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Some Blood Parasites of New Zealand Birds

Leucocytozoon fringillinarum Woodcock, 1910 — Plate 1, Figs. 13–22

Leucocytozoon fringillinarum Woodcock, 1910
Plate 1, Figs. 13–22

Leucocytozoon fringillinarum was described by Woodcock (1910) from the blood of three chaffinches, Fringilla coelebs, in England. A year later Prowazek* quotes Schaudinn as recording this parasite from the same host in Berlin. The present infection is recorded from an adult specimen of the type host which was page 6 obtained in Wellington in a dying condition in May, 1947. It is doubtful whether the presence of the parasite was more than a contributory factor towards the death of the bird, as the infection is a light one (fewer than 30 parasites per slide). Smears from two other chaffinches collected in Wellington in February, 1948, were negative for haematozoa.

Huff (1942) states that young gametocytes of L. simondi are found in lymphocytes, monocytes, myelocytes, and polychromatophile erythroblasts, and that the cells containing fully grown gametocytes appear to be macrophages. Host cells of leucocytozoa undergo rapid changes in the initial stages of invasion by the parasites, making it far from clear in many cases whether erythroblasts, mononuclear leucocytes or both kinds of cell are involved, as de Mello (1936) points out. Woodcock (1910) himself states that the host cell is ". . . undoubtedly a uninucleate leucocyte, and not an immature red cell or erythroblast. . . . He bases this conclusion on the superficial resemblance of the most recently invaded cells to leucocytes rather than to erythroblasts, as seen in Romanowsky-stained material. Two polychromatophile erythroblasts are illustrated in Pl. 1, Figs. 13 and 14. These cells have deep blue staining cytoplasm and a large nucleus with many chromatin blocks, which is placed more or less centrally. It is true that, as Woodcock (1910) says, cells recently parasitized by L. fringillinarum have an eccentric nucleus with a few large chromatin masses and light blue staining cytoplasm, strongly suggestive of the normal condition of the mononuclear leucocyte. Nevertheless, hypertrophy of the nucleus accompanied by a marked change in the condition of its chromatin, together with displacement of this structure towards the side of the cell distant from the Leucocytozoon, might well be an early consequence of the invasion of an erythroblast. The staining reaction of the host cell cytoplasm—which in the earlier stages of infection (Pl. 1, Fig. 17) resembles that of later erythroblasts (Pl. 1, Fig. 15) as closely as that of leucocytes—similarly does not necessarily indicate leucocyte affinities. During the course of an infection, this staining reaction becomes less and less marked, until the cytoplasm appears as an ill-defined blue band at the periphery of a whitish area (Pl. 1, Fig. 21) and finally disappears altogether (Pl. 1, Figs. 20 and 22). Wingstrand (1947) established that the kidney shape of the nucleus of a cell parasitized by Leucocytozoon is marked at as early a stage of infection as when the parasite measures only 1μ in diameter. This author states that "in the few cases when I have been able to establish its identity the parasitized cell has been an erythroblast." I do not believe that there are sufficient grounds for considering the host cells of L. fringillinarum in my material to be leucocytes; and regard them as erythroblasts, the normal development of which has been grossly altered by some agent secreted by the parasite during the early stages of infection.

The genus Leucocytozoon embraces two distinct types of parasite, which de Mello (1936) maintains are sufficiently clear-cut to warrant their consideration page 7 as separate genera. The one type is elongated and its host cell is fusiform with tail-like prolongations, while the other is rounded and occupies a cell which does not show any tendency towards this type of hypertrophy. Representatives of the first type, through their habit of rounding off as in preparation for fertilization in the blood of the dead vertebrate host, may become confused with those of the second (Wenyon, 1910). In such cases the relationship of the parasite to the host cell nucleus, and the condition of the host cell itself, which is ruptured and disorganized (Mathis and Léger, 1910), gives evidence of the true nature of the Leucocytozoon concerned. L. fringillinarum is of rounded form and occupies host cells showing no signs of tail-like prolongations, and thus belongs to the second type of parasite described above.

Male and female gametocytes at all stages of development occur in my material of L. fringillinarum. The microgametocytes have rather hyaline cytoplasm which stains a very light blue with Giemsa and is not markedly granular. Small masses of extra-nuclear chromatin may be present (Pl. 1, Figs. 18, 19, 20). The nucleus itself is large and rather diffuse, and stains light pink. Rounded microgametocytes vary in diameter from 3.1μ (youngest form seen) to 9.0μ, in the case of adults, while ovoid forms (Pl. 1, figs. 18, 19, 20) measure from 6.6 by 4.0μ to 8.5 by 4.0μ in their greatest dimensions. The cytoplasm of the macrogametocyte is more granular than that of the microgametocyte, and takes a much darker blue stain. Wingstrand (1947) refers to such well-defined deeply staining cytoplasmic granules as are seen in the fully developed macrogametocyte illustrated in Pl. 1, Fig. 22, as pseudopigment. The nucleus is more compact than that of the microgametocyte, and stains deeply, showing prominent dark red granules. It may be somewhat elongated and of irregular outline in younger forms (Pl. 1, Fig. 17) or appear as a line of granules (Pl. 1, Fig. 21), but in fully developed macrogametocytes (Pl. 1, Fig. 22) it is usually rounded. The size of the macrogametocyte is a little larger than that of the microgametocyte, varying between 4.6 and 10.0μ in diameter in rounded forms and from 7.2 by 5.0μ to 9.5 by 7.0μ in ovoid forms. Woodcock (1910) states that the diameter of rounded individuals averages 8.5 to 9.5μ, the female form attaining a slightly larger size than the male.

The Leucocytozoon recorded from Fringilla coelebs in Wellington agrees so closely with Woodcock's (1910) description of L. fringillinarum from the same host as to leave no doubt that it is conspecific with the latter parasite.

* According to Wenyon, 1926.