Table 6. Infective dose (ID) of some pathogenic microorganisms.

Microorganism	ID	Recipient	Administration	Infected/Total (or% infected)	Reference
Campylobacter jejuni	90 CFU	3-day chickens	Orally	9/10	(Ruiz-Palacios et al., 1981)
E. coli (O157:H7)	6000 CFU	3-month pigs	—	6/8	(Cornick and Helgerson, 2004)
E. coli (O157:H7)	<300 CFU	10-week calves	Orally	2/17	(Besser et al., 2001)
E. coli (O157:H7)	107 CFU	3-year steer	Stomach tube	2/5	(Cray and Moon, 1995)
Salmonella typhimurium	1000 CFU	10–14-day pigs	Intranasal	1/5	(Loynachan and Harris, 2005)
Salmonella enteritides	<10 CFU	>52-week molted layers	Orally	50%	(Holt, 1993)
Salmonella enteritides	6500–56000 CFU	>52-week unmolted layers	Orally	50%	(Holt, 1993)
FMD virus (strain O1 Lausanne)	1700 TCID50	20–30 kg pigs	Aerosol	5/8	(Alexandersen and Donaldson, 2002)
FMD virus (strain O1 BFS 1860)	13–398 TCID50	43–166 kg calves	Aerosol	10/12	(Donaldson et al., 1987)
FMD virus (strain O1 BFS 1860)	10–50 TCID50	26–82 kg sheep	Aerosol	7/12	(Gibson and Donaldson, 1986)
FMD virus (strain SAT 2 SAR 3/79)	25–251 TCID50	118–150 kg calves	Aerosol	11/15	(Donaldson et al., 1987)
PRRSV	10 TCID50	4–5-week pigs	Intranasal	2/3	(Yoon et al., 1999)
Porcine rotavirus	1 PFU	2-hr piglets	Pharynx	2/2	(Graham et al., 1987)
Encephalomyocarditis virus	108.8 TCID50	4–6-week pigs	Intranasal	2/5	(Zimmerman et al., 1993)
Influenza A/Texas/91 (H1N1) virus	100000 TCID50	18–33-year-old humans	Intronasal	24/33	(Hayden et al., 1996)
Influenza A2/Bethesda/10/63	1–5 TCID50	21–40-year-old man	Aerosol	4/14	(Alford et al., 1966)
Rotavirus	0.9 FFU	18–45-year-old man	Orally	1/7	(Ward et al., 1986)
Salmonella newport	150000 CFU	Human	Orally	1/6	(McCullough and Eisele, 1951)
Salmonella derby	1.5×107 CFU	Human	Orally	3/6	(McCullough and Eisele, 1951)
Salmonella bareilly	13000 CFU	Human	Orally	1/6	(McCullough and Eisele, 1951)

CFU = colony forming unit; TCID₅₀ = 50% tissue culture infective dose; PFU = plaque forming unit; FFU = focus forming unit.