17 
TABLE 9. INF ECTIVE DOSE TOR 20-5 0% OF VOLUNTEERS 
Disease or Agent 
Inoculation 
Dose 
Scrub typhus (21)* 
Intradermal 
1/4 to 3 mouse ID50 
Tularemia (22) 
Intraderma] 
10-50 
Q, Tularemia (22,23) 
Inhal ati on 
10-50 
Malaria (24) 
Intravenous 
10 
Syphilis (25) 
Intradermal 
57 
S. Flexneri 2a (26) 
Ingesti on 
180 
1 (.Sk; 
X v> C< tl HI < 
X iC 
**Antnrax (27) 
Inhalation 
>1300 (greater than) 
Typhoid (26) 
Ingestion 
10 5 
Tularemia (22.) 
Ingesti on 
10 8 
Cholera (28) 
Ingestion 
10 8 
Escherichia coli (29) 
Ingesti on 
10 8 
Shigellosis (30) 
Ingestion 
10 9 
^Numbers in parentheses indicate references. 
**1300 spores (500 less than 5 y diameter) inhaled in 8 hours in a Pennsylavani a 
and a New Hampshire Mill that processed contaminated goat hair. For many years 
employees had been inhaling 21 to 2200 viable B. a nthracis particles daily. Yet 
at the Philadelphia plant during 1933-1 May 1958 there had never been a pulmonary 
case, but 119 cutaneous infections with one death. During 1956-57, 1/3 of the 
employees at this plant were vaccinated for the first time. Sout h Car olina P lant : 
23 (20 died) monkeys contracted pulmonary anthrax of 91 monkeys exposed to the 
exhaust air from a duct that vented a hood over the picking machine. This is a 
dramatic illustration of the value of the equivalent of a microbiological safety 
cabinet, which serves the same purpose of removing contaminated air, because among 
250 employees there had been only 19 cutaneous cases during the 2-1/2 years the 
plant had been in operation. Another generality of interest to the cancer biohazard 
program, derived from these studies on anthrax, is that repeated comparati vely small 
daily doses of anthrax organisms had no cumulative effect (156). From studies with 
1,235 monkeys at Detrick, challenged with anthrax-beari ng particles predomi nantly 
5y or less in diameter, the LD50 was 4,130 spores, with 95% confidence limits of 
1,980 to 8,630 spores. Apparently, for man or monkey, pulmonary anthrax is 
produced only when the minimum infective dose is given all at once. 
Nevertheless, the absence of a cumulative human effect in anthrax may 
not apply to oncogenic viruses, judging from a study with the B/Tennant leukemia 
virus in BALB/c mice, in which it was found that "repeated inoculations with 
lew doses of virus produce a significantly higher leukemia incidence than a 
single injection with a much higher dose" (408). This suggests that the moderate 
risk viruses should be examined by inoculation of susceptible animals with 
repeated small doses approximating the amounts that a technician might accidentally 
absorb. 
[ 404 ] 
