414 FLEAS 



mission of disease is their relation to the spread of certain species 

 of tapeworms, especially the common dog tapeworm, Dipylidium 

 caninum. The larval stage of this tapeworm is passed in the body- 

 cavity of the dog flea, Ctenocephalus canis, the eggs of the parasite, 

 adhering to hair in the vicinity of the anus, being ingested by the 

 flea. Occasional infection of human beings, especially young 

 children, occurs by the accidental swallowing of infected fleas, a 

 thing which could easily happen in cases of too great intimacy be- 

 tween children and their pet dogs. As many as 50 larvae of Dipy- 

 lidium have been found in a single flea. The larvae can also de- 

 velop in the human flea. The rat flea, Xenopsylla cheopis, has 

 been found to harbor the larval stages of tapeworms of the genus 

 Hymenolepis, as many as nine cysticercoids having been found 

 in a single specimen. These tapeworms are normally parasitic in 

 rats and mice but occasionally parasitize man also. 



The relation of fleas to other diseases is suspected. A German 

 writer has put forth the theory that fleas are instrumental in 

 the transmission of typhus. If typhus is purely a bacterial 

 disease, its spread by fleas and other parasites as well as by lice 

 would be quite possible, but if it should be found to be caused by 

 an organism which requires a true intermediate host, it would 

 be doubtful whether such widely different insects as lice and 

 fleas could both function in the same manner. That fleas 

 might act as mechanical transmitters of such diseases as tuber- 

 culosis and syphilis is quite possible, though it is doubtful if 

 this often occurs. 



Important Species 



Human Flea. — The only species of flea which is known to be 

 a parasite of man primarily, with the exception of the chigger, 

 is the appropriately named human flea, Pulez irritans, though 

 in many places man is annoyed more by certain other species 

 which are primarily parasites of his domestic animals. The 

 human flea is not exclusively a parasite of man. It also attacks 

 badgers, skunks, dogs and other carnivores, occasionaUy occurs 

 on rats and mice, especially in houses and ships, and has been 

 taken on the blacktail deer, Odocoileus columbianus.^ It is now 



' Specimens of fleas taken in considerable numbers on deer in northern 

 California by F. C. Clarke, of the California Fish and Game Commission, 

 were identified by Prof. R. W. Doane of Stanford University as Pidex irritans. 

 On account of the distinctive habits of these deer fleas, Clarke (in litt.) 

 believes that they should be considered a variety of P. irritans, for which he 

 proposes the name P. irritans cervi. 



