The effect of Chlamydia infection on koala (Phascolarctos cinereus) semen quality.

Abstract Although it is well established that chlamydial disease renders female koalas infertile, there has been limited research on its effects on male koala fertility, specifically sperm quality. This study determined whether chlamydial infection adversely affects semen quality of naturally infected koalas and spermatozoa recovered from Chlamydia negative koalas co-incubated in vitro with C. pecorum elementary bodies (EBs). Semen from 102 south-east Queensland sexually mature wild koalas exhibiting varying degrees of chlamydiosis and clinical signs of disease were assessed for semen quality and compared to 11 clinically healthy, Chlamydia-free captive male koalas. For in vitro studies, semen samples were collected from 6 Chlamydia-free captive koalas, and co-incubated over 24 h with high and low concentrations of C. pecorum EBs and sperm quality assessed. Wild koalas displaying severe signs of clinical disease with C. pecorum present in the semen had significantly greater sperm DNA damage (P = 0.0267). The total % of morphologically abnormal spermatozoa was highest in wild koalas that had severe signs of clinical disease but whose semen was negative for C. pecorum (P = 0.0328). This apparent contradiction is possibly associated with wild males having resolved the infection but still possessing underlining reproductive pathology. A higher incidence of loose head spermatozoa occurred in semen of wild koalas not infected with C. pecorum compared to those that were C. pecorum infected (P = 0.026). In vitro incubation of semen with C. pecorum significantly decreased sperm motility and viability over 24h.