NO. IO COCKROACHES—ROTH AND WILLIS 21 
(Smith et al., 1948). Leprosy is not highly contagious and is prob- 
ably acquired by infecting superficial abrasions of the skin (Freund 
and Middlebrook in Dubos, 1948). Although transmission is pre- 
sumed to be from person to person, indirect transmission has not been 
disproved ; in fact, Smith et al. (1948) cite three examples of indirect 
transmission of leprosy, one in which leprosy developed after an in- 
jection of leprous blood, and two cases in which leprosy began in 
tattooed areas about three years after the tattooing. 
Moiser (1944, 1945, 1946, 1946a, 1947) observed that cockroaches 
in southern Africa bite savagely at night, leaving scars which in 
patients (Moiser, 1946a) at least, have repeatedly been found to con- 
tain Hansen’s bacillus. This observation was anticipated by Lamborn 
(1940) who stated that cockroaches may on occasion feed directly on 
the leper. These findings, together with the data from field and labora- 
tory studies of the relationship of several species of cockroaches with 
Mycobacterium leprae, warrant serious consideration (see pp. 75- 
77). Wilson (1946) points up the problem succinctly in his evalua- 
tion of Moiser’s study: “. ..1if the work of several observers, 
operating in widely separated districts, should establish the fact that 
micro-organisms resembling Hansen’s bacillus are commonly found in 
cockroaches associated with human leprosy, and are not found in cock- 
roaches generally, then the evidence of the association of leprosy with 
cockroaches would be strong enough to demand further investigation, 
and even to justify the instigation of preventive measures.” 
In 1954 Dubois reviewed the role of invertebrates in the transmis- 
sion of leprosy. He cited only Arizumi and Moiser for evidence of 
cockroach transmission, although Macfie, Tejera, Lamborn, and Radna 
had all published supplementary observations prior to 1950. Dubois’s 
main objections to accepting cockroaches as vectors are (1) that the 
exact nature of the acid-fast bacilli found in the cockroaches is not 
known (except by morphological appearance), and (2) the fact that 
cockroaches bite humans seems to be poorly established. These ob- 
jections are sufficiently valid to deserve comment. 
Man is highly resistant to experimental infection, and no other 
animal is susceptible to infection with human leprosy (Smith et al., 
1948). Hence, it has not been possible to prove that the acid-fast 
organisms found in cockroaches are identical to M. leprae. Yet the 
isolation of bacilli that are morphologically similar to M. leprae from 
insects. that have fed on leprous material is highly suggestive, espe- 
cially when similar organisms are not found in control cockroaches 
(Lamborn, 1940). Moiser (1946) suggested that leprosy may be 
