3 1 Sporozoa 



Babesiida; the question cannot be decided without further knowledge 

 of the life-cycles. 



Dactylosoma Labbe. This genus (95, 100) includes little known non- 

 pigmented forms occurring in erythrocytes of frogs, urodeles, and lizards. 

 Merogony in red cells and the development of supposed gametocytes 

 (Fig. 6. 25, A-K) have been described but the rest of the life-cycle is 

 unknown. 



Toxoplasma Nicolle and Manceaux. Organisms assigned to this genus 

 have been found in various tissue cells of vertebrates — several types of 

 leucocytes, lymphoid-macrophage (reticulo-endothelial) cells, cells of the 

 central nervous system, and in erythrocytes of experimentally inoculated 

 birds (144). In addition, extracellular stages have been observed by 

 various workers. Several strains have been maintained in chick embryos 

 by serial transfers (83). Life-cycles have not yet been worked out and the 

 taxonomic status of the genus is uncertain. However, the protozoan 

 nature of Toxoplasma has been affirmed in some of the more recent in- 

 vestigations (23, 89). 



Individual parasites range from almost spherical to elongated forms 

 (Fig. 6. 25, L-U). The larger stages are usually not more than 5-6pt long, 

 while small forms may measure only 2-3[jl in diameter. In addition to the 

 nucleus and sometimes cytoplasmic globules. Cross (23) occasionally noted 

 a longitudinal axostyle-like band ("cytostyle") just beneath the pellicle 

 (Fig. 6. 25, R, U). Supposed flagella have been described by several 

 workers, although more evidence is needed for any definite conclusion 

 (23). Within invaded tissue cells the parasites occur singly or in groups 

 (Fig. 6. 25, Q) in one or more vacuoles, or "pseudocysts." These pseudo- 

 cysts have been interpreted in some instances as the results of schizogony, 

 but most workers are agreed that reproduction by longitudinal binary 

 fission is the rule. 



The type species, Toxoplasjna gondii Nicolle and Manceaux (16), was 

 described from a North African rodent. Infections with Toxoplasma 

 have been reported subsequently from a variety of birds (143) and mam- 

 mals, including man, but there is much uncertainty in regard to the 

 specific status of described types. The problem of differentiating species 

 is complicated by the apparent lack of host-specificity (89). For instance, 

 strains isolated from cases of human toxoplasmosis have been found in- 

 fective for monkeys, rabbits, mice, guinea-pigs, hamsters, cotton rats, 

 white rats, and chickens. 



Infection with Toxoplasma seems to be responsible for several patho- 

 logical conditions in man: (1) a type of congenital encephalomyelitis 

 which appears in infants shortly after birth or even in utero (141, 142); 

 (2) a type of acute encephalomyelitis in children (119); (3) a syndrome 

 resembling spotted fever and associated with inflammation of the lungs 

 (107); and (4) mild cases, in which the mothers of congenitally infected 



