The potential impact of exotic Lymnaea spp. on fascioliasis in Australasia

The presence of the following exotic Lymnaea spp. has been recently confirmed in Australia: L. columella (North and South America, South Africa, New Zealand,) L. viridis (China, Japan, Philippines, New Guinea, Pacific Area), L. auricularia rubiginosa (Indochina, Malaysia, Indonesia) and L. peregra (Europe).In the present studies the relative susceptibility of the exotic snails noted above to Fasciola hepatica was investigated. Two of the species, L. columella and L. viridis, were found to be highly susceptible to the Australian strain of F. hepatica and a substantial number of viable metacercariae were produced. However a strong disparity in the host— parasite relationship was evident when the parthenogenetic development of the fluke in the two exotic snails was compared with that in the native L. tomentosa. It was concluded that L. tomentosa is a more suitable intermediate host for F. hepatica than any of the introduced exotic species, but it has to be considered that the host—parasite relationships between new combinations of Fasciola and Lymnaea spp. may improve by adaptation. In view of the results of the present studies the potential danger of fascioliasis spreading to areas currently not endemic in Australasia through introduced exotic snails is discussed with particular reference to Queensland, Western Australia and the Northern Territory.There is strong circumstantial evidence that the exotic snails were introduced with aquatic plants through the relatively free overseas and Australian trade. Similarly, through the introduction of infected snails, dangerous parasites such as F. gigantica of cattle and sheep or Schistosoma ssp. which cause serious diseases of man and animals could enter the subtropical or tropical regions of Australia. Appropriate State and Federal quarantine regulations are essential to prevent further introduction and spread of the snails, and monitoring of the distribution of established exotic snails in Australasia must be continuous.