DISEASES CARRIED BY FLEAS 357 



in four per cent of rat fleas, Ceratophyllus fasciattbs, and succeeded in in- 

 fecting rats by feeding them on fleas. Johnston in Australia has corrobo- 

 rated the fact that this flea is a host, while Joyeux has proven that in- 

 fection takes place easily in the larval stage, but is impossible in the adult 

 flea. Johnston has found Xenopsylla cheopis to be a host. Joyeux has 

 infected larvae of Pulex irritans and Ctenocephalus cams. He found that 

 the embryo develops independently of the metamorphosis of its host. 

 The rodents become infected by licking up infected insects. 



Hymenolepis nana (Von Siebold), the dwarf tapeworm of rats and 

 man, may possibly pass its intermediate stage in fleas. NicoU and Min- 

 chin found a cysticercoid in Ceratophyllus fasciatus resembling this 

 species, and Johnston in Australia also found a similar cysticercoid in 

 Xenopsylla cheopis. 



Nemathelminthes : Nematoda: Spiruridae 



Protospirura muris (Gmelin), a STOMACH PARASITE of rats and 

 mice, has a larva similar to one found by Johnston encapsuled in thje 

 general cavity of the rat flea, Xenopsylla cheopis. 



Nemathelminthes : Nematoda: Filariidae 



AcanthocheUonema reconditivm (Grassi), a cause of CANINE FIL- 

 ARIASIS, possibly passes its embryonic development in fleas. Grassi and 

 Calandruccio found larval nematodes in fleas, Ctenocephalus canis, C. felis, 

 and Pulex irritans that they assumed belonged to the species A. recon- 

 ditwm. 'The embryos, according to Grassi, perforate the intestinal wall 

 of the flea which has ingested blood containing the parasites. The latter 

 make their way into the fatty tissue where they are almost always to be 

 found lying singly in the fat cells. The fat cells increase in size as the 

 parasites grow, the latter being curled up once or twice within the cell, 

 the nucleus of which remains uninjured. The embryo undergoes four 

 stages of development in the flea. There is no positive proof of the method 

 of transmission. 



SUMMARY 



In summary, therefore, we may call attention especially to the fact 

 that the flea carries plague, is apparently the carrier of infantile kala 

 azar, and is an intermediate host of one of the human tapeworms. In 

 addition it is intermediate host of various animal diseases. 



Unlike the louse-borne diseases, the life cycles of the organisms caus- 

 ing flea-borne diseases are quite variable. 



The bacilli of plague and rodent plague are taken up by the bite 



