16 BULLETIN 248, U. S. DEPARTMENT OF AGRICULTURE. 



LEPROSY AND OTHER DISEASES. 



Leprosy is another serious malady with which, according to some 

 investigators, fleas may be connected. This relationship has not been 

 established, but it is well for us to consider all such possibilities. 

 The part fleas play in the life economy of certain tapeworms has 

 been mentioned, as has also their connection with certain rat-infesting 

 organisms. Various other low forms of animal life, many of which 

 are no doubt parasites of the flea itself, have been found in the organs 

 of that insect in different stages of its life. 



FLEAS AS PARASITES OF MAN AND ANIMALS. 



As has been shown, a considerable number of the common fleas of 

 this country may be concerned in the transmission of certain dis- 

 eases if these are once introduced. Several species are, however, of 

 much importance to man aside from their possible connection with 

 disease. It is with the fleas which annoy man or attack poultry or 

 dogs that the people in general are most concerned. 



The effect of the bites of fleas varies much with the individual 

 attacked and also with the identity of the flea concerned. The direct 

 effect of these bites, aside from disease transmission, has received 

 little attention. Usually in man pronounced red, itching papules, 

 in some cases with whitish centers, occur at the site of the puncture. 

 Some more susceptible individuals show marked irritation, swelling, 

 and even ulceration following attack. The papules may persist for 

 several days, but usually disappear within a few hours. The irrita- 

 tion is probably induced largely by the injection of the salivary secre- 

 tion into the wound. This injection causes a rush of blood to the 

 spot, which facilitates the feeding of the insect and in turn causes 

 irritation in the host. The question of acquiring immunity to an- 

 noyance by fleas is an interesting one. Many cases have been re- 

 ported wherein individuals have enjoyed marked immunity to the 

 effect of fleabites and comparative freedom from annoyance after 

 being exposed to the fleas of California. The species concerned in 

 these instances was without doubt the human flea. Others report a 

 similar diminution in the annoyance caused by the dog flea. A brief 

 discussion follows of the more important species from the stand- 

 point of annoyance to man and domestic animals. 



THE HUMAN FLEA. 



The species of flea known scientifically as Pulex irritans L. has long 

 been considered the human flea. It is to be found in practically 

 every portion of the earth frequented by man. It is quite distinct 

 from other fleas in structure (figs. 5 and 6), and is largely dependent 



