A.J. Lymbery

The role of companion animals in the emergence of parasitic zoonoses.

Pets offer individuals and the community significant benefits, however cognisance must be taken of the potential for transmission of infectious agents from these animals to humans. The prevalence of many parasites, such as Giardia and Cryptosporidium, has increased over the past few decades while others, such as Toxocara and Ancylostoma, have decreased. These changes could be real, associated with the ready availability of efficacious anthelmintic products or could be artificial due to the type of surveys conducted, the animals surveyed and the diagnostic tests used. Immunocompromised people, in particular, must be aware of the potential risk of acquiring parasitic infections from their pets. However, with the adoption of good hygiene and a thorough knowledge of the transmission of these parasites, immunocompromised people should be able to continue to enjoy the significant benefits of pet ownership. As many owners are not aware of the zoonotic parasites that could be carried by their pets or their mode of transmission, it is concluded that veterinarians need to play a greater role in the education of their clients.

The nature, extent and significance of variation within the genus Echinococcus

Publisher Summary This chapter discusses the nature, extent, and significance of variation particularly, below the species level, in the causative agent of hydatid disease, Echinococcus. An application of current taxonomic procedures to the classification of a group of organisms in Echinococcus ensures an important role for the explanatory and predictive value of taxonomic determinations in studies on the epidemiology and control of hydatid disease. Despite increasing access to highly discriminatory differential criteria and a more flexible taxonomic approach, problems of nomenclature are likely to remain. Many genetically distinct populations within the recognized species of Echinococcus cannot be adequately allocated to a formal taxonomic category. However, in parasitic organisms the recognition of variation may be of great medical and agricultural significance and it is for this reason that the term “strain” has been widely used to describe intraspecific variants in Echinococcus and other parasites. It is essential that strains are indentified and characterized in each endemic area if effective control programs are to be instituted. Future research should aim to develop even more reliable and practically applicable differential criteria for this purpose. Biochemical and molecular dissection of the parasite in a quest toward this end may also unravel the functional nature of strain variation and provide direction for the development of chemotherapeutic agents.

Variation in Echinococcus: Towards a Taxonomic Revision of the Genus

Publisher Summary Hydatid disease (echinococcosis) is one of the most important parasitic zoonoses and remains a public health and economic problem of global proportions. There are currently four recognized species in the genus Echinococcus : E.granulosus , E.multilocularis , E.oligarthrus , and E.vogeli . Because of the extensive variation in Echinococcus, it is very important to characterize the aetiological agents in different endemic areas to determine transmission patterns, particularly where there is the possibility of interaction between cycles. The first step in a taxonomic revision of the genus Echinococcus is to establish an appropriate species concept. Therefore, the purpose should be to update what is known about the nature and extent of variation in Echinococcus to provide a sound basis for a phylogenetic analysis. The current classification within the genus Echinococcus is not compatible with historical relationships between taxa. Phylogenetic analysis of DNA sequence data provides no support for the concept that E.grunulosus is a monophyletic group and it cannot be considered an evolutionary species. There is an urgent need for the molecular characterization of strains of E. multilocularis as well as strains of Echinococcus in lions and cervids, so that this taxonomic revision can be completed.

Parasites, emerging disease and wildlife conservation

In this review some emerging issues of parasite infections in wildlife, particularly in Australia, are considered. We discuss the importance of understanding parasite biodiversity in wildlife in terms of conservation, the role of wildlife as reservoirs of parasite infection, and the role of parasites within the broader context of the ecosystem. Using a number of parasite species, the value of undertaking longitudinal surveillance in natural systems using non-invasive sampling and molecular tools to characterise infectious agents is illustrated in terms of wildlife health, parasite biodiversity and ecology.

Genetic characterization of isolates of Giardia duodenalis by enzyme electrophoresis : implications for reproductive biology population structure, taxonomy, and epidemiology

The nature and extent of genetic variation in Giardia was used to infer its mode of reproduction, population structure, taxonomy, and zoonotic potential. Ninety-seven isolates of Giardia duodenalis, from a defined area in Western Australia and throughout Australia and overseas, were obtained from humans, cats, cattle, sheep, dogs, goat, beaver, and rats. Enzyme electrophoresis revealed extensive genetic variation with 47 different zymodemes. The widespread occurrence of certain zymodemes and the similarity of relationships among isolates inferred from independent genetic markers suggests a clonal population structure for G. duodenalis, although occasional bouts of genetic exchange may occur. The 47 zymodemes clustered similarly in phenetic (UPGMA) and phylogenetic (Fitch-Margoliash) analyses. The level of genetic diversity in isolates from a defined geographical area in Western Australia was similar to the level of diversity in isolates from throughout Australia. These data suggest that clonal lineages within G. duodenalis are evolutionarily independent. Although there was a significant overall correlation between genetic distance separating zymodemes and occurrence in different host species, we found genetically identical isolates from humans and other animals and extensive genetic diversity between isolates from humans. We interpret this as evidence for zoonotic transmission of the parasite.

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

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Trypanosomes in a declining species of threatened Australian marsupial, the brush-tailed bettong Bettongia penicillata (Marsupialia: Potoroidae)

The brush-tailed bettong (Bettongia penicillata), or woylie, is a medium-sized macropod marsupial that has undergone a rapid and substantial decline throughout its home range in the Upper Warren region of Western Australia over a period of approximately 5 years. As part of an investigation into possible causes of the decline a morphologically distinct Trypanosoma sp. was discovered by light microscopy in the declining population but was absent in a stable population within the Karakamia Wildlife Sanctuary. Further investigations employing molecular methods targeting variations in the 18s rRNA gene determined that the trypanosome was novel and was also present within the Karakamia population albeit at a much lower overall prevalence and individual parasitaemia levels. Phylogenetic analysis suggests the novel Trypanosoma sp. to be closely related to other trypanosomes isolated from native Australian wildlife species. Although it appears unlikely that the parasite is solely responsible for the decline in woylie population size, it may (singularly or in conjunction with other infectious agents) predispose woylies to increased mortality.

Rostellar hook morphology of Echinococcus granulosus (Batsch, 1786) from natural and experimental Australian hosts, and its implications for strain recognition

An analysis of the rostellar hooks of Australian isolates of Echinococcus granulosus revealed that there was less variation in larval (metacestode) than adult characters and that metacestode characters could be measured directly from adult worms. A factor analysis indicated that two factors, one representing a contrast between number of hooks and their length, and the other representing blade lengths, were sufficient to account for 87.5% of the variance in metacestode hook measurements. These results indicate that rostellar hook morphology is not useful for discriminating strains of E. granulosus in Australia. The Tasmanian and mainland domestic strains were found to be indistinguishable using rostellar morphology. Although many of the isolates from sylvatic hosts differed from those from domestic hosts, there was not a clear separation as would be expected if two distinct strains existed. Evidence was presented to show that the morphological differences seen in sylvatic hosts could be attributed to host-induced effects, and that the previously accepted existence of two mainland strains should be investigated further.

Electrophoretic analysis of genetic variation in Echinococcus granulosus from domestic hosts in Australia.

Allozyme variation was examined in 26 isolates of the Australian mainland sheep strain and 13 isolates of the Tasmanian sheep strain of Echinococcus granulosus. One isolate of the British horse strain was examined for comparative purposes. Fifteen enzymes, encoded by 20 presumptive loci, were analysed. Differences in expression of enzymes were found between adult worms, protoscoleces, and fluid and germinal layer from hydatid cysts. Major differences were found at nine enzyme loci between the isolate of the British horse strain and isolates of the Australian mainland and Tasmanian sheep strains. The Australian strains differed in allelic frequencies at two loci, but no diagnostic alleles were found. Allozyme variation was detected within both the Australian strains. The proportion of polymorphic loci (P) was estimated at 0.15 for both strains, while the total gene diversity (H) was 0.02 for the mainland strain and 0.06 for the Tasmanian strain. The pattern of genetic variation over geographic areas and the absence of multi-locus associations suggested that cross-fertilization was occurring in both strains. However, deficiencies of heterozygotes at some loci provided evidence for self-fertilization. These data are discussed in relation to proposed models of strain variation in E. granulosus.

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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