Monitoring the spread of myxoma virus in rabbit Oryctolagus cuniculus populations on the southern tablelands of New South Wales, Australia. III. Release, persistence and rate of spread of an identifiable strain of myxoma virus

An identifiable strain of myxoma virus was introduced into four local populations of wild rabbits Oryctolagus cuniculus on the southern tablelands of New South Wales (NSW) and its spread in the presence of other field strains was monitored for 6 months. The main vector in this region was considered to be the European rabbit flea Spilopsyllis cuniculi. Each population of rabbits was of a high density and living in groups of warrens covering areas from 59 to 87 hectares. Rabbits occupying centrally located warrens were inoculated with the virus in late September or early October (spring) and the subsequent appearance of myxomatosis across the sites monitored by trapping, shooting and visual observations. Samples, taken from rabbits with myxomatosis, were examined by polymerase chain reaction (PCR) that allowed identification of the introduced strain. On all four sites the introduced virus spread from the inoculated rabbits in the centrally located warrens to rabbits in surrounding warrens. On Sites 1 and 3, this spread continued across the entire site persisting for at least 118 and 174 days respectively. On Sites 2 and 4, the virus was detected for 78 and 62 days respectively and the subsequent inability to detect the introduced virus correlated with the appearance of an unrelated field strain. Using three different methods of calculation, rates of spread ranged from 3.7 to 17.8 m d(-1).

Monitoring the spread of myxoma virus in rabbit Oryctolagus cuniculus populations on the southern tablelands of New South Wales, Australia. II. Selection of a strain of virus for release

To be able to study the dynamics of myxoma virus spread following a release in the field, a strain of virus is required that is both highly transmissible and readily differentiated from other field strains. Eight strains of virus of known virulence for laboratory rabbits and with previously mapped and sequenced restriction fragment length polymorphisms, were used to infect groups of seronegative wild rabbits. Based on these trials, and on the nature of the DNA polymorphism, a virus designated Brooklands/2-93 was chosen as a strain suitable for experimental release. These trials confirmed that resistance to myxomatosis within wild rabbit populations continues to be substantial and that some rabbits are highly resistant. These rabbits probably have little role in transmission of virus. Most of the virus strains tested induced very small or invisible primary lesions at the inoculation site. Thus the secondary skin sites such as eyelids, face and ears may be critical for transmission.

Monitoring the spread of myxoma virus in rabbit Oryctolagus cuniculus populations on the southern tablelands of New South Wales, Australia. I. Natural occurrence of myxomatosis

A survey of rabbit populations in the southern tablelands of New South Wales, Australia, was carried out to establish the pattern of occurrence of myxomatosis in preparation for a deliberate release of myxoma virus. Myxomatosis was first detected in December and cases were found on most sites through to May. The serological profiles of rabbit populations suggested that their susceptibility to myxoma virus was generally low in winter and highest in spring and summer reflecting the presence of increasing numbers of susceptible young rabbits. This was consistent with the pattern of rabbit breeding, as determined from the distribution of births and reproductive activity in females and males, which occurred maximally in spring and early summer. The serology and age structure of rabbit populations on sites suggested that some rabbit populations can escape an annual myxomatosis epizootic. Although fleas were present on rabbits throughout the year and therefore not considered to be a limiting factor in the spread of myxomatosis, their numbers peaked at times coincident with peak rabbit breeding. It was concluded that mid to late spring was an optimal time for a deliberate release.

Evidence for insect transmission of rabbit haemorrhagic disease virus

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.

Use of ELISAs in field studies of rabbit haemorrhagic disease (RHD) in Australia

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.

In vivo effects of epidermal growth factor on epidermal pattern formation and hair follicle initiation in the marsupial bandicoot Isoodon macrourus

The extrauterine development of marsupial pouch young (northern brown bandicoot Isoodon macrourus) has facilitated the study of the effects of murine epidermal growth factor (mEGF) on pattern formation in skin. Hair follicle initiation and development, which in the mouse would occur from about Days 13-14 of gestation onward, occurs postnatally. In the present study the effect in vivo of mEGF on developing skin corresponding to mouse gestational ages from Day 13 onward was examined. Subcutaneous injections of mEGF (0.5, 1.0 and 2.0 microg g[-1] body weight) or equivalent volumes of saline (0.9% w/w) were administered daily, before and during hair follicle initiation and development. Murine EGF inhibited the formation of hair follicles, hair follicle sweat glands, sebaceous glands and dermal papillae. The pattern of follicle initiation was perturbed. The characteristic trio follicle grouping was absent, and follicle rudiment densities (no. per mm2 skin surface) were significantly lower in animals treated with mEGF, whereas follicle diameters were increased. These data may reflect a role for the epidermal growth factor (EGF) receptor in epidermal pattern formation. The EGF receptor and its potential ligands (such as EGF, transforming growth factor (TGF-alpha) or other yet-to-be-discovered ligands) perhaps act as parts of a pattern-forming system in vertebrate skin.

Milk Composition and Production in Free-Living Allied Rock-Wallabies, Petrogale Assimilis

Milk composition and the rates of milk consumption by pouch young were examined in free-living allied rock-wallabies, Petrogale assimilis. Milk solids concentrations were approximately 16% (w/w) at 70 days post-partum and increased to about 22% by 170 days when young first left the pouch. By permanent pouch emergence (about 200 days), concentrations had declined and stabilised at about 19%. Milk carbohydrate peaked at 12% (w/v) at 150 days; lipid concentrations averaged 8% (w/w) at 200 days. The subsequent decline in carbohydrates was the main cause of the fall in milk solids. Protein concentrations increased gradually from about 3% (w/v) at 70 days to plateau at 5.5% at about 200 days. Milk consumption rates were measured from 72 to 159 days post-partum with Na-22 turnover. Milk consumption, about 3 mL day(-1) initially, increased to an average of about 15 mL day(-1) by 150 days. The mass gained by a pouch young between 72 and 159 days for each millilitre of milk consumed was not correlated with lactational stage and averaged 0.21 +/- 0.014 (s.e.)g mL(-1).

Lactation and Energetics of Growth in the Brush-Tailed Bettong, Bettongia-Penicillata (Marsupialia, Potoroidae) in Captivity

Milk samples were collected from 20 captive bettongs at various times during the 140 days of lactation to determine milk composition. Milk consumption rates of young were measured, using Na-22 turnover, up to the time of their permanent emergence from the pouch and before solid food was consumed. Milk composition followed the general patterns of change observed previously in other marsupials and included the characteristic drop in carbohydrate concentrations associated with permanent exit from the pouch. Milk consumption rates increased from about 1.0 mL day(-1) at 35 days to about 23 mL day(-1) at 90 days, just before permanent emergence from the pouch. Increases in milk consumption were paralleled by changes in the size of the mammary glands, which reached their maximum size at about 100-110 days. The efficiency with which young used milk to accumulate body tissue ranged from 0.39 to 0.51 g mL(-1). Milk energy and protein were converted to body tissue with efficiencies of 21.3-29 6% and 70.1-93 5% respectively.

Milk composition in the northern brown bandicoot, Isoodon macrourus (Peramelidae, Marsupialia)

Milk samples were obtained at regular intervals throughout lactation from northern brown bandicoots, Isoodon macrourus, in captivity. Total concentration of milk solids was initially 7% (w/w) and increased linearly to 45% (w/w) by 55 days. Carbohydrate, lipid and protein concentrations increased from about 2% (w/w) to about 7-8% (w/w) at 30 days. Thereafter they diverged, with lipid increasing to between 25-30% (w/w) at 56 days, protein reaching maximal values of 10-15% (w/w) at just over 40 days and carbohydrate gradually declining to about 5% (w/w) at 56 days before a rapid fall to 1-2% (w/w) at the completion of lactation. The milk of the bandicoot exhibits a similar pattern of change during the course of lactation to that shown by other marsupials.

Milk Consumption and Energetics of Growth in Pouch Young of the Tammar Wallaby, Macropus-Eugenii

Milk consumption rates of young tammar wallabies, Macropus eugenii, were measured during the first 32 weeks of lactation by means of 22*Na turnover. Milk consumption rates were low during the first 18 weeks or so of lactation, rising from 1.2 to 9.0 ml d-'. Milk consumption rose to 43 ml d-' at 30 weeks post-partum. Changes in milk consumption were paralleled by increases in the size of mammary glands and weight gain by the sucklings. The mass gain for each millilitre of milk consumed (crude growth efficiency) averaged 0.23 g ml-I during the first 26 weeks of lactation, but then increased to more than 0.35 g ml-'. The increased growth efficiency was associated with massive increases in the lipid and energy content of milk from 26 weeks onwards. The conversion efficiencies of milk protein and energy to body materials were intermediate (55-87%, 23-36%, respectively) to those of other mammals, which suggests that the slow growth of pouch young during the first 17 weeks of lactation is the result of restricted milk production by the mother. Milk production and the growth of young were closely correlated with maternal mass (r=0.96; r=0.80, respectively) at 16 weeks post-partum.

Reproduction in Captive Wallaroos - the Eastern Wallaroo, Macropus-Robustus-Robustus, the Euro, Macropus-Robustus-Erubescens and the Antilopine Wallaroo, Macropus-Antilopinus

Wallaroos were bred in captivity during almost 20 years. Individual males attained sexual maturity at between 18 and 20 months old and females at between 14 and 24 months old; both sexes were capable of breeding throughout the year. Gestation was 30-38 d and extended almost the full length of the oestrous cycle, 31-46 d. Post-partum mating usually produced a blastocyst subject to lactational quiescence. Removal or loss of a pouch young usually resulted in birth 28-32 d later but up to 41 d later in the presence of an actively suckled young-at-foot. Pouch life ranged between 231 and 270 d, with vacation of the pouch usually followed by another birth 1-14 d later. Lactation exceeded 12-14 months but suckling had waned by 15-17 months. Reproductive patterns for M. r. robustus and M. r. erubescens were similar although significant differences between the subspecies were recorded in length of oestrous cycle, the interval from loss of pouch young to birth and post-partum oestrus, the length of pouch life and the time between vacation of the pouch and birth. In addition, the reproductive activity of hybrids produced by matings between the subspecies was observed, as was that of a limited number of M. antilopinus.

Changes in milk carbohydrates during lactation in the eastern quoll, Dasyurus viverrinus (Marsupialia)

1. Milk samples were obtained at various stages of lactation from 16 captive eastern quolls. 2. The mean milk carbohydrate concentration was 7.4% (w/v; total hexose) at 8 weeks post partum, decreasing to 5.2% at 17 weeks and to less than 2% at the end of lactation. 3. The predominant monosaccharide constituent of the carbohydrates was galactose, followed by glucosamine, glucose and sialic acid. 4. Thin layer and gel chromatography showed that the milk carbohydrates consisted of lactose and a variety of higher oligosaccharides, some of which appeared to be identical to oligosaccharides of known structure previously isolated from milk of the tammar wallaby, Macropus eugenii. 5. In general, both the quantitative and qualitative changes observed in the milk carbohydrates of the eastern quoll were similar to those documented for macropodids.

Plasma prolactin concentrations throughout lactation in the eastern quoll, Dasyurus viverrinus (Marsupialia:Dasyuridae)

Blood samples were collected throughout lactation from eight D. viverrinus, and the concentrations of prolactin in the plasma determined by an heterologous, double-antibody radioimmunoassay. For the first 45-50 days of lactation concentrations fluctuated between 2 and 80 ng/ml but were generally less than 60 ng/ml. They then increased sharply to over 120 ng/ml and greater than 200 ng/ml in some animals. Levels began to decline after 120-130 days of lactation and were less than 40 ng/ml in all animals by the time lactation had ceased, between 160 and 185 days, when the young became independent. The timing of these changes correlates well with a rapid increase in the growth rate of the young, the time at which they first relinquish the teat and remain in the nest, their first intake of solid food shortly after eruption of the first molars and specific changes in milk composition. The pattern of prolactin concentrations throughout lactation in the quoll is therefore very similar to that previously described for the tammar, Macropus eugenii, and the possum, Trichosurus vulpecula.

Reproduction, Growth and Age Determinatipon in the Yellow Footed Rock Wallaby Petrogale xanthopus Gray, in Captivity

Yellow-footed rock-wallabies were studied in captivity over 13 years. Individuals of both sexes attained sexual maturity from age 18 months and were capable of breeding throughout the year. The ranges recorded were: for length of oestrous cycle 32-37 days; gestation 31-33 days; pouch life 190-201 days. Parturition was usually followed by an oestrus and mating with a consequent lactation-controlled embryonic quiescence. The mean interval from removal of pouch young to birth was 31.5 days, and to oestrus without an intervening birth, 34 days. Weight of the neonate within the 1st day was <500 mg; the sex ratio of 62 young of known sex revealed a significant departure from parity with 41 boys and 21 girls (100:51). Growth curves were fitted for length of head, ear, arm, leg, foot, tail and weight. These measurements provided a useful means of determining age within the 1st year and to a lesser extent the 2nd year, length of head being the best criterion. Both sexes maintained similar growth rates when within the pouch, but males grew larger once they vacated it. Patterns of molar eruption and molar progression provided a useful means of determining age in older animals but, on the data available, accuracy was restricted to the year and possibly no more than the season of birth.

Growth of the Eastern Quoll, Dasyurus viverrinus (Shaw), (Marsupialia) in Captivity

The growth and development, from 10 to 270 days old, of eastern quolls in a captive colony was recorded. Young were able to detach from the teat by 65 days of age and their eyes were open by 80 days. Statistically significant differences in some measurements from males and females were found as early as 85 days of age. The weaning period commenced at 102 days ofage, and coincided with eruption ofthe first molar teeth. Total independence, determined by the cessation of lactation in the mother, was as early as 142 days in litters of one or as late as 200 days in larger litters. There was a high correlation between litter size and age at independence. Lactation was maintained in all previously suckled mammary glands of adult females after the death of young aged 65 days or over if some siblings remained. This was due to the ability of young of this age to detach and reattach to the teats at will. The implication of this observation is that the commonly held view that the numbers of surviving young in marsupial litters corresponds to the number of lactating teats in the adult female may not always be correct.

The effect of pregnancy on the interval between one oestrus and the next in the tammar wallaby, Macropus eugenii

In females mated to vasectomized males the interval between oestrous periods was 30.6 +/- 1.17 (s.d.) days but when mated to intact males and pregnancy intervened, it was 29. +/- 1.26 days (P less than 0.0025). After removal of pouch young, females carrying diapausing blastocysts gave birth 26.2 days later and came into oestrus 26.4 +/- 0.57 (s.d.) days later. When post-partum fertilization was prevented, removal of pouch young was followed by oestrus 30.4 +/- 0.99 days later (P less than 0.0005). These results indicate an influence of the conceptus upon the oestrous cycle of Macropus eugenii.

Comparing the Two Usual Methods for Aging Macropodidae on Tooth-Classes in the Agile Wallaby

The usual estimator of age in Macropodidae is the pattern of molar eruption obtained by direct observation. The pattern of molar progression anteriorly with age is compared in captive agile wallabies, Macropus agilis. The latter required X-rays of the skull, but improved the precision of estimation by about 21%. The two patterns are shown to be linearly related even though they differ between sexes.

Sexual Dimorphism in Molar Progression and Eruption in the Agile Wallaby

Male and female agile wallabies with the same dental pattern are of different ages. Males grow faster and acquire their teeth earlier. It seems probable that other sexually dimorphic kangaroos and wallabies have similar differences. A statistical model for molar progression is suggested.

Breeding Biology of the Agile Wallaby, Macropus agilis (Gould) (Marsupialia : Macropodidae), in Captivity

Female agile wallabies in captivity reached sexual maturity at about 12 months old and males produced mature spermatozoa by 14 months. Breeding was continuous throughout the year and birth and oestrus were recorded in every month. The mean length of the oestrous cycle was 32.4 days, and the mean gestation period 29.4 days. Females exhibited post-partum oestrus, usually mating within 1 day of birth. Sixty-four young born in captivity comprised 24 males, 30 females and 10 of unknown sex. If a pouch young were removed or lost, the quiescent blastocyst resumed its development, to birth about 26.5 days later. Failure or absence of the blastocyst was followed by an oestrus at about the time of the corresponding post-partum oestrus. Both the oestrous cycle and the interval between removal of a pouch young and oestrus were significantly longer than when a pregnancy intervened. The oestrous cycle was characterized by changes in the proportions of the main cell types in the vaginal smear, and by changes in the appearance of the urogenital opening and the pouch and teats. The approach of oestrus could not be predicted from vaginal smears but the post-oestrous condition was always recognizable even without mating. Young animals first left the pouch for short periods between the ages of 176 and 211 days, and left permanently between 207 and 237 days. Animals of known age were measured and the development of various morphological characters noted at weekly intervals from about birth until 12 months old.

Observations on the attatchment of marsupial pouch young to the teats and on the rearing of pouch young by foster-mothers of the same or different species

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.