In vitro and in vivo effects of West Nile virus propagated in cells of different passage.

Tissue cultures are used to propagate viruses for use in mosquito infection studies and to detect live virus in field-collected specimens. Microscopic evaluation of cytopathic effects is used to visualize virus presence. In this study, both low-passage (LP; n = 35) and high-passage (HP; n = 218) lines of African green monkey kidney (Vero) cells were infected with West Nile virus, and virus growth kinetics were quantitated over different incubation periods (IPs) (2, 6, 10, 24, 48, 72, and 96 h postinfection). Virus titers were significantly (P < 0.05) higher in the HP compared with LP line 24, 48, and 96 h postinfection. No differences were observed in plaque morphology between the LP and HP lines. Culex pipiens quinquefasciatus were fed infectious blood meals created using supernatant from the 2 lines and maintained at 28 degrees C for a 12-day IP. Although the virus dose was higher (P < 0.05) in the HP compared with the LP line, there were no significant differences in mosquito infection or dissemination rates at the end of the IP. The significance of these observations for assessing virus presence and pathogenicity is discussed.

The sub-energetic gamma-ray burst GRB 031203 as a cosmic analogue to the nearby GRB 980425.

Over the six years since the discovery of the gamma-ray burst GRB 980425, which was associated with the nearby (distance approximately 40 Mpc) supernova 1998bw, astronomers have debated fiercely the nature of this event. Relative to bursts located at cosmological distance (redshift z approximately 1), GRB 980425 was under-luminous in gamma-rays by three orders of magnitude. Radio calorimetry showed that the explosion was sub-energetic by a factor of 10. Here we report observations of the radio and X-ray afterglow of the recent GRB 031203 (refs 5-7), which has a redshift of z = 0.105. We demonstrate that it too is sub-energetic which, when taken together with the low gamma-ray luminosity, suggests that GRB 031203 is the first cosmic analogue to GRB 980425. We find no evidence that this event was a highly collimated explosion viewed off-axis. Like GRB 980425, GRB 031203 appears to be an intrinsically sub-energetic gamma-ray burst. Such sub-energetic events have faint afterglows. We expect intensive follow-up of faint bursts with smooth gamma-ray light curves (common to both GRB 031203 and 980425) to reveal a large population of such events.

The bright optical afterglow of the nearby gamma-ray burst of 29 March 2003.

Past studies of cosmological gamma-ray bursts (GRBs) have been hampered by their extreme distances, resulting in faint afterglows. A nearby GRB could potentially shed much light on the origin of these events, but GRBs with a redshift z