Three mice were euthanized on days 2, 4, 6, 8, 10 and 14 p.i. and their organs were collected. The collected tissues were weighed, and 10% homogenates were prepared in cold PBS. The homogenates were centrifuged at 3000 rpm for 10 min to remove cell debris, and then the supernatants were 10-fold serially diluted for viral titer determination by plaque assay in MDCK cells. Virus titers were expressed as mean log pfu/g 6 standard deviation (SD).