Over a 3-year period, a total of 646 fecal samples from pigs in 22 indoor and outdoor herds from Western Australia were screened for Cryptosporidium spp. by microscopy. Results revealed that 39 of 646 samples (6.03%) were positive for Cryptosporidium. Cryptosporidium was much more common in outdoor herds (17.2%) than in indoor herds (0.5%) and was more common in animals between the ages of 5 and 8 weeks (69.2%) than in younger animals (P < 0.0001). Molecular characterization of the positive samples at the 18S ribosomal DNA locus identified two distinct genotypes of Cryptosporidium: the previously identified pig genotype I and a novel pig genotype (pig genotype II), both of which warrant species status.

Two distinct genetically and biologically differing strains of Cryptosporidium appeared to be associated with acute diarrhoea in pigs. Whether Cryptosporidium was a primary or secondary pathogen is unclear but warrants further investigation. As the bovine genotype is known to infect humans, the results suggest that pigs can act as reservoirs of cryptosporidial infections for humans and other live-stock. The zoonotic potential of the pig-adapted genotype is uncertain and requires further study.

SUMMARYAntisera were prepared in rabbits against seven well-characterized strains of Treponema hyodysenteriae of known serotype, and reacted in agarose gel double immunodiffusion tests (AGDP) with lipopolysaccharide (LPS) extracted from 18 Western Australian isolates of the organism. Eight isolates were provisionally typed by this method, but sera raised against one 'typed' and two 'untypable' local isolates reacted in an unexpected fashion with LPS from other local and type strains. Serum raised against the 'typed' local isolate reached with LPS from other previously untyped local isolates: this indicated the presence of more than one major LPS antigen amongst certain local isolates, and was confirmed by crossabsorption of sera. Sera raised against apparently untypable local isolates reacted with LPS from certain type organisms, thus suggesting the presence of complex antigenic relationships between LPS antigens.The serotyping system for T. hyodysenteriae which was proposed by Baum & Joens (1979) uses unabsorbed antisera and is made unworkable by these observations. Instead we propose placing organisms which share common LPS antigens into serogroups A to E, members of which are defined by their reactivity with unabsorbed sera raised against a type organism for the group. We suggest strains B78, WAI, B169, Al and WA6 respectively as being the most suitable type organisms for the five serogroups identified so far. Isolates possessing additional unique LPS antigens can be regarded as serotypes within the serogroup. However the serotype of an isolate can only be established if antiserum is prepared against it, and this serum continues to react homologously after cross-absorption with bacteria from other serotypes within the serogroup.

There were no consistent differences between Australian strains of PCV and those that have been associated with PMWS in other countries and it appears likely that other factors are responsible for the absence of PMWS in Australia.

Retroviral transfer of Herpes simplex virus thymidine kinase to T cells has been used to confer sensitivity to the antiviral agent ganciclovir. This has allowed therapeutic approaches to be developed in which T cells mediating graft-versus-hostGraft-versus-host disease (GVHD) is a T cell-mediated complication of allogeneic hematopoietic stem cell transplantation (HSCT), and despite advances in immunosuppression, remains a major cause of transplantationrelated morbidity and mortality. 1-3 Donor T cells are known to mediate a potent anti-leukemic effect in patients with hematological malignancies and this has been demonstrated by the successful use of donor lymphocyte infusions (DLI) for the treatment of patients with chronic myeloid leukemia (CML). 4 The depletion of T cells from HSC grafts is associated with a reduction in GVHD, but increases the risk of graft failure and leukemic relapse. 5 Furthermore, as a consequence of the prolonged period of immunodeficiency following T cell depletion, life-threatening viral and fungal infections are of serious concern. 6 In order to harness the beneficial effects of donor lymphocytes whilst limiting adverse effects, several groups have initiated clinical trials exploring the possibility of using genetically modified T cells fitted with the Herpes Simplex thymidine kinase (HSVTK) 'suicide' gene to direct selective elimination of actively dividing cells through activation of the prodrug ganciclovir (GCV) in the event of serious GVHD. 7,8 GCV and aciclovir (ACV) are anti-viral prodrugs that are widely used for the treatment of cytomegalovirus (CMV) and Herpes simplex virus (HSV) infections. They are poor substrates for mammalian nucleoside kinases, but are efficiently phosphorylated to the monophosphate form by HSV-TK. Cellular kinases mediate subsequent metabolism to produce toxic triphosphate derivatives that become incorporated into host cell DNA, leading to the death of actively dividing cells. 9 Bonini et al 7 reported the results from the first clinical trials using the HSV-TK/ganciclovir system for the management of GVHD following bone marrow transplantation (BMT). Twelve patients who had relapsed following allogeneic BMT or developed Epstein-Barr virus induced lymphoproliferative disease after T cell-depleted bone marrow transplantation were treated with infusions of donor T cells carrying HSV-TK. The transduced cells mediated anti-tumor effects in five patients and were detectable in some patients for up to 12 months. GVHD was effectively controlled in three of these five patients by the selective elimination of active T cells using ganciclovir. One case of chronic GVHD was only partially responsive to ganciclovir, and vector-related limitations included evidence of an immune response against the transgenes in two patients. 10 The group has now treated over 40 patients using this strategy, but results have yet to be fully evaluated. 11 Tiberghien et al 8 used HSV-TK transduced T cell infusions to prevent leukemic relapse in 14 patients undergoing BMT for haematolo...