Infertility in the female koala (Phascolarctos cinereus)

Abstract

The anatomy of the reproductive tract of the female koala is similar to that of other marsupials in most respects. However, ( i ) the location of the ovary within an ovarian diverticulum and ( i i ) the absence of cranial expansions of the lateral vaginae of the koala are 2 anatomical features of its reproductive tract which differ from that found in most other marsupials. The reproductive pattern in the koala differs from that of al l but one other marsupial in that the gestation period is thought to be longer than the oestrous cycle. Further endocrinological studies of the female koala are required to verify the above statement. Neither a prepartum oestrus nor embryonic diapause have been recorded in the koala. There is also no evidence to suggest that a postpartum oestrus occurs in koalas. In this study, a disease which caused infertility in female koalas was examined. An hypothesis, that a low reproductive rate in some colonies of wild koalas was due to this infertility disease of the female koala, was tested and verified. Chlamydia psittaci was shown to be the aetiological agent responsible for infertility in koalas, and was verified by experimental infections which were carried out in the present study. Investigations of the reproductive status of individuals required the use of serological, radiographic and microbiological techniques. Radiographic and post mortem examinations were performed on adult female koalas in order to assess the prevalence of infertility throughout the range of the koala i. e. 43% of koalas sampled in a total of 8 study sites in 4 States were observed to be infertile. Pathological examination of the reproductive tract of the infertile female koala revealed vaginitis, cervicitis, metritis, salpingitis and ovarian diverticulitis. Such lesions are thought to be due to an ascending chlamydial infection, similar to that recorded for example in women and female guinea pigs with chlamydial genital infections. Chlamydial infertility is only one clinical manifestation of chlamydial infection in the koala. The role of C., psittaci in causing conjunctivitis and infections of the respiratory and urinary tracts was also established during the present study. There is some evidence to suggest that the impact of chlamydial disease may be having currently an effect on the population dynamics of the koala. If this evidence is confirmed in further studies, there is indeed an urgency to understand chlamydial infections in koalas in greater detail.