DISEASES TRANSMITTED BY FLEAS 413 



the squirrel fleas, Hoplopsyllus anomalus and Ceratophyllus acutus, 

 also have been shown to carry the infection. It is evident also 

 that other animals besides rats and man are susceptible to the 

 disease. Ground squirrels, Citellus beecheyi, guinea-pigs and 

 monkeys have been shown to be susceptible. A marmot or 

 ground hog, Arctomys hobac, common in Manchuria, is thought 

 to have been the chief reservoir of the disease in the Manchurian 

 epidemic in the winter of 1910-11, the flea Ceratophyllus silan- 

 tiewi being the transmitting agent. 



Doubtless any fleas which attack these animals and which 

 also attack man may be instrumental in spreading the plague to 

 human beings in direct proportion to the willingness with whicli 

 they will bite man, and to their opportunities for doing so. It 

 must not be inferred that only fleas can transmit the disease. 

 The pneumonic form of plague, which is relatively uncommon, 

 is transmitted by particles of sputum or mucus from the mouth or 

 lungs. The bubonic plague may also be transmitted by bedbugs 

 and perhaps by other parasitic insects. A head louse taken from 

 a plague patient was found to be infected. There can be no 

 doubt, however, that the rat fleas are by far the most important 

 spreaders of this terrible disease. 



A similar but milder disease of rodents has recently been dis- 

 covered in the United States, caused by Bacterium tularense, and is 

 believed to be transmissible by fleas. Flies have been shown to 

 mechanically transmit the disease but the role of fleas is only 

 conjectured. 



Another disease which is commonly believed to be transmitted 

 by fleas is the Mediterranean or infantile form of kala-azar 

 (see p. 83). This is prevalent in dogs throughout many of the 

 regions bordering the Mediterranean, especially in parts of Italy 

 and North Africa, and is the cause of a high mortality in the 

 numerous cases which occur among children. A number of 

 authors have carried on experiments to prove the instrumentality 

 of the common dog flea, Ctenocephalus canis, and also of the 

 human flea, Pidex irritans, with varied results. (See Chap. V, 

 p. 83.) The role of fleas in the transmission of this disease is 

 still uncertain but there is enough evidence against the fleas to 

 warrant their being looked upon with extreme suspicion until 

 definitely proved innocent. 



Another instance of the instrumentality of fleas in the trans- 



