Garden snails, such as the brown garden snail (Cornu aspersum), are common inhabitants of yards and gardens. While these mollusks are generally considered pests that feed on plants, they can carry pathogens that affect human health. The risk comes primarily from parasitic roundworms that complete a stage of their life cycle within the snail. Because snails can carry infectious agents, proper hygiene and awareness are necessary precautions when dealing with them and the produce they contact.
The Primary Pathogen Carried by Snails
The most significant health concern associated with garden snails and slugs is the parasitic nematode, Angiostrongylus cantonensis, commonly known as Rat Lungworm. This organism causes angiostrongyliasis, which can lead to eosinophilic meningitis in humans. The parasite’s life cycle involves rats as definitive hosts, where adult worms reproduce, and snails and slugs as intermediate hosts.
Infected rats excrete the worm’s larvae in their feces, which the snails and slugs ingest. Inside the mollusk, the larvae develop into the infective third-stage form. The snail or slug acts as a carrier, containing the infectious larvae within its tissues.
When a human accidentally ingests an infected mollusk, the larvae travel from the digestive tract to the central nervous system, including the brain and spinal cord. Since humans are accidental hosts, the larvae cannot complete their life cycle and eventually die. Their presence and subsequent death in the nervous system trigger a severe inflammatory response.
This response is characterized by an increase in eosinophils (a type of white blood cell) in the cerebrospinal fluid, leading to the diagnosis of eosinophilic meningitis. Symptoms often include severe headache, neck stiffness, nausea, vomiting, and neurological abnormalities. The incubation period usually ranges from one to three weeks after exposure. While many people experience mild or no symptoms, the condition can rarely result in serious permanent nerve damage or death.
Routes of Human Transmission
Infection with Rat Lungworm larvae occurs exclusively through ingestion, either deliberate or accidental. The less common route involves the intentional consumption of raw or undercooked snails or slugs. In regions where snails are consumed as cuisine, insufficient cooking can fail to kill the infectious larvae.
A more frequent route involves the accidental ingestion of the larvae, often without the person realizing they have consumed a mollusk. This happens when small snails, slugs, or fragments are inadvertently mixed into raw produce, such as leafy green vegetables. The larvae may also be present in the mucus or slime trails left by infected gastropods on vegetables and other surfaces.
Slime trail contamination is a significant mechanism of transmission because the larvae can exit the mollusk and remain viable in the mucus. Consuming unwashed fruits or vegetables that an infected snail has crawled across carries a risk of ingesting the microscopic larvae. Children are also at risk if they handle snails or slugs and then put their hands to their mouth without washing, transferring the larvae via mucus.
Safe Handling and Prevention
Protecting against the health risks carried by garden snails centers on diligent hygiene and avoiding consumption of contaminated materials. The most effective preventative step is to thoroughly wash all produce, especially raw leafy greens, before eating them. A forceful rinse under running water helps remove small snails, slugs, or their infectious slime trails from the food surface.
Gardeners should take precautions while working, as snails and slugs are frequently found in soil and on plants. Wear gloves when handling snails or working in prevalent areas to prevent contact with mucus. Immediate and thorough hand washing with soap and water is necessary after any gardening activity, especially before preparing food.
Finally, discourage children and pets from touching or consuming snails and slugs, as this is a direct route of infection. Reducing the snail and slug population by removing debris and hiding places can also help lower the overall risk of encountering an infected mollusk.