14 



Insects as Carriers of Disease. 



By H. S. Fremijn, M.R.C.S., F.E.S. Read August 27///, 1908. 



I do not think that I need apologise to you for bringing this 

 subject before your notice. 



This Society has always associated itself in all matters of Natural 

 History, and being chiefly an Entomological Society I feel that all 

 that concerns insects will be welcome. 



Of course, in a short paper I can only give you the briefest out- 

 line of the subject, for it is one that occupies the attention of all 

 medical men in the tropics, and is carefully studied by specially 

 trained men in every part of the world. 



Insects may be carriers of disease in one of three ways : 



In the first place they may settle on infected substances, and then 

 fly elsewhere and settle again, carrying the germs with them. 



Secondly, they may suck blood from an infected case, then, carrying 

 the infection on their proboscis, thrust this into the blood-stream of 

 the next host they bite. 



Thirdly, they suck blood as before, but in these cases they draw 

 up in the blood they swallow an immature parasite. This parasite 

 develops in the body of the insect, where the young forms are pro- 

 duced ; these young forms pass into the salivary glands of the insect, 

 and are carried with the saliva into the next host. So that in the 

 first two cases the insects infect immediately, in the third case they 

 only become infective after the parasite has grown up in them and 

 produced a further generation. 



Diseases may be carried by the following insects : 



Non-biting flies, biting flies, mosquitoes, bed-bugs, fleas and lice. 



In the case of the non-biting flies the method of infection is 

 shortly as follows : The fly is attracted by some infected substance 

 containing, let us say, cholera, or typhoid fever germs ; it settles on 

 this, and the infected material adheres to the feet ; from here it flies 

 off, and next settles on some cakes, meat, or fruit, depositing the 

 infection on these. Now, if these are eaten without further cooking, 

 the person taking them will be liable to develop the disease. 



Some of the non-biting flies sit at the mouths of sewers, and one 

 such fly was found to have on its feet and in its mouth 100,000 

 microbes. These flies enter the houses in the neighbourhood and 

 settle on food stuff or fly into the milk. Such flies as these may 

 have adhering to their bodies lice, eggs of tape- and thread-worms, 

 bacilli of dysentery, typhoid fever, plague, cholera, tuberculosis, etc. 



