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A SUMMARY OF OUR KNOWLEDGE OF INSECT VECTORS OF DISEASE. 



By Malcolm Evan MacGregor, B.A. (Cantab.), 

 Wellcome Bureau of Scientific Research. 



So much has been said about insects since the War began that it is, I think, advisable 

 that some attempt should be made to summarise our knowledge of the more important 

 insect-borne diseases and their vectors. While insects have long been suspected of 

 being responsible for the transmission of serious diseases, it may be said that practically 

 the whole of our knowledge of insects in this role has been acquired within the past 

 twenty years. So rapidly, however, has the charge on this offence been made out 

 against them that, although it is common knowledge that they have been proved 

 guilty, it is not generally realised upon how many counts the verdict rests. 



It has lately been my good fortune to give class instruction for the War Office to 

 officers of the R.A.M.C. who are proceeding to the East, and in order to bring home 

 to my audience the importance of the connection between insects and disease I have 

 compiled the tables which I now publish. These can in no way claim to be complete, 

 but merely present the more important insect-borne diseases, including human 

 diseases that on certain grounds are suspected of having insect vectors. With 

 these tables I also publish one (Table VI) which includes the chief insects and Acarina 

 that are directly the cause of disease in man and his domestic animals. To complete 

 the list of insect-transmitted diseases would demand the consideration not only of 

 other mammals as hosts, but also of avian and reptilian hosts. In the present instance 

 this would be to carry the subject beyond general interest, but it must be remembered 

 therefore that, long as the present list of charges is, insects are not here arraigned on 

 all the counts that might with justice be preferred against them. 



During the last few years medical entomology has been rapidly establishing itself 

 as an invaluable branch of preventive medicine, and with the outbreak of the present 

 war a great deal of interest and study has been devoted to this subject in Europe, 

 notably in connection with the transmission of typhus fever by lice, and the dissemina- 

 tion of bacteria and other organisms by flies. 



Centuries ago insects were suggested as being possibly concerned in the spread of 

 disease, and from time to time such logical hypotheses were advanced that it is sur- 

 prising that the establishment of the truth was not sooner forthcoming. In 1577 

 Mercurialis, an Italian physician, suggested that plague, which was then ravaging 

 Europe, was spread by flies feeding upon the diseased and dead, and later depositing 

 faecal matter on food consumed by healthy persons. This idea held ground, and 

 various suggestions occur as to the spread of disease by flies in the literature of the 

 X\ Illth century. Edward Bancroft in 1769 advanced the theory that yaws was 

 transmitted by flies feeding on diseased subjects and carrying the contagion by settling 

 on open wounds or scratches on healthy persons. In 1848 Dr. Josiah Nott, of Mobile, 

 Alabama, published a remarkable article in which he gave reasons for supposing that 

 yellow fever was an insect-borne disease ; but although he mentioned many insects, 

 he did not specify any one as the particular vector. 

 (C394) c2 



