Fleas and Lice as Carriers of Trypanosoma lewisi 213 



a specific poison. The majority of them are tropical in distri- 

 bution. 



Though we are concerned especially with the species which infest 

 man, we shall first consider two of the trypanosomes of lower animals, 

 known long before any of those of man had been found. 



Fleas and Lice as Carriers of Trsrpanosoma lewisi. — Trypanosoma 

 lewisi, the first mammalian trypanosome known, is to be fotmd in the 

 blood of wild rats. Like its host, it appears to be cosmopolitan in 

 distribution, having been reported from several localities in the 

 United States, Brazil, Argentine, England, Germany, France, Italy, 

 Russia, Asia and Africa. 



This species is usually regarded as non-pathogenic, but in experi- 

 mental work, especially with white rats, heavy infestations often 

 result fatally, and naturally infested specimens sometimes show 

 evidence of injury. Rats which have been infested exhibit at least 

 temporary immunity against new infection. 



Trypanosoma lewisi is transmitted from rat to rat by fleas and 

 by lice. Rabinowitsch and Kempner (1899) first found that healthy 

 rats which were kept with infested rats, showed trypanosomes in 

 their blood after about two weeks. They found the trypanosomes 

 in the alimentary canal of fleas which had fed on the diseased rats. 

 On teasing such fleas in physiological salt solution and inoculating 

 them into fresh rats they were able to produce the infection. Finally, 

 they showed that the fleas which had fed upon infested rats were 

 able to carry the parasites to healthy rats. Corresponding experi- 

 ments with lice were not successful. Prowazek (,1905) found in the 

 rat louse {Hcematopinus spinulosus) organisms which he regarded 

 as developmental stages of the Trypanosoma lewist. He believed 

 that the sexual cycle was undergone in this insect. 



Nuttall (1908) readily transmitted the trypanosomes through the 

 agency of fleas, {Ceratophyllus fasciatus and Ctenopthalmus agyrtes). 

 He believes that these insects are probably the chief transmitters 

 of the parasite. He was also able to transmit it from diseased to 

 healthy rats through the agency of the rat louse. He was unable 

 to trace any developmental stages in the louse and inclined to the 

 opinion that Prowazek was deceived by the presence of extraneous 

 flagellates such as are known to exist in a number of blood-sucking 

 arthropods. 



Nuttall concludes that since three distinct kinds of blood-sucking 

 insects are capable of transmitting Trypanosoma lewisi it appears 



