TRYPANOSOMA CRUZI 493 



Culture. — Tryjpanosoma cruzi cultivated in N.N.N, medium produces 

 the various crithidia and trypanosome types of organism seen in the 

 development of the trypanosome in Triatoma megista. Animals may be 

 infected with the cultural forms. In the writer's experience, it is very 

 difficult to obtain subcultures. Noguchi (1924a), working at yellow fever 

 in Brazil, on one occasion cultivated from a patient's blood, not only the 

 leptospira of yellow fever, but also a trypanosome, the presence of which 

 had not been suspected. The trypanosome, which was probably T. cruzi, 

 remained alive in the leptospira medium for many weeks. No statement 

 regarding subculture was made. 



Susceptibility of Animals. — T. cruzi is readily inoculable into laboratory 

 animals, though there is a marked tendency for it to change its virulence. 

 Guinea-pigs infected by inoculation of the intestinal contents of the bug, 

 Triatoma megista, frequently die in a couple of weeks. On the other hand, 

 passage through guinea-pigs for some time may lead to such a decrease 

 of virulence that the animals only acquire a temporary infection, from 

 which they recover. For this reason a strain is best kept up by changing 

 the animal host from time to time. Mice, rats, rabbits, dogs, and cats can 

 all be infected, as also monkeys {Macacus and Cercointhecus) and mar- 

 mosets. As will be seen below, the armadillo also acquires an infection. 

 The virulence of the strain may be so low that it can be kept only in very 

 young animals, which are more susceptible than older ones. 



Transmission. — As already stated above, Chagas (1909) first showed 

 that Trypanosoma cruzi could be transmitted to animals by allowing 

 infected bugs {Triatoma megista) to feed on them (Fig. 208), an observation 

 which he later (1912) extended to two other species {T. infestans and 

 T. sordida). Larvae hatched in the laboratory became infective in ten to 

 twenty-five days after feeding on infected animals, and this, according to 

 Chagas, was associated with the appearance of small trypanosomes in the 

 body cavity fluid and in the salivary glands. The details of the develop- 

 ment are, however, not as well understood as that of Trypanosoma gam- 

 biense in Glossina palpalis. Working with imported bugs in France, Brumpt 

 (1912) found that the trypanosomes of the blood type ingested by the larvae 

 quickly became changed into stumpy crithidia forms, which reproduce 

 rapidly (Fig. 209, i-8). The daughter individuals become elongated, and 

 transform themselves into flagellates of the long crithidia type, till the 

 posterior part of the mid-gut contains large numbers of these forms in 

 varying stages of division (Fig. 209, 9-12). After about twenty days 

 amongst the multiplying crithidia forms, there appear smaller trypano- 

 some forms which have been evolved from the former by migration of the 

 kinetoplast towards the posterior end (Fig. 209, 13-16). As the larva? 

 become older, the small metacyclic trypanosomes appear to be the 



