272 



PLASMODIUM, HAEMOPROTEUS AND LEUCOCYTOZOON 



different parts of the state and in different 

 years. Wood and Herman (1943) found it 

 in 93't of 27 western mourning doves in 

 Arizona and California. 



Morphology : The only stages found 

 in the peripheral blood are macrogametes 

 and microgametocytes. When mature, 

 these are elongate and sausage -shaped. 

 They partially encircle the host cell nu- 

 cleus; they may displace it to some extent, 

 but they do not push it to the edge of the 

 host cell. They contain a variable number 

 of dark brown pigment granules. The host 

 cell is not enlarged. 



When stained with a Romanowsky 

 stain, the cytoplasm of the microgameto- 

 cytes is pale blue or almost colorless and 

 their nuclei are pale pink and diffuse, 

 while the cytoplasm of the macrogametes 

 is darker blue and their nuclei are com- 

 pact and dark pink or red. 



Life Cycle : The life cycle of H. co- 

 lumbae has been studied by Aragao (1908), 

 Adie (1915, 1924) and Huff (1942) among 

 others. Birds become infected when bit- 

 ten by the dipteran vector. The sporo- 

 zoites enter the blood stream and invade 

 the endothelial cells of the blood vessels 

 of the lungs, liver and spleen. Here they 

 round up to form schizonts. Each schi- 

 zont undergoes multiple fission to form 

 15 or more small, unpigmented bodies, 

 the cytomeres, each with a single nucleus. 

 Each cytomere grows still further, and 

 its nucleus undergoes multiple fission. 

 Finally, the host cell becomes considerably 

 hypertrophied and is filled with a number 

 of multinucleate cytomeres. 



The endothelial cells break down, re- 

 leasing the cytomeres. These vary in 

 size, but may reach 60 ^ in diameter. 

 They accumulate in the capillaries, which 

 they sometimes block completely. They 

 are irregularly shaped and tortuous, and 

 may send out branches along the capillar- 

 ies, becoming bifurcate, trifurcate or 

 even multiradiate. Each cytomere pro- 

 duces an enormous number of merozoites, 

 which break out and pass into the blood 

 stream. 



According to Wenyon (1926), the schi- 

 zonts do not necessarily form cytomeres 

 but may produce merozoites directly. 

 Presumably, too, schizogony is repeated 

 a number of times. 



Following schizogony, the merozoites 

 enter red blood cells and become macro- 

 gametes and microgametocytes. These 

 first appear 28 to 30 days after infection. 

 At first they resemble ring stages of Plas- 

 modiuDi, but grow to the mature, elongate 

 form in a few days. Multiple infections of 

 erythrocytes with immature parasites are 

 not uncommon, sometimes as many as 12 

 being found in a single host cell, but in- 

 fections with more than 1 mature gamete 

 or gametocyte are rare. 



The only proven vector is the hippo- 

 boscid fly, Pseudolynchia canariensis 

 (syns. , Lynchia maura, L. lividicolor, 

 L. capensis). In addition, Arag'ao (1916) 

 stated that Alicrolyiichia pus ilia is a vector 

 in South America, but gave no experimental 

 evidence. Baker (1957) found that H. co- 

 limibae from the English wood pigeon 

 (Coluniba palumbus) would undergo sporo- 

 gony in Ornithomyia aviciilaria, but 6 

 attempts to infect domestic pigeons by bite 

 or injection of infected louse-flies failed. 



It is highly unlikely that hippoboscids 

 are the only vectors of this species, how- 

 ever. As Hanson et al. (1957) pointed out, 

 hippoboscids are extremely rare on mourn- 

 ing doves, yet H. colinnbae is common in 

 them. The discovery by Fallis and Wood 

 (1957) that biting midges (Ciilicoides) are 

 the vectors of H. nettionis of ducks sug- 

 gests that they may also transmit H. 

 columbae . 



In the stomach of the hippoboscid vec- 

 tor, the microgametocytes produce 4 or 

 more snake-like microgametes by exfla- 

 gellation. They fertilize the macroga- 

 metes, and the resultant zygotes are ookin- 

 etes which crawl to the midgut wall and 

 form oocysts on its outer surface. These 

 grow, reaching a diameter of about 36 j^. 

 They become mature in 10 to 12 days, pro- 

 ducing very large numbers of slender, fal- 

 ciform sporozoites up to 10 ^ long and 



