Release of lungworm larvae from snails in the environment: potential for alternative transmission pathways

Background: Gastropod-borne parasites may cause debilitating clinical conditions in animals and humans following the consumption of infected intermediate or paratenic hosts. However, the ingestion of fresh vegetables contaminated by snail mucus and/or water has also been proposed as a source of the infection for some zoonotic metastrongyloids (e.g.,Angiostrongylus cantonensis). In the meantime, the feline lungwormsAelurostrongylus abstrususandTroglostrongylus breviorare increasingly spreading among cat populations, along with their gastropod intermediate hosts. The aim of this study was to assess the potential of alternative transmission pathways forA. abstrususandT. breviorL3viathe mucus of infectedHelix aspersasnails and the water where gastropods died. In addition, the histological examination of snail specimens provided information on the larval localization and inflammatory reactions in the intermediate host.Methodology/Principal Findings: Twenty-four specimens ofH. aspersareceived ~500 L1 ofA. abstrususandT. brevior, and were assigned to six study groups. Snails were subjected to different mechanical and chemical stimuli throughout 20 days in order to elicit the production of mucus. At the end of the study, gastropods were submerged in tap water and the sediment was observed for lungworm larvae for three consecutive days. Finally, snails were artificially digested and recovered larvae were counted and morphologically and molecularly identified. The anatomical localization ofA. abstrususandT. breviorlarvae within snail tissues was investigated by histology. L3 were detected in the snail mucus (i.e., 37A. abstrususand 19T. brevior) and in the sediment of submerged specimens (172A. abstrususand 39T. brevior). Following the artificial digestion ofH. aspersasnails, a mean number of 127.8A. abstrususand 60.3T. breviorlarvae were recovered. The number of snail sections positive forA. abstrususwas higher than those forT. brevior.Conclusions: Results of this study indicate thatA. abstrususandT. breviorinfective L3 are shed in the mucus ofH. aspersaor in water where infected gastropods had died submerged. Both elimination pathways may represent alternative route(s) of environmental contamination and source of the infection for these nematodes under field conditions and may significantly affect the epidemiology of feline lungworms. Considering that snails may act as intermediate hosts for other metastrongyloid species, the environmental contamination by mucus-released larvae is discussed in a broader context.