362 



BIOLOGY OF THE LABORATORY MOUSE 



by certain insects including the adult Tciicbrlo molilor and T. obscurus, 

 cysticerci will develop which in turn grow into adult worms when the infected 

 insect is eaten by the primary host. 



A third possible way of infection is by the development of worms within 

 the intestine from eggs that have never passed out of the host, i.e., internal 

 autoinfection. However, Hunninen (21) has shown that this does not occur 

 in normal mice, for which he suggests two reasons: first, that the cysticerci 

 develop anteriorly to the region where the adults are found, and second, that 

 from s to 18 days after the first infection there is an absolute resistance to 



50 



^ 



Fig. 143. — Eggs of Cestodes found in the mouse. A, Hymenolcpis nana {front A nimus- 

 tine); B, H. dlminuta {from Augustine); C, H. microstoma {from Joyeux and Kobozicjf). 



further infection. He does suggest, however, that autoinfection may occur 

 in mice whose resistance is lowered as with a bacterial infection. 



Treatment of mice infected with H. fraterna is hardly feasible, which is 

 generally true with mice parasitized by helminths. Instead, it would seem 

 more advisable to make the attack with preventive and control methods. 

 With H. fraterna the fact that internal autoinfection does not normally occur 

 simplifies control measures for laboratory mice. Little difficulty should be 

 experienced with the parasite if water and food is kept so that it cannot be 

 contaminated with feces and if the cages are regularly cleaned. Keeping the 

 cages clean will also help to eliminate some of the insects which may act as 

 intermediate hosts. 



That the tapeworm may be transferred from the mouse to man makes it 

 important for one working with mice to take precaution against becoming 

 infected. One should form the habit of washing his hands each time he has 



