PET/CT and radiolabelling of Angiostrongylus vasorum- and Crenosoma striatum larvae provide a novel method to unveil migration routes in the gastropod intermediate host (Lissachatina fulica) in vivo

Background Gastropod-borne metastrongyloid lungworm infections are poorly understood despite their importance in both veterinary- and human medicine. This study intends to assess the use of PET/CT to scan radiolabelled Angiostrongylus vasorum - and Crenosoma striatum first-stage larvae (L1) while migrating in vivo in the obligate mollusc intermediate hosts. Here, the giant African snail ( Lissachatina fulica ), was used as novel animal model for lungworm-associated investigations as this gastropod species is known to act as natural obligate intermediate host in the tropics for various metastrongyloid lungworms, including the zoonotic-relevant Angiostrongylus cantonesis . ¹⁸ F-FDG radiolabelled A. vasorum- and C. striatum L1 migration was visualized through PET/CT imaging after L1 oral infection or injection. Methods Vital first-stage larvae (L1) were collected through the standard Baermann funnel technique. After isolation and assessment of larval viability, collected A. vasorum- and C. striatum L1 were incubated with the radiolabelled tracer ¹⁸ F-FDG. Thereafter, radiolabelled L1 were fed orally or injected to adult L. fulica , and in vivo PET/CT scans were performed to visualize larval migration routes at different time points p. i. through various gastropod organs/tissues. Results The most optimal incubation time of larvae and ¹⁸ F-FDG tracer was 30 min. After washing non-incorporated tracer, metastrongyloid L1 retained on average activity of 0.33 (0.103) KBq per larvae. This was the maximum activity achieved and even longer incubation times, i. e. 60 and 120 min, did not exceed this value. The in vivo PET/CT scans showed dispersal from the site of larval injection or feeding. Radiolabelled A. vasorum- or C. striatum L1 moved rapidly from either the site of injection or the oral cavity but non-specific accumulation in one or numerous gastropod organs were detected at 30 min p. i. Conclusions This study concludes that radiolabelling of metastrongyloid L1 with ¹⁸ F-FDG is achievable up to a level that can be detected in a PET/CT scan of individual snails. Detailed in vivo PET/CT scans of gastropods with not only higher infectious doses, other radiolabelled tracers but also longer observation periods might allow detection of either organ tropism or larval accumulation in certain mollusc tissues/organs for further development into infective stages.