Range decline and conservation status of Westralunio carteri Iredale, 1934 (Bivalvia:Hyriidae) from south-western Australia

Westralunio carteri is the only species of freshwater mussel found in south-western Australia and, owing to a lack of comprehensive information on its ecology, its conservation status has been speculative. To more accurately predict the true conservation status of this species, the historical and contemporary distributional records were modelled with environmental data that identified salinity, perenniality and total nitrogen as variables responsible for limiting the species’ current extent of occurrence, inferring threatening processes. The species was found to have undergone a 49% reduction in extent of occurrence in less than three generations, due primarily to secondary salinisation. Current distribution is bounded by Gingin Brook in the north to the Kent, Goodga and Waychinicup Rivers in the South, within 50–100 km of coastal south-western Australia. Field observations indicated that W. carteri was almost never found at sites where mean salinity was >1.6 g L–1. This was corroborated by laboratory tolerance trials that showed that W. carteri has an acute salinity tolerance (LD50) of 1.6–3.0 g L–1. Application of IUCN Red List criteria indicates that W. carteri qualifies for listing as vulnerable. Conservation management measures should focus on maintaining existing populations.

Reevaluating the evidence for Toxoplasma gondii-induced behavioural changes in rodents

The ubiquitous protozoan parasite Toxoplasma gondii has been associated with behavioural changes in various hosts, including humans. In rodents, these behavioural changes are thought to represent adaptive manipulation by T. gondii to enhance transmission from intermediate hosts to the feline definitive host. In this review, we have tabulated evidence of changes in motor coordination, learning, memory, locomotion, anxiety, response to novelty and aversion to feline odour in rodents experimentally infected with T. gondii. In general, there was no consistent indication of the direction or magnitude of behavioural changes in response to infection. This may be due to the use, in these experimental studies, of different T. gondii strains, different host species and sexes and/or different methodologies to measure behaviour. A particular problem with studies of behavioural manipulation is likely to be the validity of behavioural tests, that is, whether they are actually measuring the traits that they were designed to measure. We suggest that future studies can be improved in three major ways. First, they should use multiple tests of behaviour, followed by multivariate data analysis to identify behavioural constructs such as aversion, anxiety and response to novelty. Second, they should incorporate longitudinal measurements on the behaviour of individual hosts before and after infection, so that within-individual and between-individual variances and covariances in behavioural traits can be estimated. Finally, they should investigate how variables such as parasite strain, host species and host sex interact with parasite infection to alter host behaviour, in order to provide a sound foundation for research concerning the proximate and ultimate mechanism(s) responsible for behavioural changes.

Co-invaders: The effects of alien parasites on native hosts

We define co-introduced parasites as those which have been transported with an alien host to a new locality, outside of their natural range, and co-invading parasites as those which have been co-introduced and then spread to new, native hosts. Of 98 published studies of co-introductions, over 50% of hosts were freshwater fishes and 49% of parasites were helminths. Although we would expect parasites with simple, direct life cycles to be much more likely to be introduced and establish in a new locality, a substantial proportion (36%) of co-introductions were of parasites with an indirect life cycle. Seventy-eight per cent of co-introduced parasites were found in native host species and can therefore be classed as co-invaders. Host switching was equally common among parasites with direct and indirect life cycles. The magnitude of the threat posed to native species by co-invaders will depend, among other things, on parasite virulence. In 16 cases where co-introduced parasites have switched to native hosts and information was available on relative virulence, 14 (85%) were more virulent in native hosts than in the co-introduced alien host. We argue that this does not necessarily support the naïve host theory that co-invading parasites will have greater pathogenic effects in native hosts with which they have no coevolutionary history, but may instead be a consequence of the greater likelihood for parasites with lower virulence in their natural host to be co-introduced.

Implications of climate change for potamodromous fishes

There is little understanding of how climate change will impact potamodromous freshwater fishes. Since the mid 1970s, a decline in annual rainfall in south-western Australia (a globally recognized biodiversity hotspot) has resulted in the rivers of the region undergoing severe reductions in surface flows (ca. 50%). There is universal agreement amongst Global Climate Models that rainfall will continue to decline in this region. Limited data are available on the movement patterns of the endemic freshwater fishes of south-western Australia or on the relationship between their life histories and hydrology. We used this region as a model to determine how dramatic hydrological change may impact potamodromous freshwater fishes. Migration patterns of fishes in the largest river in south-western Australia were quantified over a 4 year period and were related to a number of key environmental variables including discharge, temperature, pH, conductivity and dissolved oxygen. Most of the endemic freshwater fishes were potamodromous, displaying lateral seasonal spawning migrations from the main channel into tributaries, and there were significant temporal differences in movement patterns between species. Using a model averaging approach, amount of discharge was clearly the best predictor of upstream and downstream movement for most species. Given past and projected reductions in surface flow and groundwater, the findings have major implications for future recruitment rates and population viabilities of potamodromous fishes. Freshwater ecosystems in drying climatic regions can only be managed effectively if such hydro-ecological relationships are considered. Proactive management and addressing existing anthropogenic stressors on aquatic ecosystems associated with the development of surface and groundwater resources and land use is required to increase the resistance and resilience of potamodromous fishes to ongoing flow reductions.

Cryptosporidium species in sheep and goats from Papua New Guinea

Species of Cryptosporidium are extensively recognised as pathogens of domesticated livestock and poultry, companion animals, wildlife, and are a threat to public health. Little is known of the prevalence of Cryptosporidium spp. in humans, domesticated animals or wildlife in Papua New Guinea (PNG). The aim of the present study was to screen sheep and goats for Cryptosporidium using molecular tools. A total of 504 faecal samples were collected from sheep (n=276) and goats (n=228) in village, government and institutional farms in PNG. Samples were screened by nested PCR and genotyped at the 18S rRNA and at the 60kDa glycoprotein (gp60) loci. The overall prevalences were 2.2% for sheep (6/278) and 4.4% (10/228) for goats. The species/genotypes identified were Cryptosporidium hominis (subtype IdA15G1) in goats (n=6), Cryptosporidium parvum (subtypes IIaA15G2R1and IIaA19G4R1) in sheep (n=4) and in goats (n=2), Cryptosporidium andersoni (n=1) and Cryptosporidium scrofarum (n=1) in sheep, Cryptosporidium xiao (n=1) and Cryptosporidium rat genotype II (n=1) in goats. This is the first report of Cryptosporidium spp. identified in sheep and goats in PNG. Identification of Cryptosporidium in livestock warrants better care of farm animals to avoid contamination and illness in vulnerable population. The detection of zoonotic Cryptosporidium in livestock suggests these animals may serve as reservoirs for human infection.

Trypanosomes genetic diversity, polyparasitism and the population decline of the critically endangered Australian marsupial, the brush tailed bettong or woylie (Bettongia penicillata)

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Trypanosomes in Australian marsupials comprise a heterogeneous community.

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The woylie was the only species found co-infected with different trypanosomes.

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Some of the trypanosomes found are able to colonize several tissues in the host.

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Trypanosoma copemani is able to invade cells in vitro.

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Association between T.copemani and mixed infections with the decline of the woylie.

While much is known of the impact of trypanosomes on human and livestock health, trypanosomes in wildlife, although ubiquitous, have largely been considered to be non-pathogenic. We describe the genetic diversity, tissue tropism and potential pathogenicity of trypanosomes naturally infecting Western Australian marsupials. Blood samples collected from 554 live-animals and 250 tissue samples extracted from 50 carcasses of sick-euthanized or road-killed animals, belonging to 10 species of marsupials, were screened for the presence of trypanosomes using a PCR of the 18S rDNA gene. PCR results revealed a rate of infection of 67% in blood and 60% in tissues. Inferred phylogenetic trees using 18S rDNA and glycosomal glyceraldehyde phosphate dehydrogenase (gGAPDH) sequences showed the presence of eight genotypes that clustered into three clades: a clade including Trypanosoma copemani, a new clade closely related to Trypanosoma gilletti, and a clade including Trypanosoma H25 from an Australian kangaroo. Trypanosome infections were compared in a declining and in a stable population of the endangered Australian marsupial, the brush tailed bettong or woylie (Bettongia penicillata). This marsupial showed high rates of infection with Clade A genotypes (96%) in the declining population, whereas in the stable population, Clade B genotypes were predominant (89%). Mixed infections were common in woylies from the declining but not from the stable population. Histopathological findings associated with either mixed or single infections involving Clade A genotypes, showed a strong inflammatory process and tissue degeneration predominantly in heart, oesophagus and tongue. Trypanosomes were successfully grown in culture and for the first time we demonstrate that a genotype within Clade A has the capacity to not only colonize different tissues in the host but also to invade cells in vitro. These results provide evidence for the potential role of trypanosomes in the decline of a formerly abundant marsupial that is now critically endangered.

Adaptive host manipulation by Toxoplasma gondii: fact or fiction?

It is widely accepted that behavioural changes induced by Toxoplasma gondii are an adaptation of the parasite to enhance transmission to its cat definitive host. In our opinion, this explanation requires a rethink. We argue that the experimental evidence that observed behavioural changes will enhance transmission to cats is not convincing. We also argue that cats and sexual reproduction may not be essential for transmission and maintenance of this parasite. Thus, the selection pressure to infect a cat may not be sufficiently strong for the evolution of adaptive host manipulation to have occurred in order to enhance predation by cats.

The potential of a salt-tolerant plant (Distichlis spicata cv. NyPa Forage) to treat effluent from inland saline aquaculture and provide livestock feed on salt-affected farmland

Dryland salinity is a major problem affecting food production from agricultural land in Australia and throughout the world. Although there is much interest in using saline groundwater to grow marine fish on salt-affected farmland, the disposal of nutrient enriched, saline aquaculture effluent is a major environmental problem. We investigated the potential of the salt-tolerant NyPa Forage plant (Distichlis spicata L. Greene var. yensen-4a) to trap nutrients from saline aquaculture effluent and subsequently to provide a fodder crop for livestock. Sub-surface flow wetlands containing NyPa Forage were constructed and their efficacy in removing total nitrogen, ammonia, nitrite/nitrate, total phosphorus and orthophosphate was monitored under different levels of nutrients and salinity. The wetlands removed 60-90% of total nitrogen loads and at least 85% of ammonia, nitrite/nitrate, total phosphorus and orthophosphate loads, with greater efficiency at high nutrient and low salinity levels. The above-ground yield, sodium, crude protein (CP) and in vitro dry matter digestibility (DMD) of NyPa Forage plants were measured after fertilisation with different nutrient levels and cropping at different frequencies. Yield of plants increased with increased nutrient, while nutritive value was greater when nutrients were applied but did not differ among nutrient levels. Yield was not affected by cropping frequency, but nutritive value was greatest when plants were cropped at intervals of 21 or 42 days. At optimum nutrient addition and cropping levels, the plants had a mean CP content of 16.7% and an in vitro DMD of 67.6%, equivalent to an energy value of 9.5 MJ kg(-1). Assuming an equivalent fibre content and voluntary food intake as grass hay, and no accumulation of other toxic minerals, these nutritive values would be sufficient for maintenance or moderate liveweight gains in dry adult sheep or cattle.

Identification of Anisakis species (Nematoda: Anisakidae) in marine fish hosts from Papua New Guinea

The third-stage larvae of several genera of anisakid nematodes are important etiological agents for zoonotic human anisakiasis. The present study investigated the prevalence of potentially zoonotic anisakid larvae in fish collected on the coastal shelves off Madang and Rabaul in Papua New Guinea (PNG) where fish represents a major component of the diet. Nematodes were found in seven fish species including Decapterus macarellus, Gerres oblongus, Pinjalo lewisi, Pinjalo pinjalo, Selar crumenophthalmus, Scomberomorus maculatus and Thunnus albacares. They were identified by both light and scanning electron microscopy as Anisakis Type I larvae. Sequencing and phylogenetic analysis of the ribosomal internal transcribed spacer (ITS) and the mitochondrial cytochrome C oxidase subunit II (cox2) gene identified all nematodes as Anisakis typica. This study represents the first in-depth characterisation of Anisakis larvae from seven new fish hosts in PNG. The overall prevalence of larvae was low (7.6%) and no recognised zoonotic Anisakis species were identified, suggesting a very low threat of anisakiasis in PNG.

Western Australian marsupials are multiply infected with genetically diverse strains of Toxoplasma gondii

Five different organs from 16 asymptomatic free-ranging marsupial macropods (Macropus rufus, M. fuliginosus, and M. robustus) from inland Western Australia were tested for infection with Toxoplasma gondii by multi-locus PCR-DNA sequencing. All macropods were infected with T. gondii, and 13 had parasite DNA in at least 2 organs. In total, 45 distinct T. gondii genotypes were detected. Fourteen of the 16 macropods were multiply infected with genetically distinct T. gondii genotypes that often partitioned between different organs. The presence of multiple T. gondii infections in macropods suggests that native mammals have the potential to promote regular cycles of sexual reproduction in the definitive felid host in this environment.

Additional novel Cryptosporidium genotypes in ornamental fishes

Current knowledge on the prevalence and genotypes of Cryptosporidium in fishes is still limited. This study investigated the prevalence of Cryptosporidium species in 171 ornamental fishes, belonging to 33 species, collected from 8 commercial aquariums around Perth, Western Australia. All samples were screened by nested PCR targeting the 18S rRNA locus. A total of 6 positives were identified by PCR at the 18S locus from 4 different species of fishes (red eye tetra, Moenkhausia sanctaefilomenae; gold gourami, Trichogaster trichopterus; neon tetra, Paracheirodon innesi; goldfish, Carassius auratus auratus), giving an overall prevalence of 3.5% (6/171). Four different genotypes were identified, only one of which has been previously reported in fish; piscine genotype 4 in a neon tetra isolate, a rat genotype III-like isolate in a goldfish, a novel genotype in three isolates from red eye (piscine genotype 7) which exhibited a 3.5% genetic distance from piscine genotype 1 and a piscine genotype 6-like from a gold gourami (1% genetic distance). Further biological and genetic characterisation is required to determine the relationship of these genotypes to established species and strains of Cryptosporidium.

Glochidia ecology in wild fish populations and laboratory determination of competent host fishes for an endemic freshwater mussel of south-western Australia

Glochidia (parasitic larvae) of freshwater mussels generally require a fish as a host. Westralunio carteri Iredale, 1934 (Bivalvia : Hyriidae), the only freshwater mussel found in south-western Australia, was listed as Vulnerable, but recently changed to Least Concern (International Union for the Conservation of Nature). Glochidia were found on four alien and seven native species of fish from 18 sites in the South West Coast Drainage Division. On alien fishes, prevalence of glochidia ranged from 0.0 to 41.0% and mean intensity (number of glochidia per infested fish) from 1.0 to 6.0, while on native fishes prevalence was 9.2–90.5% and intensity was 2.3–7.1. Glochidia infestation was greatest on benthic fishes, which may be a consequence of greater encounter rates, but other factors, such as host size, probably also influence glochidia prevalence and intensity. Glochidia were generally restricted to fins of infested fish, and were rarely on gills or the body surface. In the laboratory, four native and one alien fish species were found to be competent hosts for their ability to produce juvenile W. carteri, but two alien fish species were not. The inability of some alien fishes to produce juvenile W. carteri could potentially reduce recruitment success in areas dominated by alien fishes.

The molecular epidemiology of parasite infections: tools and applications

Molecular epidemiology, broadly defined, is the application of molecular genetic techniques to the dynamics of disease in a population. In this review, we briefly describe molecular and analytical tools available for molecular epidemiological studies and then provide an overview of how they can be applied to better understand parasitic disease. A range of new molecular tools have been developed in recent years, allowing for the direct examination of parasites from clinical or environmental samples, and providing access to relatively cheap, rapid, high throughput molecular assays. At the same time, new analytical approaches, in particular those derived from coalescent theory, have been developed to provide more robust estimates of evolutionary processes and demographic parameters from multilocus, genotypic data. To date, the primary application of molecular epidemiology has been to provide specific and sensitive identification of parasites and to resolve taxonomic issues, particularly at the species level and below. Population genetic studies have also been used to determine the extent of genetic diversity among populations of parasites and the degree to which this diversity is associated with different host cycles or epidemiologically important phenotypes. Many of these studies have also shed new light on transmission cycles of parasites, particularly the extent to which zoonotic transmission occurs, and on the prevalence and importance of mixed infections with different parasite species or intraspecific variants (polyparasitism). A major challenge, and one which is now being addressed by an increasing number of studies, is to find and utilize genetic markers for complex traits of epidemiological significance, such as drug resistance, zoonotic potential and virulence.

Parasites of native and exotic freshwater fishes in south-western Australia

In this study, 1429 fishes of 18 different species (12 native and six exotic) were sampled from 29 localities to compare the levels of parasitism between native and exotic fish species and to examine the relationship between environmental degradation and parasite diversity. Forty-four putative species of parasites were found and most of these appear to be native parasites, which have not previously been described. Two parasite species, Lernaea cyprinacea and Ligula intestinalis, are probably introduced. Both were found on or in a range of native fish species, where they may cause severe disease. Levels of parasitism and parasite diversity were significantly greater in native fishes than in exotic species, and this may contribute to an enhanced demographic performance and competitive ability in invading exotics. Levels of parasitism and parasite diversity in native fishes were negatively related to habitat disturbance, in particular to a suite of factors that indicate increased human use of the river and surrounding environment. This was due principally to the absence in more disturbed habitats of a number of species of endoparasites with complex life cycles, involving transmission between different host species.

Discovery of a host fish for glochidia of Velesunio angasi (Sowerby, 1867) (Bivalvia:Unionoida:Hyriidae) from the Fortescue River, Pilbara, Western Australia

Freshwater fishes are the most common hosts of the glochidia (parasitic larvae) of freshwater mussels (Bivalvia: Unionoida: Unionoidea). Velesunio angasi (Sowerby, 1867) (Hyriidae), is the only known hyriid species recorded from the Fortescue River in the Pilbara region of Western Australia. Eleven species of fish (n = 516) were captured from pools of the Fortescue River in June 2010. Small, white, bladder-like cysts were observed on Neosilurus hyrtlii Steindachner, 1867, though not on any of the remaining 10 species examined. Light microscopy of sectioned cysts revealed that they contained glochidia that were of similar size and shape to those of V. angasi. Glochidia were found on 73.2% of 168 N. hyrtlii examined, with a mean intensity of 3.3 cysts per infested fish. Prevalence was significantly greater on smaller fish (P < 0.01); however, no relationship between size and intensity of infestation was observed. This represents the first record of glochidia infestation on fish from the Pilbara region.

Larval anisakid infections of some tropical fish species from north-west Australia

Despite the commercial and zoonotic importance of larval anisakid infestations of teleosts, their distribution among Australia's diverse marine fish fauna is poorly understood. A preliminary survey of Australia's tropical north-west revealed a generally high prevalence of larval anisakids representing four genera (Anisakis, Terranova, Thynnascaris and Raphidascaris) among only seven fish species. The potential impact of high larval anisakid infections on both the health of recreational fishermen and aquaculture environments is discussed.

Fish-borne parasitic zoonoses: status and issues

The fish-borne parasitic zoonoses have been limited for the most part to populations living in low- and middle-income countries, but the geographical limits and populations at risk are expanding because of growing international markets, improved transportation systems, and demographic changes such as population movements. While many in developed countries will recognize meat-borne zoonoses such as trichinellosis and cysticercosis, far fewer are acquainted with the fish-borne parasitic zoonoses which are mostly helminthic diseases caused by trematodes, cestodes and nematodes. Yet these zoonoses are responsible for large numbers of human infections around the world. The list of potential fish-borne parasitic zoonoses is quite large. However, in this review, emphasis has been placed on liver fluke diseases such as clonorchiasis, opisthorchiasis and metorchiasis, as well as on intestinal trematodiasis (the heterophyids and echinostomes), anisakiasis (due to Anisakis simplex larvae), and diphyllobothriasis. The life cycles, distributions, epidemiology, clinical aspects, and, importantly, the research needed for improved risk assessments, clinical management and prevention and control of these important parasitic diseases are reviewed.

Teaching of parasitology to students of veterinary medicine and biomedical sciences

The teaching of an applied parasitology course suitable for both veterinary and biomedical students is described. A common lecture course is given complemented by separate and specific practical, research and problem-based learning components designed for veterinary and biomedical students. For veterinary and biomedical students, teaching of parasitology during the full course comprises a total of 46 lectures; 13 practical classes for veterinary students and five for biomedical students who also undertake an independent research project.