Health surveillance in wildlife reintroductions

Summary

The dibbler Parantechinus apicalis, is a small carnivorous marsupial endemic to southwest Australia. It was once widespread but its range contracted to only to two small offshore islands, Boullanger and Whitlock (joined at low tide; estimated population 200) and three mainland populations (<500 individuals). The main reasons for their decline are thought to be due to predation by introduced predators, and habitat fragmentation and degradation. Boullanger and Whitlock Islands however, are easily accessible and subject to frequent human visitation with associated risks, such as fire and pets. There are also possible but unknown threats posed from increasing numbers of non-native house mice Mus musculus which occur at high densities (c. 700/ha); dibblers occur at c. 4/ha in comparison.

Introduction to a third but less accessible, and mouse-free island (Escape Island, Western Australia) was therefore proposed in order to establish a new dibbler population and safeguard against human-associated risks (for a summary see: www.www.conservationevidence.com/ViewEntry.asp?ID=72). In 1997 four pairs of dibbler were transferred to captive-breeding facilities at Perth Zoo, Western Australia. Over four years, 88 captive-reared young were introduced. There was concern that parasites from the house mice may be transferred to, and persist in, dibblers taken into captivity. Captive-bred dibblers may subsequently transfer parasites to release sites. The primary aim of this present study was to highlight the importance of establishing information on some intestinal microflora and potential pathogens (protozoa, amoeba, worms, bacteria) that occur in, and which may be transferred between, animals at source, captive and release sites.

Faeces were collected for the examination of intestinal parasites and bacterial culture from a sample of dibblers and house mice at the source population on Boullanger and Whitlock Islands, at the captive-breeding facility at Perth Zoo, and from wild-born individuals at the release site on Escape Island.

For captive dibblers, faecal samples were collected over three sampling periods at 15-day intervals. For the wild animals (dibblers and house mice), trapping was conducted during the Austral winter months in 2001. Diagnosis of infection was made by direct microscopy (for macroparasites) and by bacterial culture.

Two types of faecal parasite (coccidia, strongyle eggs) were detected in captive dibblers (occurring in 50% of individuals) and 18–27% of the source population. However, these differences are not statistically significant, and may represent chance sampling. The authors therefore stress the importance of maximising sample sizes during screening and if possible, using pilot studies to estimate prevalence levels which can be used to predict appropriate sample sizes. Sampling of dibblers born at the release site revealed no evidence of parasites. Coccidia were equally prevalent among mice and dibblers at the source site. Additional parasites found in house mice but not dibblers were the cestode Rodentolepis sp., the amoeba Chilomastix sp. and the mite Demodex sp.

The predominant bacterial microflora in dibbler faeces from all sites were Gram-positive bacteria (Staphylococcus aureus, S. haemolyticus, Staphylococcus sp., Enterococcus faecalis, Enterococcus sp. and Bacillus sp.); Streptococcus sp. was detected at the source and captive sites only. At the source site 73% of dibblers harboured at least one Staphylococcus sp. compared to captives (20%) and individuals born at the release site (21%). Streptococcus prevalence was highest among captive animals. In mice, Gram-negative species were predominant.

Bacillus spp. (excluding B.cereus) were present in 36% of animals at the source site, 15% in captivity and 42% at the release site. B.cereus was detected only in captive dibblers (50%) but was found in 33% of mice at the source site. The presence of B.cereus is of concern as it is a potential pathogen; its absence in dibblers at the source and release sites suggests either that the screening failed to detect it, or that it had been introduced to dibblers whilst held in captivity, perhaps through contaminated feed. Future screening of captive dibblers should include screening for B.cereus with any infected individuals being held back from breeding and translocation, or treated with antibiotics prior to translocation.

A single mouse tested positive for Salmonella (S.bovis morbificans PT24), a potential pathogen. Many animals can be carriers without showing symptoms of infection. Dibblers in future translocations should therefore be tested for Salmonella.

Enterobacteriaceae (E.coli, Enterobacter spp., K.oxytoca, P.vulgaricus) were detected in captive dibblers but not in those at the source or release sites. These bacteria do not generally cause infections or disease. Their prevalence in the captive population decreased once the animals were released, indicating that the bacterial microflora seemed to revert back to that of species in a wild population.


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