Infection procedures

Animals were anesthetized using ketamine HCL 0.1mg/g (Bioriche Teoranta Inverin, Co. Galway, Ireland) and xylazine 0.01 mg/g (Lloyd Laboratories, Shenandoah, Iowa). Intragastric infection was effected by a 20 gauge, 3.8 cm, 2.4 mm tip, feeding tube (Fisher Scientific, cat# FNC 20–1.5, Pittsburgh, PA) which delivered 1x10⁹ genomic equivalents of MPyV suspended in 125 μl 0.9% saline. For intranasal infection the same dose of virus was suspended in 25 μl volume. After the animals were anesthetized, inoculum was delivered in 5 μl aliquots alternating between the right and left nostrils, with a 10 min waiting period between successive doses. A transient increase in respiratory rate was observed during this maneuver [11]. The dose of virus infected was determined empirically. In preliminary experiments, injection of 1x10⁶ to 1x 10⁸ genomic equivalents did not result in successful infection. Historically investigators have most often used 1E+06 to 1E+07 plaque forming units (PFU) of virus to infect mice, with 1 PFU = 100–1000 genomic equivalents as measured by PCR.