. pecorum in Victorian koalas was 15.2% (125/820, 95% confidence interval (CI) 12.9, 17.9%). Molecular evidence of C. pecorum infection in French Island koalas was detected for the first time. Only a single ocular C. pecorum infection was identified in Victorian koalas (1/459). A total of six C. pecorum genotypes were detected, the majority of which were genotype B, which has only been detected in southern koalas. Three of the genotypes were novel, each of which were found in distinct populations. Male koalas were more likely to be infected than females. C. pecorum infection was associated with ‘wet bottom’ (a sign of urinary incontinence and inflammation) in male koalas and reproductive tract disease in female koalas. Not all koalas with ‘wet bottom’ had detectable C. pecorum, suggesting another potential cause. Analysis of the genetic diversity of the bacteria present in urogenital tract samples from ten koalas, of which only five displayed wet bottom, identified 13 operational taxonomic units that occurred at a higher abundance in wet bottom-affected koalas. These bacterial families are of interest for future studies. The genomes of 57 C. pecorum samples from koalas across Australia were sequenced and assembled. The results showed that C. pecorum genomes from southern koalas were distinct from those of northern koalas. KoRV prevalence in Victorian koalas was 24.7% (160/648, 95% CI 21.5, 28.2%). Only KoRV-A was detected. Koalas with ‘wet bottom’ were almost twice as likely to have KoRV detected. There was no association between KoRV and C. pecorum detection. This research highlights that Victorian koalas are experiencing a reduced burden of infection compared to northern koalas, and this may be a factor in southern populations outgrowing the available habitat resources in Victoria, compared to northern populations. Victorian koalas free from C. pecorum and KoRV infection could be sourced from over-abundant populations to assist re-establishment of populations where koalas have become locally extinct. Overall, this research provides valuable information for both future research and koala population management.
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ItemInvestigations into pathogens of potential public health and biosecurity significance in Australian native birds( 2016)Pathogens of potential public health and/or biosecurity significance in Australian birds were investigated by screening samples collected from 409 birds presented to the Australian Wildlife Health Centre (AWHC) at Zoos Victoria’s Healesville Sanctuary for veterinary care between December 2014 and December 2015. Samples were tested for the presence of Salmonella, Campylobacter, Yersinia, Chlamydia psittaci, avian influenza viruses (AIVs), avian herpesviruses, Beak and feather disease virus (BFDV), avian paramyxoviruses and avian coronaviruses, using a combination of bacterial culture and genus- or family-wide PCR methods coupled with sequencing and phylogenetic analyses for detection and identification of both known and novel microorganisms. A low prevalence of pathogens was detected, with the exception of BFDV, which was detected from 43.8% of 210 birds sampled at post-mortem. BFDV was considered the greatest biosecurity threat to other birds at Healesville Sanctuary, particularly to threatened psittacine species for which the Sanctuary has captive breeding programs, namely the Orange-bellied parrot (Neophema chrysogaster). The findings suggest that BFDV is more common in non-psittacine species than previously recognised, with BFDV DNA being detected from 27.6% of non-psittacine birds tested, even from species with no clear ecological association with psittacines, and without showing any characteristic clinical signs of BFDV infection. BFDV DNA was also detected at 60% prevalence from psittacine birds sampled at post-mortem, in the majority of cases without exhibiting any clinical signs of BFDV infection. These findings suggest that every bird should be considered a potential carrier of BFDV, regardless of species and clinical presentation. Campylobacter spp. were detected at a prevalence of 21.5%, but it was determined that these bacteria exhibit a pattern of avian host-specificity, are part of the normal commensal intestinal flora and are unlikely to pose a significant zoonotic risk. Although Chlamydia psittaci was only detected from 0.67% of the wild birds and 3.64% of the captive birds sampled, its potential to cause outbreaks as well as severe or even fatal psittacosis in humans after zoonotic transmission means C. psittaci presents the most significant public health risk within the AWHC. Yersinia, AIVs and avian coronaviruses were not detected at all amongst Victorian birds. Salmonella was detected at extremely low prevalence, and a single case of Columbid herpesvirus 1 infection was detected from a Powerful owl (Ninox strenua). Three novel viruses were detected: an avian paramyxovirus from a Musk lorikeet (Glossopsitta concinna), and two avian herpesviruses from a Sulphur-crested cockatoo (Cacatua galerita) and a Tawny frogmouth (Podargus strigoides), which have been named Cacatuid herpesvirus 1 and Podargid herpesvirus 1 respectively. The clinical significance of these novel viruses remains undetermined. It is recommended that the AWHC consider the use of a disinfectant that is effective in inactivating the non-enveloped and extremely resistant circoviruses (e.g. Virkon®S, with main ingredient the oxidising agent peroxymonosulphate), to disinfect all exposed surfaces between examinations of all birds. This should also provide sufficient disinfection for control of C. psittaci and other zoonotic pathogens. These recommendations extend to all veterinary clinics and wildlife rehabilitation facilities that care for birds that are susceptible to PBFD.