THE HEMOFLAGELLATES 



59 



Arizona, New Mexico and southern Califor- 

 nia, but Walton et al. (1956) discovered it 

 in raccoons in Maryland, and it appears 

 that it may be rather widely distributed in 

 the southeastern states. McKeever, Gor- 

 man and Norman (1958) found it in 17% of 

 552 opossums, 2% of 118 grey foxes {Uro- 

 cyon cinereoaygentens), 1. 5% of 608 rac- 

 coons and 1% of 306 striped skunks {Me- 

 phitis mephitis) from Georgia and Florida. 

 Walton et al. (1958) found it in 5 of 400 

 raccoons from Maryland. Norman et al. 

 (1959) reported that their strains were 

 typical T. criizi of relatively low virulence 

 for mice. 



Morphology : The forms in the blood 

 are monomorphic, 16 to 20 /i long, with a 

 pointed posterior end and a curved, stumpy 

 body. The kinetoplast is subterminal and 

 larger than that of any other trypanosome 

 of domestic animals or man, often causing 

 the body to bulge around it. The undulating 

 membrane is narrow, with only 2 or 3 un- 

 dulations. There is a moderately long 

 free flagellum. The leishmanial forms in 

 the muscle and other tissue cells are 1. 5 

 to 4. 0|i in diameter and occur in groups. 

 Electron microscope studies of this spe- 

 cies have been made by Meyer and Porter 

 (1954), Meyer, Musacchio and Mendonca 

 (1958) and Meyer and Queiroga (1960). 



Fig. 4. Successive stages in the transfor- 

 mation of a leishmanial form of 

 Trypanosoma criizi into a meta- 

 cyclic trypanosome form. The 

 metacyclic trypanosome (lower 

 right) is from a Giemsa stained 

 smear; the other stages are from 

 living preparations of culture ma- 

 terial viewed with the phase mi- 

 croscope. (From Noble, 1955) 



Life Cycle : Altho the trypanosome 

 form of T. cruzi is common in the blood 

 in the early stages of Chagas' disease, it 

 does not multiply in this form. The try- 

 panosome forms enter the cells of the 

 reticulo-endothelial system, striated mus- 

 cles and especially of the heart muscle, 

 where they round up and turn into leish- 

 manial forms. These multiply by binary 

 fission, destroying the host cells and 

 forming cyst-like nests of parasites. 

 There does not appear to be conclusive 

 proof that they turn into the crithidial 

 form in mammals, as was once believed. 

 The leishmanial forms turn into trypano- 

 some forms which re-enter the blood. 

 Among recent studies or reviews of the 

 life cycle of T. cruzi in the vertebrate host 

 are those of Elkeles (1951), Noble (1955), 

 Romana (1956) and Wood (1951, 1951a, 

 1953). 



The vectors of T. cruzi are kissing 

 bugs or conenose bugs, members of the 

 hemipteran family Reduviidae. Natural 

 infections have been found in at least 36 

 species of these bugs. They get their first 

 name from the fact that in sucking blood 

 they prefer to attack the thinner parts of 

 the skin such as the lips or eyelids. 



The most important vector in South 

 America is probably Panstrongylus (syn. , 

 Triatoma) megistus. Other important 

 vectors in South and Central America are 

 P. geniculatus, Eutriatoma sordida, Tri- 

 atoma infestans, Rliodnius prolixiis and 

 Eratyrus cuspidatus. 



According to Faust (1949), 15 naturally 

 infected species of reduviids have been 

 found in the United States. Dias (1951, 



