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Blood Parasites of Mammals in New Zealand

Trypanosoma lewisi (Kent, 1880) — (Text-figure 1, Figs. 1–17)

Trypanosoma lewisi (Kent, 1880)
(Text-figure 1, Figs. 1–17)

Doré (1918) was the first to record Trypanosoma lewisi from New Zealand, stating that this flagellate was first found in rats from the Auckland area in 1912. Of "several hundred" rats from various parts of the North Island examined by Doré, 30 per cent. of those captured in the neighbourhood of sewers and 12 per cent. of those from wharves and grain stores were infected. T. lewisi is widespread in Australia (Pound, 190S; Johnston, 1909), where Bancroft recorded it as Haematomonas as early as 1888.

Sixty-five specimens of Rattus norvegicus (Erxleben) obtained from buildings in Wellington were examined for haematozoa during 1947 and 1948. Three of these proved to be parasitized by Trypanosoma lewisi, two being lightly infected and one very heavily infected, with an average of one trypanosome to every eight host erythrocytes. Doré mentions that one of the infected rats which he handled had one trypanosome to every four of its erythrocytes.

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Text-figure 1

Text-figure 1

Figs. 1–5, 7–11, 13–17: Trypanosoma lewisi (Kent, 1880), from Rattus norvegicus (Erxleben). Figs. 6 and 12: Erythrocytes of R., norvegicus. Fig. 18: Normal erythrocyte of Trichosurus vulpecula (Kerr). Figs. 19 and 20: Anaplasma-like bodies from T. vulpecula. Fig. 21 : Normal erythrocyte of Bos taurus Linnaeus. Figs. 22–24: Basophilic granulation in erythrocytes of B. taurus. Figs. 25 and 26: Anaplasma-like bodies from B. taurus.

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Trypanosoma lewisi is of long slender form, both extremities of the body tapering to a fine point. As Minchin (1909) points out, it usually appears C-shaped (Figs. 1 and 2) or S-shaped (Fig. 4) in permanent preparations. The prominent undulating membrane very rarely (Fig. 2) appears at the concavities of the curves. It usually keeps to the convex side, crossing over the body at each curve (Figs. 4 and 6), as described by Minchin. The nucleus is of oval shape, its long axis being in line with that of the body. The alveolar cytoplasm stains light blue with Giemsa. Both the nuclear membrane and the small central karyosome stain deep red, and the space between them lighter red. The flagellum varies in apparent thickness according to the degree of extraction of the stain. It originates from a blepharoplast which lies immediately anterior to the parabasal body but which cannot always be differentiated from the latter structure in Giemsa-stained material. The kinetoplast as a whole stains bright pink, and appears circular (Figs. 3, etc.) to rod-shaped (Figs. 5, etc.).

The average dimensions of 100 examples of T. lewisi from my material are given below, the figures in parentheses being those given in or determined from Minchin's (1909) account of this flagellate.

Length of free flagellum 7.1μ (6.9μ)
Length of body 22.9μ (23.7μ)
Total length 30.0μ (30.6μ)
Width of body at centre of nucleus 1.1μ ( — )
Length of nucleus 1.7μ ( — )
Width of nucleus 1.1μ ( — )
Width of undulating membrane 1.0μ ( — )

The length of the free flagellum averages 31.0 per cent. (29.1 per cent.) of that of the body. In most cases the nucleus occupies the full width of the body, and is situated 30.0 per cent. (29.6 per cent.) of the body length from the root of the free flagellum. The parabasal body is located 15.1 per cent. (18.9 per cent.) of the body length from the posterior extremity.

It will be seen that there are slight differences between Minchin's figures and mine. This may be because the trypanosomes concerned belong to different strains, or may be due to the fact that Minchin's figures are based on the measurement of only ten examples of T. lewisi.

Some of the larger examples of T. lewisi in my material have from one to many extranuclear chromatin granules in the cytoplasm (Figs. 10–14). The nuclei of such forms frequently contain several densely staining granules of similar nature, and the cytoplasm often has large vacuoles (Fig. 11) and an irregular border on the convex side (Figs. 10 and 11). It is likely that such trypanosomes are degenerative forms which are undergoing necrosis.

Numerous trypanosomes having two nuclei occur in material from the heavy infection mentioned above (Figs. 15–17). The nuclei, unlike those of normal examples of T. lewisi, are of circular shape. They average 1.0μ in diameter, and occur close together in the usual situation of the normal single nucleus. Trypanosomes with two nuclei show no other signs of division. It is probable that as Minchin (1909) suggests, they are abnormal forms, having nothing whatever to do with division.

T. lewisi is transmitted from rat to rat by the flea Ceratophyllus fasciatus, which is a common ectoparasite of Rattus norvegicus in New Zealand. Rats become parasitized by eating infective fleas or the faeces of such fleas (Wenyon, 1926).