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.

Microsatellite analysis of genetic diversity in wild and farmed Emus (Dromaius novaehollandiae)

The emu (Dromaius novaehollandiae) occupies most regions of the Australian continent and in recent times has been farmed for meat, oil, and leather. Very little is known about the genetic structure of natural or farmed populations of these birds. We report a preliminary study of genetic variation in emus undertaken by typing birds from five farms and two natural populations at five polymorphic microsatellite loci. Genetic diversity was high for all populations and there was little evidence of inbreeding, with most populations conforming to Hardy-Weinberg equilibrium for most loci. Significant heterozygote deficiencies at one locus in a number of populations were detected and may indicate the presence of null alleles. Comparisons of allele frequencies showed little evidence of genetic differentiation either among farmed populations or between farmed and natural populations.

Larvae of Contracaecum sp. among inshore fish species of southwestern Australia

Larval nematode infections were investigated in 236 fish from 17 estuarine and near-shore species in southwestern Australia. Larvae of the genus Contracaecum were found in 4 species of fish (Acanthopagrus butcheri, Sillaginodes punctata, Mugil cephalus and Aldrichetta forsteri). The prevalence and intensity of infection was highest in the 2 species of mullet: 81% infected and 9.8 +/- 1.5 larvae fish(-1) for M. cephalus; 100% and 12.7 +/- 3.7 larvae fish(-1) for A. forsteri. There was no evidence of post-mortem migration of worms from the visceral organs to the musculature of the fish.

Mitochondrial DNA polymorphisms and fertility in beef cattle

Four hundred and twenty-two beef cattle of two different breeds (purebred Hereford and composite multibreed) were characterized by polymerase chain reaction-restriction fragment length polymorphism, using the restriction enzymes ApaI, AvaII, HindIII, PstI, SpeI, SspI and TaqI in two regions (the D-loop and the ND-5 gene) of mitochondrial DNA. The association between molecular haplotypes and records on calving rate, defined as the mean number of live calves born per year over 4 years, were examined by analysis of variance. A significant association was found between calving rate and mitochondrial polymorphisms in both breeds. This may have implications for genetically improving cow fertility.

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.

Factors influencing the development and carbohydrate metabolism of Echinococcus granulosus in dogs

Echinococcus granulosus adult worms, 35 days postinfection, were measured for dispersion in the intestines of 10 dogs, a range of morphological characters, and the excreted end products of carbohydrate catabolism following 4 hr incubation in vitro. Most worms were found in the proximal sections of the small intestine, but the pattern of dispersion differed between dogs. Worm development varied both between dogs and between different regions of the small intestine of individual dogs. Overall there was a high level of variability with no simple patterns. Worm metabolism was related to worm development and, also independently, to local population density within the intestine. Larger, more mature worms produced less lactate and, at higher densities, worms tended to produce more acetate and succinate (pathways with a higher energy yield than lactate) and less ethanol. Thus, both more developed worms and high population density are associated with a shift from cytosolic to mitochondrial metabolism. The variation between worm populations along the small intestine along with the observed variation between worm populations from sibling dogs infected with genetically identical parasites suggests that the local host environment has a significant effect on parasite development.

Combining data from morphological traits and genetic markers to determine transmission cycles in the tape worm, Echinococcus granulosus

Species of Echinococcus (Cestoda: Taeniidae) require 2 mammalian hosts to complete their life-cycle; a carnivorous definitive host, and a herbivorous or omnivorous intermediate host. For most species of Echinococcus, the definitive host range is restricted to 1 or a few species, but the intermediate host range is very broad. Programmes to control hydatid disease attempt to break the life-cycle of the parasite and their effectiveness is therefore enhanced by an understanding of local patterns of transmission. Although it is known that the rostellar hooks of protoscoleces may be influenced by the species of intermediate host in which they develop, the application of this knowledge to infer transmission cycles has been limited, because the intermediate host effect has not been isolated from other environmental and genetic components of phenotypic variance. This study presents a method for separating these potentially confounding genetic and environmental effects, by combining quantitative genetic analyses of hook traits with data on population structure from neutral genetic markers. The method was applied to 5 hook traits (hook number, total length of large hooks, blade length of large hooks, total length of small hooks, blade length of small hooks) measured on protoscoleces from 2 intermediate host types (sheep and macropod marsupials) in Australia. Although genetic variance was similar for all traits, they differed markedly in the extent of environmental variance attributed to development in different host types. Total length of small hooks was the trait most affected, with 49-60% of phenotypic variance being explained by environmental differences between intermediate host species. Blade length of small hooks was least affected, with none of the phenotypic variance due to intermediate host origin. These data suggest that hook measurements of adult worms from naturally infected definitive hosts could be used to determine the intermediate host species from which infection was acquired, if the appropriate traits are measured.

Species of Echinococcus: Pattern and process

Although classification and nomenclature within the cestode genus Echinococcus has, historically, been controversial, the past 20-30 years have provided a period of relative stability. Recent calls for taxonomic revision in the genus have therefore created something of a stir. In this article, Alan Lymbery and Andrew Thompson describe the reasons for the new controversy, and suggest that the problem can only be resolved by agreement on an appropriate species concept and on operational procedures for implementing that concept.

Giardia duodenalis: exposure to metronidazole inhibits competitive interactions between isolates of the parasite in vitro

The competitive interactions of genetically distinct isolates of Giardia duodenalis with different growth rates were studied in vitro. Electrophoretic analysis of mixed cultures showed that competition between 2 cloned isolates occurs under normal in vitro culture conditions, with faster-growing isolates outcompeting those with slower growth rates. The addition of sublethal concentrations of metronidazole to clonal mixtures in vitro prevented the competitive exclusion, which was seen in normal culture. This apparently occurred because the drug reduced the growth rate of the faster-growing but not the slower-growing clone.

Finding genetic markers for complex phenotypic traits in parasites

The identification, mapping and eventual cloning of genes which determine or influence important epidemiological traits in parasites can have great benefits for the control of parasitic disease. In this review, strategies are outlined for identifying genetic markers for complex, quantitative traits. A genetic marker is a variable DNA sequence which co-occurs with a variable quantitative trait. Candidate markers are chosen because they are thought to directly influence the trait whereas random markers are expected to be linked to another DNA sequence which influences the trait. Association studies compare the value of a quantitative trait between different marker genotype classes in a population, without regard to family structure. Linkage studies compare the value of a quantitative trait between marker genotype classes within families or within a population (usually derived from a cross between inbred lines) which is segregating for both marker and quantitative trait loci. The most commonly used analytical methods for determining the significance of association or linkage between marker and quantitative trait loci, and for estimating parameters such as recombination rate and quantitative gene action, are least-squares and maximum likelihood. Both methods may be used to test either single markers or the interval between flanking markers, and both suffer from the need to minimize type I and type II error rates with multiple tests.

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.

Differences in antigen expression within and between 10 isolates of Giardia duodenalis

In this study indirect immunofluorescence was performed on both live and fixed trophozoites to determine the level of variability in surface antigen expression between 14 Giardia duodenalis isolates, using a monoclonal antibody raised against the Portland 1 isolate (ATCC No. 30888). Subsets of antigen positive cells were detected in 13 isolates ranging in number from < 1% to 50% of the total population. The differences in antigen expression between 10 uncloned isolates did not correlate with genetic differences determined using isoenzyme analysis. Examination of four clones of the Portland 1 isolate showed that all of the progeny expressed surface antigen at significantly different levels to the parent.

Genetic analysis of Actinobacillus pleuropneumoniae, and comparison with Haemophilus spp. Taxon "minor group" and Taxon C

The genetic diversity among 52 field isolates, mainly from Australia, and 15 reference strains of Actinobacillus pleuropneumoniae was examined using multilocus enzyme electrophoresis. Thirty three electrophoretic types (ETs) were recognised, with a mean genetic diversity per locus of 0.312. Australian strains of serovars 1, 2, 5 and 7 belonged to the same clonal lines as strains of these serovars in other countries, but distinct clones of serovars 3, 7, 11 and 12 were also identified. The type strains of serovars 1, 9 and 11 were placed in the same ET. Strains of A. pleuropneumoniae biovar 2 were closely related to biovar 1 strains. Twenty three isolates which did not react with the typing sera or could not be assigned to a single serovar were divided into seven clonal groups. Five strains of Haemophilus sp. Taxon "minor group" which were included in the study were distinct from A. pleuropneumoniae, and were diverse, being divided into at least two major genetic groupings. Two strains of Haemophilus sp. Taxon C were placed in another distinct ET.

Clonal analysis of Escherichia coli of serogroups O9, O20, and O101 isolated from Australian pigs with neonatal diarrhea

The genetic diversity of 87 isolates of Escherichia coli recovered from Australian pigs with neonatal diarrhea was examined by multilocus enzyme electrophoresis. The isolates were of serogroups O9, O20, and O101, and although most isolates lacked K88(F4), K99(F5), 987P(F6), and F41 fimbriae, they were considered to be involved in the etiology of the diarrhea. The isolates were extremely diverse, considering their origin from a single pathological condition in one country. There were estimated to be 18, 16, and 12 clones of the three respective serogroups in the collection, with serogroup diversities of 0.387, 0.448, and 0.275, respectively. Comparison with the results previously obtained for isolates from piglets with postweaning diarrhea suggested that bacteria from piglets with these two conditions did not come from any particular common genetic background. The overall genetic diversity for the combined collection was the same as that reported by others for representative isolates selected from throughout the species (0.47). The current results indicate that if isolates of these O groups are involved in porcine diarrhea, their pathogenicity is directly linked to their O somatic antigen type and is not simply due to the wide distribution of a small number of virulent clones.

The porcine intestinal spirochaetes: identification of new genetic groups

The weakly beta-haemolytic isolates were divided into 56 electrophoretic types (ETs), contained in three distinct genetic groups (A,B and C). Group A corresponded to the genus Serpulina, and could be divided into three divisions. It contained 17 weakly haemolytic isolates in divisions b and c, as well as all 98 isolates of S. hyodysenteriae, located in division a. All seven weakly beta-haemolytic isolates that produced indole and had alpha-glucosidase but not alpha-galactosidase activity fell into division b. These spirochaetes may represent a distinct species. The other ten weakly beta-haemolytic spirochaetes, in division c, fitted the description of S. innocens. Group B contained 17 of the weakly beta-haemolytic isolates (18.9%) in ten ETs. Isolates in this group differed from typical S. innocens in that they lacked alpha-galactosidase activity. Group B represented a distinct group of weekly beta-haemolytic spirochaetes, which may constitute a new genus. Group C contained 56 of the weakly beta-haemolytic isolates (62.2%) located in 29 ETs. The original isolate from "spirochaetal diarrhoea" (P43/6/78-Taylor et al., 1980) was located in this group, together with Australian isolates from a similar condition. Spirochaetes in group C were morphologically distinct from those in groups A and B in that they possessed only four, five or occasionally six, subterminal axial filaments, were more slender, and had more pointed ends to their cells. We consider that group C represents a new genus of spirochaetes, members of which may be associated with spirochaetal diarrhoea.

Morphological characterization of adult Echinococcus granulosus as a means of determining transmission patterns

Host induced changes in morphological characters of the rostellar hooks of Echinococcus granulosus were used to determine the origin of infection in definitive hosts in rural areas of southeastern Australia where wild and domestic cycles of transmission may interact. The morphological characters studied vary depending on the species of intermediate host (macropod marsupials, sheep) in which protoscoleces develop, and these characters are retained in adult worms. It was therefore possible to determine whether definitive hosts (dingoes and foxes) acquired infection by consuming protoscoleces of E. granulosus from macropods or from sheep. The results correlated well with the known distribution of intermediate hosts and illustrate the practical value of such morphological markers in epidemiological studies.

Genetic relationships between isolates of Serpulina (Treponema) hyodysenteriae, and comparison of methods for their subspecific differentiation

Multilocus enzyme electrophoresis (MEE) was used to examine the extent of genetic diversity amongst 98 isolates of Serpulina (Treponema) hyodysenteriae. The species contained four major genetic divisions (A, B, C and D) and 29 electrophoretic types (ETs). Division D was relatively distinct, being separated from the other three divisions by fixed allelic differences at an average of 6.6 of 15 enzyme loci. Electrophoretic differences were compared with results of DNA restriction endonuclease analysis (REA) and serological typing of the isolates. Most isolates with the same or similar REA banding patterns shared the same or similar ETs. This demonstrated that both techniques could be used as sensitive and specific methods of identifying closely related isolates. However, using MEE analysis, some isolates that had quite different REA patterns were found to be genetically closely related. Therefore ET designations had an advantage over REA patterns in that they were readily quantifiable as a means of estimating genetic relatedness between isolates. Most isolates that were genetically similar to each other were of the same serological group, but some antigenic types were widely distributed across the genetic divisions.

Further evidence for the occurrence of a distinct strain of Echinococcus granulosus in European pigs

The morphology, adult development and genetic characteristics of Echinococcus granulosus isolated from pigs in Poland were examined and compared with those of other recognised strains of E. granulosus. The isolates were characterised by their distinct morphology, rapid maturation and unique DNA hybridisation profiles. The form of E. granulosus that occurs in European pigs may therefore be a distinct strain that can be separated morphologically and genetically from other strains and that exhibits features of epidemiological significance, including a rapid rate of development in dogs and an apparent low infectivity to humans and domestic ungulates.

Human intestinal spirochetes are distinct from Serpulina hyodysenteriae

Twenty-nine intestinal spirochetes isolated from Australian aboriginal children and six strains from Italian adults (HRM1, -2, -4, -5, -7, and -14) were genetically examined at 15 enzyme loci by using multilocus enzyme electrophoresis. Results were compared with those previously obtained for 188 porcine intestinal spirochetes. DNA from human strain HRM7 and porcine strain Serpulina hyodysenteriae P18A were also radioactively labeled and hybridized with DNA from 12 other human and porcine intestinal spirochetes. Both the multilocus enzyme electrophoresis and hybridization techniques demonstrated that the human spirochetes were not S. hyodysenteriae. They belonged to another distinct genetic group of spirochetes that included P43/6/78, the bacterium recovered from the first recorded case of porcine intestinal spirochetosis. Bacteria in this distinct group also differed from Serpulina spp. in possessing only four, five, or occasionally six axial filaments, being slightly thinner, and having more pointed ends. These findings add further weight to the possibility that human intestinal spirochetes may act as enteric pathogens.