Efficient and predictable recovery of viruses from water by small scale ultrafiltration systems.

Current methods to concentrate viruses from large volumes of water are prone to inconsistent results and are costly and complex procedurally. Ultrafiltration can utilize size exclusion rather than adsorption and (or) elution to concentrate viruses and, therefore, may offer greater flexibility in developing methods that can provide more consistent recoveries among different viruses and widely varying water conditions. Two small scale ultrafiltration systems (hollow fiber and tangential flow) were tested with a virus suspended in 2 L of reagent grade, tap, ground, or surface water. Three model viruses were used (bacteriophages PP7 and T1 and poliovirus) to compare and characterize the recovery of viruses with the two ultrafiltration systems. Pretreatment of the ultrafilters with blocking agents and the use of elution agents can serve to prevent viral adsorption to the filter surface or to elute bound virus and keep viral agents suspended in the retentate. The use of a blocking and elution step concentrated viruses (>60% recovery) from widely varying water qualities, including surface water, such that a single method can be used to efficiently concentrate viruses from all of the water types tested. Both ultrafiltration systems appear to be able to efficiently recover viruses; however, the hollow fiber systems provided slightly better results in the 2-L volumes tested.     

Experimental ischaemia of the vertebral artery and its effect on brain stem auditory evoked responses in guinea pigs

The aim of the study was to examine the effect of artificial ischaemia of the vertebral artery region on brain stem evoked auditory potentials (BAEP) in guinea pigs. The results indicate that BAEP are influenced mainly by unilateral irritation of the vertebral artery. An increase in the audibility threshold was observed in the experimental guinea pigs in group C (an increase of 10-40 dB on the side of irritation of the vertebral artery and of 10 dB on the opposite side). Lengthening of the latency period of the P2 wave and of the conduction period between waves P1 and P5 was also observed.