Three or four snails, on several mornings, swallowed almost alive and slimy, without the shell, barely cleaned. That is how a stomach patient in rural Romagna, on the Adriatic side of Italy, tried to "coat" his ulcer with the animal's slime. A book of peasant memoirs printed in Rimini in 2002 records it, and adds: some still do it. In Lunigiana, in the hills behind La Spezia, a live snail without its shell was the remedy for an ulcer, and the slime "went to heal the lesion inside". The tradition is documented. The remedy is alive. What is inside it needs saying.
Inside there is mucus. Helix mucus contains glycoproteins, allantoin and mucopolysaccharides; there are test-tube and animal studies on these, and a market of creams and syrups. There is no study in humans showing a gastritis or an ulcer healed by a swallowed snail, or by drunk mucus. Those who claim it, as a rule, sell the product. Peptic ulcer now has a known cause, the bacterium Helicobacter pylori, and a treatment that eradicates it. The mucus remains a tradition.
There may be something else inside. Angiostrongylus cantonensis is a nematode that lives in the lungs of rats. The rat sheds it in its droppings, a snail or slug eats them, and the larva lodges in the mollusc. Whoever eats the mollusc raw is, for the parasite, a dead end: the larva climbs to the nervous system and dies there, and the reaction to that death is an eosinophilic meningitis, with a headache lasting weeks, tingling, sometimes paralysis. It is the leading cause of eosinophilic meningitis worldwide, with outbreaks in South-East Asia, the Pacific and the Caribbean, as the review by Wang and colleagues in The Lancet Infectious Diseases summarised in 2008. In Kaohsiung, Taiwan, in 1998 and 1999 two outbreaks struck Thai workers who had eaten raw snails. In Hawaii an adult who had swallowed a raw Achatina fulica ended up with meningoencephalitis and a cranial nerve palsy; five of nine snails collected at the site carried the parasite's DNA.
Europe is not exempt. A systematic review published in 2020 in the International Journal of Infectious Diseases counts twenty-two European cases from 1988 to 2019, almost all in travellers returning from Polynesia, South-East Asia and the Caribbean; the food most often suspected was prawns and salad, where small slugs hide. One case only is autochthonous: a 54-year-old woman in Paris in 2016 who had never been to an endemic area. Meanwhile the parasite has settled in the rats of Tenerife, then in the Balearics and mainland Spain, with little human transmission documented so far. In Italy no case from land snails is on record. But the risk has a face. Sam Ballard, Sydney, 2010, aged nineteen, swallowed a garden slug on a dare: a coma of 420 days, quadriplegia, death in November 2018. It was a slug, not a snail, and Australia is an endemic area. The mechanism is the same.
The rest is whatever the snail has eaten. It feeds on what it finds: treated leaves, slug pellets, soil. That is why snail farmers starve them before sale. And there is a story going round: that snails graze poison hemlock unharmed and store its alkaloids, coniine and gamma-coniceine, the ones that killed Socrates. The sentence appears in a 2014 poisonous-plants sheet of the Orto Botanico di Bergamo (Bergamo Botanical Garden), with no reference beneath it. The medical literature holds no human case of coniine poisoning through a snail. The passage of a plant poison through an animal does exist in another case, coturnism, poisoning by migrating quail that have eaten hemlock, described around the Mediterranean since antiquity. For the snail, until a primary source shows it, it remains a reported tradition.
Cooked, the snail is safe: heat kills the larva, and half of Italy's kitchens have known it for centuries. Raw, it does not cure the stomach and can carry into the brain a parasite no peasant remedy ever knew. Anyone with a headache that will not pass after eating raw molluscs, or on return from an endemic area, should tell a doctor: diagnosis rests on the cerebrospinal fluid, and treatment on corticosteroids and repeated lumbar punctures, not on antiparasitic drugs, on which the literature is still divided.
References
Wang Q.-P., Lai D.-H., Zhu X.-Q., Chen X.-G., Lun Z.-R., «Human angiostrongyliasis», The Lancet Infectious Diseases, 8, 10, 621–630, October 2008. doi: 10.1016/S1473-3099(08)70229-9
Federspiel F., Skovmand S., Skarphedinsson S., «Eosinophilic meningitis due to Angiostrongylus cantonensis in Europe», International Journal of Infectious Diseases, 93, 28–39, April 2020, open access. doi: 10.1016/j.ijid.2020.01.012
Nguyen Y., Rossi B., Argy N., Baker C., Nickel B., Marti H., Zarrouk V., Houzé S., Fantin B., Lefort A., «Autochthonous Case of Eosinophilic Meningitis Caused by Angiostrongylus cantonensis, France, 2016», Emerging Infectious Diseases, 23, 6, 1045–1046, June 2017. doi: 10.3201/eid2306.161999
Hotti H., Rischer H., «The killer of Socrates: Coniine and Related Alkaloids in the Plant Kingdom», Molecules, 22, 11, 1962, 14 November 2017, open access. doi: 10.3390/molecules22111962
Yeo I.-H., Lim J.-H., «Critical Tetramine Poisoning after Sea Snail Ingestion in a Patient on Peritoneal Dialysis: A Case Report», Medicina, 57, 6, 564, 2 June 2021, open access. doi: 10.3390/medicina57060564
Bascucci D. (ed.), «E' magnè. I mangiari negli usi dei contadini romagnoli, dai racconti di R. Giorgetti e di sua mamma M. Manuzzi», Panozzo Editore, Rimini, 2002 (cited via the Emilia-Romagna traditional food product sheet «Lumache fritte»).
La Nazione, Massa-Carrara, «Tradizioni. Quando ci curavano erbe e animali», 12 March 2023.
Time, «Australia: Man Dies After Contracting Parasite from Slug», 5 November 2018; CNN Health, «He ate a slug on a dare, became paralyzed and died», 6 November 2018.
