ELISA techniques developed for the veterinary diagnosis of Rabbit Haemorrhagic Disease (RHD) in domestic rabbits were used for studying the epidemiology of RHD in Australian wild rabbits. The combination of ELISA techniques that distinguished IgA, IgG and IgM antibody responses and a longitudinal data set, mainly based on capture-mark-recapture of rabbits, provided a reliable basis for interpreting serology and set the criteria used to classify rabbits' immunological status. Importantly, young with maternal antibodies, immune rabbits and rabbits apparently re-exposed to RHD were readily separated. Three outbreaks of RHD occurred in 1996-7. The timing of RHD outbreaks was mainly driven by recruitment of young rabbits that generally contracted RHD after they lost their maternally derived immunity. Young that lost maternal antibodies in summer were not immediately infected, apparently because transmission of RHDV slows at that time, but contracted RHD in the autumn when conditions were again suitable for disease spread.

Milk samples were obtained at regular intervals throughout lactation from tammar wallabies (M. eugenii). Total solids represented only 12 % (w/w) of the milk at the commencement of lactation and gradually increased to about 40% at 36 weeks. Milk proteins represented 4% (w/w) of whole milk during the first 18 weeks of lactation, followed by a rapid increase to around 13 % (w/w) at 36 weeks. Sodium and potassium concentrations were high in early samples of milk but declined to minimal values at 30 weeks. The milk was isosmotic to the plasma at all stages.

No abstract

The spread of rabbit haemorrhagic disease (RHD) virus from quarantine on Wardang Island to mainland Australia in 1995 suggested that insects could be potential vectors. Field observations and laboratory experiments were conducted to address aspects of this hypothesis. Firstly, the variation in insect populations on the island during the field trials was examined. There was approximately a 1,000-fold increase in the number of bushflies, Musca vetustissima, shortly before the spread of the virus. Secondly, M. vetustissima were tested in the laboratory as potential vectors of RHD virus, and it was demonstrated that disease could be transmitted between rabbits by flies. Finally, 13 of 16 insect samples, collected from Wardang Island and from several sites on the mainland following the spread of virus off the island, were positive for the presence of RHD virus by a specific polymerase chain reaction (PCR). Only one sample contained sufficient infectious virus to kill a susceptible rabbit. These data, combined with previously published information on fly biology, suggested that flies, particularly bushflies, may be involved in the transmission of RHD virus. Other possible routes of spread were not assessed in this study.

The buccal cavity is modified in young red kangaroos by hemispherical indentations into hard palate and tongue which receive the bulbous swelling at the end of the teat. Attachment to the teat is aided by the formation of ridges on the hard palate and the lateral fusing of the lips of the young. The epiglottis of the young red kangaroo is intra-nasopharyngeal rather than intra-narial as is stated to be the case in other marsupials. Red kangaroos less than 1 day old were removed from the teat to which they had attached and replaced on another teat in the same pouch. A grey kangaroo young aged 13 days was replaced on the teat after removal and was removed and replaced at 7-day intervals thereafter. No difficulty was experienced in replacing 15 young aged between 41 and 100 days on the teats from which they were removed. The following transfers of young less than 1 day old were made: two red kangaroos to foster-mothers of the same species, one red kangaroo to a grey kangaroo, two grey kangaroos to foster-mothers of the same species, one tammar to a red kangaroo, and two swamp wallabies to red kangaroos. All the transfers were initially successful; however, one red kangaroo and one grey kangaroo were lost soon after the transfer, apparently because the foster-parents were at the incorrect stage of their reproductive cycles. The followmg transfers of young 2-25 days old were made to foster-mothers suckling young 2-20 days old: two swamp wallabies to red kangaroos, one red kangaroo to a swamp wallaby, one red kangaroo to a red-necked wallaby, one grey kangaroo to a red kangaroo, one tammar to a red kangaroo, and one red-necked wallaby to a red kangaroo. All the transfers were initially successful except a 13-day-old tammar which failed to attach to the teat of its foster-mother. A swamp wallaby young transferred at the age of 25 days to a red kangaroo showed accelerated growth and early sexual maturity compared to control swamp wallabies raised by their own mothers. A total of 12 inter-species and intra-species transfers of young aged 41-255 days old were made. A 53-day-old young of the yellow-footed rock wallaby failed to attach to the teat of a red kangaroo but all other transfers were initially successful and, in most cases, growth of the foster-young was normal and they were reared to at least the latter stages of pouch life. Young placed in the pouches of foster-mothers were readily accepted and there were indications that the behaviour patterns of the foster-mother were altered so that they responded to calls made by the foster-young. Foster-young of species which have a longer pouch life than the red kangaroo remained in the pouches of red kangaroo foster-mothers for the time usual in their own species. Foster-young transferred to the pouches of other species were usually reared to the end of pouch life if adult sizes of transferred young and foster-mother were nearly equal. Young of small species transferred to the pouches of larger species were often lost before the end of pouch life.