Diseases of New Zealand native frogs

The aims of this project were to evaluate the health status of New Zealand native frogs (Leiopelma spp.) and to investigate what diseases, if any, were limiting their survival both in captivity and in the wild. Issues for captive frogs included nutritional and infectious diseases. For wild frogs I investigated the occurrence of declines and conducted mapping and experimental studies on chytridiomycosis. Mortality rates and causes of death were analysed for 252 wild-caught Leiopelma spp. that were held in captivity in a research program at the University of Canterbury and later transferred to other institutions between 2000 and 2006. Leiopelma archeyi and Leiopelma hochstetteri had similar overall average mortality by year (12.4% and 14.9% respectively) but different yearly mortality patterns, whereas Leiopelma pakeka had much lower overall mortality (3.5%). On further investigation, metabolic bone disease (MBD) was diagnosed in L. archeyi and L. hochstetteri in 2008 at three institutions: Auckland Zoo, Hamilton Zoo, and the University of Otago. Radiographs on archived and live frogs showed that MBD had been present at Canterbury, but at a lower rate (3%) than in the current institutions (38-67%). Micro-computed tomography showed that the femoral diaphyses of the captive frogs at Auckland Zoo had greater bone volume, bone surface, cross-sectional thickness and mean total cross-sectional bone perimeter which was consistent with osteofluorosis. On histology of the same femurs there was hyperplasia, periosteal growth, and thickening of trabeculae which was also consistent with skeletal fluorosis. An increase in fluoride levels in the water supply preceded the rise in the incidence of the above pathology further supporting the diagnosis of osteofluorosis. To determine the natural diet of Leiopelma spp., stomach contents of sixteen L. archeyi from the Coromandel and nine L. hochstetteri from the Coromandel, the Hunua Ranges and Maungatautari were analysed. Both species ate a wide range of invertebrates including springtails, mites, ants, parasitic wasps, amphipods and isopods, while L. archeyi also ate snails. The mean ratio of maximum prey size ingested to snout-vent length in L. archeyi was 0.31 (range 0.16 – 0.5), and in L. hochstetteri was 0.42 (range 0.21– 0.75). Analysis of long-standing husbandry practices showed that ultraviolet-B exposure and the dietary calcium:phosphorus ratio was deficient when compared with wild conditions – likely attributing to chronic underlying MBD. Two novel nematodes (Koerneria sp. and Rhabditis sp.) were found separately in four captive Archey's frogs showing clinical signs of haemorrhagic purulent nasal discharge and weight loss. One of these frogs also had a novel protozoal infection (Tetrahymena) in the nasal cavity. One frog was treated successfully with oral moxidectin at 0.4 mg/kg for the nematode infection and topical metronidazole at 10 mg/kg for the protozoal infection. The clinical signs abated only after both infections were cleared. Multifocal small domed lesions occurred extensively on the ventral skin of captive Leiopelma archeyi at two institutions between 2000 and 2012. Incidence was 41% (34/83) of frogs at Auckland Zoo and 9% (1/11) at the University of Otago and were not linked with an increased risk of death. The lesions had the gross and microscopic characteristics of adenomatous hyperplasia (AH) of the dermal mucous glands which are widely distributed over the skin of normal Archey's frogs. In affected frogs the size and location of lesions varied over time, even resolved completely in some animals, and sometimes reappeared. Histologically the lesions were composed of enlarged mucous glands that expanded the dermis and elevated the epidermis. They were semi-organized, with occasional acinar structures with central lumina sometimes containing mucus. Nuclei had moderate anisokaryosis and mitotic figures were uncommon. The aetiology of this adenomatous hyperplasia is unknown, but factors associated with the captive environment are most likely. Surveys were distributed to New Zealand land users in 1998 and 2008 to acquire information about the distribution and population levels of both native (Leiopelma spp.) and non-native (Litoria spp.) frogs. Overall frog populations in New Zealand were reported as declining, but were stable or increasing in a few regions. Possible causes reported for declines were disease (chytridiomycosis), increase in agriculture and an increase in the distribution of predatory fish. The current distribution, host species and prevalence where known of the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) is reported in New Zealand. I conducted histology and PCR on new and archived specimen and also collated previous test records. The data included all regions in New Zealand and six off shore islands at 135 sites with 704 records from over eleven contributors spanning collection dates 1930-2010. The earliest case was from 1999 and we report 132 positive individuals from 54 widespread sites. Bd was detected in all three non-native Litoria spp. in five out of sixteen regions but not in the six off-shore areas tested. Bd was not detected in native L. hochstetteri, L. hamiltoni and L. pakeka. Included in the data is a museum survey of 152 individuals from five species from 1930-1999 using histology and Bd specific immunohistochemistry. All museum specimens were negative. In L. archeyi at a study site in the Coromandel Ranges, the prevalence of Bd from 2006-2010 was relatively stable at 14-18%. The prevalence of Bd in Whareorino has remained both consistent and low (