The Molecular Parasitology Laboratory researches parasitic worms of humans, particularly schistosome bloodflukes, which are responsible for the potentially debilitating disease schistosomiasis or Bilharziasis, and dog tapeworms (Echinococcus), which are the cause of hydatid disease.
This laboratory is undertaking extensive human field studies in Hunan Province (Dongting Lake region) and Jiangxi Province (Poyang Lake) in China. This has included longitudinal and cohort surveys of subjects from endemic areas, treatment and follow-up, measurement of reinfection rates, water contact studies, assessment of pathology by ultrasound and specific liver fibrosis markers. We are also continuing large immuno-epidemiological surveys including antibody isotype analysis, T cell proliferation assays and cytokine responses to S. japonicum vaccine candidates following our identification of putative susceptible/resistant schistosomiasis individuals by epidemiological criteria. We have identified close associations between HLA class II antigens and resistance/susceptibility to hepatosplenic disease caused by schistosomiasis and are embarking on a new project aimed at determining whether there are additional genetic components associated with human susceptibility to advanced schistosomiasis. A new five year, NIH-supported project will investigate the hypothesis that bovine, especially buffalo, infections are responsible for the persistence of human schistosomiasis transmission in much of southern China. The project will also involve five year population-based incidence studies of infection and infection intensity of schistosome infections in humans and livestock animals. Mathematical modelling will be integral to the project so as to predict the effect of the closure of the Three Gorges Dam on schistosome transmission. Don McManus, Li Yuesheng and Gail Williams are involved in the project.
Other studies are characterising nuclear and mitochondrial genomes and investigating molecular variation both in the genomes and in key molecules that may be the targets of new anti-schistosome and anti-Echinococcus vaccines. A major finding of our mitochondrial genomics studies was the distinctiveness of the complete DNA sequences of the horse-dog and sheep-dog strains of Echinococcus granulosus which indicates that each should be regarded as distinct at the specific level.
We focus on dyneins, secreted enzymes and surface molecules, including receptors that are also likely novel targets for drugs and vaccines. The Molecular Parasitology Laboratory is currently searching for vaccines against Schistosoma mansoni(endemic to Africa, the Eastern-Mediterranean, the Caribbean and South America) and Schistosoma japonicum, the Asian or Oriental schistosome (endemic mainly in China and The Philippines). We are also working on aspects of the schistosome genome and the worm surface, which may impact on vaccine and drug development.
We aim to develop new methods of diagnosis in patients infected with hydatid disease and have cloned and expressed a novel E. granulosus antigen that shows appropriate specificity and sensitivity for a commercial test.
Schistosomiasis is caused by adult bloodflukes (trematode worms) depositing eggs in blood vessels surrounding the bladder or gut of the infected host. A serious parasitic disease that infects over 200 million people, schistosomiasis occurs mainly in rural agricultural and peri-urban areas of the developing world. Twenty million suffer severe consequences from the disease and 120 million are symptomatic with symptoms ranging from fever, headache, and lethargy, to severe sequelae including ascites, hepatosplenomegaly, and often death. Indeed, it has been estimated that 500,000 deaths occur annually due to schistosomiasis, which is testimony to its public health significance. The development of effective vaccines against schistosomiasis is a public health priority.
Schistosomiasis vaccine development
We have cloned and characterised an extensive number of cDNAs encoding Schistosoma japonicum vaccine candidates including a 14 kDa fatty acid binding protein, paramyosin, glutathione S- transferase 26, glutathione S-transferase 28, 22.6 kDa tegumental antigen, 23 kDa transmembrane protein, aspartic protease, calponin, calreticulin, dynein light chain, calpain, triose-phosphate isomerase (TPI) and heat shock proteins. In addition to understanding the molecular characteristics of many of these proteins, we have undertaken studies on their function and localisation. Further, the majority have been expressed in bacteria and/or baculovirus and have been tested for vaccine efficacy in mice and large domestic animals notably pigs and bovines in China. As a result of this large scale work, we have identified three vaccine targets, paramyosin, GST-26 and TPI which we are pursuing further. Paramyosin and GST-26 have provided very encouraging levels of protection in mice and bovines, notably water buffaloes. Paramyosin is currently being produced under GMP conditions at the Hong Kong Institute of Biotechnology (HKIB) for planned extensive use in China and possibly The Philippines. We plan to commence a new vaccine trial in buffaloes in China with paramyosin and in mice comparing QIMR and HKIB produced materials. New adjuvant formulations will also be tested. In addition, a large trial in bovines is planned in China to compare the combined protective efficacy of paramyosin and GST-26. New studies investigating the effectives of DNA vaccines will commence. Another new project will commence which involves signal peptide selection for identification of genes encoding secreted proteins and receptors, novel targets for schistosome vaccines.
Field ecology of schistosomiasis
We have undertaken extensive human field studies with our large team of Chinese collaborators in Hunan Province (Dongting Lake region) and Jiangxi Province (Poyang Lake). This has included longitudinal and cohort surveys of subjects from endemic areas, treatment and follow-up, measurement of reinfection rates, water contact studies, assessment of pathology by ultrasound and specific liver fibrosis markers. In addition, we have undertaken large immunoepidemiological surveys including antibody isotype analysis, T cell proliferation assays and cytokine responses to S. japonicum vaccine candidates following our identification of putative susceptible/resistant schistosomiasis individuals by epidemiological criteria. We propose to follow up these patients in the coming year. We have also identified close associations between HLA class II antigens and resistance/susceptibility to hepatosplenic disease caused by schistosomiasis.
The epidemiological and immunoepidemiological studies will continue in China. Extensive new epidemiological and laboratory data will evolve as a result of the work in Poyang Lake. The full impact of bovines on human schistosomiasis transmission should be evaluated as a result of this unique study and we believe this will represent a major advance and maintain the impetus of vaccine development and its use in control targeting bovine hosts. Furthermore, we are anticipating the development of new schistosomiasis field projects in Agusan Del Sur, Mindanao, which will link with the current ongoing malaria program and in Leyte and Samar. We will also be field-testing new potential diagnostic molecules we and our collaborators have produced to aid in serodiagnosis of schistosomiasis.
Parasite population diversity and genetics
We have undertaken a widescale survey of Schistosoma japonicum genotypes in China. In particular, we have targeted the mitochondrial genome as a source of genetic markers and have now totally sequenced and obtained the gene order of a range of different flatworm species including all three human schistosomes, Schistosoma mekongi, Fasciola and Taenia. These are the first flatworm mitochondrial genomes to have been completed. We are also heavily involved in the schistosome genome project supported by The World Health Organisation; we have been instrumental in obtaining an extensive number of new schistosome genes using the expressed sequence tag (EST) approach and have identified a number of unique transposable elements. We have recently commenced studies using a fundamentally new approach (signal sequence trap) to identify surface and receptor molecules, which may provide new targets for vaccine development.
The wealth of mitochondrial DNA data we have generated will be used in phylogenetic analysis and molecular epidemiology studies. We will be in a position to track the evolution and migration of schistosomes from Africa across Asia into China, Thailand and The Philippines and determine whether the South American schistosomes were introduced from Africa by the Slave trade. We will also be able to determine the extent of genetic variability in discrete schistosome populations; such knowledge is important practically as it may impact on the future use of anti-schistosome vaccines. The other genetic work on schistosomes (transposable elements, EST analysis) will be maintained. Potential students can get involved with any of these exciting projects.
The schistosome surface
The surface of larval and adult schistosomes, the tegument, is in intimate contact with the host immune system. The parasite exhibits a remarkable ability to avoid immune destruction while being constantly bathed in host antibodies and immune effector cells. While this evasion strategy is multi-faceted, one of the most intriguing mechanisms used by the parasite is the adsorption of host glycoprotein ligands such as MHC class I, complement and IgG onto the tegument to mask recognition by the host. In collaboration with Dr Alex Loukas (Molecular Helminthology laboratory) we are presently searching for the schistosome surface receptors of these host molecules using the following techniques:
- Affinity purification using biotinylated parasite surface extracts and ligands conjugated to sepharose.
- Construction of schistosome cDNA libraries in mammalian expression vectors to allow eukaryotic processing and cell surface expression of receptors – once achieved the libraries will be screened with labelled human ligands and recombinant clones identified using FACS and other techniques.
- Signal sequence trap where cDNAs encoding schistosome surface and secreted proteins are selectively identified by the ability of their signal peptides to direct surface expression of a reporter construct in mammalian cells.
Hydatid disease research
Hydatid disease, caused by dog tapeworms of the genus Echinococcus, is a major cosmopolitan disease of widespread importance and is a continuing problem in Australia. We are involved in studies which aim to produce new methods of diagnosis in infected patients and in investigating the extent of genetic variation in Echinococcus. We have recently completed extensive molecular epidemiological surveys of hydatid genotypes in Argentina, Nepal and China and plan to sequence the Echinococcus mitochondrial genome for a source of new genetic markers. We are also using the EST and Signal Sequence Trap approaches to identify new Echinococcus genes with relevance for immunodiagnosis and as markers of stage-specific differentiation. We will expand on a new project we have recently commenced aimed at using differential display to identify stage-specific expressed molecules which are of potential vaccine and/or diagnostic relevance. We are testing efficicacy of a novel compound derived from traditional medicines of China against cystic echinococcosis. We are also developing a vaccine effective against the adult stage of Echinococcus in the dog definitive host.
We encourage potential students to participate in a range of projects associated with our work on hydatid disease.