Table 2.

ED₅₀ determination according to the up–down method⁵

Challenge dose (no. of CFU)	Clinical course	Time of euthanasia (no. of days postexposure)
12	No signs	NA
16	No signs	NA
35	Fever, followed by lethargy	4
58	No signs	NA
122	Fever, followed by lethargy and anorexia	7
169	Fever, followed by lethargy and anorexia	5
174	Fever followed by lethargy and anorexia	5
198	Fever followed by lethargy and anorexia	7
208	No signs	Died at 4 d postinoculation
227	No signs	NA
262	Fever followed by lethargy and anorexia	7
264	Fever followed by lethargy and anorexia	7
295	Fever followed by lethargy and anorexia	5
353	Fever followed by lethargy and anorexia	4
374	Fever followed by lethargy and anorexia	7
479	Fever followed by lethargy and anorexia	3
759	Fever followed by lethargy and anorexia	4
3050	No signs	Died at 5 d postinoculation
4410	Fever followed by lethargy and anorexia	7
4850	Fever followed by lethargy and anorexia	4
12400	Fever followed by lethargy and anorexia	Died at 5 d postinoculation
42700	Fever followed by lethargy and anorexia	Died at 5 d postinoculation

NA, not applicable; these animals were euthanized at day 11 postexposure.

Each data point represents 1 animal.