Table 2.

Summary of results of studies investigating minimum infectious doses of rickettsiae in animal and in vitro models

Minimum infectious dose	PFUa	ID50a				FD50a	PFUb		Organisms
	Chicken embryo cells	L cell	Chicken embryo	Mouse	Guinea pig	Guinea pig	Rat	Mouse BALB/c	Non-human primates	Humans	Reference
R. typhi Wilmington	3	15	325	2	5	11					[30]
R. prowazekii Cairo 3	5	3	20	15	9	9					[30]
R. prowazekii Brenl	2	2	41	393	1	2					[30]
R. canadensis	4	138	4	9.7 × 104	1.1 × 104	2.7 × 106					[30]
R. rickettsii Sheila Smith	7	15	315	1.0 × 105	126	126					[30]
R. rickettsii R	2	0.5	7	1.6 × 106	21	21					[30]
R. conorii Malish	2	0.7	220	1,692	47	319					[30]
R. siberica 246	3	1	62	6,300	23	34					[30]
R. typhi Wilmington							0.38–1.33	0.11–0.75			[61]
R. rickettsii									1.5		[24]
R. rickettsii Sheila Smith									45		[23]
R. rickettsii Sheila Smith									450		[22]
R. rickettsii Sheila Smith										13	[25]

PFU - plaque forming units

ID₅₀ − 50% infectious doses

FD₅₀ − 50% fever dose per gram of yolk sac

^a Numbers of rickettsiae that constitute 1 plaque forming units (PFUs) or 1 50% effective dose in terms of cytopathic degeneration, infection, or fever

^b Will seroconvert 50% of the exposed mice

^c Minimum amount in organisms required to induce mortality or morbidity in at least one Rhesus monkey test group following aerosol exposure