Methods for recovering poliovirus and rotavirus from oysters

Polioviruses and rotaviruses are potential indicators of sewage pollution of water and shellfish. Several methods for detecting these viruses in oysters were assessed. Elution-precipitation involving Catfloc for clarification and skim milk for subsequent flocculation resulted in the recovery of an average of 79% of poliovirus type 1 and 37% of rotavirus SA-11 from oyster homogenates inoculated with low numbers of these viruses. Adsorption-elution-precipitation did not improve the recovery of poliovirus and was detrimental to the recovery of rotavirus. Ultrafiltration or ultracentrifugation resulted in improved recovery of rotavirus but also in higher toxicity of oyster extracts to cell cultures. We recommend the use of the described elution-precipitation method for detecting viral pollutants in sample of oysters.     

Physiologically based boundary conditions in finite element modelling

Finite element analysis has been used extensively in the study of bone loading and implant performance, such as in the femur. The boundary conditions applied vary widely, generally producing excessive femoral deformation, and although it has been shown that the muscle forces influence femoral deflections and loading, little consideration has been given to the displacement constraints. It is hypothesised that careful application of physiologically based constraints can produce physiological deformation, and therefore straining, of the femur. Joint contact forces and a complete set of muscle forces were calculated based on the geometry of the Standardised Femur using previously validated musculoskeletal models. Five boundary condition cases were applied to a finite element model of the Standardised Femur: (A) diaphyseally constrained with hip contact and abductor forces; (B) case A plus vasti forces; (C) case A with complete set of muscle forces; (D) distally constrained with all muscle forces; (E) physiological constraints with all muscle forces. It was seen that only the physiological boundary conditions, case E, produced physiological deflections (< 2.0mm) of the femoral head in both the coronal and sagittal planes, which resulted in minimal reaction forces at the constrained nodes. Strains in the mid-diaphysis varied by up to 600 micro-strain under walking loads and 1000 micro-strain under stair climbing loads. The mode of loading, as indicated by the strain profiles on the cortex also varied substantially under these boundary conditions, which has important consequences for studies that examine localised bone loading such as fracture or bone remodelling simulations.     

The postimplantation development of spontaneous digynic triploid embryos in LT/Sv strain mice

When spontaneously ovulating LT/Sv female mice are mated with fertile males, between one third and one half of the zygotes analyzed at the first cleavage mitosis are found to be triploid. This is due to the fact that LT/Sv females ovulate both primary and secondary oocytes, all of which are capable of being fertilized. Fertilization of the former group results in the production of digynic triploid conceptuses, while their diploid littermates result from the fertilization of normal secondary oocytes. The present study was therefore carried out in order to investigate the 'spontaneous' level of triploidy in these mice, and to provide insight into the developmental fate of the LT/Sv triploid embryos, as previous studies had indicated that in this species triploids invariably fail to develop beyond the early postimplantation period. This study revealed that when autopsies were carried out on the 7th and 8th days of gestation, it was generally difficult to distinguish between the karyologically normal diploids and the digynic triploid conceptuses when only morphological criteria were used. However, by the 10th day of gestation, the triploid conceptuses could usually be readily distinguished from their diploid littermates by their smaller size and (occasionally) by their disorganized or abnormal morphological appearance.