Parasitism in New Zealand wild rabbits with special reference to trichostrongylus retortaeformis

Abstract

One hundred wild rabbits were examined for parasites, and the following species were found : Eimeria stiedae (24%), E.perforans (86%), E.magna, E.media, Cysticercus pisiformis (13%), Coenurus serialis (less than 1%), Passalurus ambiguus (61 1/2%), Trichostrongylus retortaeformis (95%), Graphidium strigosum (81%), Listrophorus gibbus, Cheyletiella parasitivorax, Haemodipsus ventricosus and Ctenocephalides canis. The fauna is similar to that in rabbits in England (from whence rabbits were introduced to New Zealand) except for the absence of adult tapeworms (Cittotaenia) for which there may be no suitable intermediate host in New Zealand. The geographic distribution of the parasites coincided with that of the host except for G. strigosum (absent in the northern part of the North Island) and P. ambiguus (absent in the southern portion of the North Island). The mean population size for nematodes (as determined by dilution-sampling) was P. ambiguus (3798), T.retortaeformis (852) and G. strigosum (189). Experiments in vitro showed that the eggs and infective larvae of T. retortaeformis could withstand considerable variations in temperature and moisture, and this explains the high incidence, wide distribution and large populations. The distribution of T.retortaeformis populations along the intestine of the host followed a right-skewed frequency curve with the mode 22.06 cms. from the pylorus, and this is comparable to the reported distribution of other species of Trichostrongylus in sheep. In P.ambiguus the distribution of the population was related to the amount of space available. Except for deaths among young captive rabbits heavily infected with E.stiedae there was no evidence of mortality caused by parasites. No parasites of domestic animals were found except for one light infestation of Ctenocephalides canis. Three methods of concentrating eggs and cysts from faeces were found to be unreliable for quantitative results.