Toxoplasma sp.?
Plate 2, Figs. 13–16

Organisms answering to the description of the genus Toxoplasma Nicolle and Manceaux, 1909, were found in heart blood smears of a specimen of Zosterops lateralis (silvereye) collected at Masterton in August, 1947. Smears of the peripheral blood of 124 birds of this species, all collected at Masterton during August, 1947, were examined during the survey. One of these smears contained an artifact which closely resembled an early stage of Haemoproteus, and, as a special watch was being kept for parasites of this genus in view of their discovery in the same host in Australia (Cleland and Johnston, 1910; Lawrence, 1946), the bird was killed and heart blood and organ smears were made. The heart blood smears showed the presence of not Haemoproteus but Toxoplasma. Although this parasite was not recorded from any of the other Zosterops examined, its presence might easily have been overlooked, due to the fact that infections are often confined to the internal organs and are consequently not apparent from the examination of peripheral blood smears (Hewitt, 1940).

The Toxoplasma from Zosterops lateralis was found in the cytoplasm of endothelial cells and mononuclear leucocytes, some 20 per cent. of the latter cells being infected.

It is of elongate-oval, crescentic or reniform shape, one end often being more pointed than the other. The cytoplasm stains whitish-blue to light blue with Giemsa. It may be rather granular (Pl. 2, Fig. 14) or maculated (Pl. 2, Figs. 13 and 15), and often contains a number of small vacuoles (Pl. 2, Fig. 16). The nucleus, which may be central in position (Pl. 2, Figs. 14 and 15) or situated towards one extremity (Pl. 2, Figs. 13 and 16), is an irregularly shaped structure staining light pink. It frequently contains numerous small granules of chromatic material staining deeper pink. The average measurements of twenty individuals at their greatest dimensions are 8.5μ (7.0 to 10.4μ) by 3.4μ (2.9 to 4.5μ). The nuclei of these parasites measure some 4.0 by 2.7μ (range 2.9 to 6.2μ by 2.1 to 3.3μ). Parasitized leucocytes show a marked hyperchromatosis of the nucleus, and their cytoplasm may become pale staining and markedly alveolar, as described page 11 by Plimmer (1916) in an account of avian Toxoplasma. No cases of double infection of a leucocyte nor any indications of schizogony have yet been seen in the material from Zosterops lateralis.

There is no previous record of Toxoplasma from New Zealand. The only Australian record is that of Lawrence (1946), who found an oval organism similar to the type II Toxoplasma-like bodies of Wolfson (1940) in the mononuclear leucocytes of 27 of 91 sparrows (Passer domesticus) examined at Sydney.

There is much doubt as to the systematic position of the toxoplasms. Wenyon (1939) gave it as his opinion that these organisms do not belong to the Protozoa at all. Because of the failure of investigators to demonstrate any other means of reproduction than binary fission for Toxoplasma, this author considers the genus to be of vegetable nature and related to Histoplasma capsulatum or some other such yeast-like parasite. Some of the organisms from Zosterops lateralis superficially resemble the gametocytes of Hepatozoon and other intracellular haematozoa, as Hewitt (1940) found to be the case for a toxoplasm from the Mexican house-finch. They also resemble the Type II Toxoplasma-like bodies of Wolfson (1940), but differ from these in having a predominance of crescentic and reniform forms rather than round or oval ones. No definite developmental series can be traced out from the material available. I thus follow Hewitt (1940) in not applying a specific name to the Toxoplasma described above, believing that the application of such a name would only lead to confusion in the present unsatisfactory state of our knowledge of these organisms.

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