While often seen as harmless garden dwellers, snails can pose risks to human health. Most common garden snails are not directly dangerous, but specific types, particularly those in freshwater or tropical marine environments, can transmit diseases or deliver potent toxins.
Diseases Transmitted by Snails
Snail species serve as intermediate hosts for various parasites that can cause serious illnesses in humans. The primary concern involves parasitic infections, often linked to specific snail types and environmental conditions.
Schistosomiasis, also known as bilharzia or “snail fever,” is a widespread parasitic disease affecting millions globally, predominantly in tropical and subtropical regions. This illness is caused by parasitic flatworms called schistosomes, which spend part of their life cycle inside freshwater snails. Humans become infected when the larval forms, released by infected snails into freshwater, penetrate the skin during contact with contaminated water. Once inside the human body, the larvae develop into adult worms, continuing the cycle if eggs reach freshwater containing the specific snail hosts.
Another parasitic threat is rat lungworm disease, caused by the nematode Angiostrongylus cantonensis. Land snails and slugs can carry this parasite after ingesting larvae from rat feces. Humans can become infected by consuming raw or undercooked snails or slugs, or by eating produce contaminated with their slime or small, infected mollusks. Symptoms can include severe headache, neck stiffness, nausea, vomiting, often mimicking bacterial meningitis, and in rare cases, serious neurological complications.
While less common, liver flukes, such as Fasciola hepatica, also utilize freshwater snails as intermediate hosts. Humans can acquire these infections by consuming raw aquatic plants or by drinking contaminated water containing the parasite’s larval cysts. The flukes then migrate through the liver, potentially causing inflammation and damage.
Physical and Toxic Dangers
Beyond parasitic infections, certain specialized snail species can pose direct physical or toxic threats. Marine cone snails, belonging to the family Conidae, are notable for their potent venom. These predatory snails, found in tropical and subtropical waters, possess a unique harpoon-like tooth (radula) that injects neurotoxins.
A sting from a cone snail can cause severe symptoms, ranging from intense pain, numbness, and swelling to more serious effects like paralysis, respiratory failure, and even death, depending on the species and the amount of venom injected. The most dangerous species, such as Conus geographus, are fish-hunters and their venom is particularly lethal to humans. These venomous snails are a highly specialized marine threat, distinct from land or freshwater snails.
Common garden snails, in contrast, do not bite, sting, or produce toxins harmful to humans upon contact. While they possess a radula with thousands of tiny teeth for scraping food, these are not capable of penetrating human skin or causing significant harm. Minor physical harm, such as small cuts, could theoretically occur from carelessly handling a snail’s sharp shell edge.
Safe Interaction and Prevention
To minimize potential risks associated with snails, adopting safe practices is important, especially when dealing with wild snails or in areas where parasitic infections are prevalent. Good hygiene is essential; thoroughly wash hands with soap and water after handling any snails, slugs, or soil, and always wash fresh produce before consumption. This helps remove any potential parasitic larvae or bacteria.
Food safety practices are also important. Avoid consuming raw or undercooked snails and slugs, as this is a common route for rat lungworm infection. If snails are part of a regional diet, ensure they are cooked thoroughly to at least 165°F (74°C) to eliminate parasites.
When in tropical or subtropical regions where schistosomiasis is endemic, avoid swimming, wading, or engaging in other activities that involve direct skin contact with untreated freshwater from canals, lakes, rivers, or streams. Contact with the water itself can lead to infection.
Direct contact with wild snails, especially in endemic areas, should be limited. If handling is necessary, wearing gloves can provide a protective barrier. If exposure to potentially contaminated water or snails occurs, and symptoms such as fever, unexplained pain, neurological changes, or skin rashes develop, seek medical attention promptly. Providing travel history and details of potential exposure can assist healthcare professionals in accurate diagnosis and treatment.