Snails, often seen as harmless, can pose threats to human health. Certain species carry parasites or produce potent venoms.
Snails as Carriers of Disease
Freshwater snails serve as intermediate hosts for a range of parasites that can cause serious illnesses in humans. One of the most prevalent is schistosomiasis, also known as snail fever, affecting over 240 million people in approximately 90 countries, particularly in tropical and subtropical regions. The Schistosoma parasite’s eggs hatch in fresh water, releasing larvae that infect specific freshwater snail species, such as Biomphalaria, Bulinus, and Oncomelania. These infected snails then release cercariae, a free-swimming larval stage, into the water, which can penetrate human skin upon contact during activities like swimming, wading, or bathing. Initial symptoms can include a rash or itching at the site of penetration, followed by flu-like symptoms weeks or months later. If left untreated, chronic schistosomiasis can lead to severe health issues, including organ damage to the liver, intestines, or bladder.
Another significant parasitic threat involving snails is angiostrongyliasis, or rat lungworm disease, caused by the nematode Angiostrongylus cantonensis. The life cycle of this parasite involves rats as the definitive host, excreting larvae in their feces, which are then ingested by snails and slugs, the intermediate hosts. Humans typically become infected by consuming raw or undercooked infected snails, slugs, or contaminated produce. This parasite can travel to the brain and cause eosinophilic meningitis, leading to symptoms like severe headache, stiff neck, tingling sensations, and nausea. While many infected individuals experience mild or no symptoms and recover spontaneously, the neurological complications can be serious.
Less commonly, freshwater snails also transmit Fascioliasis, caused by liver flukes like Fasciola hepatica and Fasciola gigantica. These parasites utilize freshwater snails of the Lymnaeidae family as intermediate hosts. Humans acquire fascioliasis by consuming raw aquatic plants, such as watercress, that have metacercariae (the infective larval stage) encysted on them, or by ingesting contaminated water. The parasites then migrate to the liver and bile ducts, potentially causing fever, abdominal pain, and liver enlargement.
Venomous Marine Snails
Beyond parasitic risks, certain marine snails possess potent venom that can be dangerous to humans. Cone snails, belonging to the Conus genus, are predatory marine gastropods found in tropical and subtropical waters. These snails hunt their prey, which can include worms, other mollusks, or fish, using a specialized harpoon-like tooth called a radular tooth. This tooth delivers a complex mixture of neurotoxins, known as conotoxins, capable of rapidly immobilizing prey.
Human envenomation typically occurs when individuals handle these attractive, cone-shaped shells, often without realizing the live snail inside. A cone snail sting can range from mild local pain and swelling to severe systemic effects. The potent neurotoxins can cause numbness, tingling, muscle paralysis, and respiratory failure. Some species, particularly Conus geographus, are especially dangerous and have been responsible for human fatalities, earning it the nickname “cigarette snail” due to the rapid onset of severe symptoms. There is no specific antivenom for cone snail stings; medical treatment focuses on supportive care to manage symptoms, including respiratory support if paralysis occurs.
Preventing Snail-Related Illnesses and Injuries
Minimizing the risk of snail-related illnesses and injuries involves awareness and adherence to preventative measures. To avoid parasitic infections transmitted by freshwater snails, refrain from swimming, wading, or bathing in freshwater bodies in regions where diseases like schistosomiasis are common. If using water from such sources for domestic purposes, boiling it for at least one minute can help eliminate parasites. When preparing food, thoroughly cooking snails, slugs, freshwater crustaceans, or frogs helps destroy any potential parasites. Washing fresh produce meticulously, especially leafy greens, also reduces the chance of accidentally ingesting small snails, slugs, or their contaminated slime.
For protection against venomous marine snails, the most effective strategy is to avoid handling them entirely. Their attractive shells can be deceptive; even seemingly empty shells might contain a live, venomous snail. Wearing protective footwear, such as sturdy water shoes, when walking on coral reefs or rocky shorelines can prevent accidental stings. If a snail sting is suspected, or if there has been contact with potentially parasite-contaminated water, seek immediate medical attention. Prompt medical assessment can ensure appropriate care and minimize potential health complications.