28 SANITARY ENTOMOLOGY 



3. Can Insects Themselves Cause Disease? 



Many species of insects are known to live parasitically upon the 

 bodies of man and animals and by their constant sucking of blood or 

 gnawing, cause skin diseases. Other species of insects habitually lay their 

 eggs on or in the flesh and breed commonly or exclusively in living flesh, 

 causing a destruction of the tissues. Many .species of insects are depen- 

 dent upon mammalian blood for the necessary nutriment to bring about 

 reproduction. Some insect larvae are bloodsuckers. It is not at all 

 uncommon for insect larvae to be ingested in food and for them to con- 

 tinue their development in the intestines or other organs, often at the 

 expense of the tissues. In some parts of the world insects are eaten as 

 food by the natives, sometimes in a raw state, and it is not uncommon 

 in such case for the natives to be infected with parasitic worms which 

 pass their intermediate stages in the bodies of these insects. 



4. Where May Insects Obtain the Organisms mhich Cause Disease? 



Disease organisms may be taken up by insects directly from the blood 

 of an infected host, or they may be obtained by contact with infected 

 surfaces of the body or taken up from the feces or other excretions of 

 an infected host. The insect may take up the organisms from these 

 excretions either in its larval or its adult stage. 



5. How Cam the Insect Transmit the Organism? 



The organism may be transmitted by the insect by direct inoculation 

 through the proboscis, involving the active movement of the parasite, or 

 the passive transmission of the parasite in the reflex action which takes 

 place in the sucking of blood. The organism may be externally carried 

 on the beak of the insect and mechanically transmitted at the time of 

 sucking. It may be located in the mouth parts of the insect and burrow 

 through at the same time the insect is feeding. It may be in a passive 

 state on the insect and become stimulated to attack the host when it 

 comes in contact with the warm body. The organism may be regurgitated 

 by the insect on the body of its host and obtain entrance by its own 

 activity, or by being scratched in or by being licked up by the host. 



On the other hand, the organism may pass through the insect, and 

 pass out in its feces, or in Malpighian excretions. It may be washed into 

 the wound made by the sucking of the insect, by fluids excreted at the 

 time of the feeding. It may remain in the feces on the host and ultimately 

 be scratched in or licked up by the host. 



The organism may be taken up by the insect and never normally pass 

 out of the insect, but be inoculated by the crushing of its invertebrate 



