Radiolabeling of Angiostrongylus vasorum- and Crenosoma striatum larvae: a novel method using PET/CT to unveil larval migration in the gastropod intermediate host (Lissachatina fulica)
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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 nuclear imaging with whole-body positron emission tomography and computed tomography to scan radiolabeled 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 a novel animal model for lungworm-associated investigations, as this gastropod species is known to act as a natural obligate intermediate host in the tropics for various metastrongyloid lungworms, including the zoonotic-relevant Angiostrongylus cantonensis . Radiolabeled A. vasorum - and C. striatum L1 migration was visualized through nuclear imaging after L1 oral infection or injection.
Methods
Live 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 a radiolabeled glucose analogue, 18 F-fluordesoxyglucose. Thereafter, radiolabeled L1 were fed orally or injected into adult L. fulica , and in vivo scans were performed to visualize larval migration routes at different time points post infection through various gastropod organs/tissues.
Results
The most optimal incubation time of larvae and 18 F-fluordesoxyglucose was 30 min. After washing nonincorporated 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 scans showed dispersal from the site of larval injection or feeding. Radiolabeled A. vasorum - or C. striatum L1 moved rapidly from the site of injection or the oral cavity with nonspecific accumulation in one or numerous gastropod organs at 30 min post infection.
Conclusions
This study concludes that radiolabeling of metastrongyloid L1 with 18 F-fluordesoxyglucose is achievable up to a level that can be detected in a scan of individual snails. Scanning L1 larvae in L. fulica at 60 min still represents larval migration. After 2 h, this study found that the migration is already widespread, and the activity is too low to be narrowed to a specific organ. Detailed in vivo scans of gastropods with not only higher infectious doses but also other radiolabeled tracers and longer observation periods might allow detection of either organ tropism or larval accumulation in certain mollusc tissues/organs for further development into infective stages.
