Chlamydia pecorum: successful pathogen of koalas or Australian livestock?

Abstract

In Australia, the obligate intracellular bacterium Chlamydia pecorum is best known as the notorious koala pathogen that causes debilitating ocular and urogenital tract disease.While globally published data suggests that this species is essentially ubiquitous in livestock, little is known about the epidemiology of livestock C. pecorum infections here in Australia. My research is focused on investigating the genetic diversity and transmission patterns of C. pecorum, and why it causes disease. Using our newly developed C. pecorum-specific molecular epidemiology typing scheme we provided the first epidemiological data on infections in sheep and cattle in Australia, identifying strains associated with a range of diseases in livestock, and uncovering an unexpected level of diversity for this pathogen.Most importantly, we observed that the same strain can infect koala and sheep, indicating on ongoing cross-host transmission and 'spill-over' risks to wildlife. Further, by dissecting koala, sheep, cattle and pig C. pecorum strains genomes, we have also identified novel virulence-associated factors that could be explored as vaccine candidates for both livestock and koala infections.Chlamydiae, known for their obligatory parasitic lifestyle and distinct biphasic life-cycle 1 , are diverse and enigmatic bacteria that infect an astonishing range of hosts 2 . This phylum includes Chlamydia pecorum, a species that constantly remains in the spotlight due to its role as a major threat to the survival of the iconic koalas. In koalas, highly prevalent C. pecorum infections cause ocular disease that can eventually lead to blindness, and urogenital disease that can lead to infertility 3,4 . The pathogenic potential of C. pecorum in economically significant livestock species (cattle, sheep, goats and pigs) has been well documented in Europe and USA, and to a lesser degree elsewhere including The curious case of Chlamydia pecorum infections in AustraliaWhile the koala chlamydial infections are easily the most intensively studied of any wildlife species, almost nothing is known about the prevalence and epidemiology of C. pecorum infections in Australian livestock. Veterinarians from agriculturally productive areas throughout Australia regularly report cases of chlamydiosis in sheep and cattle 8,9 , but the information about the genetic diversity of strains infecting livestock is lacking. A range of previous molecular studies suggested that C. pecorum strains infecting koala are genetically diverse 10,11 ; however, none of the studies investigated how and whether these strains are related to livestock strains. It has been hypothesised that the origin of koala C. pecorum infections is associated with the import of 'presumably C. pecorum infected' livestock in the late 1780s 3 . The encroachment of koala habitats by sheep and cattle farming along the east coast of Australia is common and raises serious questions over the relationships and potential role that cross-host transmission may have in the epidemiology and origin of chlamydial di...

Chlamydia pecorum–Associated Sporadic Ovine Abortion

“…34 MLST has demonstrated that multiple genetically distinct C. pecorum genotypes are present in both healthy and diseased sheep and cattle, sometimes varying by anatomical site. 15,17,18 The genotype of C. pecorum found in all 3 fetuses was determined to be ST23, which has been previously associated with multiple disease states in different hosts, including ovine polyarthritis and conjunctivitis, and sporadic bovine encephalomyelitis in cattle in Western Australia, the United States, and England. [15][16][17][18]39 Although not pathognomonic, gross placental lesions were consistent with findings in experimental ovine C. pecorum abortion following intravenous inoculation, 30 and gross and histologic findings with natural caprine C. pecorum abortion.…”

“…MLST has demonstrated that multiple genetically distinct C. pecorum genotypes are present in both healthy and diseased sheep and cattle, sometimes varying by anatomical site. 15,17,18 The genotype of C. pecorum found in all 3 fetuses was determined to be ST23, which has been previously associated with multiple disease states in different hosts, including ovine polyarthritis and conjunctivitis, and sporadic bovine encephalomyelitis in cattle in Western Australia, the United States, and England. 15 –18,39…”

“…15,17,18 The genotype of C. pecorum found in all 3 fetuses was determined to be ST23, which has been previously associated with multiple disease states in different hosts, including ovine polyarthritis and conjunctivitis, and sporadic bovine encephalomyelitis in cattle in Western Australia, the United States, and England. 15 –18,39…”

“…Chlamydia pecorum is globally distributed and occurs in many species, including sheep, goats, cattle, pigs, chamois, alpine ibex, birds, and marsupials, including the highly susceptible koala. 6,7,17,39 C. pecorum has an estimated prevalence in lambs ranging from 17% to 50% in Australia and 12% to 26% in the United Kingdom. 40,41 A far greater prevalence of 96% was detected in one Australian study, which performed repeated bimonthly sampling in clinically normal lambs from New South Wales.…”

“…6 In lambs, C. pecorum infection can manifest clinically as keratoconjunctivitis and arthritis, whereas young cattle can develop sporadic bovine encephalomyelitis. 15,17,39,40…”