22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 134 
primary in the cockroach and secondary in man, and that the bacteria 
multiply in the cockroach. 
Dubois (1954) cited the opinions of three individuals who stated 
that cockroaches do not bite man. One, an entomologist, was quoted 
as writing, “I have never heard nor read a statement to the effect that 
species of Blattidae bite human beings and if I did, would not believe 
anything so ridiculous.”’ The biting of humans by cockroaches is 
discussed on pages 30 to 32. The biting habit is not characteristic 
of cockroaches, however, and is probably restricted to primitive areas 
with poor sanitation and heavy cockroach infestations, 
Infection through cockroach bites alone need not be an essential 
mechanism in the transmission of leprosy. Moiser (1946, 1946a) 
contended that the bites or the feces of infected cockroaches are the 
real source of infection in leprosy. Wilson (1946) expounded this 
idea in suggesting a mode of infection analogous to the transmission 
of Pasteurella pestis by fleas: contaminated cockroach feces may be 
rubbed or scratched into the skin. Under primitive conditions, such 
contamination may be commonplace. 
If cockroaches are entirely mechanical vectors of leprosy, they 
could conceivably transport M. leprae on their legs from leprous indi- 
viduals to existing lesions in the skin of sleeping humans without 
either biting man or excreting the organism in the feces. There are 
many references to cockroaches climbing over the bodies and faces of 
sleeping children and adults, summarized on pages 28 to 30, in addi- 
tion to the references on biting. 
The Leprosy Research Department, School of Tropical Medicine, 
Calcutta (1948), has investigated the relationship of cockroaches to 
transmission of leprosy. The examination of cockroaches (species 
not identified) captured in a leprosy hospital and in other areas dis- 
closed the presence of acid-fast bacilli in the gut contents of over 50 
percent of 398 insects. These bacilli were morphologically unlike the 
leprosy bacillus and were not more numerous in cockroaches collected 
in the hospital than in those collected elsewhere. Cultures of acid-fast 
bacilli were prepared from the gut contents of six cockroaches. These 
workers, therefore, concluded that the acid-fast bacilli in captured 
cockroaches were not the leprosy bacillus. However, when leprous 
material was fed to a number of cockroaches showing no acid-fast 
bacilli in their feces on three consecutive days, acid-fast bacilli were 
found in the cockroach feces in decreasing number for two weeks 
thereafter. There was no indication that the ingested bacilli multiplied 
in the gut of the cockroaches. On this basis, these workers concluded 
that their work did not support Moiser’s hypothesis that cockroaches 
