Slugs are soft-bodied terrestrial mollusks commonly found in moist environments, particularly gardens and shaded areas. While generally harmless to touch, slugs can pose a health risk to humans and pets due to their role in the life cycle of certain parasites. This risk stems from slugs acting as an intermediate host for microscopic organisms, not from common viral or bacterial diseases. Understanding this biological function is key to mitigating potential exposure.
The Primary Health Risk: Parasitic Hosts
The most significant parasite concern associated with slugs is the nematode Angiostrongylus cantonensis, commonly referred to as the Rat Lungworm. Slugs and snails are obligate intermediate hosts, meaning the parasite must develop within them to reach the infectious stage. Slugs ingest the parasite’s first-stage larvae (L1) from the feces of the definitive host, typically rats.
Within the slug’s tissues, the larvae mature into the infective third-stage larvae (L3), which are microscopic and capable of infecting mammals. If a human accidentally ingests an infected mollusk, the L3 larvae can travel to the central nervous system. Humans are considered accidental hosts because the parasite cannot complete its life cycle in the human body.
This migration into the brain or spinal cord can lead to eosinophilic meningitis or meningoencephalitis. Symptoms include severe headache, neck stiffness, nausea, and neurological issues. While the infection is rare, its potential severity, including permanent neurological damage, makes awareness of the transmission route important.
Understanding the Pathways of Transmission
Infection occurs when a person or animal consumes the slug or snail, or a part of it, containing the infective L3 larvae. The primary pathway for human infection is the accidental ingestion of a small, often unseen slug or a fragment hidden in raw produce. This commonly happens with unwashed leafy greens like lettuce, cabbage, or fresh garden vegetables such as berries, where a small slug can easily go unnoticed.
The slug’s slime trail can also be a source of contamination, as stressed mollusks may excrete larvae onto surfaces. Larvae released in this mucus can contaminate water sources, such as uncovered rain catchment tanks or garden hoses left on the ground. Children playing outside are also at risk if they handle slugs and then put unwashed hands near their mouths or eyes.
Pets, particularly dogs, face a distinct risk because they may intentionally consume slugs or snails, attracted by the mollusk or its mucous trail. In dogs, the larvae can migrate within the central nervous system, causing canine neural angiostrongyliasis. This neurological disease can manifest as spinal pain, paralysis, or other severe symptoms, requiring pet supervision in the garden.
Essential Prevention and Safety Measures
Mitigating the risk of parasitic infection from slugs centers on diligent food hygiene and environmental control. All raw produce, especially items grown close to the ground like lettuce, should be thoroughly inspected, leaf by leaf, and washed under running, potable water. Cooking vegetables at 165°F or freezing them for 24 to 48 hours will kill the parasite larvae, providing a safe option for consumption.
Gardeners should wear gloves when handling soil, plants, or mollusks, and hands should be washed immediately after yard work. Reducing the slug population helps lower the overall risk, which can be accomplished by removing debris and hiding spots. Pet owners should monitor their animals to prevent them from eating slugs or snails and should keep pet food and water bowls indoors overnight.
When removing slugs, it is important to kill them in a way that eliminates the infective larvae, rather than crushing them and releasing larvae into the environment. A recommended method is to drop collected slugs into a sealed container of a strong saline solution (one part salt to seven parts water) for at least 48 hours. Alternatively, slugs can be submerged in boiling water, as the larvae cannot survive high temperatures.