INFECTIOUS DISEASES OF MICE 425 



bartonellae. These observations have been amply confirmed, and Schil- 

 ling's name of Epcrythrozoon coccoides has been adopted for the mouse 

 strain on the basis of priority. 



Occurrence. — The infection is apparently widely distributed geo- 

 graphically, and has been described in various strains and stocks of mice in 

 Europe (52, 238, 32. 120, 167), in Africa (302), and in America (63, 77, 163). 

 Both laboratory and wild mice may harbor the organisms. Not all stocks of 

 mice carry the infection, however, since Marmorston (163) found that 5 of 8 

 inbred strains were, free from the disease. The incidence of infection in 

 carrier stocks is usually high, varying from 50 to 100 per cent. 



The natural disease. — As in bartonellosis, severe spontaneous infection 

 with E. coccoides does not occur. Splenectomy is usually required to permit 

 detection of the organisms in the blood, although rare organisms may be 

 seen in animals having latent infections (237, 32, 33, 167). Other insults to 

 the host, such as x-ray irradiation or experimental lymphatic leukemia (163), 

 may be followed by the appearance of eperythrozoa in the blood stream. 

 The only significant pathological change in carrier mice is an increase in the 

 weight of the spleen to approximately twice normal (163). Histological 

 examination may reveal phagocytosis of infected erythrocytes, but does not 

 show a concentration of organisms in the spleen (52, 63). 



Following splenectomy, the organisms appear in the blood after an 

 interval of from i to 19 days, but the usual period is 2 to 4 days (237, 51, 52, 

 32, 63, 120, 122, 167, 163, 331). During the next 5 days they increase in 

 numbers rapidly, showing a definite preference for polychromatophilic 

 erythrocytes. At the height of the infection, almost all the red cells may be 

 involved, but certain cells show an extreme degree of parasitism, containing 

 20 to 40 or more organisms which entirely cover the surface or form cap-like 

 colonies. Free organisms are present in the plasma. The organisms then 

 rapidly diminish in number in the course of 2 or 3 days, but may persist in 

 small although variable numbers up to 6 months. The great majority of 

 mice have no clinical signs of disease. A few may show milled fur and slight 

 weight loss at the height of the infection. The blood changes are slight — 

 mild anemia, increase in reticulocytes and polychromatophilic cells, and 

 inconstant leukocytosis. Xo significant pathological changes are found. 

 One exception to the usual clinical course has been reported by Galli-\'alerio 

 (83). Nine months after splenectomy and the initial infection the mouse 

 sickened, lost much of the hair about the head, and died. Autopsy revealed 

 emaciation, viscid conjunctival secretion, pale and edematous muscles, large 

 soft liver, and dull red kidneys. Large numbers of Eperythrozoon coccoides 



