276 



PLASMODIUM, HAEMOPROTEUS AND LEUCOCYTOZCXDN 



Prevalence : This species is common 

 in northern United States, Canada and 

 other mountainous or hilly areas where 

 cold, rapid streams permit suitable black- 

 fly vectors to breed. 



Fig. 33. Species of Leiicocytozoon in avian 

 leucocytes. A. L. smithi macro- 

 gamete from turkey. B. L. si- 

 tiiondi microgametocyte from duck. 

 X 1400. (Original) 



Morphology : The mature macroga- 

 metes and microgametocytes are more or 

 less elongate, and 14 to 22 fi long. Their 

 host cells are ordinarily elongate, up to 

 45 to 55 (J, long, with their nucleus form- 

 ing a very long, thin, dark band along one 

 side and with pale cytoplasmic "horns" 

 extending out beyond the parasite and the 

 nucleus. In some cases, round macro- 

 gametes and microgametocytes in rounded 

 host cells have been reported (Fallis, 

 Davies and Vickers, 1951; Rawley, 1953; 

 Cook, 1954); both types are mature and 

 able to exflagellate. Briggs (1960) noted 

 that there were approximately equal num- 

 bers of round and elongate forms in white 

 Pekin ducks but that elongate forms were 

 rare in Muscovy ducks, never constituting 

 more than 5% of the total number. He 

 suggested that this might be due to the in- 

 fluence of the host species. 



The cytoplasm of the macrogametes 

 is rather dark blue and the nucleus com- 

 pact and red when stained with a Roman- 

 owsky stain. The cytoplasm of the micro- 

 gametocytes is very pale blue and the 

 nucleus diffuse and pale pink. The micro- 

 gametocytes are more delicate and more 

 subject to distortion than the macroga- 

 metes. 



A good deal of controversy has existed 

 as to the type of cell parasitized by L. 

 sii>io)idi. The host cells of the mature 

 gametocytes are so distorted that they 

 cannot be recognized. Huff (1942) consid- 

 ered them to be lymphocytes or stages in 

 transformation between them and mono- 

 cytes. Levine and Hanson (1953) found 

 young and developing forms only in lymph- 

 ocytes or monocytes. On the other hand, 

 Fallis, Davies and Vickers (1951) and 

 Cook (1954) found very young forms in both 

 lymphocytes and erythrocytes. Using the 

 benzidine-peroxide stain for hemoglobin. 

 Cook found no hemoglobin in the host cells 

 containing mature gametocytes, but she 

 found at least some hemoglobin in all of 

 the 191 host cells she saw which contained 

 developing gametocytes. She concluded 

 that, while the ring stages may invade both 

 erythrocytes and lymphocytes, they develop 

 to maturity only in cells of the red blood 

 series. Whatever the host cell may be, the 

 gametes and gametocytes never contain 

 hematin pigment granules. 



Life Cycle : The life cycle has been 

 studied by O'Roke (1934), Huff (1942), 

 Fallis, Davies and Vickers (1951), Fallis, 

 Anderson and Bennett (1956) and Cowan 

 (1955) among others. Birds become in- 

 fected when bitten by a blackfly vector. 

 The sporozoites enter the blood stream, 

 invade various tissue cells, round up and 

 become schizonts. 



Two types of schizont occur in the 

 duck. Hepatic schizonts 11 to 18fi in 

 diameter occur in the liver cells; they 

 form a number of cytomeres which in 

 turn form small merozoites by multiple 

 fission. 



Megaloschizonts 60 to 164;i in diam- 

 eter when mature are found in the brain, 

 lung, liver, heart, kidney, gizzard, in- 

 testine and lymphoid tissues 4 to 6 days 

 after exposure. They are more common 

 than the hepatic schizonts. The megalo- 

 schizonts develop in cells, possibly lymph- 

 oid cells or macrophages, within or out- 

 side the blood vessels. They contain 

 numerous cytomeres and a large, conspic- 

 uous central body which may be either a 

 primordium off of which the cytomeres 



