Spontaneous Shedding of Metastrongyloid Third-Stage Larvae by Experimentally Infected Limax maximus

Abstract

Felids and canids acquire infection of most metastrongyloids by the ingestion of infective third-stage larvae (L3) in the tissues of gastropod intermediate hosts (IMH) or paratenic hosts.Direct ingestion of L3 shed by gastropods may be an alternative route of exposure.The significance of this route in natural infections is unknown.Larval shedding after experimental infection of Limax maximus with 5 metastrongyloids was tested in this study.First-stage larvae (L1) of Aelurostrongylus abstrusus, Angiostrongylus vasorum and Crenosoma vulpis (400-1445 L1/slug) were fed to laboratory raised L. maximus in separate exposure groups of 12-42 slugs.A mixture of Oslerus rostratus-Troglostrongylus wilsoni (90 %/10 %) and T. wilsoni-O.rostratus (95 %/5 %) L1 was used to infect 30 and 22 L. maximus (1600 L1/slug), respectively.Slug faeces was examined 2x/week by modified Baermann to detect L3.A small number of L3 (1.3-2.8 % of the total) was shed in all infected groups beginning 20-32 days PI.Weekly shedding levels ranged from 0-3.3 L3/slug.Longevity was tested by placing L3 of A. vasorum, C. vulpis and T. wilsoni-mix on lettuce and held at 16 o C/75 % humidity.Motile A. vasorum and T. wilsoni-mix L3 were recovered up to 12-16 days post-deposit (PD).Motile L3 of C. vulpis were still present 120 PD.Detection in all 5 parasite species indicates that spontaneous shedding of L3 into the environment is likely a general characteristic of the metastrongyloids.Prolonged survival of L3 indicates that exposure through environmental contamination may play a role in natural infection transmission with these parasites.