New Zealand is fortunate in that trematode infections of man very rarely occur. The only species previously known which are liable to infect man in this country are the adult stage of the liver fluke, Fasciola hepatica, and a blood fluke (schistosome) whose cercaria, Cercaria longicauda, causes ‘swimmers’ itch' to bathers in some of the southern lakes. In New Zealand, the definitive hosts of F. hepatica are sheep, cattle, rabbits, and deer, but these have a low incidence of infection. This, coupled with restricted localities (swampy areas) for the intermediate snail hosts, Myxas ampulla and Limnaea alfredi, means there is little likelihood of human infections. In fact, F. hepatica has not so far been recorded from man in this country. The cercaria causing ‘swimmers’ itch' does not become adult in man but according to Macfarlane (1949a), its definitive host is in all probability the black teal, Fuligula novaezealandii. Although the cercariae penetrate human skin and cause localised irritation they later die and are resorbed by the body (Macfarlane, 1949b).

Of the several trematode species which commonly infect man in other countries (vide Chandler and Read, 1962) only the Chinese liver fluke, Clonorchis sinensis, has been noted on one occasion (Dr. L. K. Whitten pers. comm.) in the faeces of an immigrant to this country. However, Dr. Whitten also considers that immigrants and visitors have probably brought schistosomes to this country but these, along with C. sinensis, have not established themselves due to the lack of the intermediate snail hosts and to good conditions of sanitation.

It is obviously in our interests to keep the country free from infection by trematode parasites. I am therefore reporting a possible source of infection that has recently come to my notice. During the examination of marine molluscs for the larval stages of digenetic trematodes, I recovered a species from the visceral mass of a small gastropod, Zeacumantus subcarinatus (Fig. 1), commonly found on rocky shores and in semi-stagnant rock pools at high tide level around New Zealand. In the vicinity of Wellington approximately 4% of these gastropods are infected. Preliminary examination of the parasite, in particular the cercarial stage, its method of encystment and the shape of the cyst, has shown that it is a species of the genus Philophthalmus, adults of which are page 183

Fig. 1: Zeacumantus subcarinatus, intermediate host of a species of Philophthalmus in New Zealand. Fig. 2: Life history of Philophthalmus spp.

page 184 normally parasitic in the orbit of birds. Mr. R. A. Fordham, Zoology Department, Victoria University, has given me specimens of a species of Philophthalmus taken from the orbit of the black-backed gull (Larus dominicanus) from the Wellington area, and these could well prove to be the adults of the larval stage in Z. subcarinatus. The life history of species of Philophthalmus is summarised in Fig. 2 which is based on the work of Alicata and Ching (1960), and West (1962).

Judging by the wide variety of experimental hosts, including rabbits, rats. mice, and several species of birds, that have been successfully infected with Philophthalmus spp. (vide Alicata and Ching, 1960, and West, 1962), members of this genus are relatively loosely host specific. It should be noted that Alicata and Ching found that mammals could only be infected by direct contact of the cercariae with the eye, whereas birds could be infected by either feeding them metacercariae or by direct contact of the cercariae with the eye.

Of great importance is the fact that on rare occasions overseas, a species of Philophthalmus usually infecting gulls has been found in the orbit of man, under the eyelids. It is thus conceivable that the species of Philophthalmus now known from Z. subcarinatus in New Zealand could be an occasional parasite of man in this country, although no cases have as yet been reported. Swimmers not using goggles in the vicinity of areas where Z. subcarinatus occurs are exposing themselves to a possible infection from the cercariae liberated from this gastropod. The effects of the parasite, giving rise to irritation and inflammation of the eyelids, could be misconstrued as irritation from salt-water, and it is therefore likely that cases may have already been overlooked.

Further work will be carried out in the near future to determine more of the biology of this species of Philophthalmus in Z. subcarinatus, which is an interesting and important addition to the trematode fauna of New Zealand.