NO. 10 COCKROACHES—ROTH AND WILLIS 19 
IV. BACTERIA 
The evidence that implicates cockroaches in the transmission of 
bacterial disease agents is largely circumstantial. Yet much of the 
evidence is so persuasive that we find it impossible to accept cock- 
roaches as only minor annoyances of little medical importance. Al- 
though papers that demonstrated natural and artificial contamination 
of cockroaches with bacteria began to appear in the last century (e.g., 
Cao, 1898), more papers on this subject have been published since 
1940 than in all the years before. This gathering momentum can 
hardly be fortuitous. 
The information relating cockroaches to transmission of pathogenic 
bacteria (Appendix B) includes isolation of bacteria from wild- 
caught cockroaches and experimental inoculation of cockroaches with 
bacteria in the laboratory. Both categories implicate cockroaches as 
potential vectors of infectious agents. The first class is particularly 
significant because it includes organisms that the cockroaches acquired 
naturally through their own activities. Certain bacteria that have been 
transmitted to cockroaches experimentally may be of lesser importance 
because under natural conditions these bacteria may be less accessible 
to the insects. 
About 45 species of bacteria that are not pathogenic to vertebrates 
have been found in cockroaches. These are not discussed. 
More species of pathogenic bacteria have been found associated 
with cockroaches than all other kinds of disease organisms together. 
Cockroaches have been found naturally contaminated with about 40 
species of pathogenic bacteria; many of these have also been trans- 
mitted to cockroaches experimentally. In addition, over 20 other 
species of bacteria have been introduced into cockroaches experi- 
mentally. At least three species of bacteria did not survive in cock- 
roaches ; this latter figure does not include negative results with bac- 
teria that were positive in other experiments. 
The diseases caused by pathogenic bacteria that have been found 
occurring naturally in or on cockroaches include various generalized 
and specific infections, dysenteries, gastroenteritis, summer diarrhea, 
enteric fever, food poisoning, typhoid fever, plague, gas gangrene, 
leprosy, and nocardiosis. 
Additional diseases caused by bacteria that have been transmitted 
to cockroaches experimentally include Asiatic cholera, cerebrospinal 
fever, pneumonia, diphtheria, undulant fever, glanders, chicken 
cholera, anthrax, black leg, tetanus, rat leprosy, and tuberculosis. 
One of the most convincing examples of the transmission of a 
bacterial disease agent by cockroaches is the report by Graffar and 
