PARASITES 375 



question arises as to whether or not the species is a rather common pest of 

 laboratory mice throughout the country having thus far escaped the 

 taxonomist's attention. 



The mites occur on the hosts for the most part only while they are feed- 

 ing, and after they have become engorged with blood they retreat to crevices 

 in the cages or racks where they breed. They migrate freely from cage to 

 cage and sometimes even from one room to another. Heavily infested 

 animals develop a scabby skin and rough coat accompanied by a generally 

 poor health condition. 



Although it has not been shown that L. hacoti transmits diseases of 

 laboratory mice, certainly such possibility exists. Dove and Shelmire (ii) 

 have reported that they were able to transmit endemic typhus from guinea- 

 pig to guinea-pig through bites of this parasite. 



In the laboratory, unless control measures are applied to these pests, 

 their numbers will reach epidemic proportions. They can be attacked most 

 effectively by thorough cleaning, and by disinfecting the cages regularly. It 

 is well also to spray or paint kerosene into the crevices of the racks. Dusting 

 the animals with pyrethrum powder or spraying them lightly with pyrethrum 

 extract aids in the eradication of the parasite. Using metal cages and metal 

 racks which do not afford good breeding places is a worth-while preventive 

 measure. 



Echinolaelaps echidninus (berlese). — This is the common rat mite 

 which is found on rats in various parts of the world and especially in warmer 

 countries. It has been reported from the house mouse in the United States. 

 This species has been found to be the vector of the pathogenic haemogregar- 

 ine (Hepatozoon muris) of the rat. 



Myobia musculi (schrank). — This mite (Fig. 151) has also been found 

 infesting the experimental mice at the Jackson Memorial Laboratory. 

 (Identification by Dr. H. E. Ewing.) These are small mites less than 3-2 

 mm. in length. They can be found clinging tightly to the bases of the hairs 

 of the host by the specially adapted front legs which are enlarged and 

 shortened with a terminal hook for grasping the hair. A pair of long stout 

 bristles extends from the posterior end of the body. They evidently cause 

 considerable irritation to the host especially around the face regions, for 

 infested mice will scratch those regions until the whole area is raw. 



These parasites are so small and they cling so closely to the host that it is 

 difficult to discover an infestation before the mouse has mutilated itself until 

 it must be discarded. However, pyrethrum extract sprayed on the other 

 members of the same cage has beenTound to be effective. 



