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Discussion

No haematozoa have yet been recorded from any of the mammals indigenous to New Zealand. The few smears from seals and whales examined during this study all proved negative for haematozoa, which is not surprising in view of the fact that no blood parasites have yet been recorded from any of the marine mammals. As already mentioned, no examples of either of our two rare species of native bats could be obtained for study. The examination of blood smears from these animals would be of the highest interest in view of the primitive status of the short-tailed bat Mystacops tuberculatus, and because of the occurrence of Plasmodium, Trypanosoma, and other haematozoa in many species of Chiroptera in other parts of the world.

Trypanosoma lewisi was first recorded from the cosmopolitan Rattus norvegicus in New Zealand by Doré (1918). This author suggested that the rapid decline in numbers of the Polynesian rat (Rattus exulans) might be due to infection with T. lewisi. As the Polynesian rat is now very rare, the opportunity of testing this hypothesis has not yet arisen. Both T. lewisi and Hepatozoon muris are known from rats in Australia (Pound, 1905; Cleland, 1906; Johnston, 1909; etc.), there being no record of the latter parasite from New Zealand. Conversely, Hepatozoon musculi, here recorded for the first time from Mus musculus in New Zealand, is not known from Australia.

Trypanosoma melophagium has not yet been found in the blood of sheep in New Zealand, although 137 thin blood smears collected from these animals at the Wellington abattoirs have been studied. In Europe and England this parasite is widely distributed (Hoare, 1923), but infections are so slight that culture techniques usually have to be employed before its presence is revealed. Hoare found at least 80 per cent. of an infected flock to be parasitized by using culture techniques, although some 300 blood smears from the same flock proved uniformly negative for T. melophagium. The sheep-ked Melophagus ovinus, an obligatory ectoparasite of sheep, is the only known invertebrate host of this trypanosome (Hoare, 1923), and the incidence of Trypanosoma melophagium in a given area closely parallels that of the sheep-ked. As Melophagus ovinus occurs in New Zealand, it would thus be premature to state that T. melophagium is absent from this country before a much more extensive survey, involving the use of culture techniques, has been carried out. The examination of negative material from 48 rabbits and 36 cattle likewise gives no grounds for assuming that the trypanosomes which parasitize these animals in Europe are absent from New Zealand.

Although Dirofilaria immitis (Leidy) has been reported from New Zealand (Reakes, 1913), the species, the causal agent of canine filariasis, is not established in this country. The case recorded by Reakes concerns a dog landed in New Zealand in the course of Captain Scott's last expedition to Antarctica. Microfilarial embryos were found in the blood of this dog when it was quarantined, and the animal was subsequently destroyed. It is of interest that a number of Scott's sledge dogs died in Antarctica as a result of infestation with Dirofilaria immitis. Atkinson (in Cherry-Garrard, 1948, p. 454) considered that the probable place of infection was Vladivostock, from which port the dogs were shipped to New Zealand on their way southwards. Dirofilaria immitis is well established in Australia and many of the Pacific Islands, notably Fiji, and it is of the greatest importance that quarantine measures directed against the importation of this nematode into New Zealand should at all times be stringently enforced.